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Unregistered
24th November 2007, 06:03 PM
Anyone else buy a first generation Apollo and now regret the choice?

Can't give it away, let alone sell it!

Joe
24th November 2007, 10:41 PM
Please expand.... what don't you like about it?

Does it plane much earlier than a formula board?

Krister
26th November 2007, 02:09 AM
I have the Apollo and in lightwind it is great, I made a new PB in national competition this year... :cool:

Unregistered
26th November 2007, 04:42 PM
I have the Apollo too, and in superlight wind with it’s monster fin it is Amazing!
But,,,,I read the hype and fell for it. I wanted to believe that it would be far superior than a regular formula in light wind, and offer better all-round performance for heavier sailors than the F161. And it does,,,,,,,,, And it doesn’t,,,,,,, I was so convinced of it’s revolutionary concept that I raced out and ordered it before it was even released.

“The Apollo concept consists of a board with lower rocker, a wider nose and a wider tail combined with a softer, earlier planing rig concept. A new, powerful 75cm R13 Race fin with a reduced rake angle is included with the board to take full advantage of the efficient design.”
“The Apollo will be class legal in the Formula Windsurfing Class and inspire the currently most popular windsurfing class in the world to go for Olympic participation. It will probably provide better all-round performance than the F161 in light wind and for heavy sailors”.
“Remember what the Formula did for the Racing class and then imagine what the Apollo can do for the Formula class!.”

With it’s magic 75cm fin it does what it say’s on the box. But with race legal fins, It doesn’t even come close to regular formula boards. Given that we often race in over 10 to 12 knots.
.
Over a period of six months testing, my tuning partner and I found that with race legal 70cm fins fitted, the light wind performance advantage of the Apollo (it' main selling point) shrunk to almost nil (comparative tuning and testing was carried out with F159 and F161 models). At wind ranges above 12knots, it was totally outclassed. So, for an almost negligible advantage in wind under 12 knots (with 70cm fins), the price is,,,,, compromised performance over 12knots. If I want to be competitive in my formula class, I must now buy a board for when it blows over 12knots.

If the 35+ guys in our formula fleet all sailed in a series where the class was ”Apollo”, then my purchase would be relevant. However, not one other sailor I know is, has, or would race an Apollo in a “formula regatta” unless they had the luxury of having different boards for different wind strengths. And being the only one able to plane in 6 to 8 knots in a regatta with 35 other guys gets me nowhere. I can’t see our race officials allowing the fleet to start because that one guy with the Apollo was planing.. (albeit without his 75cm fin)

I applaud starboard for constantly pushing the innovation envelope. I am a dedicated Formula fan myself, and one day hope to see the best in the world racing formula in the Olympics.

But please may I remind you all that I am the fool here. I purchased before I knew enough. The mistake is totally mine. Next time I will wait for more testing and feedback before I rush out and hand over my money.

At least if the IOC accept Apollo class, I’ll be ready. Hee hee hee.

Regards
Still sailing, and still loving it.

Unregistered
26th November 2007, 11:51 PM
Somebody on another thread was arguing case about standardising fins for board tests;then the board is tested ;not the fin.Another case in support of that argument ! (Which was ridiculed by many !!!)

Unregistered
27th November 2007, 09:03 AM
An apollo with a 75cm fin is an apollo.

An Apollo with a legal sized formula fin is just a big wide slow formula.

Unregistered
27th November 2007, 09:06 AM
Interesting to see how early the F160 planed with the Apollos' 75cm fin fitted!!!!

Ken
28th November 2007, 04:18 AM
From the promo that I read and the first reports of how the board performed, It seems to do what it was designed to do.

1. With the 75 fin or an 80 (Curtis made some of these), you have the earliest planing board around.

2. With the 70 fin in light wind formula racing, the Apollo should have the advantage in 6 to 10 knots, especially if you are a heavy weight (90kg+).

What else was it suppose to do?

pfaffi
28th November 2007, 12:07 PM
I am using the F161 and Apollo for competitions. The Apollo fitted with a 70cm super powerful fin gives me the chance to compete successfully in light winds against the 70kg guys. With my 92kg/185cm I make the Apollo fast, high and deep. If you guys discussing here are in the 70kg/170cm range you are wrong in the Apollo topic for competitions.

Ola_H
28th November 2007, 02:02 PM
Interesting point Pfaffi. I've "studied" peoples board choices for some time and generally it seems lighter people are more prone to choosing bigger stuff than heavier people. Logically, bigger people would have more to gain by going bigger to level out their disadvantage in early planing. But like in many other cases, human psychology dictates st towards rather improving what we are already good at than to focus on what we are not so good at. So, a heavy guy is less likely to give up his control advantage (by going super big). A light rider might be tempted to go for the Appollo to improve his already existent light wind advantage.

Randy
28th November 2007, 06:26 PM
Great observation Ola. I'm probably proof of your theory and I kind of thought the same thing. I'm about 60 kg, and used formula boards and big sails for recreational sailing. Then Hypersonic with big sails. When Serenity came along, I jumped on it. I was tempted by Apollo as well. Interesting thing is lately, I'm finding that I'm pretty happy on skinny old boards for higher wind sailing. I'm thinking that for more wind, skinny boards are easier to sail (keep on the water) than the newer, wider ones.

Lionell
29th November 2007, 03:29 AM
well maybe big guys use smaller boards because big (wide) boards also looks dummy. If you for example compare carve 122 vs. 144, 144 looks like a tanker and is also more unstable when the waves gets bigger

Ken
29th November 2007, 09:57 AM
Lionell,

Those "big guys" don't look like "dummys" when running down wind at 25+ knots of board speed in 1 meter chop hanging on to 9 meter sails in 25 to 30 knots of wind.

That's on a 1 meter wide "tanker" formula board. This type of experience seperates the men from the boys.

The "smaller boards" just reach back and fourth in these conditions and can't handle the serious downwind runs (or upwind). Not totally true, but I think you get my point.

pfaffi
29th November 2007, 01:33 PM
I remember light wind Formula races where some boys around 40kg competed with us. Of course planing very super super early on 8,5sqm sails but reaching a max speed half of us. So each kg is counting to rise the top speed. Its valid from speed surfing up to the Formula class without an upper limit.

marek
29th November 2007, 04:08 PM
Hi, just a slightly off-topic question - I understand the upwind advantage of formula (I have FT 148), but I never tried the deep downwind course so dreaded by everyone.

Why it can't be done on a regular, small board (catapult or sinking the tail?) and why Formula is best in downwind?
And what is the general problem with going downwind?

-marek

Ola_H
29th November 2007, 05:00 PM
I'm no formula sailor, but I rather understoof things the other way around. Formula boards and sails seemingly have a redicoulusly huge wind range, but in the higher part of this range, the baords are virutally impossible to sail in ANYTHING BUT deep downwind or hard upwind.

LK
29th November 2007, 08:38 PM
I dont think so Ola. FW boards ARE designed to go hard upwind or deep downwind.

Roger
29th November 2007, 09:43 PM
Hi LK,
Perhaps you misunderstood Ola.
You guys are saying the same thing!
And, Ola is correct.
Ask any top level formula racer where most of the "yard sale crashes" happen.....
yep, when race organizers put in a little reach at the end of the race that's where a majority of the crashes will happen in higher winds.
It's amazing to see sailors than have sailed very high upwind, for miles, into big rollers, and then nearly straight back downwind through those same rollers at incredible speeds and angles with huge sails that need to be trimmed differently for upwind vs downwind, manage to stay on top of their boards with no crashes for around half an hour (upwind and downwind), and then they "blow up" on a short reach across the swells to the finish line.
This happens alot in the races in Corpus Christi and the Gorge where the winds are pretty much side shore and the finish line is parallel to the beach.
Hope this helps,

marek
30th November 2007, 12:17 AM
OK, but I still don't understand what physics stand behind formula design so that it can sail downwind so well.

I think I understand why it excels upwind (long fin and the size that allows it to hold large sails and prevents the enormous force from the fin to roll the board over).

But why is it also so good in downwind course (comparing to a regular freeride board)? Fin almost not used here, so what else, wide, floaty stern that is easier to stand on?

-marek

P.S. Maybe these questions are weird, but I never tried the deep downwind sailing thus I don't know what it's like, the only think I know is that when it really blows I want to go upwind us much as I can just to slow things down :D.

Ken
30th November 2007, 12:19 AM
Roger has it right.

However, what's missing is that Formula racers rig so that they are FULLY powered for deep down wind runs, which means that they are very overpowerd on reaches and a little overpowerd upwind.

Since a Formula race course is normally up wind and down wind, they rig big. That's why they wipe out on reaches.

On some of those crazy reaches Roger speaks about, I have gone to the chicken strap and luff the sail A LOT trying to make it to the finish line.

Ken
30th November 2007, 12:30 AM
To answer Marek's question as best I can -

Formula boards are wide and short. When running fast downwind over the backs of 1 meter waves (shallow bay racing), the boards stay pretty stable (width) and they don't stick into the backs of the next wave (short), they just slide over and occasionally with enough speed, you get some air, landing on the top of the next wave.

The first generation Formula boards were a bit longer (F175) and did stick into the next wave. As they shorten them up, they found that they stuck less.

It's hard to imagine traveling at 25 to 28 knots of board speed over the backs of 1 meter chop, but it can be done with enough practice. Scary as Hell, but doable.

pfaffi
30th November 2007, 01:56 AM
First its a question of speed. If you have enough speed in high winds on a small board (and big balls) you can go very deep. But if you reach a certain downwind angle you start slowering your board speed and than you are strating to be in danger. If you are good in vector addition you will find that point. Formulas can go deeper because you use a very big sail and there is only one downwind angle where the sail force fits to your weight. If you would go higher the sail force is to much or more down the sail force is to less. Its interessting if you watch your gps track points you will find that you go moreless the same way down as your upwind track is. Very typical for Formula. Hope there are some answers in for Marek.

marek
30th November 2007, 02:36 AM
Great, thanks.
I didn't get everything 100% right now, but I'll be thinking about it. :)

-marek

Unregistered
30th November 2007, 02:58 AM
Its not (just) to do with the boards.
When sailing really deep (almost on a run) our normal sized "freeride" rigs just dont give sufficient power to maintain board on plane.Once you drop off plane you are lost.
Put an 11 metre race sail on say a Carve 145 and it will sail loads deeper (on plane)
Its sort of like spinnaker on dinghies.They can sail (plane) loads deeper when using chute of some sort.
Stick a normal 6 metre freeride sail on a Formula and I dont think it would sail any deeper than a big freeride design.

steveC
30th November 2007, 06:46 AM
Poster number 24 makes a very insightful point. The type of board and rig that you've got says everything about your focus, to include real world limitations. Some tolerance exists for the better sailor, but everything has it's limits.

Ken
30th November 2007, 08:44 PM
My first true learning experience with deep downwind slalom board sailing was about 20 years ago. Corpus Christi used to have their annual "Screaming Reach" which was a 10 mile downwind run the length of the bay.

As I recall, I was on a 120l slalom board and rigged a 6m sail and did a little reaching out and back to see if I had the right size. Good power and comfortable. However, once I started the race and tried to run as deep as possible, it quickly became clear that I was at least 1m to 1.5m too small on my sail choice. I quickly fell behind the more experienced local "bay racers" with much larger sails.

Live and learn!

Jean-Marc
4th December 2007, 03:12 PM
why Formula is best in downwind?

Marek,

It's all about wind vector addition : true wind and apparent wind are the same but they don't add up once sailing dead downwind. To keep the hull planing, you need a large sail area and a wide and short planing surface (high aspect ratio). In light wind, you'll not make it with a long and skinny planing surface (low aspect ratio), especially if you're a heavy weight rider (most probably in displacement mode only).

Check out the Jim Drake's Chronicle about the physics of windsurfing :

http://2007.star-board.com/drake_chronicles.php

"How wide is too wide?

Let's get to the guts: How wide is too wide? Is there a point of diminishing returns in regard to board width?

Well of course there is and the point of diminishing returns depends on what you're concerned about -- speed on a reach, broad reach and/or run, low end early planing, tactical maneuver, ease of jibing, pumping and the like. And there are other factors like the capacity of the x-ray machine at BKK or other international airports, the width inside your SUV, entry level instruction, etc. So it's a simple question but without a simple answer. Sorry.

Light-air boards appear to be getting shorter and wider. Why? And why haven't free-ride and wave boards followed this trend to the same extent?
Light-air boards are indeed getting shorter and wider because this allows them to plane earlier. This is because, among other things, the patch of water required for planing has a more efficient shape (lower drag for the lift provided) if it is wider and shorter. Fluid dynamicists refer to such shapes as having a higher "aspect ratio", the ratio of lateral span to average longitudinal wetted length. Free-ride and wave boards are -- in my opinion -- likely to follow this trend but perhaps less aggressively since both (think they) have the luxury of choosing better wind. The future may demonstrate the virtues of light wind attributes to them as well.

Have trends to short, wide shapes eliminated the light-air, sub-planing cruising element of windsurfing that originally helped make the sport so popular?
For the moment, yes. But only for the moment, that is, until short wide designs are developed that have at least adequate and perhaps very pleasing performance even when sub-planing. Originally, as you say, the sport grew from the pure pleasure of holding the wind in your hands and freeing yourself from the land. That changed when planing was introduced and the sport became more dramatic and athletic -- changes that were inevitable and from my point of view all to the good. These changes, however, displaced the zen of quiet windsurfing, a valuable quality that is appreciated by many but difficult to enjoy with single fin Formula style boards. All that may change if radical ideas, such as adding a retractable fore fin and a lateral mast track, bear fruit.

If the 100 cm width limit weren't in place for Formula boards, would you expect them to grow even wider? What would be the result?
I would indeed expect them to grow wider. Tests at Starbord have shown as much, at least through 120 cm. Imagine a 4' x 7' board! I can. And the benefits (except to obsolete all current Formula designs) would be as one expects -- earlier planing, quicker and maybe shorter "pump and go", quicker to the windward mark and maybe a little higher pointing.

Do you predict boards to continue to get wider in the future? What design innovations do you predict will complement this trend?
It's hard for me to predict that they won't get wider, just based on history and physics. But it's also hard for me to predict where it will all end up, namely, what will be the countervailing force. Today it's the bureaucracy -- Formula -- but that can and should change. It might be the "x-ray machine at BKK" but the x-ray machine problem and the air travel problem can be avoided as it is with all other forms of sailing. It might be the SUV but there's always the roof rack. My guess is that the limit will come by way of the requirement for longitudinal trim, that is, finding a place where the sailor can stand and counter the unbalanced couple between the sail's drive and the board's drag and still hold the board at its optimum angle of attack. (That's a bit obtuse, I know, but I'd put everyone to sleep with any better explanation.) One innovation to complement this trend could be to employ cavitating and/or ventilated planing hydrofoils to help longitudinal trim. (Well, you asked!) "

Cheers !

JM

Floyd
4th December 2007, 09:33 PM
Hi
Jean Marc
Enjoyed your explanation and agreed/understood most of it but cant quite see why aspect ratio of planing surface affects ability of a board (or any sailing craft) to sail deep down wind.A big powerfull sail is a must and in sufficient wind /control it is possible for craft to approach planing on a dead run. A kiter (perhaps when overpowered) can plane in direction of wind.High performance dinghies can for short periods maintain planing on a run.
Neither of these craft have either high aspect planing surfaces or particularly efficient ones; but in both cases control of the power is still possible whilst on a run.Not sure thats the case with boards.Launch a kite and in sufficient wind almost any board would plane on a run !
Down wind the board is a platform to utilise available power; upwind it is a sailing craft ! ???

Jean-Marc
5th December 2007, 02:02 AM
Floyd,

On a dead downwind course, the board speed is equal to that of the true wind minus that of the apparent wind. A planing hull is faster than a gliding hull.

From what I understood from Jim's chronicle :

The Apollo's 80 cm wide and last 30 cm short planing area means lower hydrodynamic drag for the lift provided. This means that the hull can start and sustain the planing which is faster in light 6-7 knots winds. The heavier the rider, the wider the tail must become to sustain the planing and speed.

The Serenity's 40 cm narrow and > 200 cm long "planing" area means higher hydrodynamic drag for the lift provided. This means that the hull cannot start nor sustain the planing, which is slow.

Try both with say an 11.0 sail, you'll be amazed at the board speed difference on a dead downwind course in 6/7 knots of true wind speed.

This is the same principle behind hydrofoil boats : the planing surface of an U-bent hydrofoil is very wide but very short to maximize the lift to drag ratio.

http://en.wikipedia.org/wiki/Hydrofoil

Cheers !

JM

Crash
5th December 2007, 03:46 AM
Just an update on the Apollo I,m 75k and use mine with a AC-2 9.7m sail in light winds and the 75cm fin. As the wind picks up I drop the fin down when its really blowing I end up with my 7.8 Lightening and a 60cm fin. I have really enjoyed the board it just takes off very easily and has extended my time on the water considerably. During the summer light winds I was often the only person on the water and had some very enjoyable sessions, but I don't race.
It will be interesting to see how the new 162 performs as it seems to be a cross between the 161 and the Apollo.
Crash

Unregistered
5th December 2007, 08:50 AM
Jean Marc, sure the high efficiency of high aspect planing surfaces is a reason to go wide - but then again, at lower speeds form drag increases by around the square of width. And before anything can start planing it has to move, and a short board has high drag at low speeds.

In many inland or confined waters the longboard is still faster a lot of the time for these reasons - the skinny shape is better at non-planing speeds, the longer hull is more efficient just before rising onto the plane, and unlike a FW they don't need the power from a big rig to push them onto the plane and into the region where FW goes incredibly well.

Unlike Floyd, I wouldn't say a dinghy has a bad planing shape - I would say that a good planing dinghy has an extremely efficienty planing surface given the other strengths and weaknesses of a dinghy design. There have been dinghies shaped a lot like Formula boards around for years (lightweight scow Moths, which had full battens, fathead sails, wide pocket luffs and weighed about 30kg back in the '60s) but if you make them short and wide enough to go like a Formula board in strong winds, then they also go like a Formula board in light winds - and that's not good in most of the waters dinghies sail. Dinghy shapes just favour more all-round speed.

Jean-Marc
5th December 2007, 03:55 PM
In non-planing conditions below 6 knots of wind, the Serenity is for sure faster than a shlogging Apollo or Formula or even a dinghy (e.g., a 420 or 470), no question. Each board is designed for an optimal wind range and course range use. The crosspoint between shlogging and planing is at ± 6 knots, so it's a pretty much interesting strategy when it comes to choose the right board for the right conditions.

Cheers !

JM

Floyd
6th December 2007, 10:20 PM
I wasnt making point that dinghies have poor planing abilities.Some do ; some dont.Reckon modern skiffs probably plane as early as anything ever built; Enterprise on other hand certainly doesnt.(Neither does 420 or 470 !!!)
Point I was trying to make was that hull shape has much less effect down wind than pure power of sail.Obviously a good planing surface is a prerequisite but put an 11 metre rig on an old Mega Cat/ F2 Lightning and it too would be pretty damned quick down wind.

Jean Marc
Looked up your link and there was no mention of high aspect planing surfaces being more efficient than low ones.(Its a point we all take for granted but I cant find any factual figures to prove it)Lift is propoprtional to CSA (I think) on planing surfaces. We make the anology to wings/rigs/fins but not sure we can.(On a wing leading edge gives disproprtionate amount of lift; more leading edge more lift;less area less drag. A foil has its Centre of Lift well forward??(Its being pulled from above aswell(Sort of)) A board has its centre of lift in geometric centre of planing surface.(If it didnt we would be in a mess)
Having said all that I still suspect high aspect planing surfaces are more efficient but the difference pales into insignificance if you are carrying 40/50% more rig.
PS True hydro foils are fully submerged and we can then make anology to fins/wings/rigs.We cant make the leap with the board on surface.(Pardon the pun)
Bottom of a board is not a foil.Its a planing surface.(And I think the most efficient is absolutely flat) Not sure its aspect ratio has any effect other than in control.(Ie we use a wide one so we can carry a massive fin !!!)

windstock anarchy
7th December 2007, 07:47 AM
http://pic40.picturetrail.com/VOL370/9999562/18441452/291882753.jpg

http://pic40.picturetrail.com/VOL370/9999562/18441452/291882757.jpg

http://pic40.picturetrail.com/VOL370/9999562/18441452/291882762.jpg

On an 11.0 as deep down wind as you can go.
???????? I'll take the FW

Unregistered
7th December 2007, 02:45 PM
Think Floyd said an old Mega Cat or Lighning .Thats neither of those !

Floyd
7th December 2007, 06:12 PM
The Lechner is a Div 2 and almost impossible to sail (by my reckoning).Its even harder to sail the damned thing downwind.Basically its a small dinghy with a displacement hull capable of planing insome (???) conditions ! Cant compare it with anything really !
Not really got anything to do with argument as the Div 2 boards are at their best (relative term) in non -planing conditions.(It would trounce most any other board upwind in 8 knots)

Anyway
Done a little more research re-High Aspect planing surfaces.
Is it just a myth High Aspect planing surfaces are more efficient ??? Not sure yet ?
Read a hydrodynamic article (Cambridege; Surface Skimmer planing Hydodynamics) which if in my wisdom I understand says that the lift produced is a function of the diffeerence in leading and trailing edge depth; water density;area and velocity.Its a momentum transfer.(ie the lift is a function of the amount/mass of water disturbed) This is not how a foil works ! Would a water skier really get more lift if he used ski sideways ??? I`m not convinced.
Suspect its another myth to propogate sales !!! High Aspect planing surface sounds so impressive !!!

Unregistered
7th December 2007, 11:31 PM
I'm astounded at how little i knew about the physics of hydrodynamics in relation to our great sport windsurfing. I've been reading all the contributions more than once, and still feel very confused. Should a degree in such things be necessary to choose the right board? What does Floyd sugest with his last comment?

"Suspect its another myth to propogate sales !!! High Aspect planing surface sounds so impressive !!!"

Who's sales?

Unregistered
8th December 2007, 01:05 AM
Suppose he meant board sales !
There is a lot of BS?
High Aspect Planing Surfaces obviously exist but are they more efficient than other ???
Dont thionk WS is first to come accross them ???
Power boats; skiing dinghies etc?
I`ve not been involved with sport long but I have noticed there are an awful lot of claims made about shapes in boards and sails.

windstock anarchy
8th December 2007, 05:22 AM
http://www.macquarie.com.au/speedsailing/design.htmPlatform design
The evolution of Yellow Pages Endeavour platform began by applying a much greater righting moment to the sailboards rig. This was achieved by placing the crewmen more than 10 metres to windward of the rig. This provided greatly increased righting moment when compared with the sailboard, thereby the ability to hold up much higher sail forces that would drive the craft faster.

To complement this massive righting moment, good fore and aft stability was required. In order to reduce windage and water drag, this fore/ aft stability was achieved by setting two planing surfaces approximately 11 metres apart. The angle of the crew beam was set to oppose the line of force of the overturning moment of the sail and balance the relative amounts of downforce on the fore and aft hulls.

The hull sizes were set to ensure adequate buoyancy during the displacement phase of the craft and the width of the planing surface (1.2m) designed to ensure the most efficient planing aspect ratio possible.

Macquarie Innovation was designed around the same principles as YPE. However, to go faster meant a wider and stronger platform was required to handle the increase in performance from the new wing.



if the Apollo can plane sooner and stay on a plane longer in the low limits, it can be a winner. Stay'n/Get'n to the plane, even if it's only a half a knot sooner, is a big advantage in a race @ the wind min.

When there's some wind and one board is faster than the other. The faster board will slowly pull ahead.

When the wind drops and that faster board can no longer stay on a plane but, you have the Apollo that stays on a plane through the hole, and you pass the faster board much faster than he pulled away from you. Then you wait at the finish line and have a drink while the faster board sloghs accross the finish line so we can start the next race.with a 70cm fin

Unregistered
8th December 2007, 05:01 PM
But if wider is more efficient surely it would have been even wider;bearing in mind its carrying a ton and half ; and was still only 1.2 m wide.(Not much wider than a Formula ???) To my mind thats pretty narrow !!!
And if High Aspect Planing surfaces are more efficient how come speed boards are narrow (relatively)
PS
True meaning of Aspect ratio is Wing span Squared /divided by area.
And High Aspect wings have much higher parasitic drag. (From longer leading edge)

From a geometric point of view best planing area would be a square; ie max area for minimum leading edge ??? (I think anyway!)
(Planing pads on speed boats (back of V) are square !!!
Bet it was square on YPE ??? (1.2 m by 1.2 m ????)
Anybody know ???

C guy
8th December 2007, 07:07 PM
High aspect planing surfaces are DEFINITELY more efficient at planing. This has been well recognised for decades due to tank tests. This effect was even known to old dinghy designers like the great Uffa Fox, but in dinghies the losses in going for a high aspect ratio are greater than the gains.

Daniel Savitsky of the Stevens Institute is the biggest name in the field and his 1964 "Hydrodynamic Design of Planing Hulls" is apparently the basic paper. I'm no expert, but I've gone through this with a bunch of guys like naval architects, academics and Boeing aerodynamacists for a project.

The reason a high aspect planing surface works well is fairly simple. What is "planing"? It is when a hull is lifted above its static centre of gravity (flotation state) by the dynamic lifting forces created by its movement. What creates dynamic lift? The acceleration of water particles downwards. When a board pushes water down, an equal and opposite lifting force is created. Thanks Mr Newton.

A wide surface hits more water and pushes more water down than a longer surface of the same area. The front edge (at the "spray root", where spray splashes forward) is the point where most of the water is pushed down, and therefore where most of the lift is created.

Further back, the water is already diverted by the leading edge; it is no longer being pushed pretty much straight down by the board, therefore it creates less lifting force - but it still has drag. At the tail, the water is pretty much just flowing along the board, so it is no longer being accelerated down much. Since the water isn't being shoved down much, it's not creating much lift back up to lift the board on the plane.

A foil does NOT have its centre of lift at the geometric centre of the planing surface, it's much closer to the front, near the spray root - Savitsky's graphs showing this are available in most basic naval architecture books.

So adding length just adds surface friction drag, pretty much. What we want is width, because that means more water is shoved down along the leading edge.

Of course, since nothing comes for free a high aspect planing surface comes complete with added form drag (rising by the square, pretty much), wave impact drag, wetted surface drag at low speeds, etc. Powerboats can use high aspect but at their speeds wave impact is a massive problem I think. Sailing skiff and dinghy designers are sometimes aware of it, but they would lose to much in form drag, wetted surface, wave impact etc, and they can't really adjust their planing length like a board can.

Some designers at the trials that chose the RSX pointed out that across the whole range of conditions, a Lechner is still faster because it's got so little wetted surface (basic geometry of surface of solids), such a long waterline (basic wavelength/speed theory), such a skinny shape (low form drag) etc etc etc. Of course, it also has a fairly limited top speed.

The high aspect planing surface effect is definetely not marketing BS, this is a very well studied and very well known effect of basic physics.

Floyd, a D2/Lechner type well and truly planes when sailed properly! And some scientists do compare planing hulls to foils.

C Guy
8th December 2007, 07:11 PM
PS I let some very non-technical terms get through in that last post, it's late and the last guests just left so I'm finishing the red wine. Apologies.

By the way, a Lechner Olympic medallist and IMCO world champ reckons the round-bottomed board is faster thn the IMCO 'till 14/16 knots of wind. In a good planing breeze, surely even with a big sail neither will come close to matching a FW board in steady winds.

Floyd
8th December 2007, 07:12 PM
By that definition a square would have an Aspect Ratio of 1.Which is probably most efficient shape for a board ???? Planing Aspect ratio of 1 is perhaps best ???
Mathematically a circle has largest area for minimum perimeter; what would its AR be ???

Floyd
8th December 2007, 07:37 PM
C Guy
Never said a Lechner didnt pane; it planes at a higher speed than flat board
of simiar width.(Lifting forces to aid planing have to be perpendicular to board.Round hull increases SA without increasing lift.(It increases grip on water to aid displacement upwind performance)But thats not what we were talking about.Didnt want to say Div 2 would beat FW in such winds but I do agree)

If the situation is as you described (ie lift concentrated towards front edge of planing surface) the planing centre of force would be towards the front; which I dont believe it is. According to what I have read planing centre of force of "any" planing surface is its geometric centre.And paper I read inferrred that lift is a function of difference in height between leading and trailng edge along the entire surface.Ie the wing anology again is not a good one because with a difference in height between leading and trailing edge the entire surface IS encountering previously undisturbed "water".Again suggesting CoE of planing surface would be its geometric centre.Is centre of Force towards front edge on planing surfaces ???
BTW
Uffa Fox`s greatest design was in Catamarans. Which dont plane ! (Except very modern ones. (Spitfire has square planing pads on its stern)
I`m not making out to be an expert but am questioning what we often see as "accepted" statements used to prove a certain board is faster than an other .
I`ve yet to find any evidence/graphs showing lift/drag ratios for different Aspect Ratio planing surfaces. From my investigation it still seems a square/flat surface gives the best lift/drag ratio.
PS
If you were stood on a square flat board being towed behind a boat whare would you stand ?? I would stand in the middle ?? If leading edge produces most lift presumably you would stand toward front ??? Wonder what would happen ???

sailquik
8th December 2007, 08:21 PM
But if wider is more efficient surely it would have been even wider;bearing in mind its carrying a ton and half ; and was still only 1.2 m wide.(Not much wider than a Formula ???) To my mind thats pretty narrow !!!
And if High Aspect Planing surfaces are more efficient how come speed boards are narrow (relatively)
PS
True meaning of Aspect ratio is Wing span Squared /divided by area.
And High Aspect wings have much higher parasitic drag. (From longer leading edge)

From a geometric point of view best planing area would be a square; ie max area for minimum leading edge ??? (I think anyway!)
(Planing pads on speed boats (back of V) are square !!!
Bet it was square on YPE ??? (1.2 m by 1.2 m ????)
Anybody know ???


I have actually experimented with 6.5m sails on a Formula in light winds (10-11 knots) and I can tell you that the Formula board planes much easier and downwind much deeper than any other narrower board with the same size sail and in the same wind. There is a feeling the the board skims the surface and the wake is very flat. It is like the board makes a very small 'hole' in the water. It is amazing how little pressure one feels from the sail and yet the board is still planing downwind at quite a deep angle. Of course, with a much bigger sail one also gains more speed and a deeper angle. In other words, the hull is very efficient at planing with very little power. That seems to bear out the advantage of the 'higher aspect' planing surface to me.

Waterskis are narrow because they go very, very fast (at least racing ones do - 100mph anyone?) and need to reduce area to stay in control and provide superior directional stability, that is they need to be narrow so they don't plane too high and fly too much and still go straight. They also have the luxury of almost unlimited power so low drag is less of a factor than the former things.

Speed boards are somewhere in between. They need to be relatively narrow to provide stability and control in chop (even the flattest speed courses are certainly not dead flat and it might surprise you how rough 15cm 'corrugated chop' feels at 45 knots) and not produce too much aero lift that makes them fly away, and they go almost twice the speed of Formula boards so they produce a lot of hydrodynamic lift. This means that at top speed (which is the prime design aim) they actually have quite a small, and short contact patch on the water. Most modern speed boards are markedly wider in the tail than '80's and '90's speed boards and actually have a higher aspect planing contact patch in comparison. They also get to 40 knots a lot easier and in less wind than their ancestors. Some of this can be down to more aerodynamic rigs and better fins, but some is most certainly down to the higher aspect planing surface.

YPE's hulls and MI's for that matter are not square, the flat surface is actually wider than it is long although the 'bow' section makes the overall hull close to square. There is a 'step' at the rear of the hulls so at top speeds the contact patch is very high aspect.

photos:
http://img61.imageshack.us/img61/2623/miafthullyd9.jpg

http://img87.imageshack.us/img87/6332/mihullsgo2.jpg

http://img61.imageshack.us/img61/76/highaspectplanningsurfaec5.jpg

Unregistered
8th December 2007, 08:45 PM
Its probably higher aspect because its more stable.
Floyds argument re centre of planing makes sense but something just seems to say Higher Aspect is more efficient. Personally cant see any reason why .
With a wing/foil its easy to see (even feel) leading edge is providing most lift. (Harness lines dont go in geometric centre of sail)
A gliders wing has its centre of lift around a third of its way back from leading edge.
In these cases its easy to see why higher aspect will give more lift; simply because they have more of whats doing the lifting.
But with a planing surface ???
Where is centre of dynamic lift on a board ???
And I`ve just examined my Formula 160; its planing surface approximates to a square. (At lower speeds anyway) (Actually its still longer than wide I`d guess up to 12 knots thinking which part is in water whilst sailing)
So it sort of fits both arguments ??? !!!
Its square (ish) and becomes higher aspect with speed ???
At speeds Sailquick is talking of its probably the square bit giving early planing ????

Argument could be settled if someone could catogorically say where centre of lift is on a planing hull ? Doesnt feel to be towards front to me? Is it in geometric centre or nearer leading edge ???

Floyd
9th December 2007, 02:34 AM
Hi Sailquick/ C Guy
Theory of optimum shapes in free-surface flows. Part 1. Optimum profile of sprayless planing surface

--------------------------------------------------------------------------------
T. Yao-Tsu Wu a1 and Arthur K. Whitney a1p1
a1 California Institute of Technology, Pasadena, California

Article author query
wu ty [Google Scholar]
whitney ak [Google Scholar]



Abstract

This paper attempts to determine the optimum profile of a two-dimensional plate that produces the maximum hydrodynamic lift while planing on a water surface, under the condition of no spray formation and no gravitational effect, the latter assumption serving as a good approximation for operations at large Froude numbers. The lift of the sprayless planing surface is maximized under the isoperimetric constraints of fixed chord length and fixed wetted arc-length of the plate. Consideration of the extremization yields, as the Euler equation, a pair of coupled nonlinear singular integral equations of the Cauchy type. These equations are subsequently linearized to facilitate further analysis. The analytical solution of the linearized problem has a branch-type singularity, in both pressure and flow angle, at the two ends of plate. In a special limit, this singularity changes its type, emerging into a logarithmic one, which is the weakest type possible. Guided by this analytic solution of the linearized problem, approximate solutions have been calculated for the nonlinear problem using the Rayleigh-Ritz method and the numerical results compared with the linearized theory.


(Published Online March 29 2006)

Yet us windsurfers know High Aspect Planing surfaces are OBVIOUSLY more efficient !!!

(This is a genuine quote from a paper; written quite a while after Uffa Fox designed boats)

Floyd
9th December 2007, 02:48 AM
And Another to just complicate it a bit more !

Abstract : The steady motion of a planing surface of moderate aspect ratio at small angles of attack is considered. Linearized theory is used with a square-root type of pressure singularity representing the flow near the leading edge. As asymptotic solution for the pressure distribution on the planing surface at large Froude number (or small beta, the inverse of the Froude number) is sought. The lowest order term of the pressure distribution, obtained by setting beta equal to zero, is found to be the same as the pressure distribution on the lower side of the corresponding thin wing. Higher order terms in beta are obtained by an iteration process. Explicit solutions are obtained to order beta squared for rectangular planforms. Numerical results are calculated for rectangular flat plate planing surfaces of aspect ratios from 0.5 to 2.0. It is found that for large aspect ratios the lift coefficient is reduced by the gravity effect and for small aspect ratios it is increased, the dividing aspect ratio being about 1.5. The results compare reasonably well with experimental data. (Author)

Note
"it is found for for large aspect ratios the lift coefficient is reduced"

I think it says the optimum AR is 1.5 !!!

But I`m not sure.

We cant simply say
"High Aspect is more efficient"

sailquik
9th December 2007, 04:40 AM
Sorry Floyd, I didn't follow any of that. It does seem to suggest a lot of 'qualifications' though. I would like to know what the 'experimental data' showed.

Are we assuming a 'large' aspect ratio is a 'high' aspect ratio?

C Guy
9th December 2007, 06:37 AM
Floyd, the area of the highest dynamic lift is very well known in aerofoils and planing hulls. Illustration 2 of Savitsky's classic 1964 paper (I think you can find a pdf at Boat Design Forum somewhere) shows the "spike" near the stagnation point/spray root area. I have a pfd but I can't find the web address I got it from, sorry.

I have been through this with America's Cup designers, Boeing aerodynamacists, Jim Drake, naval architects, mathematics academics specialising in performance prediction programmes and tank tests, and small craft designers. Some of them have checked my project, where I refer to this. It's a very well known effect. Apart from Jim, none of them use the high aspect effect in their craft so it's not marketing that makes them speak of it.

If the centre of lift was at the centre of the planing surface, you wouldn't be able to hang ten on a surfboard - but you can.

"Uffa Fox`s greatest design was in Catamarans. Which dont plane ! (Except very modern ones. (Spitfire has square planing pads on its stern)"

Catamarans? I have just about every book Uffa ever wrote, and his biography, and I think the unspectacular Bell Cat was his only catamaran design.

Floyd
9th December 2007, 02:56 PM
Sailquick
You are right about Uffa Fox ; think you`ll find he also designed a few model boats/cats.One of which was a cat which I had as a kid.
Anyway
I do think you could be totally correct and I`ve often wondered myself how surfers hang ten; not sure its anything to do with centre of planing but it could be.
My point really was that we just accept these statements without any real data/explanation to confirm.
Much of stuff I hjave read indicates that over last 15 years or so planing has conme to be looked at more simply as momentum transfer.(and along entire length)Think I quoted one of papers I found.Theres even been rumours in aero world that many of the accepted theories of lift are poor representations of what actually happens. (See tip vortices and lift)
Anyway it must be bad weather everywhere spending so much time on here.
Good sailing.

We cant just say high AR are more efficient.

Floyd
9th December 2007, 06:17 PM
Windstock
Notice Naiomi is stood to rear of ironing board;giving ideal angle of attack with the prerequisite 1.5 AR. Cant make out wether boards an F2 or Mistral.Cant be a *B , its going too fast. Second one could be *B but he`s oversheeted anyway.
Nice pics.
Good sailing.

Unregistered
9th December 2007, 10:25 PM
Who won? What's the, verdict? Conclusion? Final score?

I'm still confused! Am i the only one still confused?

What is "AR"?

Does an apollo have "AR"?

If windstock is a "NEW MEMBER" how does he know who the unregistered posters are?

Floyd
11th December 2007, 05:16 PM
Nobody won !
No; we`re all confused.
AR- Aspect ratio. Of sail ; luff squared divided by area.Of board; planing width divided by planing length.
Yes
Dont know .
Its cold.

C Guy
12th December 2007, 05:00 AM
It wasn't a competition, so no one won or lost.

As far as I can see, Floyd is right and we can't just say that high aspect is more efficient. It's just more efficient for some purposes. The high aspect planing surface does work and for much the same sort of reason as skinny wings work (ie reduction in tip loss etc).

Savitsky's 1964 paper has a good way of looking at it - if you had an extremely wide span planing surface, the tip loss is minute and almost all of the effect of the water being shoved down is acting to lift the board.

In contrast, if you had a very long skinny surface, basically all the water slips out to the side so there's nothing underneath to lift the board up. Sure, there IS actually water underneath but its effect is diffused by distance - just like the fact that we don't get squashed by air being shoved down underneath a jumbo passing overhead

But where Floyd is right to say that we may be being oversold the high aspect effect is that the marketing spin ignores the downsides - ie while induced drag when planing DROPS by the square of the width, form drag when not planing INCREASES by about the square of the width and wavemaking drag is increased by a short fat surface. And to get to plan, we have to overcome form drag, wavemaking drag etc.

So skinny works in some conditions, fat in others, and to say that fat = good is surely wrong. And for my two cents worth, we need to get away from emphasising top end speed in planing conditions so the value of long and skinny can't be overlooked.

PS Floyd, it is fascinating looking at the way people look at lift - momentum transfer seems cool, but circulation and Euler equations do my head in! :-)

C Guy
12th December 2007, 05:06 AM
Also, I'm not an aerodynamicist's underpants and so therefore I know nothing; it's just that sometimes I get to ask those who do know their stuff.

steveC
12th December 2007, 07:39 AM
I'm not so capable that I understand the real scientific/technical stuff, but my "off the top" take is that high or low aspect leverage is kind of relative to the playing field. I guess it depends on your focus. Needless to say, if it's really cranking, the narrow emphasis has obvious advantages relative to control. In light stuff, the opposite is true.

I think that it's fair to say that both wide and narrow width boards have a distinct place in the picture. A skewed perspective one way or another will affect the performance envelope. Of course, a steely nature will often figure too in the outcome.

Ken
12th December 2007, 08:50 PM
In conclusion - for the regular folks:

Wide = quick to plane, but hits the wall at some point in high winds (39 knots - see GPSwindsurfing.com). Wow!!!!!

Skinny = slow to plane, but keeps going faster in the high winds (50 knots).

Expander
14th December 2007, 12:46 AM
--

A small contribuition about ASPECT RATIO issue and relative planning abilities of a windsurfing board.


About Aspect Ratio (AR).

Aspect ratio (AR) is an indicator of the general performance of an (hydro) aerodynamic surface.
In aerodynamics, the Aspect Ratio of a wing is defined as the square of the span divided by the wing area.
It is a measure of how long and slender a wing is from tip to tip.
"HIGH" Aspect Ratio aircraft wing indicates long, narrow wings, whereas a "LOW" Aspect Ratio wing is short and stubby.

http://img110.imageshack.us/img110/4169/glidervsfighterpn9.gif


In windsurfing board design, "HIGH" Aspect Ratio term indicates wide Formula boards while "LOW" Aspect Ratio term indicates Slalom narrow boards.

http://img136.imageshack.us/img136/5797/formulavsslalomcz8.gif


In these context, in air or in water, an HIGHER Aspect Ratio has pratical effect of increasing LIFT (above all when angle of attack increases).
An analytic confirmation could be verify just considering LIFT (L) and DRAG (D) of a hydro/aerodynamic surface, and plotting a graph to see how COEFFICIENT OF LIFT (CL), given from ratio of Lift over Drag (L/D), works for surfaces with a HIGH and LOW Aspect Ratio (AR):

http://img218.imageshack.us/img218/1321/arvm9.gif


It is clear that, for a surface with HIGH value of AR (graph on left), Coefficient of Lift (red curves) is much higher than a surface with LOW value of AR (graph on right).
At same Coefficient of Lift, higher is L/D ratio, MORE efficient is a surface.
Therefore, the HIGH Aspect Ratio surface (Glider wing or Formula windsurfing board) will glide much further and will be characterized by better skimming abilities than a LOW AR surface, above all when wind is in the low-end and board is crossing from full displacement to skimming condition.

Schematizing,

IN AERODYNAMICS:

HIGH Aspect Ratio wing --> Higher Lift Coefficient --> lower stalling angle of attack (Gliders);
LOW Aspect Ratio wing --> Lower Lift Coefficient --> high stalling angle of attack (Fighter Jets)

or, IN WINDSURFING BOARD DESIGN:

HIGH Aspect Ratio board --> Higher Lift Coefficient --> better low-end planning abilities (Formula);
LOW Aspect Ratio board --> Lower Lift Coefficient --> better speed performances (Slalom).

A really empirical confirmation of better efficiency of a HIGH Aspect Ratio surface on a LOWER one is given by different kind of FLAGS: yes, I'm speaking about very common flags like ones visible in every beach in summer season; well, like visible in following drawing, a HIGH AR flag is more efficient of LOW AR flag also when wind is weak or tenuos for other one (it goes on flapping while other flag is become flabby).

http://img156.imageshack.us/img156/2033/flagsus7.gif

I hope this contribuition could be useful to clarify entire matter.


- EXPANDER.

Unregistered
14th December 2007, 01:07 AM
expander-
thanks for the great graphics

Unregistered
14th December 2007, 02:14 AM
Great explanation from expander;;;
but it does assume there is a very close anology between lift annd drag relatiopn ships for wings/fins nd to that of planing surfaces.(Which has been in doubt in a few posts)

Not sure its anything to do with it but;

An aircraft wing will give lift at a zero angle of attack.(Bernouli /venturi principle;ie air over top surface travels much further than that underneath; creates pressure difference between upper and lower surfaces and cause luift.

A planing surface (ie a board) will not create any lift at zero angle of attack because at zero AoA there iis no momentum exchange.Board /hull or any planing surface needs to be at a slight angle to direction of travel. (Ie even flat slalom boards are sat deeper at tail than front edge)

Taking all this into account dont really think we can assume wing anolgy is a good one. (Especially when we are making conclusions based on them)

Expander
14th December 2007, 02:55 AM
...a planing surface (ie a board) will not create any lift at zero angle of attack because at zero AoA there iis no momentum exchange.Board /hull or any planing surface needs to be at a slight angle to direction of travel...

--

As I've written in previous post (http://www.star-board.com/forum/showpost.php?p=17208&postcount=59), "...in these context, in air or in water, an HIGHER Aspect Ratio has pratical effect of increasing LIFT (above all when angle of attack increases)..."

And when a windsurfing board runs on water it always (and inevitably) assumes a certain Angle of Attack for board design (scoop line).

Unregistered
15th December 2007, 01:16 AM
With all repect expander thats been crux of thread for a while.
We know some have said high aspect is more efficient; some have said more efficient in certain situations and a couple have said Aspect ratio does not affect overall lift.
If Floyd`s quotes (from some Scientuific papers; listed in post) are taken to have any substance then overrall lift for a planing body is simply a matter of area.
Your post implies a longer leading edge gives more lift.
If planing is a result of momentum exchange over entire area there is no reason to just assume high aspect is any more efficient.(It would simply be matter of max area for minimum leading edge/trailng edge)
On the other hand if planing is a result of lift generated by leading edge then it stands to reason higher aspect would generate more lift.
Nobody has actually said its one or the other (for a fact) with evidence.(Infact evidence provided is contadictory)
Personally reckon leading edge argument is flawed for reasons mentioned in my last post.(ie boards do not have flow over top surface so wing anology is very weak)