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Unregistered
6th March 2008, 05:23 AM
No, I haven't made one but after watching this kayak

http://fr.youtube.com/watch?v=U95UReP4mdo

it occurred to me that a hydrofoil should be a lot more useful for the Serenity displacement hull than the planning hydrofoil boards. Looks simpler than the Moths, could be fun.

Jean-Marc
6th March 2008, 05:44 AM
Tacking, jibing or turning that thing would be a nightmare with 2 hydrofoils 15 foot apart...

Cheers !

JM

Unregistered
7th March 2008, 03:54 AM
Yeah, I guess. Unless rolling it would lean into the turn like a plane.
The hydrodynamics of that is beyond me, but intuitively it feels like it should.

Jean-Marc
7th March 2008, 06:20 AM
I'm unsure whether banking the Serenity to windward or leeward will make her turn while she's on 2 hydrofoils. With a 2 hydrofoils system, you'll need a rudder to turn. Check out some jibing or tacking of flying Moth/hydrofoils or Bladerider movies on YouTube, this is very clear the rudder is doing all the turning job, not the banking of the boat.

With 1 hydrofoil, this is a different story. Lean on the inside curve to initiate a turn (foilboarding la Rush Randle, air chair, etc...).

Speedwise, I'm not sure a hydrofoiled Serenity would be faster because once she's rised above and out of the water, the hull lenght doesn't matter anymore. I can go as fast as twice the wind speed in the 3-7 knots wind range. Same numbers with a flying Bladerider : twice the wind speed. So I'm a bit skeptical as to foresee the benefits of hydrofoils under a Serenity.

Maybe Tiesda or Jim can tell us what they think about that ?

Cheers !

JM

kimax
7th March 2008, 07:35 PM
I guess it does not work at all in a smallest chop.

Randy
8th March 2008, 07:51 PM
Another vid showing how it works. I'm not sure what he's saying, but the inventor seems to be a guy named Einar Rasmussen. Spose he's a long lost cousin?


http://fr.youtube.com/watch?v=uO54ZvDwt18&feature=related

Unregistered
10th March 2008, 02:02 AM
The C cat championship last year did pretty much prove that if your hull is efficent enough then hydorfoils aren't an advantage. But those hulls are twice the length of Serenity, which looks much more like the kayak to me,.And the vid there looks pretty convinving on the face of it.
But I've gotta concede wands and rudders would be a step to far.

Jean-Marc
12th March 2008, 03:11 AM
I agree narrow hull length is an important factor to sail fast in light wind, but it's not the only one. Sail area to weight ratio is very important as well in very light winds IMHO. This is what I've done last summer against various classes of catamaran with a Serenity + 70 cm fin + Code Red 11.0 m2 sail on ultra flat fresh water lake:

Class A cat (5.50 m lenght, 13.9 m2 main sail, 75 kg weight, one man crew) : I'm faster on all point of sail in 1-7 knots of wind. Above than that, the cat can still accelerate while the Serenity speed is topping up at around 12 knots.

Class B cat :

i) Hobbie 18 (5.50 m lenght, 22 m2 sail, 180 kg weight, 2 men crew, wing seat). I'm faster on all point of sail in 1-7 knots wind. Above than that, the Hobbie is faster while the Serenity is topping up at 12 knots Vmax.
ii) Hobbie 18 Tiger (5.50 m lenght, 21 m2 main sail, 180 kg weight, 2 men crew, wing seat). I'm faster on all point of sail. However, when the Tiger hoists her 21 m2 spinnaker, she's faster reaching & downwind.
iii) Ventilo 18' (5.50 m lenght, 20 m2 main sail, 130 kg, 1 man crew). We both are more or less on par. However, when the Ventilo hoists her 20 m2 spinnaker (2 men crew), she's faster reaching & downwind.

Class C : no drag race yet

Class 28' Ventilo M2 (8.53 m lenght, main sail 49 m2, jib 20 m2, genaker 72 m2, 375 kg weight, wing seat, 3 men crew). With only the main sail, I can barely follow her in winds around 5 knots. When she hoists the jib or genaker, I'm lost behind.

Class 35' Decision D35 (10.81 m lenght, main sail 80 m2, jib 44 m2, genoa 77 m2, reacher 128 m2, 1'250 kg weight, 5 men crew): I'm lost far behind, no questions. Being overpowered in 7/8 knots wind on a deep reach/downwind, the D35 is flying at 18-20 knots Vmax (2 x wind speed upwind and almost 3x wind speed downwind; *) , so clearly no match for any sailing boats including the Serenity in Beaufort 1-2 winds...!


So, I doubt a hydrofoiled Serenity could be faster than those large cats...

Cheers !

JM

(*) : http://mytrims.com/mytrims/trim4.asp?trimID=20273

Unregistered
15th March 2008, 07:39 AM
Well you have been sailing against the big boys.
A less experimental way of getting more speed would be a tandem Serenity, since the tandem Div 3 were faster than the solo Div2. In fact as Serenity isn't designed to plane the advantage might be greater. Maybe there is enough volume if the mast foot could be arranged ? And a dedicated light wind long board sail like the Aerotech Dagger or Demon VG5 might give you an edge when trying to embarrass those rich boys :-)
But seriously it's fascinating to think what is th fastest way round a short course singlehanded in the various winds.

steveC
15th March 2008, 11:16 AM
Hi JM,

Regretfully, I seemed to have missed your post above, but your candor is appreciated. While a Serenity sailor may not always be the most competitive race design in the mix, I'm awfully stoked about getting my Serenity very soon.

Although I'm not a formally competitive character in my efforts, I do enjoy the speed and efficiency associated with windsurfing (in higher winds its very obvious and friendly to the individual sailor). I really itch to take advantage of the low wind design from a simple fun and experimental viewpoint. Overall, it must be remembered that formal racing is very controlled and schedule focused, so I can be having fun irrespective of yacht club restrictions almost any time of the day. Nothing against formal racing scene, it just opens doors to individual enjoyment and fulfilment. I think that the individual aspect associated with windsurfing is at the core of the sport. Really, for those of us who want "no rules" time spent, it's a heaven of sorts.

andretsin
10th December 2008, 05:06 PM
I know this post stopped long time ago, but I would like to write my thoughts.
I also thought about the idea of a Serenity with hydrofoils. But when I think about that, my purpose is not to make the fastest board in any condition. That is not possible. For every condition there is a different design. For the ground there are wheels, and for the air there are wings. An airplane with wheels is slowlier than without them (that is why the hide them) and a car with wings would have too much surface (drag) (there are more reason why cars don't have wings :-) ).
A serenity with foils would be like a raceboard: slowlier than normal serenity in low winds but faster than planning boards, and faster than normal serenity in strong winds but slowlier than planning boards. But it would be the best overall wind conditions board (and spectacular).
It would need a folding hydrofoil to hide it in displacement mode to reduce drag (friction and induced), but this would make the board too complex and would brake with the main concept of windsurfing: simpliest sailing boat.
Gibbing and taking problems would be only a question of improving the design.
In my oppinion, I would put a normal "T" hydrofoil in the fin and some ski in the nose which would define the height and angle of flying, taking about 5% of the weight.

Jean-Marc
10th December 2008, 06:19 PM
A serenity with foils would be like a raceboard: slowlier than normal serenity in low winds but faster than planning boards, and faster than normal serenity in strong winds but slowlier than planning boards.

I doubt a hydrofoiled Serenity would be faster than a planing board. Below are the results of some drag racing I've made against a Bladerider (foiled moth) in light wind.

1) With a planing hull la HS105 + 11 m2 sail combo, we were equally fast side by side deep reaching in 7-12 knots wind range (typical Vmax 22-24 knots). However, as soon as I hit a 5 knots lull, I lost the planing while the Bladerider still continued at full speed hovering over his foils. I was stunned by the fact that the Bladerider has only a 8.0m2 main sail and weights around 45kg (compared to 20kg for the complete windsurfing gear). In low wind, the foils help a lot to reduce drag.

2) Another drag race in 1-5 knots of wind against the Bladerider, but this time on Serenity + 11 m2 sail combo. In 1-4 knots of wind, the Bladerider is really tippy and really slow while the Serenity is way faster, as long as the Bladerider cannot fly. She is faster than Serenity as soon as the Bladerider starts to fly over his foils in 6-7 knots wind, mainly because the Serenity's hull speed starts to top off at 12 knots in 7 knots wind. So, in ultra light wind, the foil is completely useless if you cannot make the hull fly.

That's all drag racing made so far for this year.

Cheers!

JM

andretsin
10th December 2008, 06:35 PM
I see i didn't explain it well enough. I mean that:
-In low winds (so low that is not possible to take off in hydrofoils and neigther planning in planning boards), hydrofoiled serenity would be slowlier than normal serenity (which don't have the wetted surface of hydrofoil) but would be faster than plannig board WHICH IS NOT PLANNING.
-In strong winds (flying in hydrofoils and planning), hydrofoiled serenity would be faster than non hydrofoiled serenity, but slowlier than planning board.
So, i agree with you and your experiments.

James
12th December 2008, 09:16 AM
Have any of y'all seen this video of the world's longest windsurfing board? It's a 9-man tandem, if I count right.

http://jimbodouglass.blogspot.com/2008/11/worlds-longest-windsurfing-board.html

It obviously a displacement board, but it goes fast enough that they tow a waterski behind it towards the end of the video. Not the most practical watercraft ever, obviously.

Aco
22nd December 2010, 06:13 PM
Interesting info and suggestions in this (old) post from March 2008.

Having owned more than 10 SB boards and enthusiastically followed the SB innovations from Formula to the longboard revival with Serenity and Phantom, I have to admit I am surprised that Starboard ignores Hydrofoiling:
considering the obvious advantages of Moth over Formula in light winds Hydrofoils look like a revolution on a silver Plate.

Meantime, AHD has taken the opportunity to develop the first commercial windsurf hydrofoil system:
http://www.youtube.com/watch?v=9XtY3AHUKKo

It shows that in light winds foils are much more efficient than planing, allowing a 7.5m sail to be used in conditions where a 11m2 is necessary for Formula to work (!).
Now, imagine what would a 12.5m sail do on the Hydrofoil Setup...

I sincerely Hope that SB will consider developing a Hydrofoiled Windsurfing:
Serenity looks like "the one" for hydrofoils, combining speed in displacement and foiling modes!

Interesting suggestions to resolve the height problem with a front "ski" foil is presented in
http://www.star-board.com/forum/showthread.php?t=1567&page=3

Some thoughts also under
http://www.star-board.com/forum/showthread.php?t=8526

Regards, Aco

davide
22nd December 2010, 10:49 PM
Meantime, AHD has taken the opportunity to develop the first commercial windsurf hydrofoil system:
http://www.youtube.com/watch?v=9XtY3AHUKKo

It shows that in light winds foils are much more efficient than planing, allowing a 7.5m sail to be used in conditions where a 11m2 is necessary for Formula to work (!).
Now, imagine what would a 12.5m sail do on the Hydrofoil Setup...

The AHD is very interesting, but I wander how real is the claim that a hydrofoil with a recreational 7.5 (in a video from AHD they are using a Hot Sails Liquid, no cams) can be competitive with a formula with 10-12 sail, or at least give similar performance for the recreational sailor. If it really was it would be a real breakthrough in light air design. For the AHD the long foil is a bit of a concern: if you thought a 80cm formula fin was big that THING under the hull will require some real planning when going back to the beach!