PDA

View Full Version : Isonic tuning questions


tswei99
20th August 2007, 01:58 PM
Tiesda's new videos for the 2008 boards generally recommends to put the mastfoot in the center of the mast track. Doesn't this totally depend on sail size and boom position??

The only way I can see keeping the mastfoot in the center is lowering the boom in the cutout as you use larger sails. I prefer to move the mastfoot up or back 2 cms for every 0.5 sq meter larger of smaller sail size while keeping the boom height at the same relative height in the boom cutout (for me that's dead center).

Tiesda, could you clarify???:confused:

Tiesda You
20th August 2007, 06:37 PM
Well it's an alternative way of tuning yourself. If it works, then that's all you need - fair to say that many windsurfers uses the same rule of thumb.

Moving the mast base position would affect where the mast foot pressure is applied on the board, therefore the leverage compared to where the board pivots with respect to the water surface (this pivot point would be close to your front foot). Whether you're using a big sail or a small sail you'd still want the board to trim with the same angle with the familiar leverage. Most of the riders I know move the mast track forward only if they want to hold the board down in super-overpowered conditions (more leverage). When they change sails up or down, the mast track position would again be determined by their need for added control or not.

Tiesda

geo
21st August 2007, 05:11 PM
Just my thought, whatever worth it can be.

To keep the board on a straigth line you need to have the sail center of pressure aligned vertically to the fin center of pressure. Fin position can not be changed (on iS boards with Tuttle box) unless by changing to different size/design fin, and anyhow that is by very small amounts compared to the sail COP position.
You can adjust this by means of mast foot position and/or rake; but usually a sail "feels good" with a certain amount of rake, and not else.
Sail center of pressure position depends on a) size and b) sail shape (both planform and profiles).
To my experience this is confirmed by better feeling moving mast foot forward with sails that have a) longer boom and/or b) more aft positioned draft; and backwards, with sails that have a) shorter boom and/or b) more fore positioned draft. As an example, I used a Sonic 95 during the last two seasons; when changing from TR-2 to TR-3 sails, I found new "sweetspot" mast foot positions that were moved much back; with my 7.0 TR-3 (218 boom) the mast foot is right in the middle of the track, while it was about 2-3 cms. front of that with my older 6.6 TR-2 (210 boom but more aft draft).
Other changes are useful to cope with prevailing conditions; as Tiesda says you can put the foot forward to keep the nose down in hard chop; or a bit back to "free" the board more in fast, super flat water conditions.
Reference position should be the center of the track for a "standard" designed, "sweet spot" size, sail (as an example, again: 7.0 is about sweet spot with my S95; but my TR-3 has a relatively long boom; but again it has a much forward positioned draft; so in the end it is track center; and some cms. back with 6.3).

Ola_H
21st August 2007, 05:53 PM
I don't have enough time on the water with my slalom gear to say (I still experiment a lot with different forms of tuning) but with my other gear, I generally don't move my mastfoot when changing sails. I usually find a spot on the board where is feels like I want it to feel and then just leave it there unless I want to trim the board in a certain different way for some special conditions. In fact, on my EVOs, I tend to end up with the mast foot pretty much in the same distance from the tail regardless of board size (70-100l), fin size (20-26cm) and sail size (3.5-7.0).

The exception is the EVO 62 where I have the mast foot a bit further back which, incidentally, makes the mast foot sit about as far from the front straps as on the bigger EVOs because of the tighter footstraps spread on the 62. Maybe an indication that Tiesdas explanation has some merit...

If we're gonna speculate and produce some home made theory here (which I like to do...I am after all a mathematician...), one reason that it may not be necessary to move the mast foot when changing (slalom) sails it that you often also change the fin and that will influence the balance point of the board-fin combo.

geo
21st August 2007, 07:14 PM
Ola,

I don't think so, at least for slalom kit. This because, considering possible setup changes on a given board, then fin range is not much big and anyhow it would change fin center of pressure by small amounts, probably millimeters; not comparable to possible changes in mast foot position., that are some centimeters.

I admit that, at least for me, mast foot position changes when changing sail size (same model) are not nearly as big as boom length differences would induce to think. As an example: between my 7.0 and 6.3 there is an about 18 cms. difference boom length, but I tend to change mast foot position by about 3 cms..

Ola_H
22nd August 2007, 01:36 AM
Maybe you are right. But I still think you have to consider the board+fin combo when discussing this. After all one can ride a board with a ridiculously small fin or even no fin at all and I in fact did 12 knots on my GPS sailing backwards on my nose the other day (well, the boards nose). So but that logic, we would actually get a "balance point" further back when mounting a bigger fin.

But it would be interesting to hear how the pros are trimming their slalom stuff.

Ola_H
22nd August 2007, 02:26 AM
I just asked Kevin Pritchard about if he changes any trim details like mast foot position or boom height when he changes sails and he said that he usually only changes sail and fin.

Erik Loots
23rd August 2007, 05:42 PM
I dont move my mastfoot a lot, but for speedsurfing a good position is important. My best position so far is 130cm from tail, that is with Gaastra Vapor '07. To front when conditions are gettind worse, to back when conditions get perfect. I only move (forward) when:
-My backleg is taking to much pressure
-I have to much tailwalking

Mastfoot position changes when other sail has more/less lift. The isonic I own is not a really speedmachine (Is105), I have to push it real hard, when going above 30 knots in pretty rough conditions is more flying than surfing.

Still when it comes 1 to 1 matchrace the isonic is hard to beat on the straight.

Hank
24th August 2007, 02:30 AM
...best position so far is 130cm from tail, that is with Gaastra Vapor '07.

Erik, which sail size were you using ? Isn't that quite rear ward ?

Erik Loots
24th August 2007, 05:51 AM
Yes it quite rear, the end of the rail is 129cm, middle is 136cm, front is 142cm. If you are on freerace sails or freeride sails, than I would suggest something between 135-138.

I am using:
Starboard Isonic 105 (footstraps in back position)
Gaastra Vapor 6.5 '07
Tectonics Goldwing 36 or Tectonics Falcon F1 30

I can my mastfoot @ 130cm because the sail&fin('s) gives so much control. When you are surfing everything to the back, the board will accelerate faster.

Only thing is for slalom the acceleration is not that important, for speed it is... For slalom you will get a bigger board in same conditions, to make sure you will wont be overtaken in a windgap (is that right word??). It is for sure more comftable for most windsurfers to put mastfoot in the middle, for me too, after a good day I have been surfing about 150km (100 miles) And my legs feel damn heavy, I think that the big pro's like Antoine must have strong legs to win a competitions like that, he is playing the power game.

The PWA has proven over and over that big power is still faster than efficiency, it is funny to see that in the speedcompetitions you see more and more windsurfers with less power/more efficiency and doing good speeds, but still not winning. But for the average windsurfer the big power game is not very nice thing to do.

Me personaly are changing every session from power/ to efficiency. And yes power is still faster for me too. BUT for training efficiency is very handy. Surfing in max gusts 18kn with 5.5 Gaastra Vapor + speedboard is not very nice, but you feel things you otherwise would not feel, this makes you faster when powered up.

All above is about downwind and deeep downwind for most, 135 degrees from wind mostly.
IF you are surfing most of the time crosswind, racing with friends etc. I would recommend to take a normal size sail not overpowered. Take not to small fin. And masttrack @ middle, that is what I do when I am into some matchracing, thats when the goldwing 36 is at his best.

Hank
24th August 2007, 11:37 PM
...the end of the rail is 129cm, middle is 136cm, front is 142cm.

Have just measured my iSonic 105 Wood edition, my measurements are a bit different, from the rear end of the mast track to a line perpendicular to the end of the board I've measured 125.5 cm, the length of the mast track is 16,75 (almost 17 cm), which would give a distance to the middle of the mast track to 134 cm - when measured from the rear.

Erik, are you sure of your numbers ? Measured the same way ?

geo
25th August 2007, 02:50 PM
Maybe this is going a bit too far... I don't think that when one says "middle of the box" this really implies "by the cm.".

Ola: I think that using just one foot position somewhat compensates for ususally different chop conditions when changing sails. Also, I think that a pro uses a smaller sail range for each board. As an instance, I move my track back a few cms. when changing between 7.0 and 6.3 on my S95, while KP would be changing between iS101 and iS87.
Of course leaving foot position unchanged when putting on a smaller sail implies raking more to have sail COP aligned with fin COP; this may be practical, but not over a certain point.

Erik: "power" setup implies stronger accelleration out of the turns, and obviously this is best for competition slalom. Evidently it proves good for speed also. But there is one more thing to consider, and that is time. A pro's aim is to be the first during a few minutes heat; while a non competing sailor's could be to have fun for some hours.
I am very glad because I can sail for hours at full throttle without stop and have no problem at all with my legs. But I have with my hands.

Ola_H
26th August 2007, 12:14 AM
Ola: I think that using just one foot position somewhat compensates for ususally different chop conditions when changing sails. Also, I think that a pro uses a smaller sail range for each board. As an instance, I move my track back a few cms. when changing between 7.0 and 6.3 on my S95, while KP would be changing between iS101 and iS87.
Of course leaving foot position unchanged when putting on a smaller sail implies raking more to have sail COP aligned with fin COP; this may be practical, but not over a certain point.



Probably true, but with the slalom 42 format even the pros end up with "unusual" sail sizes for a given board.

But I thought about it some more, and I think a possible answer might be the rake thing. I haven't checked out slalom sail designs that close, but isn't it possible that smaller sails are simply designed to be raked back further than bigger ones? Even the possible mast foot adjustment would not correspond to the total draft change from big to small sails, so some rake difference is bound to happen.

Someone with a lot of slalom sails could maybe confirm.

Erik Loots
27th August 2007, 06:05 AM
@hank

Maybe I'm wrong, I measured it almost 1 year ago. 136cm in middle makes good sense and works for 90% of the users. 128-129 was most back position, not the insert?? Otherwise it is maybe a difference between wood and d-ram, I own an dram, yes I am just a poor student ;)

@ola

Between different *boards I use same mastfoot position from tail. And my Gaastra Vapor '07 sails are not more raked back when they get smaller (can not see any differerance), however the last years the rake of the slalom/racesails is getting smaller and smaller... this has to do with superb control and that is why mastfoot postion is placed more in the back and the sail will have smaller rake.

I dont know if the sails can be even more controllable but if they do, than the masttrack should be placed more to the back to get the ultimate topspeed performance.