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Breaking the 30 knot barrier

Created by

Windxtasy > 9 months ago, 10 Apr 2012

Wind Foiler

142 posts

2 Jun 2012 1:02am

Hi Anita. I saw your sail the other day at cobblers. Sailing Behind you I noticed your leach wasn't as loose as it should be. Try more down haul. I found it made a big difference to my top end speed. Also a fin size. You were sailing the same size fin as me, but I was on a 68w board with a 7.8 and I ended up changing down 4 cm. something to think about.

decrepit

12802 posts

2 Jun 2012 8:06pm

Just came across this article,

deniswee.net/ApparentWind/action.htm

It's a bit technical, but I found the last paragraph very interesting.

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The interaction of lift and drag also explains a commonly known fact, that in strong winds a small sail will go faster than a large one. What happens is that a sailor using a large sail becomes overpowered and he cannot fully sheet the sail in. The angle of attack is, say, only two thirds of optimum. The drag, on the other hand, remains practically unchanged. The ratio of lift to drag is drastically reduced and the sailor experiences a loss of speed. By switching to a smaller sail which the sailor can fully sheet in, the angle of attack will be at an optimum, thus producing a lift which will be about the same as with the larger sail, but the drag on the smaller sail will be a lot less. There is therefore a greater forward component of driving force on the sail and the board travels faster. Of course, a heavier sailor who is able to fully sheet in the larger sail will be able to take advantage of the increase in lift in the larger sail.

This is a bit counter intuitive, and it's probably hard to work out where the point is for optimum sail size. But I think this means if you want to go as fast as possible, rig for the gusts.

And maybe why the guys heavier than me go faster using the same size sail, I don't feel over powered, but maybe not sheeting in as much as I think????

Windxtasy

4017 posts

2 Jun 2012 11:19pm

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Tomasz80 said...

Hi Anita. I saw your sail the other day at cobblers. Sailing Behind you I noticed your leach wasn't as loose as it should be. Try more down haul. I found it made a big difference to my top end speed. Also a fin size. You were sailing the same size fin as me, but I was on a 68w board with a 7.8 and I ended up changing down 4 cm. something to think about.

Thanks.I will try more downhaul. I don't have a smaller fin for that board (67.5W) without going to a 32.

decrepit

12802 posts

3 Jun 2012 5:39pm

Anita, I use a 31cm weedy with my 65 no problems. so the 32 may be worth a try.

Windxtasy

4017 posts

4 Jun 2012 6:06pm

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decrepit said...

Anita, I use a 31cm weedy with my 65 no problems. so the 32 may be worth a try.

I think if there's enough wind for my 32 I'd be using my smaller board anyway

evets

685 posts

9 Jun 2012 3:33pm

windxtasy if you can get to Australind tomorrow pm it is looking good. Speed on really flat water is easier than chop. Hope to see you there.

Windxtasy

4017 posts

9 Jun 2012 10:28pm

Thanks for the heads up. Unfortunately I have commitments tomorrow.
Monday could be on the cards however...

sboardcrazy

NSW

8292 posts

20 Jun 2012 5:00pm

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kato said...

sboardcrazy said...

Windxtasy said...

decrepit said...

What a lot of heavy guys don't realise is how much chop slows lighter people down.
Well at 70kg, that's where I place the blame for my lack of speed anyway.
And I'm sure Anita is a fair bit lighter than me.

Also most speed gear is aimed at bigger heavier people, those footstraps are probably too far apart.
Board trim is important, getting the entry point behind the front strap is hard if you don't have enough weight to sink the tail.
A few people have used aluminium bars to extend the front straps backwards with good results. (See Tom Chalko's page).

My fastest speeds are on a 5.3 metre sail with a fin around 20cm in flat water. with 25-30kts wind
Instead of going bigger Anita I'd try going smaller, (being in control is a big part of going fast) and looking for flat water with decent wind.
If we get a good day at yoyo's this Winter, that should do it.

Yes, keeping the board down in chop is very difficult for me, especially if overpowered.
I think I would like my footstraps closer together but they are as close as they can get without modifications.
I'd agree with being in control being important. If you're overpowered you're not using the sail at it's maximum efficiency. I have often been slightly overpowered on my 5.8. It hard to tell with the koncepts because they are manageable even when very overpowered. Now I have the 5.0 sorted I will use it more often.
I only have a slalom board, not a speed board.

I'm not doing speed runs but I find with my 95ltre Rocket the straps are too far apart to use both unless I'm going beam reach or lower.I tend to sail with my rear foot out of the strap and up against the front one as a result..Bit scary in chop.I think they don't design boards for small females..

Sue, its a common problem that we all face. Try Toms method of moving straps closer together without having to drills holes, its makes a huge difference. ~~http://www.mtbest.net/isonic50.html~~

Interesting..Might need my partner to have a look and make something up..

I don't frequent this forum much. What is an Alpha ,I know PB is personal best..any other terms explained would be good.

Windxtasy

4017 posts

20 Jun 2012 3:39pm

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sboardcrazy said...

kato said...

sboardcrazy said...

Windxtasy said...

Sue, its a common problem that we all face. Try Toms method of moving straps closer together without having to drills holes, its makes a huge difference. ~~http://www.mtbest.net/isonic50.html~~

Interesting..Might need my partner to have a look and make something up..

I don't frequent this forum much. What is an Alpha ,I know PB is personal best..any other terms explained would be good.

An alpha is basically average speed of a gybe over 250m, where the start and finish must be within 50m of each other.
I still haven't managed that 30 knots yet. Waiting for that combo of wind & flattish water.

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