fin/sail size ratio - advice wanted

fin/sail size ratio - advice wanted

Post by Spencer John Cromi » Wed, 28 May 1997 04:00:00


Thanks for your help in advance.

        I have a Bic Astro Rock (120 l) that I sail with a 7.0m cambered sail
I am wondering if my fin, a stock "race 33" that is 13 inches long and has
an
area of 42 square inches might be too small.
         Also would shorter harness lines help to keep more pressure on the mast
foot
I have a seat harness and when I am hooked in the boom is at an arms length
away.
        I bought this gear last fall ( my first "modern" equipment i.e.:
shortboard, full battened sail)
I've been hooked in and sailing quite fast, but  I seem to be stalling out
when I get back near the foot straps which is a problem because eventually
I get launched.

Please respond privately as well. thank you    
--
Spencer

 
 
 

fin/sail size ratio - advice wanted

Post by Nicholas G » Wed, 28 May 1997 04:00:00

Hi Spencer,

I did post something similar something ago and the responses were pretty
good. I would take on the advice of what someone said about looking up
www.dejanews.com and searching in rec.windsurfing for past articles about
fins. There are really lots of them!

But just to test my understanding after all the good advice that I
received so far:

1) New fins, especially blade fins, don't take _sudden_ lateral pressure
too kindly, which means that being caught fully sheeted in in a gust can
sometimes mean instant spinout.

2) Fins are like sails in that they are supposed to behave like wings
rather than like walls, which means that water must flow, and must flow
fast in order to provide the force needed. Otherwise, the fin will give
way at slow because it is not much of a "wall".

3) Therefore, if you are spinning out while getting back into the straps,
it may mean that you are putting too much lateral pressure on the fin
before it has a chance to speed up gather enough force to counteract your
lateral pressure.

4) A bigger fin can get you planing earlier and perhaps take more "abuse"
at lower speeds in terms of lateral pressure (because it is more of a wall
than a small fin), but if you can get it up to speed, it's better to go
small.

I think you are basically not suppoosed to really lean out fully on your
fin until you are at good speed.

I had the same problem some time ago, with a 5.0 and a 10.75" fin, and
carried out the advice and really do see my problems mostly disappear. I
used to spin out when getting into my back footstrap, but no longer.

As for your question about harness lines - well I don't know enough to
comment about that... but modern techniques seem to emphasize short
harness lines.

Nik


Quote:

> Thanks for your help in advance.

>         I have a Bic Astro Rock (120 l) that I sail with a 7.0m cambered sail
> I am wondering if my fin, a stock "race 33" that is 13 inches long and has
> an
> area of 42 square inches might be too small.
>          Also would shorter harness lines help to keep more pressure on
the mast
> foot
> I have a seat harness and when I am hooked in the boom is at an arms length
> away.
>         I bought this gear last fall ( my first "modern" equipment i.e.:
> shortboard, full battened sail)
> I've been hooked in and sailing quite fast, but  I seem to be stalling out
> when I get back near the foot straps which is a problem because eventually
> I get launched.

> Please respond privately as well. thank you    
> --
> Spencer



 
 
 

fin/sail size ratio - advice wanted

Post by Volker Wedemeie » Fri, 30 May 1997 04:00:00


Quote:
> Thanks for your help in advance.

>    I have a Bic Astro Rock (120 l) that I sail with a 7.0m cambered sail
> I am wondering if my fin, a stock "race 33" that is 13 inches long and has
> an area of 42 square inches might be too small.

Well, 13 inches (33 cm) is a bit small for a 7.0 sqm sail. I usually use
a 36 cm fin with my 7.0 and in winds in the lower range even a 38 cm fin.
(14.2 and 15 inches respectively). (But then, I am not exactly a
lightweight.)

Quote:
> Also would shorter harness lines help to keep more pressure on the mast
> foot
> I have a seat harness and when I am hooked in the boom is at an arms length
> away.

Well, shorter harness lines won't help you much, I think. I have never
noticed much correlation between harness line length and spinout.

Quote:
>    I bought this gear last fall ( my first "modern" equipment i.e.:
> shortboard, full battened sail)
> I've been hooked in and sailing quite fast, but  I seem to be stalling out
> when I get back near the foot straps which is a problem because eventually
> I get launched.

I suspect what you have here (even though the fin is probalby a bit
small) is also a problem of proper technique. I guess you are exerting
too much pressure on the fin when you are not yet fast enough. Try to
really bear off wind before going back into the straps. Move back in
small steps and let the board accelerate, get into the straps, close the
gap (the board will still get a lot faster, when you do this) and only then
go back to a beam reach or even head upwind. But when going upwind,
watch your speed. If you let too much speed drain away, you
will eventually get a spinout. Remember that the faster you go, the more
load a given fin can take.

Hope that helps a bit,
                          Volker

 
 
 

fin/sail size ratio - advice wanted

Post by Brian Weeke » Mon, 02 Jun 1997 04:00:00



Quote:
> Thanks for your help in advance.

>    I have a Bic Astro Rock (120 l) that I sail with a 7.0m cambered sail
> I am wondering if my fin, a stock "race 33" that is 13 inches long and
has
> an
> area of 42 square inches might be too small.
>     Also would shorter harness lines help to keep more pressure on the mast
> foot
> I have a seat harness and when I am hooked in the boom is at an arms
length
> away.
>    I bought this gear last fall ( my first "modern" equipment i.e.:
> shortboard, full battened sail)
> I've been hooked in and sailing quite fast, but  I seem to be stalling
out
> when I get back near the foot straps which is a problem because
eventually
> I get launched........................

>Spencer, try a 40cm fin if you can get one to fit your board, it will make

a world of difference.It should suit your sail size well.>
Quote:
> I think you need more time on the water to practice increasing Mast foot

Pressure (MFP).  Try keeping the lines where they are, but raising the boom
a bit. Also try staying hooked in, in very light wind conditions, leaning
forward to increase MFP. I think I progressed most in light winds,
basically becoming VERY light footed, so back straps available (but no
weight put on board there at all- just used to put a little pressure
against fin).

Hope it helps

Brian Weekes
Chalkwell windsurfing Club

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