Question on fin positioning

Question on fin positioning

Post by Harry Sh » Fri, 29 Sep 1995 04:00:00


I am sailing an older Seatrend (9'4") which has the standard American fin
base.  Depending on the fin, there is about 2-3" travel available front to
back.  The board has a 14" blade fin and sails well planing and has good
upwind capability.

My question is related to fin position and using the foot straps.  I'm
getting used to the foot strap stance, and find that the board tries to
point into the wind, unless I steer it downwind when using the straps.
This is not noticed when the board is planing and I'm out of the straps.
This steering downwind involves the need to lift the windward rail to
avoid pointing.  I don't have this problem with my 10'6" Mistral
transition board, but it has two complete sets of foot straps, and I use
the forward set.

I am also wondering if subtle changes to the mast position, harness lines,
etc may mitigate my "problem".  Any pointers (except into the wind :-)  
) would be appreciated...

Harry Shin

 
 
 

Question on fin positioning

Post by Tae Su » Sat, 30 Sep 1995 04:00:00


Quote:

>My question is related to fin position and using the foot straps.  I'm
>getting used to the foot strap stance, and find that the board tries to
>point into the wind, unless I steer it downwind when using the straps.
>This is not noticed when the board is planing and I'm out of the straps.
>This steering downwind involves the need to lift the windward rail to
>avoid pointing.  I don't have this problem with my 10'6" Mistral
>transition board, but it has two complete sets of foot straps, and I use
>the forward set.

Harry, it sounds like you need to move the mast step forward or your fin
back or both. When you get into the footstraps, you'll rake the sail back
further, which moves the center of effort in the sail back behind the center
of lateral resistance of the board. This makes your board want to
"weathervane" into the wind.

You want to balance the CE over the CLR. You move the CE by moving the mast
step and the CLR by moving the fin. Try moving the mast step an inch or two,
you won't need much to notice a big difference. Experiment with different
positions to find the optimal balance point for that sail and fin. Yes, the
position changes with every different sail :-(

Good luck,

Tae

 
 
 

Question on fin positioning

Post by IAMFLA » Sat, 30 Sep 1995 04:00:00

Oh no, not another fin sail placement question.  

Lift the rail?  How about keep the board flat untill the turn?!

Flash Alexander
Flash Buddy

 
 
 

Question on fin positioning

Post by William Bradley Lig » Sat, 30 Sep 1995 04:00:00

Yes, with a blade, definitely try the fin all the way back in its track.
I'm not so sure about the mast track. If you're more comfortable in front
of the straps and in the front strap set on your big board that suggests
that you need to pull the mast track back to use the back straps.
It might be a sail-tuning problem too. Try more downhaul so the top
of the sail twists off more and doesn't weather vane you so much when
you rake the sail back.


 
 
 

Question on fin positioning

Post by Nick Ki » Sun, 01 Oct 1995 04:00:00

Quote:

>I am sailing an older Seatrend (9'4") which has the standard American fin
>base.  Depending on the fin, there is about 2-3" travel available front to
>back.  The board has a 14" blade fin and sails well planing and has good
>upwind capability.
>My question is related to fin position and using the foot straps.  I'm
>getting used to the foot strap stance, and find that the board tries to
>point into the wind, unless I steer it downwind when using the straps.
>This is not noticed when the board is planing and I'm out of the straps.
>This steering downwind involves the need to lift the windward rail to
>avoid pointing.  I don't have this problem with my 10'6" Mistral
>transition board, but it has two complete sets of foot straps, and I use
>the forward set.
>I am also wondering if subtle changes to the mast position, harness lines,
>etc may mitigate my "problem".  Any pointers (except into the wind :-)  
>) would be appreciated...
>Harry Shin

The rule of thumb is positon the front of your fin under the***to
you rear foot strap. But then it's not just that simple to solve your
problem that just gets your fin in a good place.

There are numerous exlainations for your problem and your on the right
track in your last paragraph.

Mast Position - Generally speaking your mast should be further back as
your sails get smaller in size. The exception to this might be if you
are under powered then moving the mast position forward helps get the
board on an plane quicker.  The problem is compounded by changes in
new equipment. Newer sails tend to have their center of effort built
further forward in the sail. This means that the mast needs to be
further back with certains sails, but newer boards are building the
mast tracks fruther back so everything changes depending on the board
and or the sail. SOLUTION: if you are just beginning to get into the
foot straps you will find it easier to learn by putting your mast
further back.

Harness lines; more important than you think. But rather than getting
technical just try to center your harness lines so you can controll
your sail with equal effort from both hands. As you get more
comfortable try to move the ends of the harness lines closer together
on your boom. Length is also critical. They should be as long as you
can adjust them and still be able to push the board over onto the
leeward rail by pushing your weight down onto your feet. It's probably
to error on the short side.

Tah Surh the first posting in this thread gives a good explaination of
the dynamics of the center of effort and steering. It is essentially
the basis of everything I have said here.

 
 
 

Question on fin positioning

Post by Nick Ki » Sun, 01 Oct 1995 04:00:00

. SOLUTION: if you are just beginning to get into the

Quote:
>foot straps you will find it easier to learn by putting your mast
>further back.

Opps !!! The solution is to move the mast forward. Then it is easier
to rake the mast and this will move your center of effort forward and
cause you to have a more downwind attitude.
 
 
 

Question on fin positioning

Post by Paul A. Billing » Wed, 04 Oct 1995 04:00:00

Quote:

>>>My question is related to fin position and using the foot straps.  I'm getting used to the foot strap stance, and find that the b=

oard tries to point into the wind, unless I steer it downwind when using the straps.  This is not noticed when the board is planing =
and I'm out of the straps.

A possible cause is not being sheeted in enough.  I see a LOT
of people who don't.  In fact, a friend of mine had the
identical problem until I secretly moved his lines back about
two inches.  (He kept telling me he *was* sheeted in :-)  He
came back to the beach grinning from ear to ear.

If that's not your case, position the mast back (assuming
powered conditions) and the boom so that the harness lines are
directly between the footstraps when the sail is raked.  Put
the fin back.  This will move the center of resistance back.

Paul -- US366 (Maui)

 
 
 

Question on fin positioning

Post by Paul A. Billing » Fri, 06 Oct 1995 04:00:00

Quote:

>. SOLUTION: if you are just beginning to get into the
>>foot straps you will find it easier to learn by putting your mast
>>further back.

>Opps !!! The solution is to move the mast forward. Then it is easier
>to rake the mast and this will move your center of effort forward and
>cause you to have a more downwind attitude.

Yes, this does move the CE forward.  It also forces the nose
down, moving the CR forward (bad).  However, moving the mast
back (when powered) allows more of the board out of the water,
moving the CR back.  It depends, of course, on the board
rocker, but in my experience, it is better to move the mast
back.

Paul -- US366 (Maui)

 
 
 

Question on fin positioning

Post by chris mancu » Sat, 07 Oct 1995 04:00:00

As far as fin position, I find it rare that I have it anywhere except all
the way back on my Seatrend 9.0. If you find that moving your mast back
resolves some of your conflicts, you'll want to make sure the COF is not
behind your COLR(center of lateral resistance, ie: fin). Similar to the
previous post, the higher the wind, the further back with the mast.
Sometimes though, I find it easier to have the mast forward if I'm
suddenly overpowered to the point of "tail-walking". This helps to keep
the nose down.

Good luck
ChrisM

 
 
 

Question on fin positioning

Post by Tae Su » Sun, 08 Oct 1995 04:00:00


Quote:

>>Opps !!! The solution is to move the mast forward. Then it is easier
>Yes, this does move the CE forward.  It also forces the nose
>down, moving the CR forward (bad).  However, moving the mast

...

Aha! Light bulb in head turns on. That explains why a board with the mast
track too far forward has a tendency to round up. I was having problems
figuring out why a board with the mast track too forward has the same
symptom as a board with the mast track too far back.  

 
 
 

Question on fin positioning

Post by Duc Gy » Sun, 08 Oct 1995 04:00:00


Quote:

> As far as fin position, I find it rare that I have it anywhere except all
> the way back on my Seatrend 9.0.
> Good luck
> ChrisM

What works for me is to position the leading edge of the fin just under
the rear***of your rear footstrap.  I have tried different fin
placements but this works the best.

Duc Gybe