More Sail Size vs Wind Speed

More Sail Size vs Wind Speed

Post by Tony Gaun » Thu, 03 Dec 1998 04:00:00


How about the other way ... marginal planing, not how big a sail
can you hold on to.

If I can plane with my setup on a 6.5 at 13 knots or my planing
threshold is 13 knots, and the wind drops to 10 knots, how
big a sail will it take to get me planing on the same setup.

How much do you think a 7.5 or 8.0 would lower the planing
threshold?

Going bigger than about a 7.2 gets expensive ...
new sail + new mast + new boom == $$$

------------------------------------
Tony Gaunce
Screamer 278, Ride 282, Escape
Neil Pryde, Rushwind, Powerex
Hatteras, Emerald Isle, Jordan Lake
------------------------------------

 
 
 

More Sail Size vs Wind Speed

Post by Cxkh3 » Thu, 03 Dec 1998 04:00:00

Quote:
>If I can plane with my setup on a 6.5 at 13 knots or my planing
>threshold is 13 knots, and the wind drops to 10 knots, how
>big a sail will it take to get me planing on the same setup.

>How much do you think a 7.5 or 8.0 would lower the planing
>threshold?

This is a really good question.  Perhaps Ken Winner, Bill Hanson or any of the
other experts could weigh in on it.

 
 
 

More Sail Size vs Wind Speed

Post by TomBuckO » Thu, 03 Dec 1998 04:00:00

Quote:

>>If I can plane with my setup on a 6.5 at 13 knots or my planing
>>threshold is 13 knots, and the wind drops to 10 knots, how
>>big a sail will it take to get me planing on the same setup.

>>How much do you think a 7.5 or 8.0 would lower the planing
>>threshold?

It will lower it a somewhat - and also make you go LOTS faster at 13 mph.  That
wind begs for the biggest sail in the quiver.

Tom  - Chicago

 
 
 

More Sail Size vs Wind Speed

Post by han.. » Thu, 03 Dec 1998 04:00:00

Quote:

> >If I can plane with my setup on a 6.5 at 13 knots or my planing
> >threshold is 13 knots, and the wind drops to 10 knots, how
> >big a sail will it take to get me planing on the same setup.

> >How much do you think a 7.5 or 8.0 would lower the planing
> >threshold?

> This is a really good question.  Perhaps Ken Winner, Bill Hanson
> or any of the other experts could weigh in on it.

The key word here is 'if' as some assumptions have to be made....

Assumming planning is initiated at a boardspeed of 10kts, a rough
aerodynamic force calculation on a beam reach predicts a sail size of
9.2 for 10k of wind. This includes an adjustment for apparent wind angle
at the point of planning.

A 23% decrease or (30% increase) in wind speed is fairly dramatic as we
all know when we are 'hunting' for a puff...

 - Bill Hansen
   Sail Design/R&D
   Windwing

 
 
 

More Sail Size vs Wind Speed

Post by han.. » Thu, 03 Dec 1998 04:00:00

Quote:


> > >If I can plane with my setup on a 6.5 at 13 knots or my planing
> > >threshold is 13 knots, and the wind drops to 10 knots, how
> > >big a sail will it take to get me planing on the same setup.

> > >How much do you think a 7.5 or 8.0 would lower the planing
> > >threshold?

> > This is a really good question.  Perhaps Ken Winner, Bill Hanson
> > or any of the other experts could weigh in on it.

> The key word here is 'if' as some assumptions have to be made....

> Assumming planning is initiated at a boardspeed of 10kts, a rough
> aerodynamic force calculation on a beam reach predicts a sail size of
> 9.2 for 10k of wind. This includes an adjustment for apparent wind angle
> at the point of planing.

Addendum:
I made a small mistake on the calculation. 10kt predicts a 9.0 sail...

Assuming the original postulation of planing with a 6.5 in 13kts,
following is wind/sail chart for two boards. One which planes at 10kt
boardspeed (A) and another which planes at 5kt boardspeed (B).

Wind     Sail(A)     Sail(B)
13        6.5          6.5
12        6.8          7.5
11        7.8          8.9
10        9.0         10.5
 9       10.5         12.7

Food for thought: Does a board with a longer waterline and higher
initial planing speed need a smaller sail due to the benefits of
apparent wind and the velocity squared rule?

 - Bill Hansen
   Sail Design/R&D
   Windwing

 
 
 

More Sail Size vs Wind Speed

Post by han.. » Thu, 03 Dec 1998 04:00:00

ATTENTION!

My profuse apologies for the previous posting!
It was WRONG.

The question was:

Quote:
> > >If I can plane with my setup on a 6.5 at 13 knots or my planing
> > >threshold is 13 knots, and the wind drops to 10 knots, how
> > >big a sail will it take to get me planing on the same setup.

> > >How much do you think a 7.5 or 8.0 would lower the planing
> > >threshold?

> > This is a really good question.  Perhaps Ken Winner, Bill Hanson
> > or any of the other experts could weigh in on it.

I responded and followed up with a chart of wind vs. sail size which had
a computational error.

Please note the CORRECTED chart below:

Quote:
> The key word here is 'if' as some assumptions have to be made....

Assuming the original postulation of planing with a 6.5 in 13kts,
following is wind/sail chart for two boards. One which planes at 10kt
boardspeed (A) and another which planes at 5kt boardspeed (B).

Wind     Sail(A)     Sail(B)
13        6.5          6.5
12        7.4          7.5
11        8.4          8.9
10        9.8         10.5
 9       11.4         12.7

Food for thought: Does a board with a longer waterline and higher
initial planing speed need a smaller sail due to the benefits of
apparent wind and the velocity squared rule?

SORRY for any confusion!

 - Bill Hansen
   Sail Design/R&D
   Windwing

 
 
 

More Sail Size vs Wind Speed

Post by Cxkh3 » Fri, 04 Dec 1998 04:00:00

Quote:
>Assuming the original postulation of planing with a 6.5 in 13kts,
>following is wind/sail chart for two boards. One which planes at 10kt
>boardspeed (A) and another which planes at 5kt boardspeed (B).

>Wind     Sail(A)     Sail(B)
>13        6.5          6.5
>12        7.4          7.5
>11        8.4          8.9
>10        9.8         10.5
> 9       11.4         12.7

>Food for thought: Does a board with a longer waterline and higher
>initial planing speed need a smaller sail due to the benefits of
>apparent wind and the velocity squared rule?

That makes sense, since A has a higher board speed  and more apparent wind.
OTOH board B is not nearly as efficient.  It is only sailing 5kt in 13 kt of
wind, while board A is sailing 10kt.  It probably just takes more sail to
compensate for a drop in wind.  

Anyway, it looks like in this case it takes more than a meter in size to
decrease planing speedby 1 kt.  Returning to Ken Winner's article it looks like
weight of sailor is more important cause he said a 130 lb woman planed on an
8.3, while the 180 lb men needed 9.5+ sails.  Unfortunatley, I don't think I
can lose 50 lb!

 
 
 

More Sail Size vs Wind Speed

Post by han.. » Fri, 04 Dec 1998 04:00:00

Quote:



> > Assuming the original postulation of planing with a 6.5 in 13kts,
> > following is wind/sail chart for two boards. One which planes at 10kt boardspeed (A) and another which planes at 5kt boardspeed (B).

Corrected chart.
Wind     Sail(A)     Sail(B)
13        6.5          6.5
12        7.4          7.5
11        8.4          8.9
10        9.8         10.5
 9       11.4         12.7

Quote:
> Great info but I'm a bit confused (not surprisingly).  When you say board
> A planes at 10kt boardspeed does that mean board A needs to be travelling
> at 10kts before it will plane?

Yes.

Quote:
> If so then I would think, for a given
> wind strength, board B would plane sooner (thus requiring a smaller sail).
> Assuming both boards require the same energy (sail size) to get to
> 5 knots (at which point board B is planing), then to get board A to 10 kts
> would require still more energy (i.e. sail).  What have I missed?

That was the food for thought...
The assumption is they take the same force to plane i.e. 13kt/6.5 sail.
Not to accelerate to 5kt boardspeed. Ever notice how a long board
transitions to planing smoothly where a short board 'hits the wall' and
needs a good puff to get it going? Two things to consider: waterline
length and drag once planning. I believe the new AVS boards point this
out quite well as they initiate planning much differently than
conventional long and short boards...

 - Bill Hansen
   Sail Design/R&D
   Windwing

 
 
 

More Sail Size vs Wind Speed

Post by Tony Gaun » Sat, 05 Dec 1998 04:00:00

Thanks for the input Bill.  It's great seeing you share your
knowledge here the way you do.

I guess sail size doesn't make as much difference as I thought
when it comes to planing.  I think that going bigger than my 6.5
will make a difference but I don't want to go too big.

I'm at the point where I'm just starting to make a few of my
jibes so that is what I spend my time doing on the water.
I know the sails are getting lighter and friendlier but have to
guess that it's not practical to go work on jibes with an 8.x
sail.  Am I wrong?  I'm thinking of going to a 7.5 and that
with the new sails the handling will be ok (and the synthesis
7.5 fits on a 460).  
In light winds, I'm probably better off with a smaller sail
and bigger board working on sail handling skills,
pivot jibes, helicopter tacks, etc.

I got to demo a Windwing Race 7.7 a couple weeks ago and
was very impressed.  Powerful and seamless camber rotation.
The demo was at Barton's shop.  I had driven out (4hrs) for
the day with a SCA 20-25 forecast.  Got on the water as
the wind died.  Got a couple planing reaches on my 6.5
and 282.  One of the guys from the shop had his gear ...
7.7 WW Race and Seatrend Allstar 70.  I would guess him
to be my size (much better sailor) and he was planing
constantly, doing laydowns.  We switched sails.
I was immediately planing with the 7.7 but couldn't seem
to stay upwind as well as he was ... probably my skill level +
board / fin combo.  Sailed it for about 20 min.  Went back
to my board, never got on a plane again.  I was one of
the last off of the water.  What SCA??  Oh well.   This fall
has been that way.

Quote:

>Assuming the original postulation of planing with a 6.5 in 13kts,
>following is wind/sail chart for two boards. One which planes at 10kt
>boardspeed (A) and another which planes at 5kt boardspeed (B).

>Wind     Sail(A)     Sail(B)
>13        6.5          6.5
>12        6.8          7.5
>11        7.8          8.9
>10        9.0         10.5
> 9       10.5         12.7

------------------------------------
Tony Gaunce
Screamer 278, Ride 282, Escape
Neil Pryde, Rushwind, Powerex
Hatteras, Emerald Isle, Jordan Lake
------------------------------------
 
 
 

More Sail Size vs Wind Speed

Post by han.. » Sat, 05 Dec 1998 04:00:00

---snip---

Quote:
> I guess sail size doesn't make as much difference as I thought
> when it comes to planing.  I think that going bigger than my 6.5
> will make a difference but I don't want to go too big.

Tony:
I think sail size DOES make a difference - 10kts just isn't much wind...

Quote:
> ---snip---not practical to go work on jibes with an 8.0 sail.

A 7.5 on a 460 is pretty convenient. OTOH, practicing with big sails
makes the smaller ones seem easy and it is amazing to see what the
racers are doing with 9 & 10 meter sails ...

Quote:
> In light winds, I'm probably better off with a smaller sail
> and bigger board working on sail handling skills,
> pivot jibes, helicopter tacks, etc.

A little 'freestyle' in sub-planing conditions goes a long way.
 - Bill