Re: More help for the mathematically challenged

Thanks. I did it the triangles way and (using 7'6" for the dimension
tack-to-peak) got about 33.6 sq. feet -- that should do it.

Garth

> Anyway, to do it graphically, divide the figure up into triangles,

or rectangles and triangles (right triangles are easier) and
calculate the area that way. Don't worry about scaling errors; a
couple of percent won't make any difference in how the boat sails.

> > So, how do you calculate the area of sail (a little standing

lug) 4'3" on the luff, 5'3" on the head, 6'3" on the foot, and 7' on
the leach?

You can't do it from the information you gave. You could with the
equivalent dimensions for a triangular sail, but not a four-sided
one. There are lots of different-shaped and sized sails that could
be made with those dimensions (Imagine four sticks of those lengths,
tacked together with pins at the corners - you can change the shape
of the figure, which you can't do with a triangle). The additional
piece of information needed is the angle of any one of the corners.

Anyway, to do it graphically, divide the figure up into triangles, or
rectangles and triangles (right triangles are easier) and calculate
the area that way. Don't worry about scaling errors; a couple of
percent won't make any difference in how the boat sails.

Keith Wilson

--- In bolger@y..., garth@b... wrote:
> So, how do you calculate the area of sail (a little standing lug)
> 4'3" on the luff, 5'3" on the head, 6'3" on the foot, and 7' on the
> leach?

 

garth@... wrote:

 

 So, how do you calculate the area of sail (a little standing lug)
4'3" on the luff, 5'3" on the head, 6'3" on the foot, and 7' on the
leach?

I'm sketching out a rig for my sailing pirogue. It should be smaller
than the 40 sq. ft. sail recommended for the Bolger Pirogue -- as the
Michalak Piragua has a narrower beam.

Garth
(and who's buried in Grant's Tomb, anyway?)
 
 

Just a suggestion, turn your drawing into two triangles, solve for their areas, add them up and, voila! More important is to solve for their center of areas, combine the two and make sure that the center of area of the whole sail is not too far away from the boat's center of lateral resistance. Aft produces a tendency towards weather helm while having the sail's center forward of the boat's will lead to your having a lee helm. All lee helms are dangerous.( imho)
Jim

OK -- this is a bit embarassing, as I KNOW I once knew all this stuff
-- back in junior high school. There was even a brief time when I
could do integral calculus. Yeesh. All that useful knowledge pushed
aside to make room for "Simpsons" trivia . . .

So, how do you calculate the area of sail (a little standing lug)
4'3" on the luff, 5'3" on the head, 6'3" on the foot, and 7' on the
leach?

I'm sketching out a rig for my sailing pirogue. It should be smaller
than the 40 sq. ft. sail recommended for the Bolger Pirogue -- as the
Michalak Piragua has a narrower beam.

Garth
(and who's buried in Grant's Tomb, anyway?)