Hi all,
does anyone know if there is a formula for how tall a mast should be in
relation to the length and beam of a small boat?
Thanks for any help.

"wemfish" (wemfish AT tiscali.co.uk) writes:
Hi all,
does anyone know if there is a formula for how tall a mast should be in
relation to the length and beam of a small boat?
Thanks for any help.



the height of the mast is determined by the size and shape of the sail
which is determined by the boat's wetted surface, displacement, and beam.
you have to figure out the square footage of sail you want, then the type
of sail and how to distribute the area among sails if more than one, then
height-to-width ratio (aspect ratio) of the sails determined by where you
want the center of effort. those are the main considerations.

what kind of sail were you thinking of putting on the boat?

--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

I am happy to change it to whatever is best taking in to account that it
will mostly be a fun boat for the kids . The boat is not yet finished (only
a frame at the moment) The mast can be put where ever it needs to go and can
be built to suit the final mast/sail design...
The boat is 3.05m long and 1.05 wide at the water line
The waterline plane area is 2.59m2
Displacement is 0.103m3
Centre of displacement is X = 1.388m Y = 0.0m Z = 0.008m

) writes:
I am happy to change it to whatever is best taking in to account that it
will mostly be a fun boat for the kids . The boat is not yet finished (only
a frame at the moment) The mast can be put where ever it needs to go and can
be built to suit the final mast/sail design...
The boat is 3.05m long and 1.05 wide at the water line
The waterline plane area is 2.59m2
Displacement is 0.103m3
Centre of displacement is X = 1.388m Y = 0.0m Z = 0.008m


guidelines are sail area is 2.2 times wetted surface and also has Bruce
number of 1.3 for small boats (under 25 ft). Bruce number is square root
of sail area divided by cubed root of displacement. all sail areas in
sqaure feet. displacement in pounds of water displaced. numbers will not
agree but give range of possible sail areas. TF jones gives rule of thumb
for small boats arond 300 lb displacement of 1/4 sq foot sail area per
pound of displacement.

once you determine area of sail you then must determine shape which will
then give height of mast. some different shapes: bermudan, sprit, lug,
gaff, lateen, etc.

place mast so center of effort of sail is over daggerboard or centreeboard
or leeboard whichever boat uses.


--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned

not
used square and cube roots since collage!

Didn't know collage required that kind of maths ;-)

Steve

) writes:
thank you for your help, the sums should stretch the old brain cells, not
used square and cube roots since collage!


square roots are done automatically by most hand calculators.
for cube roots on a hand calculator I do it by stepwise refinement, ie
try a number you think might work, mulitply it by itself 3 times, and see
what you get. if it's too high pick a lower number and try that. if its
too low try a higher number. it takes about 4 or 5 tries to get a number
close enough. since the boat's design displacement doesn't
change the cube root has to be found once.

on a computer with Basic or a spreadsheet the cube root is just the number
raised to a power of one third, ie. displacement**0.333, or in some
notations displacement^0.333

--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned