yacht design

[george_jl]

guys, i am trying to make a yacht model of 42" long, but i left my books behind and i don't remember the formula to calculate it according to the lenght, can you help me out?? does any of you remember the formula??? thanks!!!!

[SailDesign]

George, old buddy - you're going to have to give more info thatn that.
What are you trying to calculate?
Steve

[george_jl]

i am trying to calculate everything, the beam and the mast height according to the lenght of the boat

[SailDesign]

George,
You are going to find that there are a LARGE number of formulae to even begin to do that - the range of possibilities is enormous, even at 42"
You could be modelling a catboat, in which case anywhere from 20:"" wide to 24" wide at that length would be good, or you could be modelling a metre-style boat, in which case a beam of 7" would be close.
You could conceivably have a mast height anywhere from 70" to 45", depending on aspect ration required.
Waterline length could be anywhere from 25" or so up to the full 42"

Steve "not trying to make it complicated, but...."

[SailDesign]

Originally Posted by Me

ration

RATIO, dangit! RATIO....

<sigh>

[PAR]

Are you rationing about ratios again?

Frankly, george jl, you're trying to design a sailing craft of some sort, without the skills necessary.

This isn't a big deal in that it's a model and will not be taking folks farther from shore then they can swim back too. If it looks good and you build it into your boat, then all's good. A few well placed fishing weights will balance her out okay. I have a USS Constitution model floating in a fish tank. The other half gave it to me for Christmas one year and it took near seven pounds of lead on the centerline to get her down to her marks. Looks pretty cool when she sways a bit when the A/C is on or when big feeted people walk past.

If you intend to build something a bit bigger then you have a bunch of work ahead of you and it has little to do with building a boat. Design of a sailing vessel isn't child's play, nor easy by any means. A great deal of education will be necessary for a successful venture in the field.

There aren't any short cuts for mast height verses length on deck, no magic formulas for beam to length ratios (that's ratios, to most of us ) or prismatic coefficients just popping out of hats . . .

What are you really after George?

[george_jl]

Guys, i already made some calculations, and i am half way with this proyect,but i am afraid the small boat will sink ,and believe me,that's frustrating.

George, there are a number of classes of rc models you might consider: the two closest development classes are the US One Meter and the 36/600 which you can find more info on at: www.amya.org under Classes.(also see the IOM a semi development class)
You can also look there under Clubs and you might find a bunch of guys racing models near you that could help you.
If you want a model of between one meter and 42" to perform well you'll need a fin keel between 14" and 19" with a lead bulb between 3.5 and 5 pounds.
You'll want to have actual measured TOTAL sail area of arond 850 sq.in for your "A" rig(see rules). Most ,but not all, racing models have three rigs: "A","B" and "C".
Sail area generally must be reduced as the wind picks up and with three rigs you can sail in the same wind ranges as full size boats.
Beam for a model to perform well should be on the narrow side : 4-7" for a one meter model-wide boats don't go and planing hull forms DON'T plane...
Some model sailors claim their boats plane but it is a very grey area and such claims are usualy made without the tell tale signs of planing: dynamic lift, spray ect.Almost all (esp. narrow) models will exceed "hull speed" substantially in the displacement mode.
All up displacement of a performance boat in this size range is from 5 pounds to 6.5 pounds for US One Metre and 36/600 to 8.8 pounds for an International One Meter(IOM).
For a manual of calculations get a copy of Skenes and /or keep the CB at about 53% and the Prismatic Coeficient around 53-55 ....Good Luck!
Carve the thing out of styro and test it in the tub(really works quite well).....

[george_jl]

thanks Doug,your info push me near what i want,i took as a reference a RC model
36-600 which i bought some time ago,let's see what happens!!