How to dimension a sailing catamaran?

Well you *were* referring to the "longitudinal underwarer lateral center"!

Mike

 

Nordic Cat thanks for your input.

What has taken time has been for me to "combine" the numbers from my Delftship model and the Terhohalmes spread sheet until i got something that i liked.

This is why i am building my half size model (Jarcat type) so that i can get a good feel on the water.

I will now start to draw the 12m cat in Cad and will post. This is what i will start to build 2009

I have found the Terho spread sheet very helpfull and basically work with it on a regular basis, i used it fot the 5m cat as well.

once again many thanks guys

 

Only just stumbled across this thread...

If only ISO and other's shared your views.....

 

this is very impressive, and may help some people to build their 'perfect' boat.

but i urge anyone not obsessive about 'my own work', to go to richard woods site, pick a boat 'close enough' and pay him for his years of experience and training. he will probably help you with any minor mods you think you need. and there's no shortage of other designers with similar background, if none of his suit you.

there's a hell of a lot more to building big boats than a few equations, valuable though they are.

 

Unfortunately, standardisation is an expensive and time consuming process. There are lot of people involved and they all need their fees. Books are not free, why should standards be? Fortunately there are public and uni libraries...

 

Absolutely.

 

As designers, we are encouraged & legislated to design vessels in compliance with standards like ISO, ABS, AS etc. Further, we are open to legal challenge should a vessel be produced that is not in accordance with these same standards - especially if there is some kind of problem with it.
Standards are produced with the safety of the general boating community in mind. As such they ought to be readily available to anyone and everyone to use.

 

Very cool to play with for someone who hardly understands the nomenclature. Anyone have time to answer a few idiot questions? I notice that changing the "width of one hull" changes nothing else (which it would obviously have to.) What am I missing here? I was punching in numbers for a 20m LWL when I notice the above. With the LDR being a locked cell, how would I change this to reflect an aluminum hull? You are using a 7.84, which according to your .pdf is a category reserved for high-tech racers (presumably something like prepreg and baked carbon at that figure.) Is the empty boat mass sans masts and other equipment, like the engines, full tanks, etc? Wouldn't the LDR also heavily change the price in materials and hours for construction? Do those last figures take into account the various build techniques for a given LDR or since that is a fixed cell is that the figure for a 7.84 construction one-off?

I'd have plenty of other questions but am still puzzling my way through this, thanks to anyone who answers.

 

The width of one hull changes the overall width of the catamaran. LDR is not locked, it's only a function of displacement (volume) and waterline length. If you chance the LBR or BTR of the hull eg. make it fuller or deeper, the displacement increases.

The table is mainly "a simple parametric toy" based on basic dimensions and relations of NA. It helps to be familiar with those terms. Have a good book like Larsson & Eliasson: Principles of Yacht Design. The idea is to design in fully loaded condition. Empty boat is just a percentage (70 %) of the fully loaded displacement.

 

Fun to play with, just seems that some things don't make sense to me. I knocked down the LBR and got some odd results. Speed and displacement drastically increased as did cost. I find that a bit puzzling since what I had in mind was (while not a stripped out racer) certainly should be less expensive materials wise than a racer built of out of pre=preg carbon.

Anyway, cool toy. Thanks

 

literary sources

I find the script of Terho Halme so interesting, that I would like to use these calculations as a start up part of my masters thesis.
In order to do so, I would need the literary sources used in the "How to dimension a catamaran" script.

Could anyone post:
*Books or articles related to this script?
*Tell me where all the empiric ratios come from?
*other helpfull literature?

You would help me a lot. Ah, and if anyone is interested: my thesis will be about a new typo of sailing cat on hydrofoils.

greetings

 

Sorry, the notes weren't too scientific. The referencies were missing. I try to correct that next week.

 

notice

alo...
i m new to this thing ... but i hav lods of apetit to mak a cat for miself nd friends nd go sailing in mediteranean sea nd greek ilands....
i found this -i think very impresiv- document some days ago nd if the formulas r gona prove ok...then i WISH i m gona hav the honour to giv this guy a great "present" som day...

i m working on a basic software which makes al the calcs for the formulas asking for the data nd giving bak the outputs...so i can play nd conclude on best dimensions for mi "beauti"

i l b more than hapy to atach it in the forum for evribodys free use...in a couple o daz

...one question i hav abaut the docs results in your example,so i m gona b sur there is no mistake in my formulas...

limiting moment in roll= 197*10^3 (my result)....133.7 .... (yours)

help?

thenx
ooo

 

yiesyisyeno i can assure you that very few people will take you seriously if you keep on writing the way you do, if you cant spell properly please get someone to help you

 

no nid 4 softwar....didnt notis .xlm