generic multihull dimensions

[CharlieKilo]

Hello, all.
Being new to the forum I'm going to ask a question that will probably be old hat to most of you, but here goes.
Can you point me in the direction of where to find general dimension design parameters for power multis? For example overall L/B, tunnel width, deck height, prismatic coefficients for a particular speed.
Any help would be appreciated.

[ancient kayaker]

This question covers a lot of ground. You will have better chance of an appropriate answer if you advise what kind of power multi and application you are interested in, IMHO.

[CharlieKilo]

Thanks. I guess I should have known that. Actually, I'm thinking of a human powered catamaran (or possibly trimaran) for use out on Lake Erie. So, I guess I'm looking at a length of approx. 16 feet; speed to lengh ratio of approx .75. What kind of min L/B for the hulls? Over-all L/B? How high does the bridge deck need to be considering I'd be working in "big" water. I understand that if the hulls are too narrow then my draft will be such that Launching might become more difficult; too beamy then my speed will suffer. Primarily looking for speed and multihull stability to enable me to cover max distance in a given day trip. Thanks for any input you might have.

[gonzo]

A circular section is the most efficient. Probably a bit of rocker. What is the total displacement, that is including crew and supplies? What is the type of propulsion?

[ancient kayaker]

For human powered boat design you might want to contact Rick Willoughby, he is no longer a member but his posts and threads are shown as Guest625101138. You can serach for his stuff, also check out his website at http://www.rickwill.bigpondhosting.com/

[Ad Hoc]

Originally Posted by CharlieKilo

Actually, I'm thinking of a human powered catamaran (or possibly trimaran) for use out on Lake Erie. So, I guess I'm looking at a length of approx. 16 feet; speed to lengh ratio of approx .75. What kind of min L/B for the hulls? Over-all L/B? How high does the bridge deck need to be considering I'd be working in "big" water.

Firstly, welcome.

Secondly, you're going about this the wrong way.

Since you have defined 16 feet, is this thumb in the air figure...or is it based upon a "requirement" that the boat must have?

You need to establish 2 things first before you start thinking about details.

1) Establish an SOR..statement of requirements. What the boat must achieve..not a wish list, we can all do those. But a proper list of requirements that the boat must achieve, no matter what. Think of it as a "shopping list".

2) Draw a GA..a general arrangement. Until you draw out to scale, try graph paper as it is easier, the outline of what you want, and where you place the equipment etc, you wont have a clue if you can satisfy the SOR. If the layout you draw, for example, shows a length of 20 feet, but your SOR has a max of say 16 feet, it is back to the drawing board. You have to start again, so the two match up and are complimentary of each other.

Until you have done #1 and #2 above, you're guessing and playing with numbers that have no meaning.

[CharlieKilo]

Thanks for the input. Perhaps I am going about this backward, however I need to know where to look for info in order to do the basic drawings. Human power seems to be limited to about 3kts. Canoes, kayaks even trans oceanic rowboats all hit about 3kts. There doesn't seem to be much point in a 25-ft hull if you aren't going to do 5+ kts.
Sixteen feet is the length of 2 plywood panels so I'm using that as a starting point. As I refine the numbers, the length can change.
Thank you, Terry for the info. Gonzo, I'm looking at contra-rotating props in a Kort nozzle. Saw a post on a submarine website that was contemplating the same, so I thought the increased efficiency could make a pretty fast (relative term) cat or tri.

[ancient kayaker]

Originally Posted by CharlieKilo

... Human power seems to be limited to about 3kts. Canoes, kayaks even trans oceanic rowboats all hit about 3kts ...

Rick Willoughby's boats go a great deal faster than 3K...