Hull design - CAD drawings

I'm thinking of making a GRP model of the hull, what's the convention for this in Navel Architecture any particular scales or is all the same for factoring performance into the real world. I was thinking of a 1:20

 

Here's an old thread that pertains somewhat to your enquiry:

http://www.boatdesign.net/forums/boat-design/scaling-laws-hull-dynamics-22528.html

 

much appreciated

 

I'm going to drop the hydrofoil idea and just have the catamaran hull can anyone point me to displacement calculations once I have my dead and live loadings

 

well your hullshape is dead simple

volume is lenght x cross sectional area.
yes you could use software,,, but a pretty reasonable answer for your shape could be used with graph paper. Say your hulls are 1m wide and 20m long ,, dispacement is 10 tonnes. That is 5 tonnes each, about 250kg per meter of hull lenght, so roughly draught will be 25cm. Now because its a bit rounded,,, thats less volume in your hulls, thus more draught, so i reckon 30cm draught.

It aint that complicated.

other option is to put in all into software etc. If your not confident with software,,, and say you get a more complicated shape,,, just work out on graph paper cross sectional area every meter... Add them all up and divide by 20, that will give a rough number.

by suggestion is use metric, 1 cubic meter of water weighs 1 tonne, makes the calcs easy. Once you have worked out your draught,, then convert back to imperial

 

Even though you are dropping the hydrofoil idea, I am curious about one thing. Can you use the basic lift equation applied in aerodynamics for hydrodynamic calculations as well? Substituting the density of water for air, obviously.



If so, the calcs for a hydrofoil wouldn't be too bad.

 

Great thanks, Ive got 7.38 m3 so that's 7.38 tonnes of displacement. Even with 10 people on board Im only at 2970KG so good to go right ?

 

gee,,, ummm what to say

yes, if your hulls are 20m long, and 1m wide,, yes you can work out draught. Thats really high school stuff, maybe even primaray school level. Probably your hullshape will be more complicated than what you have drawn... all you know at the moment is that the shape you have will have a draught of approx 30cm. If you give your hulls finer ends that means more draught, as you have less volume. Finer ends means it goes faster.

What you have is a simple pontoon, makes a good houseboat... long long way from a good power cat

Have you noticed that a lot of people are staying away from this thread... so far you have not provided a huge amount to inspire. just a pair of pontoons.

 

Hey man, I don't do much fluid dynamics but I'm willing to learn. It is a simple pontoon defo not a power cat and it will become a houseboat, I'm trying to work out the basic design limitations. I'm more use to thermal calculations and structure and I don't want to make any basic errors. I'm pretty happy I've got my first displacement calc ! Super cats next year.....

 

I went to the Southampton boat show yesterday and found a great electric jet thruster system http://www.navigatorsmarine.co.uk/jetthrust.php
Does anybody have any experience with this I was considering an electric water thruster as my main drive or maybe off a hybrid diesel engine. I'm about 3000kg fully laden and was thinking of modifying the system to provide main thrust and manoeuvring. This system runs for 4 mins but I assume you can get ones like on a jet ski

 

Are there any issues's with putting the propellors in the tunnel of the cat hull, only cruising speed required, any benefits to tapering the water towards the propellor like entrainment ??