Small Power Cat Design

[JPigott]

Don,

I find IVB hull design interesting. What are the shortcomings.

Is the flat sheer critical to the design. At higher speeds is the turbulent effect removed as the hull rides higher in the water. Just wondering if you could create a morph or blending of a cat and IVB.

I should probably take another look at the site.

Thanks
JPigott

Hi,
2 things we have found at the moment are>>
1.. they heel outwards in a high speed turn and this takes a bit of getting used to but in a normal turn not a problem..
2.. operator complacency ??????!!!!!!!!
if you look at the hulls being built by http://www.winninghoff.com have done just that but their problem is they still create a bow wave and loose half of the effect of a true ivb ..
take my word for it it will out perform any cat hull and require less horsepower to drive it , again a far stabiller platform and much lower centre of gravity ..
don

[small cat]

Thanks again for all the input.
Indeed I did have some difficulty simulating the engine weight with just one hull. So I build a second one and joined them with cross braces. However the tests were not very encouraging ..... the model will float with 2.8 oz aft but its attitude is very nose high. If the weight of a driver is added the attitude improves significantly, it actually looks normal. Anyway, I’ve decided that the current specs are unacceptable (unless I’m guaranteed to find a cheap, light and reliable outboard ... say 150 lbs) who wants to move aft and end up flipping the boat.

I’ll be increasing the length to 13’ and I’ll probably abandon the engine bracket ... keep it simple stupid.

I’ll try to post some pics when I’ve achieved acceptable trim and I’ll anxiously await your comments.
Phil

[small cat]

Just found an intresting article ..... if you're a cat fan.
http://www.hypermax.com/multihullsma...at%20hulls.htm
Phil

[JPigott]

That site does a great job of covering your options and trade offs. Also don't forget the motor can be inset. With a cat your not sacrificing displacement flotation area since it would be in the tunnel area anyway.

Best results.

Jpigott.

[KaiCarno]

May I ask what computer program people are using to make their pictures?
I'v tried Prolines which is good but it's somewhat old when it comes to 3D graphics. And I've only got the demo...no saving =) And I'm not going to spend 900$ on a program quite yet.

[Ilan Voyager]

Hulls are not the most expensive part in small boats...Engine and hardware are the most expensive. Also by experience, the design of small boats is very tricky, as they have tendency to "overreact" to the smallest mistake of design.

Keep the 30 HP and try to see what is the longuest hull you can move with this power. Make also a decision if you want a planing boat, or a semidisplacement one. With very slim hulls it's very surprising to constate the speeds attained with very modest powers, and the average speed that these boats are able to make.

Connecting the hulls of a motor multihull is a simple task (on sailing multihulls is a very difficult one) and in the small sizes it becomes very easy. Even simple aluminium pipes would work, do not worry about that.

A scale RC boat must have at least 4 feet long to be representative of the behaviour of full scale one. Smaller it's miniaturism, and becomes to difficult to make.