4.0 x 2.0 meter polyethelene catamaran

[foilcats]

4.0 x 2.0 meter polyethelene catamaran

Im looking for any design ideas for a small runabout to suit a diesel 10hp engine 65kg,

the boat needs to plane easily and not be too ugly,

must be open boat with no cabin,

stable and be able to carry the outboard load of up to 25hp manual or helm,

any good ideas to help and design features that one would expect to be on it please coment,

will give praise to who ever helps,

any sugestions be appreciated,

have a student to draw it over 500 hrs in next 3 months and will show it as it progresses,

[HJS]

Please, have a look to this one.
Close to what you are looking for?
Let me know.
Don't built this one!
There are some bugs in this design.
This is not the final design.

JS

[Fanie]

10hp inboard on an easy planing cat in polly is cutting it a bit thin. And that on a 2m thing ?

The smallest planing boat I have seen was a 2.8m baby cathedral hull with a 15hp outboard on it.

You left safety out of the equasion. Don't give students the idea they can design / build a boat without doing the safety thing, one of them may go off and build something and not come back to class the next day. Unless it's only a model boat.

[foilcats]

trying to keep to the basics and more a cat design with more deck room,
looks good though any back end views?

Please, have a look to this one.
Close to what you are looking for?
Let me know.
Don't built this one!
There are some bugs in this design.
This is not the final design.

JS

[Fanie]

Cat hulls have less buoyancy than mono hulls. You have to calculate the booyancy, take into consideration the weight of the boat as well as the rest of the stuff, motor, person, fuel etc.

Keep in mind the boat cannot float at deck height, there has to be reserve buoyancy left. To achieve this the hulls have to have some depth. If the hull height exceeds a certain height to boat width ratio to get enough buoyancy the cat is going to become top heavy and difficult to keep upright.

My opinion is such a small cat is going to be unstable never mind getting it to plane easily.

[PAR]

I don't think it would be that difficult to develop a cat hull to fit those needs, though a good working understanding of yacht design would be especially helpful. This wouldn't be one for a student of design, you're going to want a real designer.

I'd personally recommend a "sea sled" design for this size range to gain capacity and more usable internal volume. If you're not familiar with a sled, then picture a cat bows attached to an inverted V, mono hull, stern section. I have an 18' sea sled design that works very well, especially in shallow water on low HP. The sled design will plane more easily than a cat too. Contact me by email (click on my name) if interested.

[HJS]

trying to keep to the basics and more a cat design with more deck room,
looks good though any back end views?

It is very important to check up the total weight on a planing cat
check up the planing area - total weight relation
one hull planing area must have the ability to carry the total weight
when planing in rough sea it can be that one hull has to carry the total weight
and if the planing area is to small it goes down in displacement mode
with much more drag
while the other hull is still planing with less drag
this way the cat can go into an uncontrolled sharp turn
or capsize
thats also why the over all beam has to be moderate

if you need more deck space
made the boat bigger

the suggested design can go 30 knots with 15 hp
so 10 hp is my recommendation

js

multihull designer since 1966

[foilcats]

Here is a basic idea of what i want it to be like its double skin and has top and bottom mould parts, the hull design im working on now and appreciate the imput,

[foilcats]

heres the picture i forgot to attach it,

[sabahcat]

Sort of getting there but not quite but it is plastic

http://www.polycraft.com.au/300_tuff_tender.php

Heres the boat I like, but its in alloy

http://www.websterstwinfisher.com.au/2008models.htm

A 4m cat would be pretty weighty I reckon