Aluminum Power cat designs

[GMI]

Hello I am on a quest to locate some different power cat designs for aluminum construction. I have been reading the different forums and see that there is a lot of knowledge within . The basic design would be as followed.
36 – 40 feet LOA
Beam of 12 feet.
Draft if we could keep it under 2 feet that would be great but I understand if it’s not.
Would use outboard power. Not looking for high speed 10 -14 knot would be plenty.
This boat would be used as a day boat ( no staterooms) more for entertaining. Would be used on the great lakes and connecting rivers and lakes. Would also like a small fly bridge helm station.
The boat is not intended for heavy weather operations but should be able to get you home if caught in some bad weather.
So if you have some suggestions please share. These are not exact specs so anything close would be great. I total understand that there is a lot more information required to dial in a design just wanted to get something started.

Thanks

 

[Alik]

We have about 40 catamaran designs launched from our drawing board, both alu or composite. Can do such design on order, if required...

 

[Richard Woods]

If you want an aluminium powercat you would be well advised to check out Alik's designs

I have a 36ft powercat, the Skoota 36, but it is built in plywood as a live aboard cruiser, although one is building in foam sandwich as a day charter boat for the Mediterranean. A few wood ones are building, see here

http://sailingcatamarans.com/index.php/designs/6-powercats/265-skoota-36

there should be no problem keeping to under 2ft draft as that implies 4ft on the WL or less, thus a 10: L/B ratio which is what one might expect for an efficient hull

Would you build it yourself? Would the "entertaining" be commercial day charters?

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

[JSL]

fairly narrow beam for a cat!
Are you carrying people (private boat) or passengers (commercial boat)??

 

[Ad Hoc]

Hi GMI

At 10-14knots..it is hardly a power-cat in the true sense.

I designed an ally cat with almost those dimensions several years with outboards. She did 22knots (with a cabin for 6 passengers), thus your 10-14knots would be very easy to achieve.

 

[Mr Efficiency]

As JSL says, the beam seems too skinny for a slow cat to be running efficiently.

 

[GMI]

Update,

Ok I see I am in the right place. As I suspected there are a million and one different opinions about Cat’s and Cat designs . Let me update a few things so I can dial this in.
1) This would be a private boat not interested in carrying passengers for hire. Nor building a chapter T boat
2) I will be building this in my shop, this is one reason I threw out the 12 foot beam. I have a 12 foot door to the building shed. With that said If I need to increase the beam to get a boat with proper performance characteristic so be it. Just increase’s over all build costs to move to a bigger space. But If I am going to put money into a project it should be right or it’s not worth doing.
3) Speed, I stated that I would like to do 10 to 14 knots. I understand that I should be able to double that speed and be in most cats sweet spot. I guess I was just trying to state that speed is not the key points to this project. Sure if I had the chance to cruse at 20 knots and do it efficiently that’s great, but most of the time we would be entertaining along the rivers or bays where we might not be able to use that speed so why spend extra money on HP. I would like to keep hp to say twin 150’s
4) Some other things that might help the discussion
a) Like the look and like working with aluminum so that is why I would like to stay with that material.
b) Have a dock in front yard that boat would be moored at, depending on weather, it can get a little shallow so draft is a factor and again if we pull her into a beach alum seems to handle that the best.
c) One of the key factors in my thinking cat’s is, we are looking for a stable plateform. Some of our friends don’t like the rolling around we do on our current mono hull and what fun is boating if you can’t take your friends.
Well I hope this puts this into perspective. Like a stated in my first post I am hoping to get insights from people that have the experience and passion for Power Cat’s
Thanks for reading and our inputs.

 

[Richard Woods]

Thank you for the update, as you have already realised the more information you can give the better the replies will be

12ft wide is narrow even for a 40ft monohull. The first thing to do is to check out all the similar boats already on the market that meet your requirements.

You'll see that the hull for a 36-40ft powercat is likely to be 5ft wide, that would only give 2ft between the hulls, so you can see immediately that that you will need a wider boat

On a 36ft powercat twin 40hp-60hp should get you 10-14 knots. I own a 28ft powercat with twin 20hp outboards and even when cruising we can motor at that speed

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

[Ilan Voyager]

Just a word about the material; for a 35-40 feet you'll suffer to build a cata at a decent weight in aluminum compared to a similar one in plywood/glass epoxy. Welding thin aluminum sheets is not easy, welding them in structural welding is pretty difficult. I predict that you'll have a lot of work straightening, debumping and filling after the welds. Make a trial MIG welding 2 sheets of 5xxx alloy 1/8 thick over 20 feet at 120 degrees with a 5356 wire without deformation, you'll understand...On this size the decks will be 1/8 thick with a lot of structure under, 3/16 or better 4 mm on the topsides and 1/4 or better 5mm on the bottom. The weight of the bare hull will be simply twice of a plywood one, and you have to make all the insulation and inside lining...The worst is that the aluminum hull will be less strong than the plywood hull, and far noisier.

 

[Ad Hoc]

On this size the decks will be 1/8 thick with a lot of structure under, 3/16 or better 4 mm on the topsides and 1/4 or better 5mm on the bottom. The weight of the bare hull will be simply twice of a plywood one,

Greeting IV...and a happy NY to you

I had 4mm all-round on my cat, designed to DNV too. Hull weight was 2.0tonne..on a 4.0m beam..which is just a tad wider than the OP's after.

 

[Mr Efficiency]

c) One of the key factors in my thinking cat’s is, we are looking for a stable plateform. Some of our friends don’t like the rolling around we do on our current mono hull and what fun is boating if you can’t take your friends.
.

Cats have a different motion, but not always more agreeable than a mono's characteristics.

 

[Ilan Voyager]

Greeting IV...and a happy NY to you

I had 4mm all-round on my cat, designed to DNV too. Hull weight was 2.0tonne..on a 4.0m beam..which is just a tad wider than the OP's after.

Hi Ad Hoc, happy NY to you. Aluminum is a nice material, but it asks a "technicity" beyond the possibilities of 99.9% of the DIY builders. You're a pro in alu so...

 

[GMI]

last comments

Hello all,
just wanted to say thanks for the input. Some I agree with, other not so much, but all helpful in deciding what direction I want to go. I will keep searching for information and if I need input I have learned where to ask. Thanks and have a great 2015

 

[Wavewacker]

Hello all,
just wanted to say thanks for the input. Some I agree with, other not so much, but all helpful in deciding what direction I want to go. I will keep searching for information and if I need input I have learned where to ask. Thanks and have a great 2015

Any progress in your plans? You certainly drew a great crew here to comment, what would you not agree with?

 

[Steve P]

Aluminum power cat designs.

You may look at Specmar's web site at www.specmar.com. All of their boats are CAD lofted.