Efficient power cat

Here is something that I have been kicking around in my head for the past few days. 24-27' catamaran built to offer the capabilities of Bolger's Sneakeasy but with additional room & stability. The Sneakeasy with current fuel prices makes more sense now than ever, yet to many the beam is to narrow.

Here are some of the features I am aiming for with this:

Low power 9.9-30 hp
Good speed 30+ with 25-30
Comfortable (Beam of 6'+)
Shallow draft 8-10" with light -medium load
Safe (Should be able to make it through bay chop without feeling unsafe.
Stable (225# man should be able to walk around the boat comfortably.)
Stylish (lets be honest lack of style has killed/limited some other wise good designs)
Free plans (I would like to see the design be offered free to not for profit builders, depending on who is involved this may change)


If anyone wants to kick around kick around ideas please join in.

I'll work on some sketches this weekend of what I have in my head.

 

Please be aware that Professional Boatbuilder magazine is currently running a design challenge for many of the qualities you are describing. If you can stomach the thought of drawing a smaller boat, you might just have a winner there!

 

Hi Nomad,

Sneakeasy's beam is 4'3" and that's already wider than necessary for a boat that's so long. Why do you think people consider the Sneakeasy beam to be too narrow? I think this sounds more like your personal theory than any real consensus of opinion ...

30+ mph requires planing so the lighter the better -- but you want a catamaran which requires more materials (and labor) thus a catamaran will be substantially heavier (and cost more) than an equivalent length planing monohull.

Should we presume that you want the wing deck higher than the bay chop so the waves do not hit it? I think you should decide how high the wing deck will ride above the waterline. Please post the height of your 'bay chop' then post the height you want for the wing deck above the waterline.

Shallow draft is not an issue, the hulls will be flat bottoms (and not very narrow aft) to provide the required planing surface, and this results in shallow draft automatically if the boat is light enough -- which it had better be if you expect it to plane at 30+ mph with low power.

Will the boat have twin engines, one on each hull? If not, there's more work to design a fairing or pod or some kind of fin to be installed in front of the outboard so the prop stays 'in the water' and does not ventilate or create undesirable splashing in choppy conditions.

6 feet beam is very narrow for such a long catamaran, why not make it 8 feet wide so you can get more initial stability out of the two hulls?

You haven't provided any weights or capacities (how many people on the boat?) so please fill us in here.

I'm interested in your concept, but I view it as being relatively difficult to get all the features you listed in one boat. Which ones are optional and which are required?

 

this has already been done albiet with 10 more horsepower
see http://www.boatdesign.net/forums/showthread.php?t=23634
sean

 

This was discussed a couple of times before. This one is possibly lighter than you have in mind but it is stable and economical:
http://www.stillwaterdesign.com/pages/Newick32.html

If you are serious about exploring this I can produce optimised hull designs for your set conditions using Godzilla.

The other thing that is promising is a trimaran underneath and a mono on top. There is a thread that discusses this. Here is the basic idea:
http://www.boatdesign.net/forums/attachment.php?attachmentid=21228&d=1210326655

Rick W

 

Sean, the problem here is that Nomad specified only 25-30 HP so using an additional 10 HP doesn't give him what he wants in terms of engine size.

Rick, the problem here is that this boat is too long and it still goes only 23 mph with a 30 HP engine, yet Nomad says he wants 30+ mph from the same size engine.

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Guys, I'm not arguing about this for the sake of argument, but Nomad listed specs that in my opinion are very hard (if not impossible) to achieve -- that's why I asked him to tell us which items on his list are actually required and which are optional.

I think it would be *great* to see a 30 HP engine pushing a 24-27 foot long catamaran at 30+ mph, but my gut tells me he's never going to get this kind of performance with displacement hulls no matter how efficient they are. And 30 HP seems like too little power to get such a big boat onto plane and moving at 30+ mph so I'm not convinced that planing hulls will provide a solution either.

So where do we go from here? Has anyone ever seen such a short boat hit 30+ with displacement hulls? Or a boat this long plane at 30 mph with such low power? I would like to think that one of these options might be possible -- but I am also realistic enough to have serious doubts ...

 

Ken
You are right. Could not be done with simple construction without using foils. The Faux-tri would be the best solution. At a displacement of 1.5t it requires 25kW on the hull to do 24kts. A catamaran with same displacement requires 28kW for same speed.

If you could build lighter then it would be possible but then you are building to a weight rather than durability. A 1t boat would require 18kW at the hull to do 24kts. So get out the honeycomb and carbon fibre and away you go.

Rick

 

Thanks for confirming what I had anticipated Rick.

Given the fact that I live in the Philippines I can easily imagine a 1-2 person boat with bamboo pole hulls, bamboo connecting beams and an open bamboo deck (or just a trampoline made of fishing net) that might be light enough to hit 30+ mph on 30 HP ... so if this is what Nomad wants I think we are making incorrect assumptions when we talk about one ton displacements and such.

Let's see what he has to say about this and other important factors such as displacement, carrying capacity, chop height, wingdeck height, construction type, etc. before we get too far off in the wrong direction ...

 

Maybe it would look like this?
http://www.multihulldesigns.com/designs_stock/28cat.html
Gary

 

The specified requirement was to do that speed with less than one third of the horsepower of the craft in the link provided.

Rick W.

 

Of course you’re right Rick; I only posted it to give another example of how difficult it would be to meet the stated requirements. This cat weighs less than 1000lbs and it uses100hp for 24 knots. Not my idea of efficient. Nomad’s target will be hard to hit but I am watching with interest.

Gary