Super economical wave piercing catamaran cruisers

[warren mosler]

Nice looking design!

A few comments-

Tops of lower bows look flat which will limit upward acceleration if they bury into a wave?

Upper bow far enough forward to come into contact with waves relatively quickly?

Looks like clearance over the water is relatively low limiting performance through waves over a few feet?

Looks like it would be fine in calm water at modest speeds?

[yacht371]

The design is preliminary only, although we have done some model testing.

The hull is almost a trimaran, with the central hull quite close to the water, but it has a very deep vee angle and is intended to contact big waves and provide reserve buoyancy.

After some experience with power and sailing cats of various types, any that have a bridge deck at all (as opposed to an open space with netting) will eventually slam when the wave height reaches a critical level. Up to that point they ride better than a monohull, often dramatically so, but once the bridge deck starts to slam, the ride rapidly worsens.

This design will actually start to slam sooner than a flat high bridge deck, but the ride will not deteriorate so suddenly. It will be able to continue in reasonable comfort at a slower speed in worse conditions than a more conventional shape.

Disadvantages? Expensive to build, the forward protruding bows can throw up spray in some conditions. We tried a similar concept without the forward protruding bows on the Motorcat 29 produced in Poland. The ride is very smooth until the waves get over about 4 feet (steep short ones, not long swells) then you must slow right down. Still in tests we did 20 knots into seas that had monohulls 10' longer turning for home.

The bigger the size of the boat, the better all this works. All I need is well heeled clients!

A 36' concept similar to the MC29 is below.

Grahame Shannon

[masalai]

yacht371, That looks like it is designed to fit in a standard marina berth. Have a look at the SharkCats and PowerCats - production designs developed for use offshore of the Australian Gold Coast, so as to be able to tend the shark nets set of the beaches to "protect the swimmers". Up to about 28 ft could not be surpassed and would do in ANY weather/seas, up to 40knots with twin outboards. They became a popular choice for the volunteer rescue services and sometimes as an adjunct to surf lifesaving operations of occasion...

They are highly regarded by those who need all weather short haul (200 miles or less) capability.

[Greenseas2]

When we address the design restrictions on a wave piercing cat, the most significant operational restriction is wave slap to the underside of the deck. Recently we tried a variety of WP cat designs for a major ship for the USMC and USN to be built after 2010. Testing was done at the Carderock USN test tank in Maryland. The vessel sign called for operations in seas state 3 and be able to straddle a pier for self loading/unloading with internal hoists.

In addressing larger wave piercing cats, wave slap has to be considered and it is generally found that this feature limits the height of the seas in which a WP cat can operate. Also, when considering wave piercing cats, different docking arrangements are in order other than slip width. As mentioned above, larger wave piercing cats for passenger or cargo carrying make good use of a pier that they can straddle and load/unload either through inner hull doors or from hatches in the under deck. Primary considerations of design are operating sea state conditions, economy of operation, speed (mostly moderate) and docking arrangement. The straddle-the-pier arrangement offers ease of handling passengers or a self loading capability, with no need of passenger "jet-way" type ramps or external gantry cranes and associated equipment.

[kengrome]

We aren't looking for engines in the hundreds of horsepower, but lesser hp with more efficient engines.....possibly a diesel outboard.

Since there's no such thing as a diesel outboard, how about a 4 stroke gasoline powered outboard? They simplify things a great deal and they are easy to work on and replace as needed. Besides, most Americans have far less 'fear' of outboards than inboards.

The end goal is for a wave piercing cat that can accommodate a max of 4 people in relative comfort and burn approximately 200 gallons of fuel for the 1,200 trip at a max of around 18 to 20 knots and leave no wake.

Good concept. What's your target retail price? What type of construction is preferred ... or accetable? Do you plan to build them in the USA or have them built overseas and ship them to the USA?

[masalai]

Originally Posted by kengrome

Since there's no such thing as a diesel outboard, how about a 4 stroke gasoline powered outboard?

I understand Yanmar make one rated at 27 hp, but it appears a bit dated & heavy however I believe there is other diesel outboards being developed?...

"retractable" electric legs with the motor at the bottom (propeller end) are being developed by "AfricanCats" for their hybrid sailing cats - by the address somewhere in Northern Europe... this link GREEN MOTION Retractable Drive System 31-05-2007 at this site http://www.africancats.com/

[kengrome]

I understand Yanmar make one rated at 27 hp, but it appears a bit dated & heavy however I believe there is other diesel outboards being developed?

Well, Yanmar used to make them, but they were apparently so costly and unpopular -- or possibly problematic -- that they discontinued them with no plans for re-introducing them.

[Greenseas2]

Actually the are two manufacturers of diesel outboards that still offer them Yamaha is one (rather than Yanmar) and China Diesel Imports in Jotul, California is the other. The reason that Yamaha isn't in the united States is that the engines don't meet US environmental standards. This, by the way, is also the reason that European diesel autombiles that represent a high percentage of sales in Europe aren't in the US.

In addressing diesel versus 4 cycle gassers, there are few, if any, gas engines that have the fuel economy of a diesel. Also, due to much higher torque, the diesel engines support a significantly larger prop than gas engines. In discussing design for a wave piercing cat, we're looking at a fairly large cruiser where engine weight of the outboard is a secondary consideration, but range is primary. In essence, the over all economy is a package that includes nfactors such as hull design and power plant efficiency. Another train of thought is the use of internal diesel generators with twin electric propulsion motors mounted in the hull. Food for thought.

[kach22i]

Originally Posted by masalai

... this link GREEN MOTION Retractable Drive System 31-05-2007 at this site http://www.africancats.com/

Cool link, great idea.

[rambat]

I think this new design will fit into the thread, we are showcasing a new 66' Swath type yacht that can ballast up to transit as a catamaran/wave piercer. We have had the test model running for several years and now have styled it for the up-market. like the GPH efficiency's discussed here, it is remarkable:

TOTAL FUEL OPTIONAL TANKAGE MILES/GAL(8KNOTS) RANGE(8KNOTS) MILES/GAL(20KNOTS) RANGE(20KNOTS)
250 BASE 3 750 1.5 375
570 320 3 1710 1.5 855
820 250 3 2460 1.5 1230

NOTES
1. FUEL TRANSFER SYSTEM REQUIRED WITH OPTIONAL TANKAGE
2. TESTS WERE TAKEN UNDER GOOD CONDITIONS

The new topside looks have been well received and most yachts magazines have showcased it in the last two months, that's a good sign it may not be too odd looking for the target market. That seems to be the challenge for many twin hull design of late. Running picture of the test bed and new design render attached.

[Greenseas2]

I'm rather surprised that the sponsons aren't totally enclosed . In a relatively high chop with water coming over the tops of the hulls, there would be 6 areas for water to impact and act as resistance whereas if they were enclosed, the water would simply flow down the sides. The designs are beautiful and as far as public acceptance goes, I sincerely believe that the public is ready for new and fresh designs as long as the designs represent greatly enhanced economy of operation. One suggestion though, being that hull speed is determined by the square root of the waterline length, it may be worthwhile extending the hulls further forward.

[rambat]

Our speed is limited by too small of waterjets right now, however the hull will project farther on the new design for more recovery buoyancy. The hulls are up only when running as a cat in smooth condition, otherwise the boat is better in Swath model when seas are rough.

[Pericles]

A coincidence, but the Ax Bow being discussed elsewhere on this forum is also a wave piercer with the added benefit of not being deeply immersed in waves.

Here's the article. Pages 5 & 6.

http://www.hiswasymposium.com/pdf/2006/J.%20Gelling.pdf

Pericles