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Old 08 August 2003, 16:57   #1
Country: USA
Town: Fairfield
Boat name: Sunrider
Make: Zodiac
Length: 7.3
Engine: MerCruiser (bio)diesel 180hp I/O
Join Date: Jun 2002
Posts: 296
Electric RIB - any ideas?

I'm working with a company that just received a contract from the US Navy to develop a high-performance/stealth RIB powered by an electric motor. I would be very interested in receiving any thoughts or ideas on this subject which may be offered by forum members - especially novel concepts, complimentary products or technologies, and ideas/considerations for civilian applications for RIBs of all sizes.

We will be using a unique new motor that has been designed specifically for the marine environment, called the Electric Wheel. You can find more information about the company, the technology, and current applications at this web site: It's too early to provide specs on the RIB to be developed, but the web site will provide all current technical details on the motor.

Our project is in the first phase, concept development. This will be followed by prototype building and testing, and then production of the resulting craft. Any comments or suggestions would be greatly appreciated.

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Old 09 August 2003, 18:29   #2
Country: USA
Town: Los Angeles
Make: Custom Catamaran
Length: 9
Engine: Twin Merc Optimax 225
Join Date: May 2003
Posts: 8
A couple random thoughts: You really have to attack this as a total systems problem, not just an engine issue. Whittle down your performance requirements as much as possible, top speed and time to plane. Look at every dimension of the craft and see where you can eliminate weight, drag, and energy loss/consumption.

Look hard at the hull shape, consider cat/tri hulls. Investigate the hysucat or other foil systems for milking every possible ounce of efficiency out of the hull. You'll have to squeeze every drop of weight out of the thing with modern materials. If you have foils for dynamic lift, and tubes for static/low speed buoyancy, the hulls now take on a more specialized role.

Take look at the propulsion/water interface, water jets, surface drives, or perhaps a very large slow turning prop (sacrifice top speed for low-mid range efficiency), submarine prop geometries? other custom geometries. I don't know what the state of the art is, but I would think the props are where the biggest gains are to be made. Do they really need 60mph top end, or is 30-40 enough. Will make a big difference in all your systems.

You don't mention if this has to be pure electric (e.g. battery/flywheel/other storage) or a hybrid solution. Given the drag involved in any kind of boat, and weight issues, I'm having a hard time imagining how you'll have a pure electric solution with any kind of range or speed.

As for hybrid systems; with a bit of battery storage to give you the boost you need to get on plane/foils your requirements for the engine change quite a big. It's either the Honda Insight or Toyota Prius that uses an engine with an Atkinson cycle, instead of the standard Otto thermodynamic combustion cycle. It's also much lighter, cooler running, tops at 3000 rpm. This totally changes cooling and bearing requirements, which makes the engine much lighter and more efficient. Using the battery boost to get over the hump to get on the plane also opens up other options. Micro turbines are very efficient, but have poor transient behavior. Since they run at a the same rpm all the time, they are much easier to silence than a normal engine that runs at various rpms. Also check into rotary and sterling engines. With all the water available for cooling, sterlings could be an interesting option. Again, the acceleration is poor, but for just driving a generator, and using the batteries for peak power, the engine requirements change quite a big.

When I first read about the Electric Wheel in Multihulls mag a couple years ago, I spent a couple hours surfing around the net trying to understand the issues for a hybrid electric rib. I was thinking of a hysucat rib with a large 30" surfacing piercing prop in a duct between the hulls. I could never find any good numbers for the prop efficiency and the true overall HP requirements. Then again, if you are trying for a "stealth" boat, I'm not sure if a surface piercing prop would be an option.

If you haven't already, you might also try

Would love to know what you come up with, keep us informed!

Mark424 is offline   Reply With Quote

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