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Old 14-09-2011, 05:45   #1
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Catamaran and Single Outboard

I have found that two outboards are needed for a catamaran due to cavitation. Can a single outboard be efficient by extending a transom further back on a cat? Say a 24 to 28 footer...okay, up to 32 feet?
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Old 14-09-2011, 06:05   #2
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Re: CAT & Single Outboard

Twin outboards will be just as likely to cavitate as one if not placed right. Stern extensions will help cavitation.
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Old 14-09-2011, 06:16   #3
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Re: CAT & Single Outboard

adding wings to the cavitation plate (normally designed to lift a mobo onto the plane) will also help to reduce cavitation.

Moving the engine forward will help (or adding length to the stern) as it will move the engine closer to the pivot point and thus reduce the impact of pitching.

getting a longer leg will reduce cavitation

motor/sailing will ensure less cavitation than just motoring.

I only had one engine on my Catalac / an ultra long legged diesel outboard with wings on the plate. No cavitation on a boat that can hobbyhorse for the olympics.
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Old 14-09-2011, 07:39   #4
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Our cat has a single ob mounted on a large electric hydraulic bracket. You can raise and lower it to handle most sea states with the flick of a switch. It rarely cavitates in rough weather
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Old 14-09-2011, 11:04   #5
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Re: Catamaran and Single Outboard

Thanks guys! So, if a "small" cat were in the works to be built, one outboard would do the trick. We call those wings a whale tail around here and they do make a difference.

Gato was using two 5hp, I'd rather buy a 9.9!
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Old 14-09-2011, 11:07   #6
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Re: Catamaran and Singel Outboard

And I see there is no way to edit my title! LOL!
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Old 14-09-2011, 11:26   #7
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Re: Catamaran and Single Outboard

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Thanks guys! So, if a "small" cat were in the works to be built, one outboard would do the trick. We call those wings a whale tail around here and they do make a difference.

Gato was using two 5hp, I'd rather buy a 9.9!
A single outboard will only work if you can turn the engine to take advantage for manoeuvring. In strong winds it can be more than a little exciting as you slow down in a marina! Having the outboard turn as the rudders do is relatively easy, but this is not so effective for the manoeuvring, and also when motoring into a nasty sea, causes a reduction in thrust in the required direction as you adjust the rudder.

I had a seperate steering system similar in concept to that used by Prout with the sillette legs. Much more effective, but not for the helm who does not instinctively understand the interplay between thrust and rudder angle.

A 9.9 will also have much more electricity generation than 2 x 5hp, and more grunt as well.
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Old 14-09-2011, 15:22   #8
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Re: Catamaran and Single Outboard

Depends on how often you visit marinas. Friends of ours have a single outboard and have no problem.

"Magic Carpet" circumnavigated with a single Yamaha 9.9.
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Old 20-09-2011, 07:48   #9
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Re: Catamaran and Single Outboard

The marinas I have been in have certainly been rather sparse compared to some I have seen pictures of on the coast. And some appear that there is no rhyme or reason to where some drop anchor and would be a nightmare navifating through and not crossing another's line.

Not sure I'd want to go into some. Wounder if a trolling motor would make a good bow thruster for a poor man's cat? LOL

Well, that's inland and marinas, has anyone been in aa river with a significant current, like the Mississippi? Does one engine work well in such conditions?
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Old 27-09-2011, 11:54   #10
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Re: Catamaran and Single Outboard

Our Gemini has one inboard with tilt up drive leg and when we bought a year ago we were advised to get a wheel knob to be able to spin the wheel quick enough to spin the boat 360 deg's in any marina. It does take a little getting used to spinning the wheel knob and throttle foward and reverse but it does work great. In addition having our center boards down in tight places keeps the breeze from blowing our boat around while parking in a moorage and we've never hit the dock unintended.
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Old 27-09-2011, 12:29   #11
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Re: Catamaran and Single Outboard

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...we were advised to get a wheel knob to be able to spin the wheel quick enough to spin the boat 360 deg's in any marina. It does take a little getting used to spinning the wheel knob and throttle foward and reverse but it does work great. ......
Even better if the outboard can be steered seperately using something like the wheeled knob on a lever. (attached to normal outboard steering system and thus seperate from the rudders).

I used this system for nearly 20 years on my catalac. Not as good as twin engines, but manageable in all but a major blow.
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Old 28-09-2011, 01:45   #12
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Re: Catamaran and Single Outboard

Our out drive stears along with the rudders so I can let my wife off the back steps at docks without any problems. At this point I would have to relearn everything to use 2 motors.
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