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Old 21-12-2016, 18:27   #1
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Counter rotating engines on catamarans

I am a newbie to sailing and catamarans, have been studying adds for catamarans for about a year now and I have yet to see any one mention the use of counter rotating engines. I have run across discussions on prop walk with strait shaft inboard engines. Could it be that they all have counter rotating engines so they do not even say any thing in the specs? Or would this not have any bearing on the handling of a catamaran?
I have tried searching for other posts to no avail, maybe I'm a dummy and it would not any effect on the handling of a twin hull.
Any answers or links would be appreciated, thanks.
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Old 21-12-2016, 18:34   #2
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Re: counter rotating engines on catamarans

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I am a newbie to sailing and catamarans, have been studying adds for catamarans for about a year now and I have yet to see any one mention the use of counter rotating engines. I have run across discussions on prop walk with strait shaft inboard engines. Could it be that they all have counter rotating engines so they do not even say any thing in the specs? Or would this not have any bearing on the handling of a catamaran?
I have tried searching for other posts to no avail, maybe I'm a dummy and it would not any effect on the handling of a twin hull.
Any answers or links would be appreciated, thanks.
I say very little difference. Why? Because I used to build aluminum powerboats. Many of these got 2 x 200hp or 2 x 250 hp outboards on the back. Our standard installation was to have counter-rotating engines. More than once we tested boats with both engines standard as the counter did not arrive in time or other issues. We found almost un noticeable difference. One a cat with lower HP and much wider apart, I say zero effect.
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Old 21-12-2016, 19:23   #3
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Re: counter rotating engines on catamarans

High powered boats with props close together it does matter, low power and far enough apart that the wash doesn't join, maybe not so.
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Old 21-12-2016, 19:58   #4
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Re: counter rotating engines on catamarans

I'd expect that any prop walk would be totally masked by the turning moment resulting from an absolutely minimal difference in RPM between the two widely spaced engines.

I've never experienced any on my cat.
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Old 21-12-2016, 20:13   #5
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Re: counter rotating engines on catamarans

These days almost no counter rotating engines are produced, although 35 or 40 years ago it was very common to see counter rotating gasoline engines. This was largely because the gear boxes were made to have output shaft rotation the same as input shaft rotation, thus opposite rotation props required opposite rotation engines.

Today most large engine gear boxes allow full time rotation in either direction with the same ratio, and most saildrives also counter rotate with the same reduction ratio lessening the need for opposite rotation engines.

Sailing catamarans usually have enough beam between the props that maneuverability isn't hampered whether or not the props have opposite rotation.

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Old 21-12-2016, 21:18   #6
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Re: counter rotating engines on catamarans

When I purchased my cat, the props were both right hand drive. I switched port transmission to left hand drive and maxi prop to left hand. Both props turn outboard. Seems to help handling around the docks, can walk it sideways and spin easily in it's own length. Yanmar 4jh2e's
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Old 21-12-2016, 23:50   #7
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Re: counter rotating engines on catamarans

I would have to check on the new cat...never even gave it a thought.


On our old flybridge power boat, the engines both turned the same direction but the transmission reversed the one.


As others have said with the extra width of a cat, propwalk is less of an issue.
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Old 22-12-2016, 00:21   #8
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Re: counter rotating engines on catamarans

I had counter rotating props on my cat. Replaced a damaged leg and missing prop and now they both turn the same way. Never even noticed a difference. But now one spare prop will cover either side...
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Old 22-12-2016, 04:25   #9
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Re: counter rotating engines on catamarans

Greetings and welcome aboard the CF, acp.
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Old 22-12-2016, 08:11   #10
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Re: counter rotating engines on catamarans

Thanks for the answers. I guess "P" factor must not have much effect in water. With air plane props the effect can be quite dramatic. I know that a lot of things that seem good on paper, can be a waist of time and money in the real world, this seems to the case here . Having one spare prop would be a huge savings.
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Old 22-12-2016, 10:31   #11
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Re: counter rotating engines on catamarans

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When I purchased my cat, the props were both right hand drive. I switched port transmission to left hand drive and maxi prop to left hand. Both props turn outboard. Seems to help handling around the docks, can walk it sideways and spin easily in it's own length. Yanmar 4jh2e's
Can you share your sideways technique?
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Old 22-12-2016, 11:21   #12
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Re: counter rotating engines on catamarans

Both mine rotate the same way as they did on the last cat I had. Never noticed any effect.
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Old 22-12-2016, 11:31   #13
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Re: counter rotating engines on catamarans

As a WAG I doubt it would make much difference. It does an a go fast boat with the props relatively close together.
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Old 22-12-2016, 12:07   #14
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Re: counter rotating engines on catamarans

Hi,
You will probably find all cruising cats have counter rotating props. Achieved via the transmissions. I drive large catamarans for a living and prop walk is definitely present regardless of how far apart the hulls are. So basically you can steer the vessel to port or to starboard in astern by the choice of engine.
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Old 22-12-2016, 12:45   #15
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Re: counter rotating engines on catamarans

Bigger boats/ships using counter rotating props steer a straight line better, besides the maneuvering issues. Modern transmissions do the reverse rotation. About 30 years ago it became common for most dual engines to have the same rotation. In merchant ships, the engine runs in either direction for fwd or rev.
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