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Old 16 December 2009, 12:28   #1
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Counter Rotation

A quick query, and possibly a stupid one....

Is there any reason not to buy a counter rotation OB (second hand) and run it as a single set up? Are the gearboxes any weaker /more expensive to repair than standard?

I assume the offset would need to be over the other side to a standard rotation?

Have done a search of the forum, but can't find the answer so any info appreciated....

Dan
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Old 16 December 2009, 12:33   #2
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No reason why not. Some people run counter rotating props on twin installations.
I think the boxes are the same apart from the gear selector, just from from memory on my Dads stern drives.
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Old 16 December 2009, 12:33   #3
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I believe that is exactly what Hightower has done here.

I can't see any reason why in normal circumstances it shouldn't work OK. I guess if something goes wrong and you need to get spares for inside the gearbox it could be harder/more expensive but you might well need to replace the whole box then anyway. The only other headache might be the availability/range of props?
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Old 16 December 2009, 14:12   #4
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Thanks Chewy.... Thanks Polwart......

It's a 175 Opti XL from overseas.....

I'm awaiting a print out on the OB to pass to the mech / guy who looks after the boat. I am really lucky in that respect, he's a great guy and a Mercury expert....he was the race mechanic for the four time F1 World Powerboat Champion....

Will let you know how we get on.

Dan
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Old 16 December 2009, 14:25   #5
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Turbo Diesel or Uncle Al on here should be able to help.
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Old 16 December 2009, 14:46   #6
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As Polwart has mentioned, I run a Left hooker with no problems. Just remember to get the outboard offset correct when installing.

As for Props. If you're buying New there aren't any problems, but they might have to wait for stock or order something you want.

Second hand props are rare, but keep your eye open on ebay ( I was the only bidder) as I bought a New SST for 45 and a little used BRP Viper for 90 Those two props would be easy over 600 quids worth brand new. So be eagled eyed and pick up a bargain.

The other disadvantage is that you cannot borrow props to try out. Other than that the only prob you might have is if the RIB was set-up with a standard rotation outboard. The battery and fuel tanks etc might have been placed to one side to counter the force of the Prop Torq and with a CCW Outboard might cause you balance problems. Or landing off a wave on one side. This can be overcome with weight distrabution but due to the size of RIB I doubt that will be an issue.
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Old 16 December 2009, 16:00   #7
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On the other hand, without realising it, I've been running a counter rotating gearbox in reverse with a std prop for several years.

It's a long story

Nasher.
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Old 16 December 2009, 16:05   #8
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Thanks Andy....

Agree that balance shouldn't be an issue...my fuel tank is below deck (like Nashers) and teh triple battery system is centrally located.

I've also got Hydraulic Trim tabs which help with balancing (esp. when laden with Dive Gear etc.)

Take your point re offset

Hope this ones a goer...it's a 2005 Opti with 340 hours XL shaft with 21 SS prop.

I understand it was from a marine police RIB (Dorset?) and was sold as pair at auction (engines upgraded to 225 Opti's I'm told, but who knows...)

Went to dealer in Holland...that is who's selling (not been used since). have asked some more questions and asked for a diagnostic report to show my mech....wait and see.

Thanks again guys!!

Dan
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Old 16 December 2009, 16:11   #9
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Quote:
Originally Posted by Nasher View Post
On the other hand, without realising it, I've been running a counter rotating gearbox in reverse with a std prop for several years.

It's a long story

Nasher.
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Old 16 December 2009, 16:43   #10
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Quote:
Originally Posted by Dan Worth View Post
I understand it was from a marine police RIB (Dorset?) and was sold as pair at auction (engines upgraded to 225 Opti's I'm told, but who knows...)
I don't want to put you off that engine, because it may well be in perfect condition, but I got the distinct feeling from the tender documentation that their boats (and so possibly their engines) were not as 'loved' as we might expect for ex government stuff.
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