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Old 18 July 2005, 10:47   #1
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Optimax 225 legs not long enough??

I have an Optimax 225 engine which is the long shaft model. However I have cavitation problems when not running at high speed. I have done a lot of investigation into this and the only solution would appear to be a longer leg/shaft. I need to install an extra long shaft onto the engine but my local engine dealer says that there is not a conversion kit available, his only solution is a new engine I am a mechanical neanderthol and have no argument against this.

If any of you can offer specific mechanical advice I would appreciate it.

Kind regards

Ollie
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Old 18 July 2005, 11:17   #2
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Can the engine not be mounted lower on the transom to stop this?

Just make sure the exhaust is above waterline.

Chris.
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Old 18 July 2005, 11:28   #3
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Ollie,

Im not an expert here but I can guess the first few questions for clarification.

How high is the engine - ie how high is the cavitation plate from the bottom of the hull at the transom.

What prop are you running If it is a Laser 2 it could be worth experementing with the grommety type things on the prop described better here as the perfomance vent system :
http://www.mercurymarine.com/chapter...opeller_parts2


Cheers

Phil

Edit - Sorry Chris I'm too slow - just saw youre engine height comment
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Old 18 July 2005, 11:37   #4
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If it's just better grip that you want, perhaps consider a different prop, for example maybe a 4-blade? Bear in mind that any "tuning" that you do is likely to lower your top speed as your boat appears to have had considerable effort put in to maximise this.
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Old 18 July 2005, 11:45   #5
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Without hacking into the boat structure there is no way to lower the engine, it is already at it lowest setting. Already running a 4 blade prop, problem is simply that the engine sits too high which reduces drag at top speed and presents no problems when doing that. With the stepped hull and low speed manouvers causing slightly confused water there is a tendancy to cavitate. I am happy to loose some top end to obtain better ow end performance but a new leg or engine does appear to be the only solution.

Ollie
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Old 18 July 2005, 12:07   #6
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Maybe the only thing that would avoid major modifications would be a jack plate to allow you to raise and lower the engine.

A word or two of caution though... lifting too high can loose water pickup pressure, and lowering too much could immerse the exhaust port. Race boats manage to overcome these problems though.
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Old 18 July 2005, 12:34   #7
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Hi Ollie,

Have you spoken to Graham regarding this? He has recently sorted the same problem on an 8.5 stepped hull with a new prop. If it can't be resolved like this, he may be able to alter the transom for you.

Ian
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Old 18 July 2005, 18:02   #8
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Brambles: Thank you for that thought, I will contact Scorpion tomorrow and check it out.

Richard: Excuse my ignorance but what is a jack plate??

Ollie
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Old 18 July 2005, 18:11   #9
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Quote:
Originally Posted by qcamel
what is a jack plate??
OK, I'm not an expert on this, so here's my attempt at a description...

It's a bracket arrangement which slides up and down (hydraulic ram I think) so that you can adjust your engine height as you're going along. They are widely used on race boats so the driver can lower the engine to grip on a turn, then accelerate out of the turn and raise the engine again for maximum top speed.

Have a look here: http://www.k4plus.com/shop.asp?catid=2
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Old 19 July 2005, 02:16   #10
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The jack plate looks rather clever!!!!

I have a busy daya ahead, avoiding all work responsibilities and trying to resolve my boat issue, the perfect day...

Ollie
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