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Old 24 December 2012, 19:05   #1
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Country: UK - England
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New rib still keeping me up.

Quick silver 410. 30 hp tohatsu Efi

well I tried the new rib I bought on a popular English power boat testing lake yesterday 23rd dec.....and the engine being set 61mm too high ( cavitation plate set above keel line height) made the boat.................... Pretty bad, ventilating straight away on the plane, unless engine is trimmed fully down.

I intend lowering the motor 65mm with a jacking plate type block i will machine, with a set back of 100mm to clear the clamps from the transom. I will mill the blocks from solid Ali, and bolt it on to the existing holes in the transom and motor. I think lowering the motor 65mm will not drown it. The motor will be mounted on its middle holes so I can fine adjust it up or down a bit if needed.

Is there a fancy prop that will work with the engine set as is?

Thoughts please...
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Old 24 December 2012, 22:00   #2
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Any set-back will cause quite a bit of spray over the transom. The motor should bite fine with the cavitation plate level with or up 1" from the keel. Too low and the motor may cause some premature chine walking as it lifts the transom at speed while trimmed 'in'.
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Old 25 December 2012, 13:33   #3
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Should I lower motor level to keel.

Should I try a cupped / 4 blade / stainless. Prop....?

What did wolf do to the outboard setup when they made the boat to make it work, that someone has consequently undone?
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Old 25 December 2012, 13:34   #4
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Once you have set correct transom height for that engine, a 30 should give ample power, place an induction tach and check at wot your max rpm achieved with just you and then go from there if needing to play with prop pitch.

If Tohatsu sits too low will have unwanted water splashes inside back deck, engine must work perpendicular to rib and cav plate paralell to water level with a well ballanced rib when under way. Sorry, but for boating perfection, a fine height tune is needed under trail & error. Tohatsu tail issues.

Happy Boating
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Old 25 December 2012, 14:37   #5
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Will fit engine flush with keel with one mounting hole available up and down .... boat struggled to get on plane with 9.9. X. 13 inch prop... Is it over proped or will it get on plane ok with 30hp and this prop when mounted at a good height?
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Old 25 December 2012, 15:22   #6
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I personally had a hard time finding the right prop for my applications and went with this...

Propulse – English | Fuel efficient and variable pitch propellers for outboard engines

It has been a lifesaver...when light I can back it off a couple degrees and when heavy I can go the other way. I did notice a major hole-shot difference and about 2mph loss at full throttle. I have had these on 2 boats now and have a zero failure rate. One boat had a 40 Merc 4-stroke and the current rib has a 2-stroke Merc 115.

You are on the right track...set the cav plate flush with the keel and give it a shot.
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Old 26 December 2012, 09:19   #7
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Why don't you post pictures of your rib, back transom, last height engine was sitting at to have a look, how tall is your transom to keel distance in centimeters ? That rib/engine configuration should work well with delivered standard medium pitch prop.

It's not a matter of just aligning cav plate to keel as this will depend on rib's hull shape, depth and tubes diameters as all ribs are not built same. What Tohatsu states on their owners manual regarding engine height installation is just a refference from where to start, but a fine tune height must be performed if wanting to get the max power of that horse and best rib performance under all water conditions.

Happy Boating
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Old 26 December 2012, 10:44   #8
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You haven't said if it is a Short or Long Shaft engine you have? You didn't confirm this on the last thread you started about this problem. The guys are working blind offering advice if they don't know...
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Old 27 December 2012, 18:37   #9
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It's a short shaft motor, and the plate is 61mm above hull bottom, with no adjustment available to lower the motor.

http://s1186.beta.photobucket.com/us...80566361438286
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Old 28 December 2012, 00:37   #10
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Shaft length is the only problem I see. Not much to do about that but a jack plate and live with the spray. Personally if it were an option, I would replace the motor.
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