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Old 08 May 2011, 15:02   #11
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Country: UK - England
Town: The wilds of Wiltshire
Boat name: WhiteNoise/Dominator
Make: Ballistic 7.8/SR5.4
Length: 7m +
Engine: Opti 225/Yam 85
MMSI: 235090687/235055163
Join Date: Jul 2005
Posts: 12,692
Originally Posted by Courageous View Post
Hmm bigger pitch? I have a 19 but am running a 17. Could this make a difference guys do you think? OR did the jackplate make the bigger difference in Keith's case?
It'll be the jackplate.
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Old 08 May 2011, 17:27   #12
Country: UK - Wales
Town: west wales
Make: humber destroyer 5m
Length: 5m +
Engine: 90 yamaha
Join Date: Apr 2010
Posts: 202
I suppose cutting out the top three inches of the transom and glassing it over and then dropping the engine down will put the powerhead too close to the water?
I've got the reverse problem with a new humber 4m,the boat is built for a long shaft motor (apparently) but the longshaft 30 honda that I fitted (was on an SR4) ended up with the cavitation plate three inches below the bottom of the transom,and ran BAD,so I raised it up to normal height and its ok but looks odd. I need to speak to humber and measure the honda first.

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Old 05 July 2011, 06:26   #13
Country: Other
Town: Rosas
Boat name: Conqueror
Make: Valiant
Length: 7m +
Engine: Outboard 150hp Merc
Join Date: Dec 2010
Posts: 549
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Ok it's update time: Changed 17inch prop for 19inch and found a definite improvement but not enough. Bought a Whale Tail planing fin off the bay of fleas and fitted that today and the sea trial showed a vast improvement with us up to 26 knots at 6k RPM on a flat seas. The engine behaves much better than before as it seems to have stopped ventilating after passing over a wave top which was most disconcerting. We simulated this condition as best we could using other boat's wake. There's no doubt that we're not going to win any competitions especially on the economy front but I'm happier than before. We get the impression that we could cope with a higher pitched prop so if anyone has a stainless unit for a merc 150 greater than 19inch then I have a good home for it

Thanx again for all your advice so far. We're still on the lookout for an XL engine as the long term solution.

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