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Old 01-06-2013, 01:16 PM   #1
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Country: england
Location: surrey
Engines: none at the mo
Cruising area: south coast

Join Date: Dec 2011
Location: surrey
Posts: 472
prop question

obviously if an outboard is set up so that the bullet of the gearbox is flush or just under hull line, a big leaved prop, surface prop, chopper etc is best, just wondered if any one has tried a chopper prop when gearbox is a lot lower, say totally under hull, im not setting anything up just a general question really ?
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Old 02-06-2013, 12:24 AM   #2
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I will tell ya tommorow as im about to try out a few different props on my boat.

my anti vent plate is only about 2.5 inches above the bottom of the boat pad.

So i wll see what the semi-cleaver does with the gearbox under water.ha ha

phill..
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Old 03-06-2013, 04:34 PM   #3
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Ok the answer is terrible holeshot if you can call it a hole shot.
The slippage when pulling away is a total disaster and the boat hardly seems to move just brings up the nose very high.

Then once its on the plane its like a turbo boost hitting you then takes off.
With the gearbox fully under water is what i tried.
The cav plate about 2 inch above the very bottom of the boat,so all the bullet and more is under water..
Top speed with a 13 3/4 x 23 omc silver streak semi-cleaver is just 1.5 mph better than a 13x19 omc sst prop at 39.8mph.
(omc SST 13x19 stainless = 38.3
But the 13x19 pulls away instantly.

With the semi-cleaver i got to 5400rpms max, with the 19 i ony got to 5200 max but less slippage.

now i also tried a 12 3/4x23 alloy prop and that just dont like the cav plate being 2 inches up at all.
This prop slipped and cavitated terrible and just wasnt much cop to be honest.
i got 5400 rpms and just 36mph from that one
I can get 34.9 with 2 people on just a 13 1/4 x 15 alloy but with terrible steering reactions from it.

So it looks like i need a jack plate for the semi-cleaver or use the omc sst (original race prop from 1972) for a good all round prop.

Once i find a cheap jack plate i can then see what results the semi-cleaver will do on this boat.

Now before anyone says these are slow speeds, i must point out that all these tests were carried out on a
13ft orkney dory thats only realy designed for a maximum of 30mph !!!!
so im not doing to bad with a 1995 evinrude 60hp triple on it.

And i must say the rooster tail you can get with the cleaver is brilliant
but 1mph slower than leveling the engine off ha ha

I think they hate me on the upper thames...


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