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Old 13 March 2019, 17:55   #11
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Country: UK - England
Town: York
Make: Bombard Aerotec 380
Length: 3m +
Engine: 15hp Mariner 2stroke
Join Date: Jul 2012
Posts: 23
Thank you for the reply Fenlander.

My original thought process was because it’s such a light boat with a light load that I could add an inch to the pitch for a bit more speed. But if Max’s isn’t reaching max RPM (says max 6000 on my outboard) then that wouldn’t work.

I think there’s a whole lot of messing about for minimal gain and, like you say it’s probably not going to do the motor any good driving on the redline constantly.

It seems the Aerotec is quite draggy and more power is the law of diminishing returns to some extent. I noticed someone on the forum trying to iron out the ‘hump’ before he transom using bracing, perhaps this would be a more useful pursuit.
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Old 14 March 2019, 04:22   #12
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Country: UK - England
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Boat name: Bombard, Y-162
Make: Aerotec 380, Y-Class
Length: 3m +
Engine: Mercury Mariner 15hp
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I think if max is 6000 and it's reaching 5750 then that's pretty ideal, the extra 250 isn't going to have much effect in all reality. All props are a compromise and I would not want to gain 1/2 knot or less but lose the holeshot (which is much more important).

As you say it is a draggy boat that drives a little like a RIB and dropping off power will see it come off plane easy so pick up is the most important aspect IMHO.

Not sure if you have read the 'maiden voyage of a bastard son of a Y class' (or something like that!) but that is one of many Aerotec topics with lots of useful info on set up, splash guards, raising the transom etc.
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Old 14 March 2019, 05:30   #13
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Country: UK - England
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Boat name: Nimrod II
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Ahh sorry Kong I made a mistake thinking you wanted to pitch down to reach higher revs. Yep re pitching up I agree with Max so little to be gained if anything at all and possibly a negative at other points in the speed range.

I'd be interested to know an actual measured speed with a 25hp because as I said above the 20hp didn't much improve things re top end.

And as is so often said with a sib the frequently found UK sea conditions prevent maximum speed running on most trips.
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Old 14 March 2019, 05:38   #14
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Country: UK - England
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Make: Bombard Aerotec 380
Length: 3m +
Engine: 15hp Mariner 2stroke
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I don’t want to think about it. I had a peach of a Mariner Marathon 25hp left over from when I sold my Quicksilver which would’ve made the bombard rapid. Unfortunately it was a slipped-disc waiting to happen and would have made the difference between being able to beach launch by hand and not! :’(
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Old 16 March 2019, 18:28   #15
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Boat name: Awesome !!!
Make: F-RIB 375(S)
Length: 3m +
Engine: Suzuki 9 / 15 & 20HP
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As said, you really need a tach on to get a correct reading at wot.
With my old T38ie & Suzuki DF15, i ran a 9.25 x 10 Stainless Steel.. A slight top end gain over the standard DF15 ally prop 3x9.25x9"
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