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Old 25 December 2010, 18:49   #1
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OEM to Laser swap worth it?

Hi,

I have a v6 Merc 150 with a stock Ali 21p x 14.5" prop - performance is OK when loaded (6 x up plus kit) although struggles out of the hole - 1 or 2 up it flys..

Would changing the prop to the same pitch Laser 2 21p or similar offer any better performance (assuming the same pitch) - aware dropping down to a 19p would help out of the hole but I'd like to keep at 21p for top end.

Will it rev higher with a stainless prop of the same pitch as the Ali one on it now?

Much prefer the look of the stainless if I'm to be honest!

Cheers,

James
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Old 26 December 2010, 05:54   #2
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I'm no prop expert but generally swapping an alloy for a stainless of the same pitch will normally drop your WOT i.e. hole shot will be worse.

If you run you boat at the two extremes (Heavy and Light) then I would suggest keeping the alloy for when you're two up and then changing over to a finer pitch for heavier loads.
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Old 26 December 2010, 06:37   #3
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Thanks Andy - so keep the Ali 21p for speed and get a 19p Stainless for skiing or when loaded?

Are the Laser 2's a good prop?

Cheers

Jim
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Old 26 December 2010, 06:47   #4
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My suggestion would be to borrow some props and try them. It's all a bit of a dark art in selecting the right one. On paper a given prop might well be ideal, but in practise it rarely is. Don't ask me why! I guess that there are many factors involved.

When I selected my prop/props for different boats I've have I gauged prop performance on my cruising speed at a given RPM and chose the prop based on the fastest speed it could push me along at say 3000/3500 rpm. Obviously you need to check that the prop runs in the recommended WOT range too.

Have a look at the prop thread Here and see if there is anyone with a prop that suits you and would be willing to lend you. You might have to pay some P&P but might help you sending hundreds of pounds in the search of the holy grail.
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Old 26 December 2010, 17:01   #5
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I might be completely wrong, but when going from ally to stainless i would go up a pitch!, So if i had a 19" Ally i would try a 21" stainless. They cut through the water better and dont bend like ally props. So you can go up and get more top end. The most important thing is get your tacho working first and see what max rpm your getting!. The prop it so suit your needs!
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Old 27 December 2010, 05:22   #6
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Stainless: They're heavier, so they spin up a bit slower. The blades are more rigid, so you don't "lose" pitch as the blade flexes, so they keep the rated pitch whereas aluminum tends to drop pitch. They are usually cupped more aggressively than aluminum, which creates more bite than aluminum.

In general aluminum to SS, assuming identical blade size and contour (which you probably won't find), will yield between 200 and 400 rpm less WOT. Cupping and actual blade differences usually mean dropping an inch or two of pitch to get the same WOT rpm.

My $.02 (sorry; don't have the pound or euro symbol)

jky
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Old 27 December 2010, 09:35   #7
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Suggest fixing the Tacho first.

However, I went from an aluminium 19" to Laser II 20" on my 90hp Mariner and made the same top end RPM with speed a lottle improved.

Went from 19" SS Vengence to 19" Laser II on the 150 optimax. Top speed not altered but propeller gripped much better when re-entering the water. The Vengence wasn't keen when driven hard!
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