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Old 31 March 2009, 11:03   #1
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Country: UK - England
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Boat name: blazer
Make: BWM
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Laser 11 prop

Could some kind person tell me what the holes with rubber grommets are for and what difference smaller or filled in grommets make thank you in anticipation.
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Old 31 March 2009, 11:32   #2
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something to do with allowing the prop to slip at lower rpm (of the prop).

If you have a light boat, you can plug them up i beleive.

If you have a heavy boat and a big pitched prop (for top speed) the engine can get bogged down - the holes allow some "slip"

Someone might be able to explain better that me
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Old 31 March 2009, 16:21   #3
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That's pretty much it Daniel.

When accellerating up onto the plane (high load, low boat speed, possibility of engine bogging down) exhaust gas can be forced out of the holes, aerating the propeller allowing it to slip and increase in RPM. Once boat speed increases the aeration seems to stop and propeller grips again.

Had a Laser II on my SR5.4 with 90 Mariner. Blocked holes gave best performance.

Have one on my 6.5 Scorpion with 150 opti. Best performance with them blocked.

Would think that they only really need to be open on a heavy cruiser type of boat?
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Old 01 April 2009, 02:11   #4
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Country: UK - England
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Thank you for your replies it gives me somthing to work with.
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Old 03 April 2009, 10:53   #5
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I think it's best to try both ways, with and without the plugs... I think with 115hp and 6+ meters it could help you with quicker planing.
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Old 03 April 2009, 11:24   #6
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Searider has it right.

The aeration stops due to the speed of water past the prop sucking the exhaust and cooling water out the back. It's the backpressure when starting off that allows aeration through the vents. The plugs are intended for fine-tuning of the effect, I think (my prop has no such vents. Sort of wish it did, as takeoff with a load can be a bit trying. Maybe next time.)

jky
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Old 03 April 2009, 16:48   #7
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Give it a try.

I tried without the plugs and the sensation was very strange - engine speed increasing and boat speed lagging. Bit like a slipping clutch / prop hub.

Best try and see what works best in your case.
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