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Old 02 March 2005, 04:59   #1
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Country: UK - Scotland
Town: Lochgelly
Boat name: Purrdy
Make: Northcraft
Length: 5m +
Engine: Mariner 135hp ob
MMSI: 235029446
Join Date: Nov 2004
Posts: 46
Plastimo 4 blade manual pitch adjust props.

Hi folks has anyone any experience of these props?

Last November I bought a 3 year old dive RIB set up by ODD people.

Purrdy is a 5.5 Northcraft commercial with a 135 Mariner on her.
She pulls if trimmed spot on 50 knots at 5300rpm on a flat calm with just Cox.

Her prop is a 14.5 /21 Stainless Laser II with 7mm vents before the blades.

However she drops off the plane if you look hard at the throttle and has 1 micron throttle movement between 3000 and 4000 revs and a further 1 micron between 4 and 5.2.
The throttle box is a quicksilver.

With that engine she is ass heavy but I think some of her problems stem from the prop. I am currently considering a new prop (see title of thread)

Other options are Doelfins, semi auto trim tabs or diving on my own.

The odd thing though is that she is on the plane in her own length with 4 of us on board. Ok no dive kit as yet.

Basically I would like her to be able to heave six divers about at upto 35 knots without struggling onto the plane and be a little less throttle sensitive.

P.S. when you move the throttle that one micron, the revs instantly increase to the next (SET) speed and the boat speeds up more reasonably to match.

P.P.S. Yes the motor seems set at the right height on the transom, I think (shoot me down in flames) it`s partly due to the exhaust gas vents in the prop just in front of the blades.

Ideas please.

Andy.
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Old 04 March 2005, 05:20   #2
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Country: UK - Scotland
Town: Lochgelly
Boat name: Purrdy
Make: Northcraft
Length: 5m +
Engine: Mariner 135hp ob
MMSI: 235029446
Join Date: Nov 2004
Posts: 46
Hum. Nobody out there has any info at all.
Or opinions which tend to happen even without info.
Might have to change the thread title to something simpler, like which prop should I buy since I`m a N00B.
Ok this is just a bump really so don`t get offended.
I still think it`s the vent holes in the LaserII causing the problem but since I`m skint for a couple of months and a new prop will be a big hole in herself`s wedding budget I was hoping for some knowledgeable advice.
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Old 04 March 2005, 07:00   #3
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Country: UK - Scotland
Make: HumberOceanOffshore
Length: 8m +
Engine: Volvo KAD300/DPX
Join Date: Oct 2002
Posts: 4,962
Bung somthing into the holes and retry it.
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Old 04 March 2005, 09:28   #4
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Country: UK - England
Town: Farnborough
Boat name: Eleven
Make: Arrow
Length: 8m +
Engine: 557cu, 700hp
Join Date: Jul 2003
Posts: 1,255
Agree with jw, try blocking them. (Don't laser II's come with the bungs so you choose whether or not to use them?)

Laser II's are generally known as a good all round stainless prop's on fairly light boats. The vent holes are to help increase the amount of slippage whilst getting on the plane - it helps get the engine rev's into the power band. Once running fast, the vent holes should be making little difference, just look at the over hub type props use on many race boats.

I would certainly consider any plastic prop hugely inferior. Though I could see that since you are wanting to lug huge amounts of kit and divers around you might decide you want something with a bit more blade area than a Laser II.

Are you sure the rev issue is not just suffering an over sensitive throttle control?
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