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Old 05 June 2002, 14:17   #1
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Country: Netherlands
Town: Hoorn
Boat name: skip
Make: revenger 25
Length: 7m +
Engine: mercury 250 pro xs
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prop

can anybody tell me what type of prop I need if I want to go for the real topspeed?
I have a speedy hull, 23 foot, and a optimax 200hp.
Now I use a mirage plus which is a very good allroundprop for skiing etc. but I'm looking for a "race"prop.
With my mirage plus 21 my speed is 63mph (gps),rpm is perfect.
All sugestions are very welcome.
Sorry for the (perhaps) strange language.

greetings,
Niels (try to fly dutchman)
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Old 06 June 2002, 07:27   #2
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Country: UK - England
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I will prob. be shot down here but if the RPM is spot on then I think you have the correct prop.

John
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Old 07 June 2002, 10:42   #3
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thanks

No I will not shoot you , but there are lots of types of props with different sort of behaviour (it's not the size that counts but the shape ha ha) and i'm looking for a high speed prop.
Does anybody knows the "hi-five"(?) prop?
But thanks for your reaction.

greetings Niels
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Old 10 June 2002, 16:37   #4
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I have a laser 2 on a Mariner 150 hp. But I think what your looking for is a surface pearcing prop. Mercury used to do a racing catalogue full of exotic goodies might be worth having a chat with your local dealer or try Chris Lewis Racing, think he is in Hampshire, used to have a reputation of putting a fast engine together for race boats and blue printing engines etc. But its big bucks for coned gearboxes and water pick ups etc. Also might effect how the boat drives in normal use.
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Old 11 June 2002, 14:32   #5
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thanks

but i'm looking for prop which I can mount on my regular 200 optimax.
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Old 13 June 2002, 17:48   #6
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Country: UK - England
Town: Maidstone
Make: Ribtec and Avon
Length: 6m Ribtec and 3m Avon
Engine: Yamaha Pro V100 and Mercury XR10
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Prop

Hi all, i'm new to the board.

I think a high-5 prop is best as a skiing prop because it has large blade area and a great hole shot for pulling skiers up. But as an ultimate top speed prop, a cleaver surface-piercing prop is best. Mercury racing do them, but these are priced accordingly.

If you speak to David at Steel Developments, he can advise on the best prop. They do a race - prep service which will make your prop into a cleaver style for a LOT less than to buy a new mercury cleaver. Running at this height to will mean your water pickups are out of the water. As Pete7 said, Chris Lewis is the man to speak to because me can either fit you a nose cone with low water pickups or can mount a pickup on the hull and pipe it into the engine.

You may also need a transom jack as the standard engine mounts won't have enough lift .

Unfortunately, running a surface-piercing prop isnt all good news. It has less grip than a normal prop so may not be able to pull a skier. Steel developments sell stainless steel props at great prices which could then be made to run as a surface-piercing prop and leave your mirage for skiing and for use when the boat is loaded up.

It would be good to ask owners with outboards running surface piercing props to get their views on the handling of the boat and its performance.

If you still want more speed, steel developments do a hull coating which reduces the drag and increases speed. I bought some at RIBex for my Ribtec 585 and will tell you the performance differences once I have applied it and tested.

There are two American companies which do lots of products for making outboards go faster - http://www.land-and-sea.com and http://www.bobsmachine.com.

A surface-piercing prop when run at the correct height should give better performance and a great engine sound because the exhaust is half out of the water when the boat is on the plane.

I hope this has been some help. If you have any questions, please email me and I hope i will be able to answer them!

Ralph Payne (Age 15)
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Old 14 June 2002, 04:11   #7
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wow

thanks for all the info.
greetings
Niels
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Old 18 June 2002, 16:27   #8
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Hi niels,

Glad you found the information helpful.

Something else i forgot to add, steel developments web address is http://www.steeldevelopments.co.uk

Please post if you decide to go down the surface prop route. I am considering this for my Mercury XR10, i already have a nose cone for it .

Does anyone on the forum run a boat with a surface prop? I am very interested to find out the difference in grip on the water is like because i don't want the prop cavitating badly when i go through some waves.

Regards,

Ralph Payne (Age 15)
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Old 18 June 2002, 18:45   #9
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I think Hot Lemon 3 had a surface prop on a stern drive which nearly caused the boat to be lost when in a heavy stern sea they couldn't spin the engine up fast enough to get on the plane. The prop requires air to loose some of its grip so the engine will spin the exagerated pitch used for high speed. Problem was later solved by adding a tube to suck air down into the prop, bit like a divers snorkel. there was an article on it either on here, hotribs site or Rib Magazine about two years ago. Pete
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Old 19 June 2002, 06:09   #10
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Thats a problem with surface drives. When the boat is not on the plane, the prop is fully submerged, which is why many inboard race boats struggle to get on the plane if they dont have 2-speed gearboxes. The trimax surface drive overcomes this and uses some of the engines exhaust gases to let to prop spin up quicker.

With an outboard however, if a hole is drilled in front of each blade on the prop hub, exhaust gases can pass out here so the prop can spin easier.

Ralph
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