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Old 12 April 2005, 17:30   #21
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Originally Posted by Pete7
In fact it would make quite a good article on the effects of different props on a boat.
Certainly would
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Old 12 April 2005, 17:36   #22
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OK....

Are we going to have a prop swap on the 23 & 24? If so where? We need quick access to fast water and somewhere shallow and calm to drop our nuts in!

I know Andre is free then too!!!!! Anyone can try my 23" ali!!!!

Mike C
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Old 12 April 2005, 17:38   #23
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Originally Posted by Mike C
....JWalker...

Not exactly.... I dropped PITCH size to 21" but the increase was in DIAMETER. This would seem to counteract the pitch drop to produce something that gives about the same WOT revs as my ali.
Yeh, that's wot I said. And I thought you said they only suggested the 19" after the 21" didn't work.
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That’s why they suggested dropping another 2" in pitch for the Titan..
Anyway, I reckon you need a 19"or 20" S/S of the same diameter as your alloy one. It depends a bit on the shape of the power curve for your engine.
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Old 12 April 2005, 17:46   #24
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Quote:
Originally Posted by Richard B
I've never read anything on RIBnet or anywhere else to suggest that either a Vengeance or a Titan would perform any better than a Laser II.
My understanding is that the Laser II is a higher rake prop than the vengeance or Titan. Apparently this gives bow lift whereas the other two will tend to give stern lift. Bow lift, they tell me, is a good thing in lightweight boats with outboards but with a heavy diesel engine on the back, the stern lift may be better. Also the extra torque of a diesel may be better with the chunkier Vengeance or Titan.... (In theory)

The Laser II also has a very special device, (called a hole drilled in it) to help reduce cavitation/ventilation.... again useful for high set outboards. The hole should be bunged up for diesels..... apparently!

This mean for high performance speedboats a Laser II would be better…. But I’m not so sure about my 1.2 tons of Humber!

Then again the Laser works OK on André’s boat…. But even he would like to try a Vengeance for curiosity if he’s honest
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Old 12 April 2005, 17:57   #25
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Originally Posted by Mike C
Are we going to have a prop swap on the 23 & 24? If so where? We need quick access to fast water and somewhere shallow and calm to drop our nuts in!
Sounds like a good idea to me - I think this will be good for us.

I reckon that any pontoon with a right angle that we can reverse up to will do the job. Any friendly marina, or perhaps somewhere on the Hamble?

Quote:
My understanding is that the Laser II is a higher rake prop than the vengeance or Titan. Apparently this gives bow lift whereas the other two will tend to give stern lift
This may well explain why we get excessive cavitation from our Titan, as our engine is set quite high.
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Old 12 April 2005, 18:00   #26
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Quote:
Originally Posted by jwalker
Yeh, that's wot I said. And I thought you said they only suggested the 19" after the 21" didn't work.


Anyway, I reckon you need a 19"or 20" S/S of the same diameter as your alloy one. It depends a bit on the shape of the power curve for your engine.
Thanks Jwalker,

Yes, that's why I originally wanted a 21", 2" down from my original. I didn't realise the extra diameter would negate the drop in pitch. It really is an impossible thing to get right without trying them! That’s the attraction of the Vengeance to me. It’s the same diameter/size as my ali one so I hope 2” off should give me that 400revs!

Mike C
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Old 12 April 2005, 18:05   #27
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Originally Posted by Richard B
Pete - IIRC you once mentioned that Lee Fairweather keeps them in stock? If so I might be able to pick some up one lunchtime.
You gonna buy spacers just for a trial?
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Old 12 April 2005, 18:09   #28
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Originally Posted by Hightower
You gonna buy spacers just for a trial?
Yes!

I don't anticipate them being more than a couple of quid each... I keep a standard set on the boat along with a couple of split pins so I can change a prop at sea without risking dropping the only ones on board!
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Old 12 April 2005, 18:11   #29
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You gonna buy spacers just for a trial?
I have one or two going spare at the moment, but most should fit, just not sure about Richards Yam, still only one way to find out.

Suggest you launch at Saxon/Drivers Wharf's as tides are mid day and use the slip at Hythe opposite to change the props. Top end of Southampton water has a good area for speed testing.

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Old 12 April 2005, 18:12   #30
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Quote:
Originally Posted by Richard B
Sounds like a good idea to me - I think this will be good for us.

I reckon that any pontoon with a right angle that we can reverse up to will do the job. Any friendly marina, or perhaps somewhere on the Hamble?
OK, well I'll be in touch later in the week and maybe we can get a few other people to do a real prop swop! High water is 11:38 BST at Portsmouth on the Saturday. Not quite maximum spring but close The Hamble sounds OK... I would like somewhere shallow to stand behind the boat though.

Anyone else coming? - maybe we should start a cruise thread??

Mike C
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