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Old 22 September 2005, 09:05   #31
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Quote:
Originally Posted by Pete7
Cool, would you ask if they do a 23", fancy going a little faster.
Try the Volvo prop, then. I suppose it depends on the blade tip shape but I can't imagine the last 3/8" does a great deal of work. My understanding is that larger diameters are required for greater load carrying capability and thicker sections are required when the load carrying is at lower speeds (blade speeds). A bit like an aeroplane with bigger/thicker wings.

Pete, what weight is your boat?
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Old 22 September 2005, 09:29   #32
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Iím glad youíve brought this thread up again cos I am really struggling to find anyone who will quote for the original style prop.
Sonic are a stockist who have a gentlemanís agreement (I quote) with Lancing to not supply this prop to anyone else and Iíve also spoken to a couple of other prop Ďmanufacturesí but no quote. I think part of the issue is that it is a cushion hub and large diameter prop so other than Volvo of a rare beast
Going down the Volvo route requires a hub adaptor which makes the first prop very expensive but cheaper thereafter.
So I am lost as to what to do next any ideas Des

Ps weight in the book 1600kgs light, 2200 heavy.
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Old 22 September 2005, 10:06   #33
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Quote:
Originally Posted by Scary Des
Going down the Volvo route requires a hub adaptor which makes the first prop very expensive but cheaper thereafter.
Ps weight in the book 1600kgs light, 2200 heavy.
Des, is it an adaptor (as in requires splines) or just a spacer that's required?

That's not too heavy. Is the drive's gearing such that the prop speed is particularly low? I suppose, with the lower powered engines, that you're going to need big diameter and low pitch to be able to carry a heavy load as well as the boat.
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Old 22 September 2005, 11:07   #34
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It is an adaptor and possible a spacer as well.
I am told that the Propellersí hub is 1 1/8th" dia. 2 1/4" long with 17 Splines, end thread 7/8-9 UNC x1.
Prop size 16.75" x 21"pitch Left hand SMC807 Michigan wheel.
In standard configuration the Mermaid produces 140hp at 2600rpm driving a 1:1 Velvet Drive Gearbox
My outdrive is 1.26:1 although RN boats were 1.32:1, not sure if the 0.06 makes any difference Des
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Old 22 September 2005, 11:25   #35
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Quote:
Originally Posted by jwalker
Pete, what weight is your boat?
I recon 2 tonnes with a couple of passengers, although haven't weighed it. Must take it around to Drivers one afternoon and have her lifted on the crane.

If its just an adaptor to switch to the volvo long hub prop, then its just a bit of lathe work. Need to spend a day down at Foulks boat scrap yard. they have an ISO container full of old props, so a volvo ought to be available.

Des, the only other source of original props will be that bloke in Plymouth Nev mentioned a while back or the scrap yard in Portsmouth.

You have me thinking about ratios now, I will measure it when she comes out for the winter. My SMC 807 was dreadully slow to accelerate (before it fell off) compared to a lancing 16.75 x 21 which makes me think it was about 25". I have 2800 revs with the lancing prop, didn't get chance to check the revs with the SMC before it failed.

Pete
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Old 22 September 2005, 11:48   #36
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Youíve got me thinking now
I donít know that I have this right but given the same engine and boat a 1:26:1 outdrive is doing 3276 rpm at the prop at wot, whereas 1.32:1 would be 3432. So a standard boat is doing 156 more revs than my one.
And yet my boat, with the lancing prop on, did 28 knots (gps) which is about the same as everyone elseís boats

How do you measure pitch Des.
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Old 22 September 2005, 14:28   #37
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P22

Good evening. I am new to thi site. I bought a P22 earlier this year and am interested too in the speeds achievable with different props.

I had an 809 prop which i believe was a 16 3/4 x 21 standard military issue.

When i bought the boat from Nevilles outfit it went fine with this on at 140 hp. I then had the pump adjusted so that it was 165 hp apprx and put on a 19 x 18 prop. As the drive was a 113 it takes a 19" prop.

Light, it just makes it and a touch over 30 knots. I think (and i havent tried yet) but if i put more than 2 people on board it wont reach wot.

So i think im going to try a 19 x 17 by sending it away and having it repitched. Changing the diameter to 18" is the optimum i think but i dont know if these prop places can do work like that - any body know?

Neville put me on to someone called SR marine in Plymouth but they seem to have moved on somewhere. I think that was my only chance of a cheap prop!
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Old 22 September 2005, 14:28   #38
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I always thought the ratio was the other way round, 1.32:1 so the prop is travelling slower?

This would give 1970 revs for a Naval boat and 2063 for a 1.26:1 for your boat. That could explain your 28 knots over 26 knots for a standard boat. Or, I could be completely wrong

Oops seems 3 of us have posted the same thing at once, anyway found this pic on Streamlines Web Page. Or I supose you could use a lathe and offset the carridge.

Here
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Old 22 September 2005, 14:29   #39
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Des, are you sure you have that the correct way around. Normally the prop runs slower than the engine. Just did a little calc for you... If your engine is at 2800, your prop pitch is 21, slip about 20% and ratio is 1.26 then you should be making 30.4kts.
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Old 22 September 2005, 14:31   #40
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Des, i think you have the gear ratio calculated the wrong way round. A 1.32 : 1 means for every 1.32 the input turns, the prop will turn by one thus decreasing the shaft speed. I think your boat would go fractionally faster.

Ive been studying hard since i bought the boat!
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