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Old 27 April 2015, 08:15   #31
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Sorry if this seems terse, but it sounds like you're trying to have your cake and eat it.

If you want more speed, choose the right prop for that. If you want something else, choose one for that instead. Since variable pitch props for outboards are at best very unusual, why not carry two?

Or you can fiddle with tiny things in the hope of making a tiny difference.
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Old 27 April 2015, 10:42   #32
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Quote:
Originally Posted by JamesF View Post
Sorry if this seems terse, but it sounds like you're trying to have your cake and eat it.

If you want more speed, choose the right prop for that. If you want something else, choose one for that instead. Since variable pitch props for outboards are at best very unusual, why not carry two?

Or you can fiddle with tiny things in the hope of making a tiny difference.

+1, if I didn't know any better I'd say Jeepster was back😎


.....sh1t happens.......
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Old 27 April 2015, 12:27   #33
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+1, if I didn't know any better I'd say Jeepster was back😎


.....sh1t happens.......
He's not suggested drilling holes in the hull to make it lighter yet...
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Old 27 April 2015, 12:39   #34
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He's not suggested drilling holes in the hull to make it lighter yet...
Give it time, probably still doing the calcs
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Old 28 April 2015, 00:12   #35
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Quite correct yes carry a few props. I have two, a 11'' P and the 25P. Might try a 21 or 18". I wonder how much Royal Mail would be to Hong Kong. One thing I learnt when I was younger and working on cars was that if the max hp is in 5500-6000 rpm then the engine is highly tuned, meaning radical cams etc and will never be super fuel efficient. I suppose I could de-tune it....but heading for a diesel I think. The small TDIs compare now in power density to the most advanced outboards. Safer too.
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Old 28 April 2015, 03:24   #36
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cars are four stroke, with a 2 stroke the power band can be wider, having a low revving 2 stroke is not suitable for small craft applications, unless you want a very very top speed.
I'm not sure what you're trying to do but I think you're going about it the wrong way...
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Old 28 April 2015, 04:18   #37
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Okay, I haven't had time to digest al lthis buit would I be right in thinking the following summary:

- You want a low RPM quiet engine for your daily commute with one aboard.
- You want it to do decent performance outside these times wth much extra weight aboard
- You have been doing a lot of maths to try & achieve this.

OK. I have a 1984 45m hull, transom only rated to 110Kg / 60Hp. Reason for this - it's made from 1/2" ply. The modern version of my hull is rated for something like 75 Hp / 150 Kg. - Why? - it;s 50% thicker, and the hull has a lot more reinforcing round the transom = much heavier. I have a Clamshell for a reason - it weighs 83Kg. My entire boat incl engine & full tanks clocks in about the same weight as the modern hull, and guess what - I can do 30 knots and drink 0.8l/NM just like the higher powered modern one.

if you want a quet 4 knot commute and a performance rib I think your best bet would be to buy a second boat with no transom (i.e a sweeping counter) and power it with either a small 4- stroke or an electric. Then re- tune your 60 to be the engine it was designed to be and put up with the noise when at full power, coz you are ging to need that power to plane.


Lift the hull out - you need buckets of power for that (do the lift - wing calcs or just have a quick look at hydrofoil boats & the size of the foils. Ignoring that, even if you do have this magic wing, a) will your vent plate be able to support the lift? and b) if you are lifting the hull out wil lthe engine's tilt bearing be able to support it?

I reckon lightening the boat and arranging the weight would be better use of your time, and If you can make this happen my suggestion would be to patent your findings before posting back with the results!
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Old 28 April 2015, 05:46   #38
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Kind of got to agree with D9280. although I'd probably go for a 3m rib with a 15HP. you'd get more noise on the commute but you'd only have to put up with it for a quarter of the time. If the water you're using it on isn't sheltered enough for that, your hydrofoils ain't going to work anyway.
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Old 28 April 2015, 11:17   #39
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Quite correct yes carry a few props. I have two, a 11'' P and the 25P. Might try a 21 or 18". I wonder how much Royal Mail would be to Hong Kong.
Aren't most props made in China anyway? Why get it delivered from the UK?

jky
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Old 28 April 2015, 17:44   #40
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Good article in POWER BOAT and RIB magazine on angles of outboards and hulls. issue 126 May 2015 out now.
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