Aberdeen
new user
Reged: 22/03/2006
Posts: 4
Loc: Australia
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I have a 20HP Honda o/b
I want to build another wooden boat (Hartley designs) and use this motor with it (cheaper that way)
Any thoughts on how a motor that size would perform with the following:
15' x 6'6" 400 lbs ( 4.57 x 1.98 181Kg)
14' x 65'1" 350 lbs ( 4.27 x 1.85)
Not looking for anything high speed as would be obvious
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Hartley Boat nut
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Talbot
regular
Reged: 23/08/2003
Posts: 12444
Loc: Stavanger, Norway
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not really a question that can be answered easily. speed will depend very much on the shape of the boat, ultimate speed is balanced against sea-keeping capability in most designs.
The weight of the boat will also be factored into this , as will weight and position of crew, weight (and position) of fuel, capability of the engine - is it designed for grunt or for speed, and is it producing power in accordance with original design (very unlikely)
so this question is really like
"how long is a piece of string"
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"Be wary of strong drink. It can make you shoot at tax collectors - and miss."
Robert A Heinlein
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oldharry
regular
Reged: 30/05/2001
Posts: 3796
Loc: North from the Nab about 10 mi...
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Quote:
Any thoughts on how a motor that size would perform with the following:
15' x 6'6" 400 lbs ( 4.57 x 1.98 181Kg)
14' x 65'1" 350 lbs ( 4.27 x 1.85)
Thats a b****y funny shape for a 14 footer isnt it Aberdeen?
Even with a 20hp on it its going to andle a bit strange.....
Otherwise the 20 is goin to be well be well OTT on a 14 footer. I used a Honda 8 on a 19'6 boat weighing around 1500lbs, and got full waterline speed out of it - around 5.8kts quite happily at 3/4 throttle. any more just made waves. The only point of using a bigger engine would be to get the hull op on the plane, if it is capable of it.
I used to have a wooden 12 footer with a 9hp Evinurude. This would just about plane with 1 up. With any more people it could not quite get over the hump.
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If you cant fix it, get a bigger hammer...
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Peterduck
regular
Reged: 10/04/2002
Posts: 1010
Loc: Melbourne, Australia
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Being four-stroke motors, the Hondas have a surprising amount of grunt for their size. I used a 7.5hp one on my 23ft trailer-sailer, and it worked just fine, sending it along just as fast as I wanted to go. In my mis-spent youth 20 hp was considered about right for a 20ft runabout, and they would get up on the plane quite well. Then this new craze for ski-ing behind a boat came along, and suddenly outboards had to be bigger and bigger in a testosterone-fuelled game of one -upmanship. This was encouraged by the engine manufacturers for economic reasons [ie greater profit]. For a 15ft boat I would be looking at nothing larger than a 12hp outboard, and even a 10hp would be quite adequate. I think that a 20hp outboard would find a 25ft hull easier to push than a 15 footer.
Peter.
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Aberdeen
new user
Reged: 22/03/2006
Posts: 4
Loc: Australia
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I like to be different - guess one that wide compared to length would draw some attention.... maybe I'll scale the beam down to 6' 1" instead of 65' 1" - sort of a crash diet 
The new one should get on the plane, Hartley boats have a tendancy to do that
Regards to all
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Hartley Boat nut
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Aberdeen
new user
Reged: 22/03/2006
Posts: 4
Loc: Australia
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I agree, size isn't everything, it is how it performs for what you need it to do. Speed can be fun or necessary at times but mainly interested in just cruising out on the Gulf of St Vincent. (any guesses where that is?)
My latest intelligence received suggests that the boat config. with the 20hp should return about 20+ mph (32kph), plenty for this ageing bloke.
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Hartley Boat nut
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Aberdeen
new user
Reged: 22/03/2006
Posts: 4
Loc: Australia
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I think the truth will be in once I build her and get her bottom wet. It is a planing hull and most times will only be in semi protected waters with maybe 2 villains on board.
Glenn
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Hartley Boat nut
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oldharry
regular
Reged: 30/05/2001
Posts: 3796
Loc: North from the Nab about 10 mi...
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Should plane alright with 20hp - as long as you havent eaten too many sandwiches 
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If you cant fix it, get a bigger hammer...
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