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25 September 2006, 15:49
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#1
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Member
Country: France
Town: Côte d'Azur
Boat name: Beaver Patrol
Make: Avon Searider SR4
Length: 4m +
Join Date: Jan 2004
Posts: 5,934
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Props - different for 4/2 stroke?
I have a Ribcraft 4.8 with a 2-stroke Mariner 60 on the back. The boat is fitted with an A-frame and twin jockey seats.
The uni rib is exactly the same, only has a Mariner 4-stroke not a 2-stroke on the back. Jimbo has got 5 knots more with the uni rib than mine, which to me doesnt make sence because the 4-stroke weighs a lot more than my 2-stroke. I intend to raise the engine a couple of holes to see what happens; hopefully this will make a difference. My main area of concern however is the prop. I don't know what size my one is but will check. (I don't have a rev counter fitted yet but I wouln't say the engine sounds like its over-reving)
My question is: are boats comparable to one another when one has a 2-stroke and one has a 4-stroke in terms of prop size. Ie if I buy the same prop as the uni rib will I get a similar (probably slightly faster) speed?
Edit: the prop is 11 x 12
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27 September 2006, 11:40
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#2
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Member
Country: UK - England
Town: Dorset
Length: 4m +
Join Date: Oct 2003
Posts: 1,410
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Tim, would I be right in saying the Uni RIB engine is a 'big foot', if this is the case im sure they have an uprated gearbox/ high thrust prop or something there is a difference, so I wouldn't go out and buy the same prop.
Get a revcounter and see what revs its pulling 12" sounds abit small on your application, I had a 13" on my 4m/ 40HP and that was very underpropped. You could take a revcounter off another of your fleet and just mount it for a few test runs.
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27 September 2006, 14:37
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#3
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Member
Country: France
Town: Côte d'Azur
Boat name: Beaver Patrol
Make: Avon Searider SR4
Length: 4m +
Join Date: Jan 2004
Posts: 5,934
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Arh yes I had forgotten the uni one is a bigfoot. I'll borrow the rev counter off Neptune and see what it says
Thanks Alex
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27 September 2006, 16:16
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#4
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Member
Country: France
Town: Côte d'Azur
Boat name: Beaver Patrol
Make: Avon Searider SR4
Length: 4m +
Join Date: Jan 2004
Posts: 5,934
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I phoned Ribcraft a moment ago just to see what they thought. The guy I spoke too said that the a good top speed for a 4.8 with 1 up was 35 knots which is the best he's got with a 60 E-tec (my best is 33, 2 up). I'm going to raise the engine a hole and see what happens, although I am a bit more re-assured now about my speed. He did say he reconed I could go up a pitch or two on the prop so I might get steel developments to bend my prop a bit and see if that gives me any more.
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28 September 2006, 01:15
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#5
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RIBnet admin team
Country: UK - England
Town: The wilds of Wiltshire
Boat name: Dominator
Make: SR5.4
Length: 7m +
Engine: Yam 85
MMSI: 235055163
Join Date: Jul 2005
Posts: 13,069
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I've got a 10.5x13" ally prop that'll fit yours-bring spanners and you can try it out on Sunday-or if you want it I've got a well shagged 14"pitch you can have. If you get that repaired/repitched then you'll have a spare too...
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28 September 2006, 11:25
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#6
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Member
Country: France
Town: Côte d'Azur
Boat name: Beaver Patrol
Make: Avon Searider SR4
Length: 4m +
Join Date: Jan 2004
Posts: 5,934
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Nos that would be great
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28 September 2006, 17:40
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#7
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Member
Country: UK - England
Length: 6m +
Join Date: Sep 2004
Posts: 1,850
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Quote:
Originally Posted by Tim M
Jimbo has got 5 knots more with the uni rib than mine, because he floats across the water with the grace and style of a sliver swan, as befits his skillful status...
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Why, cheers Tim
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28 September 2006, 17:43
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#8
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Member
Country: France
Town: Côte d'Azur
Boat name: Beaver Patrol
Make: Avon Searider SR4
Length: 4m +
Join Date: Jan 2004
Posts: 5,934
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Hmm. Tell me more about when you got 37 knots out of it. Had you had a few cans of beans for breakfast or were you being pulled along by the solent dolpin?
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28 September 2006, 18:16
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#9
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Member
Country: UK - England
Length: 6m +
Join Date: Sep 2004
Posts: 1,850
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Quote:
Originally Posted by Tim M
Hmm. Tell me more about when you got 37 knots out of it. Had you had a few cans of beans for breakfast or were you being pulled along by the solent dolpin?
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No no, it was quite simple really. I used a JATO unit.
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