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Old 05 September 2010, 14:10   #1
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Ribcraft 5.85 max design speed.

Hi,
Just wondering what the max speed you could squeeze out of a 5.85?
I have one with a 150hp ficht and with 3 on board with around 40ltres of fuel fully trimmed it hits 43.5kts, only 1.5kt faster than what the same boat with a 115 4 stroke goes. Have I hit the max design speed or does the engine need some attention?
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Old 05 September 2010, 14:13   #2
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Hi,
Just wondering what the max speed you could squeeze out of a 5.85?
I have one with a 150hp ficht and with 3 on board with around 40ltres of fuel fully trimmed it hits 43.5kts, only 1.5kt faster than what the same boat with a 115 4 stroke goes. Have I hit the max design speed or does the engine need some attention?
I'd guess you might not be running the optimal prop set up. Either that or you've made the fatal mistake of believing someone else's data was accurate.
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Old 05 September 2010, 14:19   #3
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I'd guess you might not be running the optimal prop set up. Either that or you've made the fatal mistake of believing someone else's data was accurate.
That doesn't sound too far off, three up. If your revs are high at WOT, you might look at the prop.

However, I agree with P. - FIBnet strikes again
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Old 05 September 2010, 14:21   #4
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Yes the Fibnet phenomenon is all around us, particularly where top speed is concerned

What is your rpm at 43.5 knots?
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Old 05 September 2010, 14:23   #5
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IBWET's got one with a DF150. He gets 45kts
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Old 05 September 2010, 14:29   #6
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43.5kts sounds right too me. I'd be surprised if anyone can get 42kts with a 115!

On a good day with the wind behind me I can get 45kts with a Yamaha F150.
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Old 05 September 2010, 14:33   #7
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Top speed on a RIB seems to be a touchy subject. I've been told some whoppers by people that I didn't expect to hear them from. Lads on piers express disbelief when I tell them my real top speed - they expect it to be higher at 50kts or something 'cos the others are lying feckers
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Old 05 September 2010, 14:40   #8
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Top speed on a RIB seems to be a touchy subject. I've been told some whoppers by people that I didn't expect to hear them from.
Mine did show 49.1 knots once, it's not gotton near it since. "What's it's top speed mate?" "49 knts".

A 50knt+ rib is a rare thing.
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Old 05 September 2010, 14:42   #9
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Doesn't engine height (relative to transom) have alot to do with max speed, in a straight line, in a flat sea? (going down hill, with the wind behind you)
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Old 05 September 2010, 14:56   #10
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Doesn't engine height (relative to transom) have alot to do with max speed, in a straight line, in a flat sea? (going down hill, with the wind behind you)
Yes, and this also is dependant on prop type,some props like to run higher up and then will give that little bit more speed however you are potentialy risking how well the prop will "grip" once the going gets rough.

Its all a bot of a trade of and the whol prop thing is never cur and dried.

43.5 knots for a 150 with 3 up on a solid boat like a Ribcraft sounds about right to me. I get similar speeds on my 6.5 with the same HP and just me on board (so three up basically )
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