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Old 02 September 2004, 02:40   #11
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Talking with Andre and he reckons he gets a maximum speed of 33 Knotts from his 6.3m, with a comfortable cruising speed of 26/28 knotts, which seems realistic I guess. Will let you all know when it eventually gets on the water again.
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Old 02 September 2004, 04:18   #12
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Quote:
Originally Posted by ribnwheels
simmons0 boat is a 6m, not a 6.5 for what that is worth.
My mistake! With a relatively low powered rig that half a metre might make quite a difference I suppose.

There seems to be a general and widespread tendency for people to be rather generous with their top speed assessments. I still think that 45 knots is optimistic in this case, but would be happy to be proved wrong.!

John
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Old 02 September 2004, 05:25   #13
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Mercruiser 1.7 Turbo

I have the Mercruiser 120 Hp in my Prosport 6.5 Mt

It will cruise at 25-28 Knots at 3300 RPM dependant on the sea conditions.
Top Speed is around 36 Knots at 4200 RPM

This is with a 23” prop and the leg trimmed out correctly

Incidentally the RIB can make 20 Knots in to a head sea of around 2 Mts without backing off

Fuel used is 3 Gallons per hour as expected, A good power unit in my opinion.

Alan Priddy might get 40+ Knots down one of his big swells around Greenland but I don’t wish to try it!!!!!!! ***By Big Swells I do mean the sea type***
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Old 02 September 2004, 05:38   #14
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Quote:
Originally Posted by Dave B
Alan Priddy might get 40+ Knots down one of his big swells
In his dreams!
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Old 02 September 2004, 05:45   #15
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length va consumption

Is there a rule of thumb as to how fuel consumption rises with length? If someone gets 1.3Nm per litre with a 150 Opti in a 6m Rib, what would the similar figure at similar crusing speeds be for a 6.5m, a 7m and an 8.5m?

Does consumption differ significantly due to hull design?

What are the most important factors?

RPM
Speed
Weight
Length
Hull
Phase of moon

It should surely be possible to come up with some simple guidelines here?

Bruce
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Old 02 September 2004, 09:15   #16
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Quote:
Originally Posted by brucehawsker
Phase of moon
The three different makes of 6 meterish ribs that I've driven this season, fitted with the 1.7 mercruiser, have only managed 32knots and that includes the Pro sport.

Maybe they go faster when there's a full moon.

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Old 02 September 2004, 09:41   #17
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As I said in my last post with a 23” prop my Prosport will make 36 Knots dependant on the sea conditions,. I have tried the same rib but with a 21” prop and that was not very good but with no GPS or log I am unable to tell the exact speed.

Using a chart plotter and a Garmin 126 (to determine Speed) out on a flat calm sea with little or no wind and two crew the Prosport will make 36 Knots.

Just for interest my last rib was a 5 Mt Humber Attaque with a 50 Hp Honda. Flat out and I mean flat out I was paced at 32.5 knots.

With a 23” prop the Mercruiser will not rev out to 4500 but is within the limits set by the manufacturer.

No need for a full moon, but it does help on a night passage.
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Old 02 September 2004, 10:21   #18
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Quote:
Originally Posted by davidmanning
The three different makes of 6 meterish ribs that I've driven this season, fitted with the 1.7 mercruiser, have only managed 32knots and that includes the Pro sport.

Maybe they go faster when there's a full moon.

DM
I go along with David 32/33 knots is the very max speed and hv tried the s/steel 23" prop (Laser of course) and the s/steel 21" . Kept the 21" cos has better acceleration
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Old 02 September 2004, 10:49   #19
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If your around the solent for the charity cruise ill show you 40 knots+ for yourself.
Racing a friends boat in small chop with 3 people and 80 littres of diesel we hit 43knots and on the boats maiden voyage up the river from fareham hit 47.7knots with barely any fuel, a few knots of tide and Kevin from solent ribs driving.

This is with a 23inch Ali prop reving at 4500-4600 rpm.

edit: I did have a photo of 43knots on the gps somewhere. Ill see what i can do.
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Old 02 September 2004, 11:26   #20
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The Shakespeare 600 space cruiser (advertised on Boatmad..go on treat yer self, you know you want to!) with this engine in recorded 33 Knts (GPS average for two way run) at 4200 RPM. 1.4 tonnes displacement, 2 "lardies" on board swinging a 21" x 14" 3 blade alloy prop.Trimmed for speed...

...but Ooo! what a hoot! If I wanted a hardboat, this would be it... smooth, smooth, smooth... and the wonders of diesel economy It's currently at Pwllheli if any one fancies a demo...


actually, I shouldn't have said "two" lardies, sorry Jo...
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