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Old 27 June 2010, 07:02   #1
DGR
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Country: UK - Wales
Town: Barmouth
Boat name: Blue Marlin
Make: Ribcraft
Length: 7m +
Engine: Yanmar 315/Bravo 2X
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3 vs 4 vs 5 bladed props...

I'm looking to replace my prop - it was sized by Ribcraft for a relatively heavy commercial load (10 passengers and 250 kgs fuel) - but now tends to be used much more lightly loaded. I can over-rev the engine by 300rpm - and would like to get that back down to 3800 at WOT!!

The current SS prop is three bladed - so I could just increase pitch - but was wondering whether anyone has played with 4 or 5 bladed props, and what effect they've had?

Grateful for any opinions!!

Cheers,

D...
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Old 27 June 2010, 11:52   #2
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From what I've read on that engine ( www.boatdiesel.com well worth the fee) You are pitched perfectly. Don't mess with it. I considered purchasing a hard boat with that Yanmar (an Albin 28) and the recommendation was to pitch for 4000+ rpm to prevent overloading.
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Old 27 June 2010, 17:11   #3
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Hi
I would not rev the yanmar over 4000 rpm as thay valve bouce and can cause big damage


If i was to Prop that boat i would prop it to 3850 to 3900 to help stop over load when you get a dirty bum or big load


Josh
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Old 27 June 2010, 22:24   #4
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Their rev limiter is set at 4400.
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Old 28 June 2010, 08:27   #5
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Four blade would be good, five blades are good for getting over turbo lag and spinning the engine up but you do loose top end speed. 4 blade is a good all rounder, we prop lots of heavy boats with 4 blade props. Also with a 4 blade you might find you need one pitch down from a three to keep the rpm up, so for your boat i would suggest keeping the same pitch and going to a four blade as it will reduce the revs naturally.
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Old 28 June 2010, 12:13   #6
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Revs

Quote:
Originally Posted by Screaming04 View Post
Their rev limiter is set at 4400.
Flight Speed On a Yanmar 315 6lp ste is 4200 rpm Which is fuel pump stop

To Be Proped To 3800 But I would Prop It to 3850 To 3900

If you rev them past 4100 thay Start to valve Bouce so you dont want to be proping to 4000+.

Josh
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Old 28 June 2010, 15:30   #7
DGR
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Country: UK - Wales
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Flight Speed? That's happened at much less revs than that!!

Thanks everyone for all the advice - it's good to hear views and opinions from those that know and have tried things. It sounds like I'm not far away from being propped right - but maybe try a 4 bladed prop.

Cheers!!

Dylan...
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