Prop size and pitch

T

ted_reshetiloff

Contributing Partner
What do you have now and what is max rpm you get when it it clean? There are other posts on this topic and you can search for them here but you basically want a prop that allows the engine to reach full rpm (stated in owners manual) at full throttle. This will ensure you are not over revving or lugging your engine. It will also ensure you are getting the maximum horsepower out of your motor. Of course others with your boat on this site may have more detailed answers. BTW any chance you were sailing up the South River on Labor day? I passed an E-27 who was under sail as I was motoring up the river.
 
A

Annapolis E-27

Member III
Ted,

Thanks...no unfortunately I was not on the water Labor Day weekend. Still trying to work out the loss of power and black soot in the exhaust issue.
 
D

Dave Hussey

Member III
I'm searching for the same info myself for my E27 powered by a Volvo diesel, with a redline of 1400 rpm. I think I currently have the orignal screw that is for an Atomic, and easily over rev my motor now...with no appreciable increase in thrust...so, got to increase pitch and diameter I guess...but I cant seem to get a firm answer from the sources I've tried on the web . Have you found any info on the right prop?
Dave
 
T

ted_reshetiloff

Contributing Partner
If I am understanding you correctly you are only getting 1400 rpm max with the volvo diesel? That sounds rather low as crusing rpms are generally 2000-2500 with a max of 2800-3k. At least this is the case with the ones I have worked with. Had an old MD 20 Volvo on my fathers boat and that was the spec. So if you are only able to get it up to 1400 when in gear (ie not an engine problem) then you have either to large a diameter prop (less likely) or too much pitch. General rule of thumb is 200 rpm for every degree of pitch. So lets say you have a 12 X 16 prop now. If you went to a 12 X 10 or 12 X 9 you would probably get up to the engine's optimal rpms. I don't know what size prop you have now so I'm making up a for instance. Again you need to consult you engine manual and see what the max rpms are and what cruising rpms should be, then set your prop to get there. Best solution ($$$) is to buy a feathering prop and try a few different pitch settings until you get the best one. All this of course assumes youe engine is in good working order, bottom clean and prop clean. Hope this helps
 
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