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Post by albi on Sept 21, 2011 10:15:02 GMT
i think my sun odyssey 35 has wrong prop fitted. our speed under motor is only 5/5.5 kts at 2500 rpm. can anyone advise usual performance. present prop is 3 bladed type .i understand 2 blade was original factory option. a spec for original prop would be appreciated.
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Post by rene460 on Sept 21, 2011 11:16:12 GMT
Hi Albi, You did not mention if this engine speed was at full throttle or not. I am not sure of the prop for a SO 35, but we recently replaced the prop on our SO 30. Original prop was three blade, and new prop same diameter. Our mechanic (Yanmar Serviceman) was most insistent that we check that it was correctly pitched for the motor. This means that at full throttle, the engine speed should reach or just exceed the rated motor speed. For our motor this is 3600 rpm, and the new prop proved just right. When it comes to boat speed, I have found that this reduces significantly for any engine speed as fouling increases, (more revs required to reach the normal 5 knot speed limit in our channel) and is restored (revs required reduce to normal) as soon as we clean the hull. But one occasion I noticed that the motor would not reach its normal full revs (original prop) by a large margin. I had a diver inspect for issues and there were just 2 barnacles on the otherwise clean prop blades. He brushed them off and like magic, normal revs for normal speed. Fortunately I was just about due for slipping. Just 2 little critters, it seemed unbelievable, but my new prop supplier confirmed that this is normal as propeller is also a foil like a sail, rudder, keel or wing, rough spots increase drag (torque required to drive it) without proportionate increase in lift (thrust). So first check that engine reaches full revs at full throttle. If not, check for barnacles or other rough spots on the propeller. Also while you are there, check your anodes! Then check for accumulating weed/slime on hull and do an interim brushing in the water or a full slip and clean if necessary. I hope that this helps. Other members may have additional observations and suggestions. rene460
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Post by Deleted on Sept 21, 2011 15:54:21 GMT
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Post by sitara on Sept 22, 2011 1:58:15 GMT
Hi all, Note that the correct size of a propeller is governed by waterline length, displacement, available shaft horsepower, engine RPM, gearbox ratio and your desired maximum speed. When you have all this it is easy to calculate the ideal propeller pitch.
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Post by Don Reaves on Sept 22, 2011 3:08:06 GMT
My Sun Odyssey 35 was delivered with a two bladed 16x11 prop. The rated engine speed for the Yanmar 3GM is 3600 RPM, which means normal cruising RPM would be somewhat less, maybe 3200 RPM. But definitely higher than 2500 RPM.
I've since replaced the original with a 3-blade Kiwi prop. I often cruise at 2800 RPM, and this gives me 6 to 6.5 knots, depending on the wind and waves. So I think that at 2500 RPM your 5 to 5.5 knots is probably about right.
Don
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Post by pbunning on Oct 5, 2011 12:54:44 GMT
We recently found our SO34.2 was a little slow. On checking (when we had her lifted out) found the shaft key had sheared.
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