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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 10-20-2003
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Three Blade Prop

I am sailing a 30 ft sefarer with a 2gm10 diesel. While motoring out of the creek and the channel to the river/bay I have motor at about 1500 rpm I make about three knots, I know that the hull is clean because under sail it is moving right along at six knots which is probably the best I''ll get with a full keel boat would a three blade prop help me go a bit faster while motoring ,and will the 10hp support a three blade prop. It''s getting inbarrassing being passed by jellyfish thanks in advance for your input.
kd
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Old 10-20-2003
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Three Blade Prop

A couple thoughts here, I believe that cruising speed on a Yanmar 2 GM is closer to 2800 rpm. You are doing your engine no favor operating at a lower speed and you would probably get more speed out of the boat with a higher rpm. If 1500 rpm is the max that the engine will turn then you either have an engine problem or you are over-propped. If you are over proped then the three blade won''t help a bit. A 10 hp diesel engine should push you at close to hull speed in flat water and moderate winds. You would noticable decrease performance with a 3 blade prop.

Jeff
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Three Blade Prop

You also seem a little unsure of your boat''s bottom condition. While some light growth is unlikely to be very noticeable on a breezy day and a "non performance" boat, your symptoms could be explained by growth on the prop blades.

Last year, while my bottom cleaner was slowly putting himself out of business, there was a period where the job wasn''t getting done, and I didn''t know about it. While the hull had fairly fresh paint and didn''t get too ugly, the metal bits were crusted over to extreme. The prop blades looked like two baseball bats, instead of blades. Under power, the engine lugged, and top speed was 4 knots under power, and fuel efficiency was terrible. Under sail, there was practically no effect from the crusty prop on the boat''s performance.

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-Chad
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Old 10-20-2003
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Three Blade Prop

You also seem a little unsure of your boat''s bottom condition. While some light growth is unlikely to be very noticeable on a breezy day and a "non performance" boat, your symptoms could be explained by growth on the prop blades.

Last year, while my bottom cleaner was slowly putting himself out of business, there was a period where the job wasn''t getting done, and I didn''t know about it. While the hull had fairly fresh paint and didn''t get too ugly, the metal bits were crusted over to extreme. The prop blades looked like two baseball bats, instead of blades. Under power, the engine lugged, and top speed was 4 knots under power, and fuel efficiency was terrible. Under sail, there was practically no effect from the crusty prop on the boat''s performance.

Best,
-Chad
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Old 10-21-2003
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Three Blade Prop

Thanks all for thoughts on three blade prop. The engine was rebuilt last year and I assumed that 1500 was the proper rpm to motor at, using the higher rpm for emergencies. the instructor at sailing school had us running at that rpm.on my last boat with a 35hp turbo 1500 was plenty to go 4 to 5 knots and it was 16000 lbs thanks again I''ll just rev up a bit in the future I will also check out growth on prop bottom is ok
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