- This topic has 5 replies, 2 voices, and was last updated 17 years, 4 months ago by
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I guess that explains why I have been motoring backwards all these years
with my Max prop… They must have a leftie also.Pete
Rich Carter wrote:
Quote:Double check the direction of rotation before you buy anything. Most
props are righ handed. The 424 is left handed because it has no gear
reduction in the transmission.Regards
Rich
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The 17×10 sounds small to me. I think you’ll find that your top speed will suffer. Others with the same engine might comment.
In my opinion, Pearson should have provided a little more gear reduction when they designed the driver train for the 424. They could have then used a smaller prop with a little more bite. This would have reduced the tip speed and provided better efficiency, but you can’t reduce prop size and keep the same gear ratio without cavitation. Your 17×10 is both smaller in diameter and has less bite.
Fuel consumption curves typically assume that the engine is loaded over the entire curve. If the engine is under-loaded such as would happen with a prop that is too small, fuel consumption would be higher than necessary but below the curve as published by the manufacturer. If you try to power into a head sea, having a prop that’s a little smaller will give you better performance. The trade-off is that you’ll burn more fuel when cruising and you’re top speed will be lower. Your engine will be running faster than ideal for all cruising speeds, so you’ll have more noise and vibration in general.
All the manufacturers seem to recommend running diesels hard. There’s a lot of evidence that indicates that frequent idling is bad for a diesel, but I’m not convinced that the 80% rule is needed either. We run two launches at my yacht club with Yanmar 75 hp engines. We run them at about 50% of their rated redline speed. Any higher and we kick up a huge wake. Both have over 3000 hours on them with no problem (except some dummy improperly installed an oil filter and blew one of the engines). I take my boat out and drive it hard for about 15 minutes every few hours of operation.
Regards
Rich
BlackSheep #47
Original Message
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2.05 : 1
— On Wed, 7/1/09, joe shimkonis <> wrote:
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Joe,
My RV-20 Walter V-drive, the original in this boat, has a metal ID plate on the face that states the ratio as being 2.05/1.
Tor
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Silver Heels, P-424 #17
http://www.SilverHeels.us
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Original Message
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I believe the original fixed prop was 18×13 and I agree that 17x 10 is small.
My Yanmar manual recommends running hard for 15 minutes every 10 hours. If you have a turbo, they even like you to run hard 15-20 minutes just before you come to your destination.
The idea is to burn off any carbon buildup.
Joe,
Half Moon #71— On Wed, 7/1/09, <> wrote:
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