I notice that my H34 propellor is a 15 x 12. The boat specs on this site specify a 15 x 15. What's the deal? Was there a change in the fitted prop at some point? Mine doesn't seem to have much "bite", particularly in reverse, and I wonder if the extra pitch would help. My yard manager says it would slow the diesel down several hundred rpm. (I have a vague recollecion that this has been discussed before - couldn't find it in the archives) Happy sailing, Derek
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big bite!
My h34 had a folding prop with absolutly no reverse at all. I spent a great deal of time looking for the appropriate sized fixed two blade prop. As you found, specs call for a 15 x 15. All boats in the yard where my boat is kept are equiped with a 15 x 12. I purchased a 15 x 12 and am happy with the results.
My h34 had a folding prop with absolutly no reverse at all. I spent a great deal of time looking for the appropriate sized fixed two blade prop. As you found, specs call for a 15 x 15. All boats in the yard where my boat is kept are equiped with a 15 x 12. I purchased a 15 x 12 and am happy with the results.
Don't be Timid
I think most folks don't give enough throttle at first. I used to give our 34 quite a bit of throttle until it bit and then backed off. This also helped get past the port prop walk problem because you get great reverse steering with a 34 once it starts actually moving in reverse. Good luck with your 34, we really liked ours. George
I think most folks don't give enough throttle at first. I used to give our 34 quite a bit of throttle until it bit and then backed off. This also helped get past the port prop walk problem because you get great reverse steering with a 34 once it starts actually moving in reverse. Good luck with your 34, we really liked ours. George
Need more RPM's
Derek: Don't be fooled into thinging that a bigger prop is going to help. These Yanmars are typically a high RPM engine. Your prop should be able to turn the max RPM while underway. If you are rated at 3600 rpm (max) this is desireable to be able to run your engine upto this RPM. The mfg recommendation is to operate these engines in a range of 70-80% of the max rating. This is usually about 2800-2900. I have the 2gm20f engine in my H'31. The specs for these engines have the boat over-proped. Should be running something like a 15x9 or 10 but the specs were 15 x 12. As a rule of thumb 1" pitch is 250 rpms.
Derek: Don't be fooled into thinging that a bigger prop is going to help. These Yanmars are typically a high RPM engine. Your prop should be able to turn the max RPM while underway. If you are rated at 3600 rpm (max) this is desireable to be able to run your engine upto this RPM. The mfg recommendation is to operate these engines in a range of 70-80% of the max rating. This is usually about 2800-2900. I have the 2gm20f engine in my H'31. The specs for these engines have the boat over-proped. Should be running something like a 15x9 or 10 but the specs were 15 x 12. As a rule of thumb 1" pitch is 250 rpms.
What was on hand
Early '83 H34's had Westerbeke engines and needed 15X12 props. Yanmar equiped H34's needed 15X15. I can get a bit over 3400 RPM's with my new 15X15 two blade prop. Originally I had a 15x12 and was always the last one to arrive if our group of H34s were motoring (often on the Chesapeake Bay in summer). All the other Yanmar H34's in our group had 15x15. Hunter often uses what they have on hand when building a boat. 15x12's might have been available (used also for the H31) while they were building my boat and Hunter could not find any 15x15's. If I was buying a Hunter today with their "free" giveaway, I would expect that many of the free items would be substitutions for what they originally said they would provide. Same as if they did not have pressure treated wood on hand to use as a mast kingpost…. (yeah, I know I opened up a Pandora's box…
Early '83 H34's had Westerbeke engines and needed 15X12 props. Yanmar equiped H34's needed 15X15. I can get a bit over 3400 RPM's with my new 15X15 two blade prop. Originally I had a 15x12 and was always the last one to arrive if our group of H34s were motoring (often on the Chesapeake Bay in summer). All the other Yanmar H34's in our group had 15x15. Hunter often uses what they have on hand when building a boat. 15x12's might have been available (used also for the H31) while they were building my boat and Hunter could not find any 15x15's. If I was buying a Hunter today with their "free" giveaway, I would expect that many of the free items would be substitutions for what they originally said they would provide. Same as if they did not have pressure treated wood on hand to use as a mast kingpost…. (yeah, I know I opened up a Pandora's box…
Reduction Ratios
Confirming DJ's post, the difference between the two engines is the gearbox reduction ratio. The Yanmar's is a higher numerial ratio than the Westerbeke, hence the prop spins slower at a given engine speed and needs the greater bite of the 15X15 prop.
Confirming DJ's post, the difference between the two engines is the gearbox reduction ratio. The Yanmar's is a higher numerial ratio than the Westerbeke, hence the prop spins slower at a given engine speed and needs the greater bite of the 15X15 prop.
Westerbeke or Yanmar
To D. J. Dreyer You mentioned you changed you prop from a 15 x 12 to a 15 x 15. What engine do you have?
To D. J. Dreyer You mentioned you changed you prop from a 15 x 12 to a 15 x 15. What engine do you have?
stayed with 15x12
I was going to change the prop on my h34 this year based on the previous discussion some months ago. I went to the Mich. Wheel website and gave them my specs. The naval architect there recommended that I stay with a 15x12. Said a 15x15 was too much pitch for the h34 with Yanmar. Now you guys got me thinking about this issue again. The boat is a bit slow under power, but maybe I'm too stingy with the throttle. I like to keep it at 2500-2800 cruising. I hate to make the change and then find out I'm overloading the engine! We should poll all h34 owners to see which prop they use.
I was going to change the prop on my h34 this year based on the previous discussion some months ago. I went to the Mich. Wheel website and gave them my specs. The naval architect there recommended that I stay with a 15x12. Said a 15x15 was too much pitch for the h34 with Yanmar. Now you guys got me thinking about this issue again. The boat is a bit slow under power, but maybe I'm too stingy with the throttle. I like to keep it at 2500-2800 cruising. I hate to make the change and then find out I'm overloading the engine! We should poll all h34 owners to see which prop they use.
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