Is the published h34 prop size correct?

[Paul Bryan]

My prop size for my '83 h34 is 15x12. The chart on this site calls for a 15x15. I was told my prop was stock. I assume my prop is undersized because I can only do about 5.5 knots at 3000 rpm. What do you 34 owners use? I have the yanmar 22/24 hp engine.Thanks,Paul BryanWhisperIII

 

[Barry Olsen]

Previous Discussion about Props on h34's

The early '83 boats had Westerbeke 21 motors. They switched engine suppliers sometime during that year but never changed the prop to match. I have hull #56 with the Westerbeke and it will hit 7.1 knots under power. There was a thread here some time ago about this issue. I don't know my prop size but I recall the Yanmar owners were not satisfied with performance. Try to find it in the archives if possible.Barrys/v "PER DIEM too"

 

[DJ Dreyer]

673 and counting

My '84 34 is hull 673. It also came with a 15X12 prop. I was friendly with several other H34 owners in our area and some had 15X12 and some 15X15. For the Yanmar engine, 15X15 is the better prop. I ended up getting a 15X15 prop for my boat. Unfortunately there is not enought room to go to a 16" prop diameter (you should have about 15-20% of prop diameter clearance between hull and prop tip-about 2" clearance presently with a 15" wheel). I am thinking of going with a Max Prop 3 bladed with a 15" diameter to get more push from the engine. Presently, I can only do about 6.1-6.3 with the engine turning 3400 RPMs.

 

[Allan Hadad]

Number 798

My H34 has the original 15x15 prop. We cruise at about 6.3 knots at 3200 rpm with a clean bottom and flat seas.

 

[David L]

Good Question

Mine is a 15 x 12 I think. Hull #29. Only get about 6 to 6.5 @ 3000 rpm. Have the Westerbeke and am thinking of going to a 15 x 15 next haul out.

 

[John K Kudera]

Martec

Hi Folks,Ours is Hull # 686 84 H43We have been using a 16X12pitch Martec for six seasons, no speed or backing problems.John

 

[Clyde Lichtenwalner]

For the record

15X12 is the size provided by the factory for the Westerbeke diesel in early H-34s15X15 is the correct size for Yanmar diesel-equipped H-34s; the vast majority.When the switch was made from Westerbeke to Yanmar, some Yanmar equipped boats got factory 15X12 props. The Yanmar engine has a greater transmission reduction ratio than the Westerbeke, hence a slower prop speed for a given engine speed, hence the need for the higher pitch. There should be no difference in performance between the two if the prop and hull are equally clean. Both should take the boat to hull speed (7.2 knots) at full engine speed. Both should cruise comfortably at 6.5 knots at crusing RPM as recommended by the individual manufacturers. If your boat has the correct prop and still does not meet those parameters, check for calibration of both the tachometer and knotmeter. Don't forget that a slipping fan belt will give incorrect tachometer readings. Also don't forget that other factors, such as boat displacement (heavy load) and fouled prop can change performance.