H31 engine questions

[Don]

I spent a lot of time cruising my ’84 H31 under power this weekend and am reviewing my engine situation. 5 hrs under power both days was my first time running the engine this long. I would appreciate any constructive comments.Maximum RRM under power is about 3200. I spent most of the weekend at 3000 doing an avg of 6+ mph, which is fine (actually pleasantly surprising.) All in all, the engine ran fine, no overheating, black smoke, etc.There were times, however, when I could have used a little more power. Winds were high and lots of boats around. But pushing the throttle from 3000 to 3200 adds nothing.I'm running the factory 2 blade prop and have not yet cleaned my hull this year (boat stayed in Chesapeake all winter.) Nor have I done any major repair/maintenance on the engine, the riser, heat exchanger, etc. all are as I bought them 2 years ago. And, the boat had been maintained minimally before then.Should I be concerned here or is there anything I can do to improve matters? I've read posts about changing props, obviously I can and will clean the hull. Just wondering what I should put on the to do list and in what order.Thanks

 

[Steve Dion]

Hi Don

Don:I also still run the two blade prop. From my experience a clean bottom will do more for you than these expensive props (of course you need to keep the bottom clean). If you read MOST of the posts they get better backing control and better speed under sail. I think that the variable pitch props will give you a little more speed but at what cost $2-3k? And one of the recent posts indicated that Yanmar does not recommend these props (suppose they put additional load on the engine?) You need to do the bottom anyway so do that as see what it does for your speed and then evaluate the alternatives.

 

[Don]

Steve, what's your max RPM under power?

nm

 

[Steve Dion]

Well, that's a very deep subject.

Don:Well, I think my engine is still slightly over propped. But to answer your question, I can get about 3200-3300 in gear. I think that I should be able to get 3600 in gear. My prop is a composite 2 blade. If I run my engine over 3100 for any length of time it will set off the over-temp alarm. My speed is hard to determine. We are dealing with a current that runs in and out 2 times daily, so we are constantly running with it or fighting it. I try to operate the engine at 2800. This is at the upper end of the optimum range, but that is assuming that you are pitched properly.We made a run from our harbor to Richmond the weekend before Memorial Day and we were making 9mph over the ground. We did the entire 60+ miles in 7.5 hours. Our trip home was a different story and the SOG was indicated at about 6 mph but we were going against the tide.