Join Date: Sep 2010
Location: Boston area
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Thanks, casey. I did replace the anodes last year, almost. I missed that there was a third behind the fuel filter, sothat is on this winter's list.
On yours, the ratings I have in the manual are 3400 max continuous, and 3600 max for not over 1 hour. 3700 does not appear. The Yanmar tachs are known for being off - don't know if that is always to the low end or not, but I think most references I have seen are for ones that were low. I found that my tach case had completely rusted through with 1/8" + holes through in a lot of places, but it still read pretty well. The new one reads a little higher, but not by over 100 rpm or so. I also changed out the three engine wiring harnesses, from the back of panel to all of the engine connections. The back of the panel, where the tach rusted, had a cou0le of bad connectors in the plugs as well, and I found a couple of bad connections inside plugs in the engine bay that looked perfectly good until i pulled them apart. Overall, it turned out to be good preventive maintenance, and all of the parts were in stock at Torrenson. My panel is out in the open in cockpit, and the seal wasn't good after 25 years.
I'm not sure I agree with pitching the prop to hit hull speed at 3600. In my case, I can push boat beyond hull speed by close to a full knot (7.5 with a 21' waterline). Usual advice is to pitch it so that you reach max rpm target of 3600 at max throttle. That would let you reduce rpm's to say the 3400 max for continuous running and still be around full hull speed, for instance. My boat is a little unusual in that it has so much power for a small boat, but the basic physics rules still apply. However, pushing beyond hull speed is really inefficient, as consumption jumps, as does teh size of teh wake, teh depth of teh standing bow wave, etc. In your case,m I'd check teh tach before relying on it for max readings.
There could be other causes for teh engine not being able to reach over 3300. For instance, blockage building in teh exhaust elbow where teh water enters the exhaust. That is a classic ppoint where the inside space gets reduced by carbon adn teh resulting back pressure reduces the max rpm.
1985 Marshall 22 catboat