mbsl98
New Member
Hi folks,
First post after lurking for a while. I have recently acquired a Marshall 22 gaff rigged catboat with a Yanmar 3GM30. (see http://www.marshallcat.com/M22Lines.htm for details) I don't believe the boat is much known in Europe, but the Yanmar obviously is. I bought a 1985 example, with low hours, light use, and good maintenance for the most part, although the prior owner of last 9 years was not a tinkerer and there are various projects on my list for the winter. I am most interested in the amount of engine vibration to be expected at various speeds. I knew it needed a new shaft and cutlas bearing, and probably new motor mounts, and have sort of viewed the vibrations while underway as mostly due to those things. However, as I tinker with it, I find that there is a good bit of engine vibration at different RPM's while running out of gear. In particular, there are vibrations that come and go as the RPM's rise, so that there are speed levels that are pretty smooth, and others that have more significant vibrations. I had a Volvo 3 cylinder in a Dufour 35 for 15 years, and remember that 3 cylinder as being pretty smooth once above idle, so this Yanmar seems to me to need some attention. I expected it to be smoother than the Volvo. If it should be pretty smooth at unloaded speeds, what are the usual things to chase down to get it there? I expect it is time to send the injectors out for cleaning, spray pattern, etc., and probably there are areas that build up carbon deposits that could start to impact running, but this is just guessing and that's why I am asking this august group. Aside from vibration, it does seem to run well, burning about 2 liters/hour at cruise (2500 RPM and about 6 knots), and lots of power as would be expected with this much motor in a 5600 pound boat. I have found that the motor wil top out at only 3200 RPM's, about 7 knots, while the manual rates it for short bursts at 3600. Assuming that the manufacturer spec'd it properly (they have produced this boat as is for over 40 years), I would have expected to be able to reach 3600 at full throttle, so that may also suggest that some attention is needed. All thought very welcomed.
First post after lurking for a while. I have recently acquired a Marshall 22 gaff rigged catboat with a Yanmar 3GM30. (see http://www.marshallcat.com/M22Lines.htm for details) I don't believe the boat is much known in Europe, but the Yanmar obviously is. I bought a 1985 example, with low hours, light use, and good maintenance for the most part, although the prior owner of last 9 years was not a tinkerer and there are various projects on my list for the winter. I am most interested in the amount of engine vibration to be expected at various speeds. I knew it needed a new shaft and cutlas bearing, and probably new motor mounts, and have sort of viewed the vibrations while underway as mostly due to those things. However, as I tinker with it, I find that there is a good bit of engine vibration at different RPM's while running out of gear. In particular, there are vibrations that come and go as the RPM's rise, so that there are speed levels that are pretty smooth, and others that have more significant vibrations. I had a Volvo 3 cylinder in a Dufour 35 for 15 years, and remember that 3 cylinder as being pretty smooth once above idle, so this Yanmar seems to me to need some attention. I expected it to be smoother than the Volvo. If it should be pretty smooth at unloaded speeds, what are the usual things to chase down to get it there? I expect it is time to send the injectors out for cleaning, spray pattern, etc., and probably there are areas that build up carbon deposits that could start to impact running, but this is just guessing and that's why I am asking this august group. Aside from vibration, it does seem to run well, burning about 2 liters/hour at cruise (2500 RPM and about 6 knots), and lots of power as would be expected with this much motor in a 5600 pound boat. I have found that the motor wil top out at only 3200 RPM's, about 7 knots, while the manual rates it for short bursts at 3600. Assuming that the manufacturer spec'd it properly (they have produced this boat as is for over 40 years), I would have expected to be able to reach 3600 at full throttle, so that may also suggest that some attention is needed. All thought very welcomed.
If 3200 is the factual limit, wouldn't it be better if the prop was slightly re-pitched to let the motor reach its max power at the same boat speed? That is certainly the typical outboard motor target, but not sure if the same reasoning applies to an inboard diesel. On an outboard runabout, it is said that the boat/motor will run better at all speeds if it is pitched to reach max rated RPM on full throttle. The Yanmar manual says the motor is rated at 24 hp at 3400, 27 hp at 3600, with 3600 being only for shorter periods (under an hour). If the curve follows downward, then it would only be putting out around 22 HP at 3200, and straining. I am not trying to get more boat speed, just getting the motor to run at its best with least vibration and least strain for the long haul.
