Short version: observed unusual engine vibrations (2GM20F, front of engine bouncing up and down) when the transmission was in neutral, engine idling at 1200 RPM, the prop was free-wheeling, sea state was higher than I'm used to. 18 year old engine, never aligned, original engine mounts look to be be in good shape, but what do I know? I'm worried that the engine mounts may be shot, but how do I tell?
Long version: On Saturday, I motored all the way from near Baltimore down to Annapolis (20 miles, 4 hours, 5 knots, 3000 RPM, no wind). I always check on the engine for vibration, and noticed nothing unusual. My wife joined me (by car) for a pleasant evening in Annapolis, and I left Sunday morning for a solo return trip. The wind was 12-15 knots, gusting to 17-19, so I started out with full sail up, put in one reef shortly, put in a 2nd reef next. A bit higher wave action than I usually see: maybe 4 feet. (Yeah, I know: wimpy for most of you. It is what it is, though.)
Anyway, I left the engine on at my usual low-vibration idle of 1200 RPM for a while in neutral, because I was solo and needed the extra safety factor. By the time I'd put in the 2nd reef (maybe 1 hour in), I was less busy, so I went below and checked the engine. It seemed to be hobby-horsing, with the back of the engine stationary and the front bouncing up and down 1-2". I've never seen this motion before in 18 years. Made me really nervous, so I shut the engine down. Strangely, the motion continued just from the prop auto-rotation (trans. still in neutral). I've _really_ never seen anything like this before, so I put it in reverse. Engine vibration stopped, and I proceeded to sail for 6 hours all the way back, in a big L-shaped course that took me roughly 1.5-2 hours out of my way compared to a direct course. I figured I'd chance using the engine just to get into port when I was really close. It was actually sort of a fun adventure, as the wind was still high, it was raining, I was on my own with a sketchy engine. But with the wave action, it was pretty tiring after 6 hours, as I hand steered almost all the way (wind from 130 degrees for most of the way).
When I got into Rock Creek (in the Patapsco: there are a million Rock Creeks, ours has White Rocks Marina where we keep the boat), the wind had died down to 5-6 knots, so I chanced the engine. The vibration was maybe a little more than I expected at 2000 RPM, but not bad. Ran it up to 3000 RPM, and the engine looked rock solid: no vibration to note. Docked with no issues.
Other observations: the 4 original Yanmar engine mounts look normal to me, but I was fried by this point after 6 hours of hand steering, so I forgot to take pictures, and didn't investigate much further while I put the boat to bed. So I strongly suspect I may need to replace the engine mounts, but heck: it's a large investment of money, time, and energy just as I'm getting close to my big Fall trip, so I don't want to do unnecessary work.
How do I test whether or not this is really needed? Could it be that the sea state was just higher than I'm used to, so I haven't observed this level of engine motion before? 1-2" of bouncing just from a free-wheeling prop with the engine shut down seems extreme to me.
Thanks for your thoughts!
Long version: On Saturday, I motored all the way from near Baltimore down to Annapolis (20 miles, 4 hours, 5 knots, 3000 RPM, no wind). I always check on the engine for vibration, and noticed nothing unusual. My wife joined me (by car) for a pleasant evening in Annapolis, and I left Sunday morning for a solo return trip. The wind was 12-15 knots, gusting to 17-19, so I started out with full sail up, put in one reef shortly, put in a 2nd reef next. A bit higher wave action than I usually see: maybe 4 feet. (Yeah, I know: wimpy for most of you. It is what it is, though.)
Anyway, I left the engine on at my usual low-vibration idle of 1200 RPM for a while in neutral, because I was solo and needed the extra safety factor. By the time I'd put in the 2nd reef (maybe 1 hour in), I was less busy, so I went below and checked the engine. It seemed to be hobby-horsing, with the back of the engine stationary and the front bouncing up and down 1-2". I've never seen this motion before in 18 years. Made me really nervous, so I shut the engine down. Strangely, the motion continued just from the prop auto-rotation (trans. still in neutral). I've _really_ never seen anything like this before, so I put it in reverse. Engine vibration stopped, and I proceeded to sail for 6 hours all the way back, in a big L-shaped course that took me roughly 1.5-2 hours out of my way compared to a direct course. I figured I'd chance using the engine just to get into port when I was really close. It was actually sort of a fun adventure, as the wind was still high, it was raining, I was on my own with a sketchy engine. But with the wave action, it was pretty tiring after 6 hours, as I hand steered almost all the way (wind from 130 degrees for most of the way).
When I got into Rock Creek (in the Patapsco: there are a million Rock Creeks, ours has White Rocks Marina where we keep the boat), the wind had died down to 5-6 knots, so I chanced the engine. The vibration was maybe a little more than I expected at 2000 RPM, but not bad. Ran it up to 3000 RPM, and the engine looked rock solid: no vibration to note. Docked with no issues.
Other observations: the 4 original Yanmar engine mounts look normal to me, but I was fried by this point after 6 hours of hand steering, so I forgot to take pictures, and didn't investigate much further while I put the boat to bed. So I strongly suspect I may need to replace the engine mounts, but heck: it's a large investment of money, time, and energy just as I'm getting close to my big Fall trip, so I don't want to do unnecessary work.
How do I test whether or not this is really needed? Could it be that the sea state was just higher than I'm used to, so I haven't observed this level of engine motion before? 1-2" of bouncing just from a free-wheeling prop with the engine shut down seems extreme to me.
Thanks for your thoughts!
