Prop Shaft Height

[mjsb]

Recent issue with a dock line and my prop shaft. After getting back to the slip (towed) and having the line cut loose, and hearing a “thumping sound”, had the boat pulled out and the prop, shaft, cut-less, couplings and engine mounts checked. Found that the tube for the shaft was touching the prop shaft. So as a precaution to all of the above the motor mounts have been replaced and the engine / shaft aligned and sighted ((mechanically). I ran the engine prior to connecting the shaft to the transmission and the engine was pretty smooth, when attaching shaft and aligning all was good and the ran the engine again. Did not put into gear. I listened and watched. Ever so slightly I could a thumping at the stern.
Now I ask is it possible to raise the motor/trans to “lift the shaft” off of the tube, without putting the mounts to high? Don’t want the motor way up on the mounts.
yThe engine is a Yanmar 2GM20F, with 1104 hours on it. Cut-less bearing was deemed ok as well as shaft.
Any thoughts or help very much appreciated, in advance thanks.

 

[dmax]

While raising the mounts will "soften" them a little bit because of increased leverage on them. you're probably only talking about 1/4" or less. On my boat, the shaft is 1" and the tube is 1 1/2" so there's 1/4" space between them when centered. The mounts tend to sink as they age so not unusual to have to raise them a bit to keep the shaft centered. If you are worried about extending your mounts you can put a pad underneath them to raise them up (e.g. 1/4" thick G-10) so the mounts aren't over-extended. You do need to stop the shaft from hitting the tube as you know, it can cause major problems that can sink your boat.

 

[mjsb]

While raising the mounts will "soften" them a little bit because of increased leverage on them. you're probably only talking about 1/4" or less. On my boat, the shaft is 1" and the tube is 1 1/2" so there's 1/4" space between them when centered. The mounts tend to sink as they age so not unusual to have to raise them a bit to keep the shaft centered. If you are worried about extending your mounts you can put a pad underneath them to raise them up (e.g. 1/4" thick G-10) so the mounts aren't over-extended. You do need to stop the shaft from hitting the tube as you know, it can cause major problems that can sink your boat.

Thank you for your response, I had a marine engineer from our sailing squadron out to my boat today, and after about 10 minutes checking my motor mount install, giving it the OK, we started the engine and put it in gear and the bad news was defined, a bent shaft. This makes sense, even though earlier in the season i had one of the yard techs take a look at the cut-less bearing, prop and shaft, their response was it seemed ok. So now it comes out again and will have a new shaft fabricated and install a new cut-less. All in the life of a boat.