Drive shaft vibration

[DSHELL]

Hello.
I'm 2 days into a sailing trip in Georgain Bay and experiencing a bad vibration in the drive shaft. The boat is a 1986 Mirage 35 with a volvo penta 2002 engine. The vibration is quite bad above 1500 rpm. I swam under the hull and noticed a bit of play in the shaft, more than there was before launch.

There is no vibration over 1500 rpm when it is in neutral.

I'm currently anchored at a remote island nowhere near a mechanic.

I've been sailing all my life but new to cruising. This is my first diesel boat so I'm not that familiar with them. Should I continue my trip, try to fix this myself or head back home?

[Toccata]

IMHO, Check the simple things first.
1. Coupling bolts tight? (Between gearbox flange and propeller shaft flange and coupling to shaft clamp bolts if it has that system)
2. Prop nut tight?
3. Basic alignment; Loosen the coupling bolts (the ones holding the flanges together) and slide a ruler or something solid between the faces at 12 3 6 9 o'clock positions, similar tightness all round? Are the edges of the flanges in line? Yes, OK. No, adjust the feet of the engine until the flanges are as parallel as you can make them, and the flange edges in line.
4. Engine mount bolts and nuts all tight?
5. Engine in gear at idle, hold something close to the shaft, is it bent/wobbling side to side?
Beyond the above you probably need help.
OR
if everything is tight (not going to fall apart) just use the motor for minimal assistance and sail everywhere
Hopefully others will chip in with further ideas
Good luck

[boris]

Have you got a fixed prop or folding ?
If folding check that it is opening properly