Yanmar 1GM10 gear issues

[RenoirIII]

Greetings all,

As you know, the only thing that works on a second hand yacht is the owner...

So in that context I need some advice.

My 1982 Yanmar 1GM10 with XXXXX hours was starting and running fine.
Then I started noticing that it may take 2 or 3 goes getting it into gear.
Ie, I put it into gear and the engine goes but nothing happens.
After some repeated attempts it will kicks into gear and off we go.
Then this morning I noticed that there was unusual vibration throughout the boat combined with a noticeable lack of power.
Any trouble shooting hints?
I'm not sure how to get to the gearbox as it is behind the engine in my Bon Bridge 27.

I have 2 left hands but can normally figure things out OK after some research and Googling.

Thanks in advance for any suggestions...

Rene

[RaymondR]

Take the cable of the shift lever on the side of the gearbox and try putting it into and out of gear by moving the shifter lever by hand. If it shifts reliably the problem is in the Morse shifter system and not the box. Come back and tell us what happens.