Duncan Heenan wrote:

If his girlfriend is 60+ she's old enough to make her own mind up.

Not if she lacks the awareness of the potential danger to herself.

Is it the father's happiness the daughter's worried about, or her
inheritance going on a boat and a girlfriend.

There's no need for such insulting remarks. The last thing to leap
out at me from this story is the daughter's concern for her "rightful"
inheritance. Hell, if her dad is serious about this girlfriend of
his, he's probably willed her most of his worldly possessions anyway.

It's not good enough merely to say that it's his life and he can do
what he likes with it. Even if he were to sail alone, without this
lady, he is still a potential danger to others if he can't handle
the craft well enough. Add the inexperienced and weak crew, and
you have an additional potential victim, without a reduction in
the danger the boat could pose to others.

On the other hand, I do agree with the sentiments that he should
be left to follow his dream and enjoy happiness in his twilight
years.

I suggest that the best solution would be to see if the lady can be
persuaded to become a competent and useful crew memeber capable of
handling the boat on her own if necessary. Get lessons and experience.

This would at least reduce the danger to which she and others (and
he) would be exposed. I think that could work quite well. The
only remaining thing is the concern about the allegedly poor
condition of the boat. That would need to be looked at and sorted
out.