Hi Scott,
Welcome to the forum.

You started off really well by saying:-

"I quit my job in December and intend to crew from boat to boat, all the way round the world if I can manage it,"

and then sort of blew it at the mention of insurance.

Concise Oxford English Dictionary:-

adventure.........risk, danger, daring enterprise, hazardous activity.

adventurer........one who seeks adventures, soldier of fortune, speculator, one who lives by his wits.

Do you want "safe passage" or "adventure"?

I have been where you are now and at that time my will to gain " a deep sea sailing adventure" was greater than my fear of "not coming back home". I didn't know there was such a thing as "travel insurance" then.

The only insurance I had was my savings from three years work.

Older and maybe wiser now, but if I had then, the wisdom I have now, I would have adventured further.

If you are still young, just do it, because you won't ever be young again.

By the way, Keep Your Wits About You.