I have a Beneteau 461 and have sailed from Alaska down to Mexico. I
mention this only because the trip requires you to travel through crab
pots, commercial salmon nets, fog, and tuna lines in Mexico.

My experience was that no matter how hard you looked, you were going to
"find" a float that you could not see. As a result you needed to
assume you would get caught and have a plan. Most of the time you
could put the engine in reverse and free your self. In mexico I got a
nylon tuna line wrapped around the prop. With mask, fins and a knife I
tried for 30 minutes to dive under the boat and cut the line, which had
literaly melted on the shaft. With a one knot current, there was no
way you could swim to the prop, make any kind of cut and then get back
for air. Based on this I believe for both coastal and open water
sailing I need a "small" scuba air tank so that I can get down, fix the
problem, and get back out. The "spare air" tanks cost less than $150.
Money well spent. In Maine your going to need at least a 5 mill wet
suit to get in the water to untanggle your prop

Some other options that you might consider are a prop cutter or a hook
knife.

http://www.quickutter.com/

http://www.captnhooksolutions.com/index.html

Regarding the fog, several of the new VHF radio's come with a "hailer"
/ fog horn option. I found mine to be extremely helpful. If you don't
have this then you will be using a "bell" every 60 seconds, even when
on the hook. No one is going to hear your bell over their engine.

-Mark
www.goreads.com