mother of all shaft coupling battles

NOTE: This jobs was done out of the water in dry dock. If you were in the water and in a bind, you would want to tie the propeller to the boat(just in case is slides out to far) and have a plug and rags ready to fill a hole and stop the boat from sinking. The risk is real!

A common approach to removing shaft couplings is to place an appropriately sized socket in between the reduction gear flange and the shaft(inside the coupling). Ensuring the socket is centered, you then place a few extra long bolts in the aligned flange holes and tighten them evenly. (this is important so you don't jam the coupling on the shaft) Tighten each bolt about a quarter turn, then tighten the next, repeat untill the coupling slides off.

In addition you can use a break loose penetrating oil, a hammer, more bolts, a blowtorch(heat the coupling not the shaft) The heat will cause the coupling to expand (make sure you are careful, protect the hull if necessary).

As you can see from the pictures I broke a bolt I turned so hard.

I eventually cut the coupling off with 5 inch angle grinder with a metal cutting disc. Cut all the way through to the key. Make sure you cut to the key, it will save you cutting time, and protect the shaft from damage from the disc. Also, make sure you protect the boat from slag and sparks.
(depending on your situation, you may want to cut the shaft instead, you could then press out the shaft at a machine shop and save the coupling. You may need a new shaft, or perhaps you'd be ok with a shaft a few inches shorter, each case is different, counsult a professional)

Once the slot was cut, I tapped in a wedge and HURRAY I was finally able to slide the coupling off by the method mentioned in the first paragraph.