That pesky final bolt
Managed to free the fourth and final bolt from the prop shaft. The flats had rounded off slightly and so the wrench just slipped off. If you just use a single wrench, the shaft spins, so you have to put another wrench on a bolt on the other side, and they are so tight you then end up standing with one foot on each wrench and gently bouncing until the bolt gives.
For this last one, I figured a ring spanner would work best, but the housing of the coupling is so close to the bolt head that there's not enough space to get a normal ring spanner over the bolt. But there's little an angle grinder can't help with. I ground down the end of a ring spanner to remove a lot of the metal of the ring, hoping the remainder would be enough to hold together and deliver the required torque.
First attempt was going ok when there was a twang and my right foot landed in the bilge. The ring spanner was fine, but the wrench on the other side had snapped one of the arms.
Tools of the job - the failed wrench, and the ring spanner with the ground down end
Fortunately, there's a spare wrench and the second try had the bolt shift gently under my foot, then backed away and bingo, clear air between prop shaft and gearbox. Celebrations...