Well, fast connections and some luck have eluded me. Here's an update: We spent a night in Victoria Dock, in Caernarfon.
The next day, we dried the boat out in the river, and adjusted the pitch of the J-prop. This was tricky, because somehow the 'zero' calibration setting had been lost. I worked out where this was by experiment, and then added some pitch based on various speculative calculations that we did ...
We got it nearly right: the cruising speed under power is now about 6 knots or a little more. Another notch up would probably get the 7 that the previous owner said we should expect.
We transited the Menai straits the evening after fixing the prop, losing the daylight completely as we approached Beumaris. In the dark, we found a lot of yacht moorings that weren't marked on our chart, and were glad to get out into the Irish Sea again.
We were able to sail during the night a little, but the wind dropped by dawn and we were motoring as the sun rose. We hoped to reach Portpatrick, but the engine stopped off the south end of the Isle of Man and would not be re-started.
This time we didn't inform the Coastguard, and decided to do some more investigations and wait for wind instead. Meanwhile, the tide swept us up the Eastern side of the island.
I phoned the local Yanmar dealers (Bottom Line Engineering) and spoke to Dean, who thought we probably had a dirty fuel problem. There had certainly been something nasty in the filter, which I had attempted to clean. He though we probably had problems with the high pressure end of the system as the filter we had was not very effective.
We had some discussions with Douglas Harbour, as well, in case we were able to go in there. A breeze sprang up when we were off Port St. Mary, however, and we got in there instead. As we tried to pick up a visitors' mooring, someone came out in and RIB and asked us if we'd like to be towed over to the wall - Douglas Harbour had phoned him and said we might need help. I couldn't find him later to thank him, but we were certainly thankful.
Dean came down and took away various engine parts, promising to return on the Sunday to fix everything. He was true to his word, but made the slightly embarrassing discovery that the real reason the engine had stopped was that we had been running on the reserve tank only and had run out of fuel - the rubbish in the filter was from the bottom of the tank.
He had found some problems with one injector, though, and did fit a much better filter. He also found that the valve from the main tank couldn't be opened, and managed to fit an alternative supply so that we could use the fuel in the tank.
Russell had to leave me in the Isle of Man, as he had used up his week. He missed Dean's return on Sunday, and also the storm that kept me in Port St. Mary until Monday. The wind increased sharply on Sunday night, and I had some problems with the warps alongside - I didn't have proper mooring lines, and was using some old halyards and other rough stuff. I now know why mooring lines need to be stretchy.
On Monday evening the weather moderated, and I departed Port St. Mary, taking the Calf Sound and heading north again. Instead of stopping at Portpatrick, I carried on north, arriving in Crinan on Tuesday evening. I was doing quite a lot of motoring, but also some sailing.
I had headwinds, and partly contrary tides, from Crinan to Corpach on Wednesday.
I left the boat in Corpach until Friday night, to take it up the canal at the weekend. Gordon and Arden came with me for the canal.
Tonight, I'm in the marina at Muirtown, planning to lock out tormorrow (Monday) morning and sail along to Findhorn. Probably motor, again, looking at the forecast ...
High tide - neaps unfortunately - at Findhorn is about 21:20 tomorrow. I will have about a metre under the keel in the marked channel, but shallows either side.