Having improved matters by removing the hydrofoil, I decided to lower the engine by one hole even if it meant the effort of raising it back again. It was the right choice.
For the benefit of those who never did it before, you put some wood under the skeg and extend the jockey wheel so the rear of the trailer goes down and the skeg takes the full weight of the engine. You take the top bolts out and loosen the lower ones so they can slide in the slots. You raise or lower the jockey wheel to align the next set of top holes. Apply sealant and nip the top bolts, then remove and re-seal the lower bolts followed by final tightening. All done on the campsite. Used black PU40 Polyeurethane from the local Toolstation branch.
Pleased with how efficiently I did the job I reversed the trailer down the slipway to wait for some water which was a couple of hours away. Unbeknown to me, the edge of the slipway did not run parallel to the pontoon. The prevailing wind had moved it and the edge of the concrete was invisible due to mud. Near the bottom the tyre slipped to the side and the trailer lurched at an angle and the metalwork touched down on the ramp, sinking black mud to the top of the mudguard. I couldn't pull it off as it would have damaged the galvanizing.
I could have waited, floated the boat off then lifted the trailer back on the ramp but as I had nothing better to do, got out my wellies and cleared some mud with an old plank. Then used my trolley jack to lift the axle onto a railway sleeper then skidded it back onto the ramp again. Glad it was a private slip with nobody watching my embarrassment!
While I waited for the tide I found an old shovel and cleared the slipway, also creating a water draining trench down the side of the ramp. Because I'd cleared the mud, was able to go lower on the ramp and launch at 3.1m instead of 3.5m of tide.
Heading out to sea the difference was immediately apparent. A light bow returned and trimming the engine had the expected effect. When I cleared the speed limit and opened it up against strong wind and tide it instantly reached 32 knots no problem, but I slowed down out of consideration for my passenger the partner of the campsite owner. I then let him take the helm and get a feel for the boat. Incidentally in his boatshed/mancave he has a Sealine 215 cruiser and a Jeanneau Merry Fisher 795 powered by a 150hp Mercury. Would love to get out in that!
I have no doubt that it would have struggled to reach 30 knots in those conditions (with the engine on the highest hole), so although I wasn't able to test it more thoroughly I know it will be faster than before and that currently stands at 34 knots. Performance is fantastic and my initial disappointment is gone. The 17" pitch is spot on and typical of what is used on 70hp engines so it confirms the result of the work by West Wales Tuning.
Also I managed to get the SMG4 trim gauge working correctly. There's two settings, 'sender' or 'sensor'. With the latter you calibrate fully up and full down positions but it never really displayed the full range, but with the former setting it worked better. Just teething problems.
Another job I was really pleased to do was fine adjustment of the trailer. I moved the rear swing beam back and the rear carriages inwards slightly. Now it would be possible to dry launch the boat and on shallow ramps and less water the bow won't contact the center of the rear swing beam before the rollers take over. It was damaging the keel guard. Having a private ramp was invaluable, simply can't hog a public slip doing this kind of thing.
