I could not resist the weather today, so I have been out prop testing. The conditions were just right; a slight chop to 'unstick' the hull, but nothing to cause me to back off.
The boat was originally provided with the engine set at this lowest setting. I was running a 19" Viper at one hole up from the lowest engine height. This is where the Viper seemed happiest and Mike Vincent has told me that the Vipers like to run 'high'. At this setting I saw 5900 max revs. On the basis that I had to start somewhere I bought a 21" Apollo of the same diameter. The first thing that I noticed is that there is a greater surface area to the blades of the Apollo.
I ran it at the same height and it ventilated some, particularly in the turns, but I could only pull 5300 max revs. I have now dropped the engine by one hole and the boat feels a lot better. No ventilating in the turns and I can really feel the boat accelerate, as opposed to just spinning up the Viper as it did before
. The numbers are still 5300 max revs, best one way speed 48.2 knots, with 43.5 knots on the return leg. This is a good 2 to 3 knots up on what I was seeing with the Viper. The tanks were almost full, 200+ litres, and one pax on board.
Before I go out and spend another £400+ on a 19" Apollo, does anyone think I should be looking at something different?