Something else to consider before entering the rabbit hole of prop pitch etc. You mentioned the bottom was clean. Fair enough, fresh bottom paint and a little dockside scrub on a stick will accomplish that. But how about the prop? Since they don’t enjoy the benefit of bottom paint, if you have not had the boat hauled this year in Puget Sound, or had the prop cleaned by a diver in the last 15 -30 days, it’s safe to assume your prop is not clean. A tiny little bit of growth, even soft growth and little weeds on the trailing edge will destroy prop efficiency. Especially in reverse, but in forward too. I’m further north in Port Madison (e32-3) and already my prop is growing stuff steadily this spring. Especially with the crappy cool wet weather we’re having, I have not been out often. Unless you know the prop is fresh and clean, get a diver to scrub it, then go try for speed under power. A slightly scummy prop will not produce thrust at normal engine speeds as one would expect. Engine loads up, revs, and sounds normal, but the thrust is just not there. Doesn’t need to be barnacles either, just the thinnest layer of growth. We seem to have some kind of hairy weed that forms on props in Puget Sound, and it just wreaks havoc on performance. First 6-9 months after haul out is great, after that need a diver often, especially in spring and summer. I left the dock today after not being out for a month, and could barely get to 3 knots. I was able to partially clean the prop by going forward and then going full throttle in reverse. With the dirty prop it cavitates very badly, a frothy sea of tiny bubbles, very little reverse braking. Then quickly forward, then back and forth several times maybe 10-15 seconds each, idling between shifting of course. The cavitation (basically low temperature boiling on the low pressure sides of the blades) does cause some growth to break away. That process can restore maybe half or more of the lost thrust, but only a real manual scrub can give you a true sense of what’s going on. Diver is your friend! And have them do the speed transducer if have you have one too! Unless your boat has always been plagued by this problem, you most likely have a dirty prop. When the hill and prop are both clean, by boat which is shorter than yours will top out about when the transom starts to dive from hill speed, which is maybe 6.5 knots motoring level. I’d think an e38 should be good for 7 or 7.5 knots in flat water based on waterline length, when everything is clean and smooth.
Oh well..... life goes on.
