3 Blade prop to 4 blade prop

Yep, understood. But 1” of pitch is not going to gain you 4-5 knots no matter what. Do you know of others with same model boat with same power making 24-25 knots? And are you talking about cruise or WOT? Do you have a dinghy on your bow? Big tower? Other sources of added weight and drag? Bottom clean?

1” pitch isn’t going to get you any measurable speed and just going to overload the motors. You’re better off spinning them 25 rpms more with the props you have. You want speed, soda blast off the years and years of bottom paint you probably have. I picked up 2.5-3 knots on a yacht that was less than 10 years by doing that

How many knots do you think I might pick up blasting the bottom paint off my 42 - there is anywhere between at least 10 and potentially up to 40 years worth

Forget the speed, you'll gain what you'll gain.
With that background, you'd better do it regardless.

I just hope you don’t end up over propped. Sounds like you were propped right at 25” if you got to 2,350 fully loaded and probably why someone previously took some of that pitch out. If you were under propped you would have seen 2,400 + range . Any way, hope it all works out for you. Please report your findings when you get back in the water.

Ak-OK, my bad, I thought they were 2,350. Makes more sense now.

I gained 10% in speed. Think of all of the weight of a can of bottom paint, half of that weight stays on the bottom after it dries. Then the un-even bottom.

Thanks J. I've had two different yards vehemently talk me out of it. I usually get "Unless you can't sleep at night by occasionally dropping a bottom paint flake on the bottom of the bay you'd be (*&^ing crazy to go through all that just to gain a knot."

It's still on my list, however it's priority level has never been high enough to beat out other projects.

They look great. Let us know how the numbers look once you get back in the water. Are you doing a blue-fit to check your contact area % on the shafts? Did you do aN NDT on the shaft ends while you had the props off?