I've got a 1978 glastron cvx-20 sprint with a mercury 175hp black max v6. I bought it without a prop. The previous owner ran some super fancy $500 24p stainless prop. He said he got a hair over 60mph out of the boat. I have no real reason to doubt him, but I never got a chance to be in it with that prop on so I have no way to verify. I, being a cheap azz, declined to buy the prop with the boat for an extra 300 bucks. I plugged the prop pitch and my lower unit's 1.87 drive ratio into a prop/speed calculator and it said that 5500rpm would give me over 60mph, so I put on an el cheapo solas aluminum 23p 3-blade prop. I think 5500rpm is the rated max rpm for this engine.
I could get the boat to do about 4500rpm at full throttle and be doing close to 55mph with just me or me and one passenger in the boat. I dinged up the prop pretty good one time by stupidly going in an overly low river. So now I don't go quite as fast, top out at around 4100rpm/50mph. With one or two people in the boat, if I mash the throttle, it leaps out of the water and planes in less than 5 seconds. With 5 people in the boat or 2-3 in and two people on the tube, it takes maybe 8 seconds or so to plane, not bad I think. With two knee boarders it takes noticeably longer, in the 15-20 seconds range and the motor starts to bog and slow down at any less than full throttle when in this high engine load zone. One knee boarder, no problem, two 180lb knee boarders and it gets tougher. I don't tow two knee boarders very often and when I do, it wouldn't be a big problem to swap on the spare 19p prop that I have(which I've never actually tried on this boat because that prop needs a new hub) so I'm not too concerned about that.
What I would like is a little more low rpm pickup and a bit more max rpm and a little more mph. What do you guys think? Doable? Need to go stainless? 4-blade? Different pitch?