Prop Slip?

[burtonrider11]

Hello, trying to dial in a new (to us) boat. Earlier this season we bought a 1997 Starcraft 2010SS with 5.7l Merc, 2 barrel carb, 235hp. The boat came with a 4 blade 22", 3 blade 19", both stainless. Also a 3 blade alum which will probably just sit in the garage Alpha Gen 2 drive with 1.62 gear ratio

When I bought the boat, the owner had said that in optimal conditions IE, just him and a quarter tank of fuel, he has seen 54mph via GPS. I thought that sounded about right based on weight and horsepower, unfortunately, he didn't say which prop....

In any case, out yesterday with 4 adults and two young children, gear and 3/4 tank of fuel. I finally opened it up. Top speed was 45.2 (GPS) at 4400 rpm and this was with the 4 blade 22" stainless. I believe it is an Apollo XHS. I was thinking that even with this load, I would see something in the upper 40's. We were working our way up river as well (Grand River for those of you in Western Michigan). Does this sound about right? Using a prop slip calculator, it calculated to 21% slip, is that accurate or do I need to perform testing with just me and low fuel and gear.

Also, does this prop seem like the correct prop? To me, it seems a tad big despite the fact that I am right in the correct rev range (4200-4600) assuming the tach is correct. I can't seem to get the 19" on the prop shaft for some reason, but that's another story. The 4 blade doesn't seem to provide a ton of bow lift and is slower to plane that I would like. Top end isn't really what I am looking for, I'd rather have a good cruise speed at 3000-32000 which is 28-32mph and better hole shot. We typically cruise with at least 2 adults, 2 kids. Maybe I should just be happy with the 4 blade?

Just looking for some feedback on whether I am propped right or not. If not, if there are any recommendations...Thanks in advance!

 

[steelespike]

Generally a 22" 4 bld. would be slower than the same prop in a 3 blade.Certainly can't call that load a light test.Did you move people around to try to find a sweet balance? I guess if going up river you need to take into consideration the current. You can use the gps to figure the current.
I guess you could do a test up river and down river too.Going up river would tend to make slip appear higher.
Tachs are always suspect when slip appears high.
Long story short I think your 45 mph seems reasonable.Cracking the 50 mph barrier is a tough assignment.
I think you can see if you take out the dead weight and make a down river run you could press close to 50 and that would be with a prop not intended for top end performance.