Prop Advice Needed, Go 4-blade?, Pitch?

[imported_Voyager]

My 1957 Crestliner Voyager 18 with 50hp Merc classic runs at about 27mph and 5500rpm at WOT when lightly loaded. When carrying a typical load, it runs at 5000rpm and just over 20mph at WOT. This calculates to a lot of slip (about 35%) and the boat "feels" like the prop is not hooked up very well. The prop is a stock Mercury 13 pitch (about 10" Diameter and somewhat beat-up).

This hull is easy to get on plane, but has a lot of wetted area and isn't a go fast kind of boat. Hull, motor and gear weigh about 700lbs, a "light load" would bring total weight to about 950lbs. Loading the whole family brings the total to about 1250lbs (about 30% increase!) so the sensitivity to loading makes sense.

I typically cruise at 3800-4000 rpm, which translates to 15-18 mph depending on loading, and I'm often asked to pull the kids on a tube. Also, even trimmed down fully, the current prop will ventilate in a sharp turn.

I'm interested in improving performance and economy at cruise (and pulling a tube), and don't care so much about top end speed. I'm considering a 4-blade Solas prop and dropping the pitch to either 10" pitch (11.4" Dia.) or 11" pitch (11.1" Dia.). Any thoughts?

[imported_Voyager]

Available stock forced the decision, no 10" pitch props in stock, so the 11" is on the way. I'll try it out and report...

[nineteensixtycaddy]

was just going to say.. if you're getting veltilation/cavitation on turns, it might not be a prop problem at all, it could mean your outboard is not low enough in the water. I know I know... everybody is working hard to raise their motors most of the time, using plates and increasing transom height, but perhaps, just maybe, putting your outboard down further in the water, might help it get a better "bite" on the water.

Just my $.02

[imported_Voyager]

When trimmed down, the cavitation plate's leading edge is even with the bottom of the boat, trailing edge is slightly below, so I don't think that's an issue. These hulls heel quite a bit in turns (very fun to drive, like an airplane banking), and the existing prop isn't in great shape. If the weather cooperates, I'll try the new prop (4-blade, 11 pitch) this evening.

[imported_Voyager]

The 4 blade prop really stays hooked up, though a very sharp turn will start it ventilating, easing the turn slightly will let it hook back up without touching the throttle. With the 3 blade, I had to throttle back to get it to hook back up.

The 11 pitch is still a bit too high, my WOT rpms are about the same as the 3 blade, top speed is down a couple of mph, cruise is up slightly for a given rpm. I may have the prop adjusted to lower the pitch a bit, but for now, I'm dead in the water with no spark.

[Randybeall]

You might consider trim tabs. Cut the roll keep hooked up and crusing.

[truckinfavis]

TRY a 10-3/4"x 12" I'd bet thet will work

[junior1113]

that motor puts out 50 hp @5500. +,- 200 is good. i would have just put a 3X12 on it. my 2 cents

[steelespike]

Yes a 4 blade should stay hooked up better.And they do generally perform better at lower planing speeds.Personally I think a Turning point hustler in the same pitchh would have done as good or better overall.Without losing top end.
Stainless performance at al prices.I have a 18ft 57 Crestliner Buccaneer
about 400 lbs dry.
w a 65 Merc 500.Unfortunately the Turning point is not available for the 65 motor or I would have one.