[Fr. Frank]

Originally Posted by Commander Coo1

looks like you have about 15% slip at WOT which seems pretty high. The Enertia got me about 2% slip and the Rebel was "0%". you may end up needing to come down in pitch unless you pick up a decent amount of speed. My setup weighs about 4000lbs loaded and tops out at about 43mph/37kts.

No prop swings without slip, period.

An extremely well matched prop-motor-hull setup will have around 10% slip. Average minimum slip used to be 15-18% for most dealer setups. Occasionally, you may see a setup down around 8%, but that's pretty rare. If I recall right, ESD gets about 51-52 mph at best trim WOT with that 19" Stilletto on his XRi 200, which with the most common gear ratio on that motor being 1.81:1, puts him near that magical 8% ratio. (Correct me if I'm wrong on that speed) OTH, if he has the available/optional 1.65:1 gear ratio, then his slip is a more normal 14%.

Here are three examples:
The most efficient setup I have ever seen on a regular (non-race) hull was on a '69 16' Whaler with an '85 90 hp Yamaha turning a Yamaha 21P SWS semi-cleaver SS prop which got an astounding 6.7% slip at 5800 rpms/46 mph.

I once rigged an 21' Allison XTB mod-V race hull with a Yamaha Excel 220 with a blueprinted hull, nose cone, hydraulic jackplate, and a custom one-of-a-kind Second Effort Marine 31"P through-hub prop which got all the way down to 4.5% slip at 6470 rpms/108 mph.

Back in the early days of PowerTech, I had them design and build me a custom prop for my '72 Seafari running a blueprinted Mercury XR4 150 (190 hp) with a 1.65 gear ratio. It was a 15"Dx16.5"P 3-blade, and at 6050 rpms and 53 mph, I was achieving only 7.5% slip.

If you see a slip ratio being reported of 8% or under , I would suspect the accuracy of the propeller specs, such as prop labeled as 17"P actually being 16"P or so. It is not uncommon for aftermarket props to be as much as a full 1" different from their labeled pitch.

The amount of slip will also vary on the same hull-motor-prop setup depending on the efficiency of the trim and rpm setting being used. While I achieved as low as 7.5% slip at 6050 rpms on my Seafari, when I was cruising at 3800 rpms, my slip ratio was up to 14%, achieving 30 mph.