GETTING THE RIGHT PITCH
A HIGH-TECH PITCHOMETER LETS PROPELLER SHOP
SUPER-TUNE ANY WHEEL
Yachting Magazine.

Getting Maximum Efficiency and the best possible match between the propeller and your boat/engine combination is one of the surest ways to improve performance.  Until very recently, though, there was no cost-effective way to measure propellers accurately enough to be certain they were ideal for the job.  Worse still, the bright shiny new wheel you just received from the manufacturer may not be all that accurate.  You see, in the U.S. there is no standard for measuring and grading propeller accuracy.

PROP SCAN
This has changed radically over just the past few years.  An Australian company, Propeller Dynamics, founded by Terry Ryan, invented a new way to measure propellers.  Actually, they computerized the old way, which was to measure propellers with a pitchometer.  This is a gizmo with a radial arm, that fits via an adjustable chuck into the shaft bore of a prop's hub.  By rotating the arm and dropping a vertical measuring rod, a technician could measure pitch accurately. Measuring each propeller took several hours, if not more.  Propeller Dynamic's new Prop Scan® measuring unit does the same thing, but is hooked up to a computer.
The first time I watched a Prop Scan® being used, I thought the two-minute process was merely the setup in preparation for at least 20 minutes to an hour of work.  How wrong I was.  In these bare two minutes, the propeller's entire geometry (for each blade) was fully defined down to better than a thousandth of an inch.  What's more, the results could be displayed and plotted, or both, graphically in several different forms (instantly), permitting me (and the technician) to visualize each blade's exact shape and precisely how to tune, correct or adjust for maximum performance.  Further, these measurements and plots are saved on a disk for future reference, allowing continuous fine tuning in subsequent seasons, or for exact duplication of that ideal prop, should the original one be severely damaged.

AN INTERNATIONAL STANDARD
Better still, although the U.S. doesn't have a propeller standard, Europe and the rest of the world does (the International Standards Organization, or ISO), and using this standard in conjunction with Prop Scan®, a propeller can be easily corrected and certified to ISO Class-I (high accuracy).  A Class-I is an extremely precise propeller with pitch varying from specification and between blades no more than plus 2.5 percent and minus 1.5 percent.  Incredible as this may seem, many props manufactured in the U.S. don't even meet the minimum ISO Class-3 standard (wide tolerance) of plus 6 percent and minus 4 percent.  This is extremely inaccurate and can be the cause of many otherwise unexplained engine and vibration woes.  Indeed, with Prop Scan®, the technician can even exceed ISO S-Class standard.  Such props are considered to be of very high accuracy, or S-Plus Class propellers.

BLACK DOG AND COASTAL PROP
Prop Scan® is only half the equation.  Although this $60,000 device saves time and takes the guesswork out of measuring props, a shop still needs a skillful technician to hammer the metal into shape.  There are only two prop shops in the U.S. that have Prop Scan®, Black Dog Propellers, of Solomons, Md., and Coastal Prop Technology, of Fort Walton Beach, Fla.  Larry Carlson and his wife, Alison, preside over Black Dog, while Art Barnes and Mark Daily run Coastal Prop.  Both of these shops have a skilled staff of propeller technicians.

REAL-WORLD IMPROVEMENTS
Truing up your propellers to ISO Class-1 and adjusting and tuning their pitch and camber to optimum can generate some substantial real-world improvements.  A typical case was the owner of a 34' Bertram, that was running "just fine." He thought there was no vibration, just the usual background engine/water noise.  Carlson persuaded this fellow to check his wheels for free (which is standard-you only pay for shipping), and as usual found considerable difference in pitch among the blades.  Keep in mind, these props looked superb and ran well enough.
Gene Thomas, Black Dog's top prop man, trued up the blades and reinstalled the prop.  Carlson said he wouldn't charge for the prop work (as opposed to the free measurement) unless the owner was satisfied.  Well, the Bertram's owner fired up the engine and backed out of the slip and instantly looked stupefied.  He exclaimed that the boat was so quiet he wasn't sure it was running right for a moment.
Small boats gain as well.  Thomas related that a typical outboard ski boat picked up 6 knots top speed after a full Prop Scan® and adjustment.  Then, with the computerized data on these wheels stored in their computer, Black Dog took the props back again and added camber (a moderate and spread-out form of cup) to the blades for a further increase of 1/2 a knot.  All this with the same load, the same engine, the same horsepower, and with identical fuel consumption.
Still another case was a California tour-boat operator who gave hour-long tours throughout the day.  A standard cruise was timed to end up back at the dock at, say, 1:55 p.m. After Black Dog's full Prop Scan® treatment and reconditioning, this tour operator found himself pulling into his slip at 1:45 p.m. (running at the same rpm he had previously), with a full 10 minutes left to kill on his "onehour tour." He also found that, where he used to fuel up every seven days, he was now filling up every eight days.

THE COST OF ACCURACY
Both Black Dog and Coastal Prop perform the Prop Scan® measurement for free.  You only pay for reconditioning work, if needed (but some usually is).  Because there's such a wide variety of propeller types and of the diversity of the work, each job must be priced out as custom work.  As a rough guide, Carlson gave me the following estimates: A 22" Nibral, 3-blade prop, completely reconditioned and trued up (without damage to repair, or a pitch change of more than 1" adjustment) would run about $245.
On the other hand, if you ran your boat up on the beach and mangled her blades and needed a full rebuild, with pitch change, and also decided to clip the blades to reduce diameter an inch, it would cost about $440 per prop.  As far as I can tell, all this money would be very well spent.

** This article partially excerpted from Yachting Magazine, Article written by Dave Gerr.