It wouldn't make much sense to spend a lot of money on a high-performance SUV and then put bald, unbalanced tires underneath it - but that's essentially what a lot of boat owners do when they fail to pay attention to the balance and tuning of their propellers. Prop tuning has been a pretty crude science over the years, but it too is coming into the 21st Century, and one of the leaders is Prop Scan.
Prop Scan is a franchised technology developed in Australia by boat racer Terry Ryan. Ryan devised a simple system of measuring prop blades and charting those measurements so the entire prop could be sculpted for maximum efficiency. A series of pitch readings in three dimensions, fed into a software package, allows for the tuning of props to exceptionally high standards. The results are dramatic.
Currently, there are 31 shops licensed to use the Prop Scan technology and software in the U.S. and parts of the Caribbean. One such shop, Accu Tech Marine Propeller in North Hampton, New Hampshire (603-964-3682), is owned by Larry Kindberg, who was a satisfied customer before opening his own Prop Scan franchise.
What It Does
"My own boat got me into this," says Kindberg. "I had a Wellcraft Coastal 33 that I used to run fishing charters. We had vibrations in the boat we couldn't figure out. Not being a prop guy and not being a mechanic, I didn't question it. We were told it was normal."
Then a lucky thing occurred. Kindberg ran aground while on a charter off Kennebunkport, Maine.
"After we grounded, the vibrations got bad," he says. "None of the shops could handle the repairs, so we found Prop Scan on the Internet. The company claimed it could eliminate vibration, increase speed and reduce fuel consumption with its system. I had my props tuned at a shop in Rhode Island, and what a difference it made! The boat tracked straight, backed straight and there was no more vibration. Fuel consumption dropped ten percent and speed went up 15 percent."
Kindberg called Australia, where Prop Scan is based, and talked to the company about the technology. One thing led to another, and after a year's worth of conversations he opened his own shop. Kindberg reports that business has being "going like gangbusters" ever since.
How It Works
The first step in prop tuning is data gathering, and that means determining what the props are called upon to do. The way a boat is used, according to Kindberg, provides an initial picture to determine if the props are designed for the job. For one thing, you must determine how many people are usually aboard and how much fuel the boat carries. All this information factors into how the boat runs with regard to propeller selection.
"Manufacturers develop their prop specifications based solely on the weight of the empty boat, which allows them to advertise a higher speed," says Kindberg. "But boats get heavier when they are used, and props are very sensitive to weight in terms of performance. I had added a lot of gear to my boat and the props weren't tuned right. They were essentially over-pitched for the weight.
"When you drop a propeller off at a conventional shop, they never talk to you about your boat. We approach it differently. We want know if you are getting redline rpm and what kind of speed you're getting. With that data we can better match the prop to your boat and determine if you are running the right pitch for the load and the power. The more accurate the data we get up front, the more accurate we can be on the other end."
Once the data is gathered and the proper pitch has been determined, the props are carefully measured on the Prop Scan instruments. A vertical rod with a wheel at the bottom traces the contours of the prop blades, and the gathered information is organized and displayed through Prop Tech software on a computer screen.
The traditional way to tune a prop is with a pitch block. This is basically a negative form over which the prop is placed before being hammered and cold-formed to match the top of the block. The prop is hammered onto the form, polished and the job is finished.
The problem with using a pitch block is two-fold, according to Kindberg. First of all, it is tough on the propeller because the entire prop is hammered and work-hardened. Secondly, the pitch-block method is unable to approach the accuracy of the Prop Scan procedure.
"Pitch blocks are inaccurate," says Kindberg. "We do not use them. We freehand everything, using the computer as a guideline. We only work the areas that need it, so we don't put stress on the whole prop. The potential damage is lessened and the accuracy we can achieve gives us much higher tolerances. We work to ISO (International Organization for Standardization) tolerances. There is a standard for the repair of boat props. Our equipment measures down to 1/1000 of an inch. We match prop blades to within 50/1000 of an inch of each other."
Kindberg explained the Prop Scan diagnosis deals with four different pitch areas: overall pitch, pitch of each individual blade, section pitch (measured progressively in ten-percent increments from the hub outward) and a selection of points along those section lines. This information, displayed graphically on the computer screen, allows the individual blades and the entire propeller to be mapped, then worked for consistency and balance.
Aside from the measuring and analysis, the rest of a Prop Scan shop is pretty basic. Once the inconsistencies have been identified, they are hammered out by hand. "We are just high-tech blacksmiths," says Kindberg.
Mark Tomlinson of Precision Prop Tech, in Fort Lauderdale, Florida, echoes this simple approach. "We are simply reducing drag," explained Tomlinson when we toured his shop, which was stacked with monstrous propellers waiting to be tuned. "We start on the inside of the blades," he said, tracing the work to be done on a prop mounted on the bench. "After we do an analysis, we identify the places that need to be worked and start at the hub and the inside of the blades. Then we chase the problems out to the edge and work them out of the blade, working towards the outside edges."
Does It Work?
"I can say without reservation that if the prop is inefficient, and most of them are out of the box, we can improve them," says Kindberg. "We have found new props with individual blade pitches that differ by an inch and a quarter."
Kindberg is doing most of the work on the Boston-area Coast Guard boats, and he is conducting seminars for Coast Guard engineers on prop tuning. His files are also chock full of testimonials from customers, and his success stories are numerous.
"One of our customers had a Tiara that was burning 16 gph," recalls Kindberg. "After we tuned his props he dropped to 12.5 gph.
"And last summer a customer with a 37 Bertram couldn't get his rpm correct. He was getting a max rpm of 2000 and a speed of 19 knots. After we tuned his props he was turning 2200 rpm and went to 27 knots.
"We worked with the owner of a Bayliner with twin diesels who had spent three years chasing vibrations. He had replaced mounts and shafts, but nothing helped. In idle you could see the motors move up and down with vibration. It disappeared when we tuned his props."
Terry Ryan originally developed the Prop Scan system for outboard motors, and though most of the Prop Scan work is aimed at inboard power, there are cases where outboards can still benefit. Kindberg explained that the costs for outboard tuning are a little higher. Also, the accuracy may not be as great, because there is more variation in the type of hulls that outboards are called upon to push. But with high-performance outboard boats, where speed and efficiency are critical, the same technology can help, too.
When it comes to dealing with specialized situations, whether it's outboard prop tuning or an unusual challenge, the network of Prop Scan shops around the country comes into play. "We're all trained on the same equipment and use the same procedures," Kindberg explains. "And we can rely on each other for assistance. I can call another shop and tap into their experience when I encounter a new set of problems."
Prop Scan tuning is all performed on a time-required basis. In other words, there is no standard estimate on the cost of a tune-up. Props requiring extensive work will cost more than a minor tuning. Every job is delivered with a documentation package that includes the original scan data, work performed and a complete map of every propeller. Repairs and maintenance become predictable and the results are repeatable.