AN INVENTION WHICH KEEPS ITS PROMISES

The ProPulse - With replaceable blades and adjustable pitch
Text: Vesä Leppä; Picture: Juha Virtanen; Measurements: The Kippari working group

The angle of the blade can be adjusted to suit the situation. If damaged, it is easy to repair and its performance matches that of a normal propeller. This is what the manufacturers say about ProPulse. New inventors often claim miracles, but generally speaking they turn out to be exaggerated, but ProPulse seem to keep their promises. For those needing special qualities who are ready to pay for them, ProPulse is something to be reckoned with as an alternative to normal propellers.

The world is full of new inventions, in the world of boats too. New products are developed for boats which are marketed as epoch-making and described as incredibly useful. Especially the propeller has been redesigned in many  workshops and generally speaking the inventor believes he has changed the laws of physics or the laws of nature. Most inventions don’t turn out to be any better, but rather worse.

A sore point for inventors has been the question of how to adjust the angle of the blade. The idea is not new, but crops up every few years. In general, the “problem-solving and grandiose” solutions have not achieved all that much, and the price of the invention has resulted in very little benefit compared with the totally elevated price.

Tests in general have proved that there has been “much ado about nothing”. Old, tried-and-tested methods have been simpler and more reliable, cheaper and more functional than new ones.

Realistic ProPulse

The inventors of the Swedish ProPulse propeller made a realistic start. The idea was to create a propeller with adjustable blades which are replaceable if damaged. Adjustment wasn’t just a means to produce better performance but rather to make it possible to adjust the propeller to meet practical needs.

Nor does the information leaflet exaggerate except on one point, where a user claims that speed has improved by four knots. True -  they were wise enough to leave out details as to how speeds were compared and what happened at top speed.

The ProPulse propeller is made of modern composite plastic, which in practice is nylon reinforced with glass fibre. The propeller has four blades. The angle of the blade can be adjusted so that the pitch can be increased from 12 inches to 16 with mid-pitch being 14 inches.

Adjustable and replaceable

If the boat is heavy the angle of the propeller can be adjusted to make it easy to pass the planing threshold. Setting the pitch is an important function e.g. when fishing, when a slower speed is desired than can be achieved with a normal propeller.

Another basic idea with the propeller is that the blades can be easily changed when damaged. They’ve been successful here too. With the propeller right in front of you it is possible to fit a new blade in five minutes. Provided of course there is a spare blade on the boat.

The four-blade propeller and ability to replace the blades has a further benefit: if one or two blades are damaged these can be removed. If one blade is faulty, two can be removed and the remaining ones can be positioned opposite each other. This balances the propeller and makes it possible to drive to an emergency port without needing to be afraid of damaging the engine. The ride is naturally a bit rough but rather that than being marooned on a deserted island.

You need dry land under foot however to change the blades, and it is not possible to adjust or replace blades at sea. Anyone knows this who has ever had to free the propeller from string or netting. A dip is unavoidable and using tools in the sea is an impossibility.

It works as promised

We tested the ProPulse in a Buster L with a 50-horse Evinrude four-stroke engine. The control propeller was an ordinary aluminium propeller, with a 14-inch pitch. Under windy conditions fuel consumption varies somewhat, but one gains a clear picture of consumption as also of speed measurement.

With the ordinary propeller we achieved a top speed of 30 knots and the engine revolved as recommended at 6000 revs. We got roughly the same result with the ProPulse, with the pitch adjusted to 14 inches. When measured, the difference was only 0.3 knots, i.e. one percent. When driving, the difference is insignificant and there was some margin of error due to the windy conditions.

We got the same results also at lower revs. Fuel consumption also stayed within the margin of error, and there were few real differences. ProPulse passed the first acid test well. It was no better or worse than the ordinary propeller. Nor was much difference noticeable when running. When reversing and braking the propeller’s characteristics were positive.

Running was better than with the ordinary propeller.

When the ProPulse pitch was reduced to 12 inches, one began to see the difference. The engine revs sped round well and “sang” best, even at 600 revs above the recommended rate. The planing threshold rose by around 500 revs. Tick-over speed fell by 0.3 knots, or 15%. Top speed fell by 2.5 knots. The propeller would quite definitely have been able to give a heavier boat a more comfortable ride.

The hunt for economy

When the ProPulse was adjusted to its highest setting, 16 inches, results were as expected.

Surprisingly, top speed was just as good as at 14 inches, but revs fell by 500.

Normal speed was also reached at 500 revs less. This means that the drive was somewhat more economical. While we achieved 22.8 knots with the ordinary propeller with a fuel consumption of 0.5 litres per sea-mile, the ProPulse managed a speed of 23.9 knots with a 16-inch pitch, with a fuel consumption of 0.48 litres per sea-mile. We achieved similar results also at other speeds. The advantage is small but noticeable.

The results measured only relate to the newly tested boat/engine combination. Tests with other combinations changed the results, sometimes for the better and sometimes for the worse.

Is it worth it?

ProPulse propellers are currently available for almost all 20 – 300 HP outboards and stern drives. They cost between  $265 to $414 depending on the model and spare blades cost from $54 to $71 (AUD) depending on the type.

Changing blades requires the propeller either to be removed or a proper quay or shore where the boat can be handled. Adjustment takes a few minutes. The axle nut needs slackening a couple of turns so as to be able to turn the propeller components. A damaged blade can be changed by a novice in a quarter of an hour.

Whether it’s worth while buying a ProPulse requires a split answer: if you know how to trim different things and the boat is often loaded in different ways, the purchase will be definitely worth while. If you move in stony waters where propellers often get broken, replaceable blades are definitely  a good idea.

On normal occasions a ProPulse is comparable to a standard propeller.

ProPulse propellers are available from Olds Engineering.

Results measured, speed

Measurements were carried out with two people and the measuring equipment as the load, = around 200 kg.

Results measured, 14"

Measurements were carried out with two people and the measuring equipment as the load, = around 200 kg.

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