Sailboat Propeller test – same four boats, four different propellers
The purpose of the sailboat propeller test was to benchmark four different types of sailboat propellers: a fixed pitch propeller, a feathering propeller, a folding propeller and an Autoprop propeller. However in order to benchmark the propellers against one and other for a true comparison it would be necessary to test all four of them together at the same time on the same boat. As this is not possible, the four propellers were tested on four identical Oceanis 37 sailboats at the same time. This allowed for as many variables as possible to be removed such as underwater hull form and weather / sailing conditions. The only thing that the sailboat propellers had in common was that they were all shaft driven propeller with clockwise rotation, no sail drive legs were used. Each design was a different method of propelling the sailboat with some better under motor and others under sail.
The design of these propellers was written about extensively in Sailing 4/2009. This test was performed with the help of staff at the French Voiles et Voiliers (April 2009) and the German Segeln Magazine (10/2008) to help thoroughly test the very different types of sailboat propellers. This article has been translated from the Zeilen (2012) article.
Six tests were performed to thoroughly benchmark the propellers. First the engines were used to accelerate the boats to maximum speed. Then speed intervals were tested where the boat speed was noted at certain rpm’s; this was performed in both forward and reverse. An emergency stop test was performed to check the propellers under severe thrust conditions and the test concluded with a long sailing leg determine the resistance of the propellers under sail.
The Sailboat Propellers
The characteristics of the selected propellers was known before the test and it was expected that for the performance under sail would be the best for the folding propeller or the feathering propeller and the performance using the propeller would be better for the Autoprop and the fixed pitch propeller.
The fixed propeller and the Autoprop would be significantly more efficient, because they have better pitch distributions. In addition, the difference in efficiency in the Autoprop to the fixed pitch can still increase in efficiency with the fixed propeller can still enlarge by automatically changing speed.
The pitch of the Autoprop is automatically adjusted to the rpm and boat speed through the water. This gives a greater speed for the same rpm or a lower rpm at the same speed. The feathering propeller and folding propeller were expected to cross the finish line first because of their resistance reducing properties under sail. The blades of the feathering propeller take the path of least resistance when in sailing mode by feathering in the flow. The folding propeller on the other hand swings its blades behind the hub out of the flow, which in theory results in even less frictional resistance. With slight wind this should result in an excellent advantage compared with the other sailboat propellers.
The Sailboat Propellers in practice
In the first acceleration test, the fixed propeller and Autoprop were the fastest off the line and maintained a good lead up to the maximum speed, slightly higher than folding and feathering propeller. The difference between the fastest and slowest boat was less than half a knot, but the differences in rpm’s was a more clear indication of performance. The engines of the boat with a fixed pitch propeller and the Autoprop ran at a top speed of 3600 rpm. In the folding propeller this was 4000 rpm – a clear difference in efficiency.
The same acceleration test was repeated but for motoring in reverse to show the differences in speed and rpm. The folding propeller had a speed of 4000 rpm but by far the lowest boat speed. Autoprop made a maximum speed of more than six and a half knots with 3800 RPM followed by the feathering propeller that made slightly less RPM. As it is not common to sail for long periods in reverse, this test shows that the difference in efficiency is less important than the difference in good thrust when moving backwards.
The thrust of the propeller in tough conditions is extremely important and allows the boat to maintain momentum in heavy seas against waves and wind. Just like the previous test the engine rpm for fixed speeds were recorded for the four boats. The differences at low speeds were very small between all the propellers. Only the fixed propeller was able to pull away fast from low speeds. Then the Autoprop starts a stroke efficiency make from 2200 rpm, followed by the folding and feathering propeller. The fixed propeller accelerated very well but faltered at 3600 rpm / five knots. The other propellers came close to each other at 4000 rpm. Autoprop was clearly the fastest in this test, but was located on the cruising speed between three and four knots near the fixed propeller.
For the distance traveled in an emergency, also known as track reach, the boats were initially set to run at six knots. The Beneteau’s engines were put in neutral once close to a marker bollard a few meters from the jetty. At the beginning of the twenty-five meters long dock side marker the Beneteau was given full reverse throttle. After several attempts this test clearly showed that the propellers that were more efficient in the forward, backward, and drag test, were also faster at stopping. The fixed propeller and Autoprop stop at about twenty meters. The feathering propeller follows with twenty-five meters and the folding propeller with twenty-six meter stopping distance. In terms of helm correction during the stopping test, the propellers were again grouped in two. The fixed pitch and the Autoprop propeller cause the stern to prop walk a little as they came to a stop, while the folding and feathering propellers already began to prop walk when the test was beginning.
After the engine tests, the final and most important test was to see the differences resulting from resistance under sail; or propeller drag test. The boats were sailing parallel with four to six knots wind on a large course heading north. The first boat to take the lead from the start was the folding propeller. Within a period of a few minutes the field exploded with a big lead for the folding propeller, followed by the feather and Autoprop in short succession. The difference between the folding propeller and the fixed propeller was clear after sailing for half an hour and was about eight boat lengths. With a speed of three knots of fixed propeller means that the folding propeller roughly one third knot – or ten percent – faster . The folding propeller was about eight boat lengths followed by feathering propeller , which is about three boat lengths ahead of the Autoprop .
Testing four propellers on similar sailboats gave a good indication as to the differences in the performance under power and under sail. It is clear that the price / quality ratio, type of boat and the sailing style are very important factors. Each of the propellers offers differing combinations of these factors so it is not possible to make a definitive statement about which sailboat propeller is the best. One sailor may be on a fixed propeller budget while another sailor may prefer to win races and sail faster or choose safer maneuvering in ports. The sailor therefore determines which is the successful design for them, but for the test team, the faster sailing remained the best!
What the sailors had to say…
From the various tests performed above it was fairly clear what the qualities of the different sailboat propellers really were .
A folding sailboat propeller is the fastest
The owner of the Beneteau fitted with the feathering propeller , was asked whether he temporarily wanted to exchange with a folding propeller. In the test the folding propeller gave good sailing performance (it’s best quality), the stopping distance was the longest, but it had good thrust. The owner commented, “After yesterday’s very extensive play with the folding propeller I am beginning to appreciate the thing. The ability in reverse however is a dramatic change from the feathering propeller and that’s the reason why I would not buy one. My wife would not sail in stronger winds with the propeller. Although I could maneuver in a little wind during the test, I feel sure if I had wind force seven I would be at the back of Lock Invaar. ”
A feathering sailboat propeller is the all rounder
The feathering propeller, like the folding propeller, is a product for the sailor who wants to experience less drag under sail. If the feathering propeller is compared to the folding propeller, it is clear that there is comparable performance drop as the feathering propeller works slightly harder to maintain the same speed. The feathering propeller is just that much faster backward in the all-round use something more attractive than a folding propeller to many sailors. Although the propellers are mainly purchased for “less resistance through the water during sailing, so more hull speed, the appeal to the day sailor is undeniable for ease of maneuvering. However the owner felt that the drag test was not ‘real’ representative conditions. “Last year I had been sailing the boat to Stavoren. We ended up in a big storm with wind speeds of 45 knots and more. Against the wind we were more like a submarine than a sailboat. With full power we barely made headway: a half knot, but certainly no more. There was no end and we were glad we had made it. What a trip! ”
AUTO PROP Sailboat Propeller as an all rounder
The Beneteau / Autoprop owners, did well above average in all of the tests. The Autoprop is altogether an excellent all round propeller. It was not as good as the folding propeller when sailing, but there was negligible difference with the feathering propeller. How the performance curve looks in which the influence of the screw on the boat speed becomes less with increasing wind remains to be seen, but in the end was negligible with this strong wind . The owners were satisfied with their new propeller: “a little RPM does give a lot of speed!”
Fixed sailboat propeller as a baseline
The fixed propeller cannot compete with the sailing performance of the others.
The owner of this propeller, says that after selecting several optional extras when buying her Beneteau, selecting a sailboat propeller was not possible. The propeller turns out to really be a handbrake when sailing, but did just fine in all of the other tests, matching their style of sailing.