It's a moment that many sailors love: leaving the harbour, sails set, engine off. The wind takes hold of the sails, the ship sets off. Silence. Marvellous. Unfortunately, this moment of calm is soon interrupted by the whirring of the gearbox as the propeller turns. At least that's what a fixed pitch propeller should do, if the manufacturers of saildrives have their way. With Yanmar it must turn, with Volvo it should. This is better with mechanical transmissions.
The clutch and gears then have to absorb lower forces; the loadless spinning is less damaging. Nevertheless, there is wear on the shaft seal, in the shaft bearing and also in the gearbox as well as in a flexible coupling, if one is installed. In short, it would be better if the shaft could remain stationary under sail.
Folding or rotary blade propeller better for shaft and gearbox
A folding or rotary blade propeller is the ideal solution to ensure that it is able to do this without putting any strain on the gearbox or saildrive. When the engine is off, it moves into a position that favours the flow, thus reducing resistance and forces on the shaft. When the gear is engaged, the gearbox does not suffer and there is virtually no wear on other components. And there is peace and quiet in the ship.
Another advantage: the ship sails faster due to the lower resistance of the propeller. Depending on the type of propeller and ship, this can add up to 1.5 knots of speed. That's a lot; the advantage is usually around one knot. So five becomes six knots. In practice, this makes a huge difference: a trip of 60 nautical miles no longer takes twelve hours, but only ten. Possibly the difference in reaching a destination in daylight.
The propeller needs care
In order to enjoy this range of advantages, the folding or rotary blade propeller requires a little attention. This is because, unlike the fixed pitch propeller, all other types have moving parts. They work under water and are exposed to fouling and abrasion from suspended particles in the water, such as sand. If the propeller collapses, it grinds up pocks that have attached themselves to the teeth - this causes further abrasion on the surfaces. Therefore, anything that moves must be lubricated and protected against fouling.
Corrosion is another risk for the propellers. A sacrificial anode protects against this. All manufacturers have taken this into account in their designs. The owner must ensure that the sacrificial metals are regularly replaced so that they can fulfil their task. But first things first.
Clean the propeller thoroughly
The first thing that happens as soon as the boat comes out of the water is a thorough hosing down of the props. This can be done with a high-pressure cleaner. The more fouling that disappears while still wet, the easier the final cleaning will be afterwards.
Anything that does not disappear with the pressure washer can be scraped off with a scraper. The root brush then helps to remove soft growth. However, mussel remains cannot be removed in this way. The only thing that helps here is more pressure in the form of metal brushes, preferably with brass wire, as this leaves no traces of rust, or sandpaper.
An 80 grit or finer is fine, depending on the fouling. The aim is not to sand the surface, but to remove growth. Proceed as carefully as possible. The hub of the propeller must also be cleaned. During the sanding process, water and grease will continue to escape. Always remove the latter with a cloth before continuing sanding, as this prevents the grease from being spread unnecessarily over the surface.
Apply anti-fouling protection
Once the prop is metallically bright, it is time for the fouling protection. If your boat is moored in a freshwater area, you probably don't need any fouling protection at all. Bronze, which is what most props are made of, more or less protects itself. In addition, the high speeds at which the propeller rotates ensure proper cleaning when travelling.
A protective coating should be applied to bodies of water with problematic fouling conditions. There are many different ways to do this. From doing nothing and cleaning in season to milking grease, polishes and antifouling, everything is possible.
If you have problems with fouling, you can ask your jetty neighbours or the harbour master whether there is a suitable solution for the area in question. But be careful: once a primer and antifouling have been applied, it takes some work to remove it completely if the protection has not worked. It therefore makes sense to start with simple means before shooting sparrows with cannons.
One such simple method is a polish such as Telfoprop from propeller manufacturer SPW. It is applied in the same way as similar products for the hull and deck - apply, leave to work, polish, done. The areas on the propeller are small, so the procedure is completed quickly. As the polish wears off, it has to be reapplied every year. If the polish works, this is a tried and tested way to achieve a good result with little effort.
If polishing does not help, antifouling must be applied to the propeller
The next step, if fouling remains a problem despite polishing, is an antifouling. "The problem is not so much the antifouling as the primer. Almost nothing sticks to the bronze surface at high speeds in the water," explains one expert.
"The colour usually starts to fall off at the ends of the blades, as this is where the speeds are highest," says David Sheppard from Bruntons Propellers, which builds and sells the autoprop. According to the expert, this is where fouling builds up first. Possible corrosion is also concentrated on these areas, which can lead to accelerated pitting.
"We have had positive experiences with silicone-based products. It worked well, but was also gone from the surface after two to three seasons. A coating like this then costs several hundred euros. The question then is whether it's worth it," one expert points out.
Antifouling should therefore be the last option for protection. If painting cannot be avoided because other methods are not effective, an individually suitable solution should be sought in consultation with the manufacturers of the propeller and the paints, as well as with information from the neighbours on the jetty. In any case, there is no patent remedy. If the propeller is sufficiently protected against fouling, it is lubricated.
Don't buy too cheap
A special water-resistant grease should be used for this purpose. These greases usually contain lithium. The manufacturers provide specifications or sell the appropriate grease straight away. Although this is usually expensive, such a cartridge will last for several years. So why save money here with such an expensive component as a rotary blade propeller?
The procedure for folding propellers is very simple: grease all accessible moving parts inside the hub with a brush. Then move the blades back and forth a few times and repeat the procedure - done.
This is somewhat more complex with rotary blade propellers, although it can be done without any problems. All manufacturers have described the process in great detail in their operating instructions. The necessary tools are included in the scope of delivery. So ask for them when buying a used boat with a rotary blade propeller, otherwise maintenance can become difficult.
Firstly, remove the screw from the grease duct and remove the anode. The grease leaks out from under the anode and is displaced by the new grease inside the hub. The anode must therefore be removed to see whether enough grease has already been pressed in. Then screw in the grease nipple. Caution: Bronze is soft, proceed very carefully and cautiously! Next, apply the grease gun and press. Grease and water will then come out at the rear. After each pump stroke, turn the blades once from stop to stop; repeat this procedure until new grease comes out. Then remove the nipple and screw in the screw. Remove the leaking grease. That's it.
With Brunton's Autoprop, the whole process is similar, except that two screws have to be removed: One where the grease nipple goes and another where the old grease comes out. Here too, continue until fresh grease can be seen.
No fear of wear and tear
A special feature of the autoprop is that it has no gearing. The rotation automatically sets the optimum pitch. Advantage: The teeth cannot wear out. However, the bearings around which the blades rotate must be replaced regularly. This is also easy to do thanks to clear instructions and the appropriate special tools. However, the propeller should be removed from the shaft for this. According to the manufacturer, the autoprop is as good as new afterwards. The procedure can be repeated as often as required.
What is possible with rotary blade propellers such as the Variprop from SPW is that the pitch and even the direction of rotation can be adjusted. So if a new engine is installed and it rotates in the opposite direction to its predecessor, there is no need to purchase a new propeller. Even if a ship goes on a long voyage for a season and is then significantly heavier than before, it can be useful to temporarily adjust the pitch accordingly. These procedures are described in detail in the manufacturer's manuals.
In the course of its life, a folding propeller inevitably develops play in the sprockets and on the running surfaces between the blades and the hub. If the play becomes too great, the prop begins to rattle. "You can clearly feel this," says one expert. "But it's not a problem: send the propeller to a specialist dealer and they'll make sure it's repaired with washers. Then it will last a while again," continues the expert.
Turning and folding propellers have a lot of advantages: faster and smoother sailing, less wear on the drive train and flexibility in the pitch. A little attention every year is certainly not too much to ask for.
