Yachting Monthly reported the results of testing fixed, feathered and folding blades propellers (http://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807), and provided the graph below to demonstrate that a locked three blade propeller has around twice the drag of the same propeller free to rotate while sailing, and that this drag can be a significant proportion of the total drag. This seems to make it a good idea to leave the engine out of gear while sailing - except that the same article says that the gearbox may suffer. We have a fixed two-bladed prop on Delphine (which will presumably have less drag than a fixed three-bladed) and we normally leave it free to rotate. However, it would be very interesting to hear what props other boats have and whether you leave the engine in gear while sailing. If you have a two bladed fixed prop and fix it in gear while sailing, do you line the blades up with the skeg (which would presumably reduce the drag still further), and, if so, how?

Many thanks

Gilliane

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Hi Gilliane,

It's good you bring this up. We were roaring back to port after the recent Proms rally at Wooton Creek and I was thinking about the terrible racket our spinning prop was making. The reason it was spinning was that I read on PBO forum last year that the shaft should not be locked while under sail. For the previous fifteen or so years I had sailed with the shaft in reverse gear and locked. To lock or not to lock for me is less about drag and more about what's best for the engine. My old theory was that the shaft should rotate only when the engine was actively pumping lubricating water through the prop shaft. Then I read the advice on the forum that the engine manufacturer says the engine should be out of gear under sail. I very much doubted this until a forum member posted an extract from the Yanmar 1GM20 manual confirming the advice. That was the end of my scepticism.

So it seems I have been enjoying the benefit of reduced drag as well as following Yanmar recommendation. On the other hand, the prop spin can be noisy and I would prefer it to be water lubricated by the engine water pump when it spins. Let's see what other advice we get here.

Ken

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Hi
To me leaving the prop to spin to reduce drag is a no brainer, so I'm glad to see it confirmed. As to noise I would have thought if the seal makes a noise there's something wrong with it, more likely wear in the cutlass bearing, which is water lubricated all the time.
With my folding prop on rascal I need to put the engine in gear for a moment to get the blades to fold.
Philip
Superseal 50 rascal