Fitting a saildrive folding propeller? Ask the experts

Stu Davies

PBO reader Peter Dunlop has a question about fitting a saildrive folding propeller. Engine whisperer Stu Davies has this advice...

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Peter Dunlop writes: “I have a Volvo Penta MD20-30 with saildrive and three-bladed folding propeller on my 1998 Dawn 39 (a Contessa 38 lookalike from the same mould). Some years ago while sailing in the Finnish, Aaland and Swedish skerries the prop met some hard rock.

“Local sailors say that if you don’t hit the odd rock then you’ve never been anywhere! Anyway, the blades got a bit deformed at the tips and one tooth on the meshing gears was broken so I bought a complete new prop. I took the new blades and easily fitted them to the old boss which had been previously modified to fit a ropecutter.

“Later I found an engineering shop that has modified the new boss to take the ropecutter so I spent a long time trying to fit the new (now slightly used) blades to the new boss. I couldn’t do it myself and needed a second pair of hands and some wooden spoon handles as drifts and plenty of lubrication to get it all together.

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“The blades are numbered as was the old boss so I was always able to assemble it easily, but the new boss didn’t have numbering so I got the shop to hard stamp some on it so I know how it goes back together next time I have to disassemble it.

“However, it is one thing assembling it on my dining room table and another entirely doing it in the yard – it being of course necessary to take all the blades off to fit the nut onto the drive shaft and the locking screw and tab washer too.

“Incidentally, despite great care with the tab washer I’ve lost more than one locking screw and washer over the years and that is part of the reason for getting around to using these new, very tightly fitting parts.

“So do you have any tips for getting the blades and their pins in place? And for getting the tab washer to do its job? It seems clear to me that the old boss has worn a bit allowing the pins for the blades a little slackness – and made it easy to put the new blades on the old boss.

“The same workshop has fashioned a new tooth and located it in the damaged old blade with two brass pins – worth a try as a spare since the nearest propeller specialist was not interested.

“I’ll try the old pins in the new blades to see whether they’re any easier to get in but I suspect any wear is in the softer bronze blade and not in the hard stainless steel pins.”

PBO engine expert Stu Davies replies: “The boss/hub goes on first – make sure the splines are good. Then tighten the nut to 70Nm. There’s a really good tutorial on YouTube (see below).

“The locking washer needs to be bent over properly, some lugs forwards, some backwards. Again it can be seen on the video. The timing of the blades is easier with two pairs of hands, although it can be done solo.

“As for the repair using two pins to hold a gear tooth? Hmm! Very much for emergency use only. Think about it, the area of the two pins compared to the area of a complete tooth. All that horsepower going through the pins… I suspect they won’t last long.”

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This feature appeared in the January 2024 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.

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