Ask SAIL: Saildrive Conundrum

 My 35ft Cooper 353 sloop, Rhumb Line, has a Volvo MD2030 saildrive. The zinc between the saildrive and three-bladed folding Volvo-supplied propeller comes loose and rotates on the shaft.
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 Rhumb Line experienced trouble with its zincs

Rhumb Line experienced trouble with its zincs

Saildrive Conundrum

Q: My 35ft Cooper 353 sloop, Rhumb Line, has a Volvo MD2030 saildrive. The zinc between the saildrive and three-bladed folding Volvo-supplied propeller comes loose and rotates on the shaft. The zinc is secured to the saildrive housing by four(?) machine screws. They come loose and fall off after just a few hours of operation. This summer we logged about 70 hours over a five-week period, and the zinc was loose long before the summer was over. I have sought solutions from two local Volvo dealers and a boatyard. All of them say, “That’s the way it is.” The zinc begins to waste, and the screws fall off. One dealer says the solution is to replace the housing and admits this is a $2,000 repair job. I am reluctant to have a diver disassemble the prop to replace/reattach the zinc, and a haulout is several hundred dollars several times a year. I would hope a company as large as Volvo would have a redesign or engineering solution, none are apparent. Do you have any ideas? 

Tony Ford, Monore, WA 

 Nigel Calder is an author and expert on boat systems and diesel engines

Nigel Calder is an author and expert on boat systems and diesel engines

NIGEL CALDER REPLIES

I ran this issue past the technical folks at Volvo-Penta in Sweden. They had not heard of it before. They are wondering if the zincs have been secured without locking fluid on the fasteners or, even worse, with grease. In that case, the fasteners will work loose—they need to be locked in place (after a thorough cleaning if grease has been used). There are stainless steel Helicoil inserts (thread inserts) in the aluminum saildrive leg into which the zinc retaining bolts go. If the threads in the leg have been stripped off or damaged in any other way it may be possible to replace the Helicoil inserts, but if not, the suggestion is made to use 1/4in Powerlok self-tapping stainless steel machine screws. In conclusion, Volvo-Penta writes: “We are confident the above measures will cure this unusual problem. We wish the owner the best of luck.”

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