Sail drive water tightness

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   As my boat (370e) will be 20 in August I now have to have a survey for it to meet insurance requirements with all items of concern being addressed. As part of my pre survey work I was replacing the sail drive diaphragms (Yanmar SD20). When the oil was drained it had taken on the ‘milkshake’ appearance of water contamination and I assumed that it must be the failure of the oil seal lips on the propshaft. On dismantling the bearing carrier the lip grooves in the propshaft were minimal and no concern, as was the lip wear on the seals. Being concerned that the shaft / seal wear was not the culprit, I examined the seal to carrier contact face in the bearing carrier and found a light corrosion path across both seals. Similarly when I unbolted the leg from the gearbox to remove the diaphragm, the o ring seal between also had a light corrosion path across it. I suspect that the water that entered the leg and emulsified the oil entered the sail drive due to the light corrosion path across the aluminium surfaces that the o ring and oil seals are located. The outer of the two o rings on the bearing carrier was also showing a similar light corrosion path, but the inner o ring was fine. Has anyone else noticed similar corrosion across the o ring and oil seals location surfaces? Or replaced the propshaft seals and still found the oil going milky?

My plan when reassembling in addition to cleaning up the light corrosion on these surfaces is to coat them and the o rings and seals liberally with anti corrosion grease. This should eliminate any further problems with them.

 Simon

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sgrhma2 Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 20 November 2021 Location: Northern Irelan Status: Offline Points: 271	Post Options Post Reply Quote sgrhma2 Report Post Thanks(0) Quote Reply Topic: Sail drive water tightness Posted: 10 April 2025 at 17:37
	As my boat (370e) will be 20 in August I now have to have a survey for it to meet insurance requirements with all items of concern being addressed. As part of my pre survey work I was replacing the sail drive diaphragms (Yanmar SD20). When the oil was drained it had taken on the ‘milkshake’ appearance of water contamination and I assumed that it must be the failure of the oil seal lips on the propshaft. On dismantling the bearing carrier the lip grooves in the propshaft were minimal and no concern, as was the lip wear on the seals. Being concerned that the shaft / seal wear was not the culprit, I examined the seal to carrier contact face in the bearing carrier and found a light corrosion path across both seals. Similarly when I unbolted the leg from the gearbox to remove the diaphragm, the o ring seal between also had a light corrosion path across it. I suspect that the water that entered the leg and emulsified the oil entered the sail drive due to the light corrosion path across the aluminium surfaces that the o ring and oil seals are located. The outer of the two o rings on the bearing carrier was also showing a similar light corrosion path, but the inner o ring was fine. Has anyone else noticed similar corrosion across the o ring and oil seals location surfaces? Or replaced the propshaft seals and still found the oil going milky? My plan when reassembling in addition to cleaning up the light corrosion on these surfaces is to coat them and the o rings and seals liberally with anti corrosion grease. This should eliminate any further problems with them. Simon



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