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Old 14-01-2021, 05:01   #16
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

Thanks for sharing!

Since there has been so little first-hand knowledge presented of failure from "natural" causes...age in particular...I'm thinking that diaphragm failures are most likely from a violent event. Bumping on a submerged piling or pinnacle. Having a dock line wrap around the prop. Being hit by the periscope of a submarine passing underneath.

This is the sort of real data I was hoping to learn.

So I'm now thinking that owners of these sail drives are just leaving them in place until a leak occurs. And I'm not hearing much of that.
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Old 28-12-2021, 08:27   #17
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

Diaphragm made out of rubber, so keep everything away that is damaging rubber and they last very long.
If you get rubber softner or vasiline on the top one every 3 years or so that will reactivate the rubber and keep it intact.
There are 2 ways they are failing: mostly the rubber gets hard, they bridle and develop cracks that over time lets water pass. Slow process and you have plenty time to discover and then replace.
2nd battery acid, engine cleaning detargent, other acid, diesel or oil gets in contact with the rubber and simply destroy the rubber. It gets mashy and very soft (most people think, thats good its rubber and have to be soft.. nope not at Lall good) , then it just need a shock load like a small hit or a very rough stop from eg full throttle to full reverse emergency stop and the diaphragm rips big time and lets a lot water in... Thats the dangerous fail as you have no prewarning and only notice it when the bilge alarm screams. Only chance dump in as many as pump capacity as you have and call next boat yard for emergency haul out....
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Old 15-10-2022, 01:47   #18
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

My Hunter 356 built 2002 is still on its original diaphragms. It has been my intention to replace them but still reluctant to blow a wad of cash on something that still works. No leaks, no issues. HOWEVER, during a scrub off I noticed some Oysters growing in the recess, removed the lower flat rubber fairing to remove them. The Oysters were growing up against the rubber diaphragm, and would have cut through it given time and vibration from the running engine. I put a load of antifoul up there and have not had any regrowth. I have not replaced the flat rubber fairing for inspection purposes.
On a separate issue, my standing rigging is also original (the boat was only sailed 6 times by the previous owner). I go up the 'chair and inspect it twice per season, and still can't justify (other than insurance purposes) replacing it.
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Old 15-10-2022, 03:30   #19
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

That kind of lifespan is good to hear! I'm at 22 years.

But you might want to invest in a serious bilge pump or two. I take comfort that my engines and sail drives are in an isolated compartment behind a relatively water tight bulkhead...in an unballasted boat. And I still upgraded the bilge pumps.

Just saying.
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Old 11-02-2023, 06:38   #20
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

It is now approaching time to replace the diaphragms again, and even my insurance surveyor rolls his eyes at this requirement. At some point, I’ll go rogue with only liability insurance.
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Old 11-02-2023, 08:31   #21
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

Let's keep this thread alive. I see more and more saildrives installed and very few failures, However, almost no one seems to be following the maintenance schedules, and these drives are aging every year.

As the results of failure at sea can be catastrophic, I am trying to come up with a rule on saildrives for my offshore deliveries. I say no thanks to taking boats offshore with standing rigging over 20 years old. Should I say no to 20 year old saildrives that have the original diaphragms
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Old 28-02-2023, 04:05   #22
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

Just an update still have original sale drive diaphragms on both sd sail drives... The boat was finished and splashed in 2006 from the factory... I'm going to inspect them closely this year , I'm preparing to do an Atlantic crossing along with a full Mediterranean crossing...
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Old 04-11-2023, 20:17   #23
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Re: Why Change out diaphragms in a Yanmar SD20 Saildrive

Another update. Original diaphragm seals on my SD 20 still in boat. Bought boat new in 1985. (Yes that's 38 years)
For the 1st 25 years I hounded my Yanmar dealer/mech. that I wanted to change. He always put me off citing older diaphragms still in service.
Nowadays I sail/cruise coastal NE USA with no far offshore plans and saildrive access/visibility to inspect is very easy.
Over the years have just changed zincs and seals. And deal with horrible Yanmar RW valve.
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