Prevalence of catastrophic saildrive seal failure

[Paul Howard]

Originally Posted by ohthetrees

Thanks for the report. Aren't these typically two layers? If one layer was a crack in a fold, do you know how your 2nd layer was compromised?

Some have two layers with a water sensor in between. Some older ones, like those I had, 1992, were a thick single layer.

[hugosalt]

FWIW...
Bought my boat new in 1985
with Yanmar saildrive SD20.
They still make them.
Have 2 robust seals with water sensor alarm between the seals.
This will be 35th season with original seals. Never a problem.
After some years, asked my Yanmar dealer to changed them. He always said no need to. I examine often,
still look new.
Do coastal cruising, if were passage making I would change.

[sowwaninii]

Thanks for all the replies to my original post. I suspect if I made the same infinity regarding conventional shaft drive, I would have gotten a similar distribution of responses.
Thanks everyone!!

[SofiaB]

In 2015 I spent many hours researching this topic when trying to find a boat. Forum question produced similar comments with many who ignored Volvo Service Protocol (S3 Every 7 Years S-Drive, Rubber Sealing between Drive and Hull - Replace) with some reporting over 15 years of life, and when replaced reported the seal in like new condition. At that time I found no reports of "normal failure" from normal use. I sea trialed both shaft and sail drives and found maneuvering improved with the saildrive. I keep questioning how long I will risk going past the 7 years, but have 10 years in mind for my Volvo Penta D2-55F/130S-C combo from 2016. Also discussed this issue with Volvo Penta personnel at boat shows and they have stated that 7 years is suggested mostly for liability, but not practicality. At the time, I questioned why I was worrying about a seal instead of worrying about sailing; forest for the trees argument.

[belizesailor]

Originally Posted by ohthetrees

Thanks for the report. Aren't these typically two layers? If one layer was a crack in a fold, do you know how your 2nd layer was compromised?

Yanmar SDs have 2 bellows, Volvos have 1. Ive never personally seen a catastrophic failure in either (except where SDs have been nearly ripped out of the bottom of the boat by severe grounding) and only once or twice the sort of crack leaking as described above. The rubber is thick and tough (natural rubber I suspect....which is more durable than many synthetics). Ive replaced my own and been around when many have been replaced on charter boats. Ive yet to see one that didnt look nearly new even when many years old...like 15!

Ive replaced my own, but they were in such good condition that I kept them as spares just in case.

I replaced mine at about 12-15 years old respectively just because they were getting old. The bellows themselves appeared in good condition, but I did discover other maintenance issues which needed addressing in the process. Discovering other issues is one good justification for changing them.

[redneckrob]

Originally Posted by roland stockham

For me the issue is similar to gas safety, it is not whether it happens or how often but the fact thst it introduces a weekness. In the case of gas I can see positive benifits and many people are happy with the risk. With legs the advantages over a conventional shaft are less clear. If there is no overwhelming advatage to having a leg why take the risk however slight?

There are certainly benefits in many applications. For example, it's not possible to build most cats with a conventional shaft without at a minimum putting the engines in your staterooms. It also enables boats to be built for less; being able to afford a boat is often seen as a pretty big benefit for many folks.
And yes, how often or if something happens is most certainly relevant when deciding if it's something we should worry about. If you can get a boat for $10k less because it has a sail drive and the weaknesses of the saildrive have proven to be miniscule, most of us will take that cost savings against the tiny risk and perhaps invest it in extra survival equipment which statistically would be a far better risk mitigator than sinking it into a conventional shaft.

[Jahwork]

Greetings all,

After growing up on power boats and monohulls, as well as owning several of each myself, I was a staunch shaft only guy and nary had a good word to say of saildrives. When we made the switch to cats I even specifically chose to only look at catamarans with traditional shaft drive and we ended up buying a TPI Lagoon 35 with twin Yanmars and shafts. Loved that boat but sold it two years ago to “upsize”.

Due to many circumstances far too long and boring to type here we ended up purchasing a 1993 Solaris Sunrise 36’ sport catamaran with twin yanmars and SD20 saildrives. Being anti-saildrive made it a difficult decision but the price was far too enticing to pass up and being recently retired I needed a project. Got it for a steal as it has been sitting unused for about 15 years and is in need of a complete retrofit. The engines have just over 600 hours each so barely used. Spent the first six months on the hard, pulled both engines, saildrives, rudders, every thru-hull......etc.etc.etc and either rebuilt or replaced it all.

The port side diaphragms, which I am certain were both original from 1993 as I had to chip the factory paint to get the bolts out, were in pristine condition. I replaced them all anyways, and kept them for spares, as I went through the entire saildrives including gears, bearings, seals......etc.

The starboard side was not so good. Through no fault of the saildrive design or equipment it was a gooey soft mushy mess and was actually slowly allowing water to seep though prior to us hauling out. The previous owner, or perhaps one of the many brokers or fender kickers that had looked at it prior to us buying it had ran it with the diesel return line removed from the fuel rack and as a result the bilge had filled with about 6 inches of diesel oil. It was full when I went for our initial inspection and helped the owner, actually I pretty much did it for him, bail it out and clean the bilge. I also pointed out to him the source of the diesel in the bilge and repaired it.

Long story short, the diesel bath didn’t do any favors to the diaphragms and had turned them into a gelatinous goo.

After removing and rebuilding the saildrives I am now a convert. I am no longer at all concerned about the “big hole in the boat” or the craftsmanship of the design. We do have water tight bulkheads well above the waterline for each engine bay which also boosts my confidence.

If you read all that and are still here........or if you have skipped to the end of my ramblings then the condensed version is....

Don’t let any oil/diesel or any solvent or petroleum products come into contact with the diaphragms. I have always been very diligent about clean engine rooms, I was a machinery technician in the Coast Guard, but I am now OCD, as my wife puts it, about keeping the bays spotless and the diaphragms free of any contaminants.

Just one poor mans prose,

Safe Journeys all,
~Jake

[David B]

Originally Posted by Rucksta

Yanmar sail drives have a "water in leg" sensor.

Actually the sensor is between the two diaphragms (the lower main one, and the upper one you see from the engine compartment. This is one of the pluses for Yanmar (and ZF) drives - they have that second back-up diaphagm.

[Mrkva]

Last autumn I bought a boat with VP 120S with leaky saildrive seal. According to previous owner, it started to leak this season (approx. 5l/week when idle, significantly more when motoring). When replacing the seal, I found out the bottom is a bit cracked, and the leak was most likely caused by rubber giving way and clampdown force reduction.


The year of manfucature of that seal was 1985... Don't worry.

[Lake-Effect]

My only knock on saildrives (prior to reading this thread) is that in the older boats that I mostly hang around, the saildrive seal becomes a maintenance expense and hassle that the older boats with a shaft don't see. So a saildrive could be something to avoid when shopping for older boats, unless it's been replaced recently.

Then again, when I worked a summer for a diesel mechanic, I remember one owner with a shaft catching a rope in their prop; torn motor mounts, bent shaft, bent strut... north of $15k before that boat was properly fixed.