Saildrive risk?

[EugeneR]

Hi all,

I’m considering buying a semi-custom 50–55ft cruising cat from the 2010s, currently in a remote location in South America.

We plan to keep her 5–10 years and are budgeting accordingly e.g. a rigging inspection recommended replacing the original standing rigging, which we're taking on (at our own cost).

One area of uncertainty / concern is the aluminium sail-drives:

- A prior survey for the current owner’s purchase in 2021, noted the drives were coated with the same antifoul as the hull, and warns about possible copper / galvanic corrosion. The survey also noted poor quality hull preparation.
- The owner believes there is an epoxy barrier under the antifoul.
- The boat has not been antifouled since remediation of the poor quality hull anti-foul application later in 2021. The owner says he plans to do a new bottom job this season.
- I asked about sail-drive seal history (boat approaching ~15 years). The owner said he replaced “lower-end o-rings/seals” himself during a recent haul-out, describing it as “an easy job, not very technical”. It’s therefore unclear whether this refers only to prop/leg seals or includes the drive-to-hull diaphragm, and there’s no yard documentation.
- Before sale, the owner plans to “tidy up” the sail-drives (e.g. epoxy fairing and "maybe something proper like PropSpeed") alongside a bottom job, which could make survey inspection harder if there’s any pitting.

My concern is the combination of infrequent antifouling (and by inference, inspection), possible coating incompatibility with risk of localised pitting/corrosion if the epoxy barrier has degraded over the ~5 years, uncertainty over the hull/drive seal replacement (it's late in the game to ask), and the risk of cosmetic remediation before a buyer's survey.

Given that mix, what would you do in practice?

- Insist on specific inspection steps e.g. stripping back in places? I won't mind a surveyor scraping off some anti-foul but how might they check the sail-drive integrity?
- Assume/budget for remediation - if that is even possible?
- Or, perhaps budget for full replacement and price accordingly? That would give long-term reliability - but I can't expect the current owner to cover all of that.
- Or walk away unless certain conditions are met before survey?

Any practical owner or surveyor experience would be appreciated.

I have an alternative lined up - but it's something completely different, so want to see if / how we can make this one work, first.

 

[Tranona]

The saildrive housing is originally coated with a very good epoxy layer. The advice not to use copperbased AF is because there is bare aluminium on the aft face of the lower leg where the anode is located and there is a possibility that antifouling could get in there and set up a galvanic cell. However if the original coating is sound and there is no sign of corrosion at the edge of the lower housing it is safe to carefully remove the old AF and if necessary use an etch primer on any exposed aluminium. Then you have choices of what to use. The simplest is to use Ecopower or Prop o Drev in spray form. Not supergood as a long term AF, but in my experience in both the Med and UK fouling on the housing is not a big issue. The alternative is to use Velox but that requires more skill in preparation and application, but pays off in the long run. I have used on both saildrive propellers and conventional stern gear with success following the instructions but using a Hammerite special metals primer rather than Velox primer. Mechanically there is not a lot you can check with the drive, The seals that have been replaced are the common sources of water in the oil, so a check for water in the oil and possible drainage and replacement would be prudent. They will be 130 model drives and the anodes are easy to replace. The diaphragm is a very different job from the lower leg seals requiring disconnection and movement of the engine before the leg is removed. While the recommendation is to change at 7 years they seem to last just about forever. However it is a good bargaining point if they have never been changed, £4-5k tops cost for both sides and you may want to do this anyway if you plan long term ownership.

As to the hull bottoms, the ideal is to remove all the AF and start again. Doubt there will be reliable blasting where the boat is but maybe plenty of cheap labour to remove it manually.

Hope this helps

 

[dunedin]

…..
- I asked about sail-drive seal history (boat approaching ~15 years). The owner said he replaced “lower-end o-rings/seals” himself during a recent haul-out, describing it as “an easy job, not very technical”. It’s therefore unclear whether this refers only to prop/leg seals or includes the drive-to-hull diaphragm, and there’s no yard documentation.
….

Difficult to tell but my guess is that the seals he is referring to there are the oil seals on the drive shaft.
And the rubber gaiters that keep the sea water out have never been touched. Which would probably be fine for 15 years, but taking to 25 years in a remote location could be risky.
The expensive bit as you have surmised is if there has been corrosion of the saildrive legs.
Is the boat being lifted for a survey? If not certainly want to do a very detailed photo dive inspection.

Are there locations nearby able to lift a big cat to replace the saildrives water seals? Saildrives are fine if maintained, but more of a concern if neglected.

 

[VicS]

Difficult to tell but my guess is that the seals he is referring to there are the oil seals on the drive shaft.
And the rubber gaiters that keep the sea water out have never been touched. Which would probably be fine for 15 years, but taking to 25 years in a remote location could be risky.
The expensive bit as you have surmised is if there has been corrosion of the saildrive legs.
Is the boat being lifted for a survey? If not certainly want to do a very detailed photo dive inspection.

Are there locations nearby able to lift a big cat to replace the saildrives water seals? Saildrives are fine if maintained, but more of a concern if neglected.

On the prop-shaft ITYM.

The make of drive is not stated but Id expect to see a pair of oil seals on the shaft and an O ring on the bearing housing

 

[EugeneR]

Thanks - very helpful.

Yes, the boat can be lifted but that would be later. For now, I’m working from viewing, previous surveys and owner emails.

Drives are SD60-4's. I’m treating hull/drive seal replacement as the minimum, but still worried about need for full replacement if we cannot confirm they are OK.

The previous surveyor suggested that even pin-hole damage in the epoxy can, over 5 years, have caused pitting and possibly structural risk.

If they get “tidied” before survey as planned, how do we confirm the underlying condition during the out-of-water survey?

How would others deal with this?

 

[Tranona]

OK so they are Yanmars but the same principle applies. Maybe the surveyor is being pessimistic. In my experience corrosion starts from an exposed edge rather than a pinhole in the main body. Even if there is a more extensive breakdown in the body it is unlikely to lead to any structural issue such as breaking through and allowing water in or oil out. The casting is pretty thick and robust. I have seen many drive housings with surface corrosion made good by grinding back, built back up with epoxy filler, etch primed and recoated. If there is existing corrosion underneath the AF it is very likely to show visually on inspection.