Saildrive Diaphragm DOM Stamp

[Tsb]

Hi All

New to these forums. They are amazing btw. You all do a great job of providing valuable information. I am in the shopping phase and may become part of the Bavaria family, fingers crossed. Can anyone confirm the date stamp on from this saildrive diaphragm? The dial on the Left is pointed at the 2 and the dial on the right is pointed at the 8. Any help would be greatly appreciated.

[Salty]

Welcome to the best Bavaria forum on the planet.

I am not 100% sure regarding these markings, but I have just taken a look at a diaphragm I had taken off my B36(2002) back in the winter of 2010/11. The left stamping shows a very similar marking to yours and to which I think it might mean it was made and marked in the year 2000, while the right stamping points like yours to an 8 which might mean the change to a new diaphragm should be eight years after the year of manufacture. Volvo recommend that these diaphragms are changed after seven years, though Having changed mine in the winter following the boats purchase, I discovered that the diaphragm once removed was in perfect condition. Now with hindsight I am inclined to agree with the viewpoint of many that seven years is way too soon to be thinking of changing, so don’t get hung up over it’s age. Indeed one person reported that theirs was not changed until after about nineteen years, and that it was still in excellent condition. On my old diaphragm there is also a yellow label written in one of the Scandinavian languages which I think Suggests a date for change, but where that information apart from an 8 is impossible for me to decipher.
The additional photos (if I can add them) show the external condition of the old diaphragm, under and upper sides, which had been used for nine years after the 2002 date of the boat build.

[Odysseus]

This is my hobby horse,
I have been in contact with Volvo over the years, directly and through their agents in UK, and Europe,  on every occasion  I meet or email them I ask for the specification they used to substantiate  the 7 year change of this rubber gaiter, 

I am sorry to Inform you they never supplied one, lots of long emails but no actual specification.

This leaves me with the only conclusion that they do not have one.

I inspect my rubber each year at lift out top and bottom, so far its perfectly good. Now for the so called surveyors and yard engineers, when they say you need to change the gaiter, ask them for the specification that is used to justify that, not word of mouth, or Volvo said, but the Engineering FMEA they base the need on.

I await with baited breath you Engineering reply.

Odysseus

[sy_Anniina]

The Yellow label says nothing about change interval, but contains a note:

 NOTICE: This detail need careful installation (or mounting). See instructions.

BR,

Tommi
s/y Anniina

[tckearney]

I changed mine myself as the boat second hand and I had a receipt for it being done ten years ago.  It was as new.   When I fitted the new one I took a photo on my phone of the saildrive hole and the fitting of the new one. I put a news paper showing the date next to it.  Just in case I was questioned. 

[Symphony]

I understand the 7 year change recommendation came from the early days when the saildrive was introduced in the US. There was real resistance to the product on 2 counts. The first was related to corrosion - remember the US is home to large numbers of outboards and outdrives with aluminium casings that rot away in salt waater, mainly because of poor anodic protection. The second was the idea of a big hole in the bottom of the boat reliant for security on a bit of rubber. Once these sort of ideas take root it is very difficult to shift them, so Volvo introduced the 7 year change rule to allay fears. Interestingly when Yanmar brought out their saildrive they went OTT and fitted a double diaphragm with a warning sensor in between the two. 40 years on there have been virtually zero failures of either type of diaphragm!

There is no pressure on Volvo or Yanmar to change their recommendation as it does not influence sales of new units and why cut off a very profitable business in replacement sales and work for agents!

The 7 year rule belongs to the same family of "urban myths" as all hoses below the waterline should be double clipped, rigging should be changed after 10 years and closer to home, keels fall off Bavarias. No evidence, either theoretical or empirical to support these myths. In many cases they get institutionalised by such mechanisms as insurance conditions or even regulations.

Such myth creation is an integral part of our society as the current pandemic is demonstrating.

[Rampage]

I changed mine at the 17 year point.  On close examination of the old one, I could find no evidence of deterioration whatsoever and I’ve come to the opinion that the 7 year rule is based on ...... nothing.

[sy_Anniina]

A bit ot, but still:

Interesting point on Yanmar double seal + water sensor design I just noted with my medical device safety design / FMEA & risk mitigation background:

If the upper seal fails first, the water sensor will not alarm, unless bilge water reaches the saildrive... years pass by... no warnings...once the lower seal fails, the sensor will give a warning, but also the upper seal will allow water to flow to bilge. The design for sure sounds safer, but may not be significantly so.

Unless of course there is a purposely designed significantly longer lifetime (and more user error resistant design) for the upper seal.

BR,

Tommi
s/y Anniina

[Keweetoo]

When I bought my yr 1999 boat in 2016 the surveyors report indicated the saildrive diaphragm was the original. Replacement was part of the sale negotiations. I wish I had taken a photo as once the old one was out and alongside the new apart from the external face having some 'crud' it was almost impossible to tell the difference!
The attached shows the original date stamp from surveyors report and whilst the boat was built 1999 the date stamp is showing 98  3 (March 98) according to my surveyor.

[Symphony]

A bit ot, but still:

Interesting point on Yanmar double seal + water sensor design I just noted with my medical device safety design / FMEA & risk mitigation background:

If the upper seal fails first, the water sensor will not alarm, unless bilge water reaches the saildrive... years pass by... no warnings...once the lower seal fails, the sensor will give a warning, but also the upper seal will allow water to flow to bilge. The design for sure sounds safer, but may not be significantly so.

Unless of course there is a purposely designed significantly longer lifetime (and more user error resistant design) for the upper seal.

BR,

Tommi
s/y Anniina

Not sure there was ever any technical justification, or anything as sophisticated as a stronger inner compared with outer seal. Suspect it was just a marketing point to differentiate their offering from that of Volvo. They still recommend regular replacement.

A good example of a (possible) solution for a problem that does not exist. It is clear that time has shown that the choice of material and design for the original Volvo installation was sound. I am sure they will have done accelerated fatigue testing before choosing the material but would not of course had the benefit of long term realtime testing.

[Alphadug]

Hi All, when we purchased our 3 year old boat in 2018 the surveyor said you HAD to change the diaphragm every 7 years. He said that if you had an insurable failure, water in the boat, sinking etc. , that the insurance companies here in Canada would void your insurance if the diaphragm was more than the allowable 7 years old. My mechanic says he's never seen a failure! So,at our next haul-out in 2 years do we pay the close to $3,000.00 to replace it or take the risk? Maybe we should start a discussion with the insurance companies and repair folks to change the requirement although I expect the insurance companies would then want it changed annually to really lessen their risk. I know that here in Canada tire shops can't touch a tire more than 5 years old regardless of mileage due to rubber degradation. Like you, I'm at a loss.

Doug
S/V Vivia

[Lazy Pelican]

If the diaphragm was over 7 years old and failed then your insurance co might refuse your claim. The question is how likely is it to fail. My own view is it won’t happen. Ours is 15 years old, looks as good as new and I’ve no intention of changing it.

[Salty]

The Yellow label says nothing about change interval, but contains a note:

 NOTICE: This detail need careful installation (or mounting). See instructions.

BR,

Tommi
s/y Anniina

Many thanks for deciphering what it says on the yellow label Tommi, that’s greatly appreciated.

I wonder if anyone on the forum has actually seen or experienced a diaphragm failure, or even felt that perhaps they had only just changed theirs in time and that leaving it any longer would almost definitely have resulted in its failure ?

In theory my saildrive diaphragm is again overdue for a change, but on the basis of the one I changed back in winter 2010/11, I am going to leave the present one where it is.

[Symphony]

Hi All, when we purchased our 3 year old boat in 2018 the surveyor said you HAD to change the diaphragm every 7 years. He said that if you had an insurable failure, water in the boat, sinking etc. , that the insurance companies here in Canada would void your insurance if the diaphragm was more than the allowable 7 years old. My mechanic says he's never seen a failure! So,at our next haul-out in 2 years do we pay the close to $3,000.00 to replace it or take the risk? Maybe we should start a discussion with the insurance companies and repair folks to change the requirement although I expect the insurance companies would then want it changed annually to really lessen their risk. I know that here in Canada tire shops can't touch a tire more than 5 years old regardless of mileage due to rubber degradation. Like you, I'm at a loss.

Doug
S/V Vivia

It would likely be the same in the UK as policies have a catchall condition that the boat should be properly maintained in seaworthy condition and a claim could be rejected under this condition. The reality is that they do not fail catastrophically so as a number of people have said here (and many thousands more decide) this is a risk they take themselves. Personal decision.

In the UK insurers as a group publish tables of reasons for claims. structural failures such as this never even make the table, they are so rare, neither do rigging failures. The vast majority of claims both by number and value are for minor damage from collision or weather and theft. Such claims are usually settled without any fuss. Unfortunately insurance for yachts is a very fragmented industry and collecting meaningful data on claims is difficult, hence the reliance on blanket exclusions and "rules of thumb". Very different from car or household insurance where there is vast amounts of data and extensive sharing within the industry.

Risk assessment is all about the probability of an event occurring and the consequences. So with saildrive diaphragms the probability of failure is close to zero and the consequences are significant (loss of boat worth a lot of money). The cost of insuring against the consequences in your case is $3000 every 7 years or $430 a year over your normal insurance.

Tyres are interesting. It is the carcase rather than the tread that is time lifed (tread is mileage based) and in general modern carcase compounds have a shorter life than older types. In most cases the tread wears out before the carcase degrades. Degradation is primarily caused by environmental conditions, particularly UV. In the UK the law has been changed recently for trucks and coaches making it illegal to have tyres over 10 years old. Although treads rarely last that long, tyres are regularly retreaded to extend their life. The change in law was the result of overwhelming evidence of tyre failures on older tyres.

On the other hand I have a Morgan sports car I bought new in 2003 and it still runs on its original tyres. The treads are just over half worn at 22000 miles but there is no sign of degradation of the carcase. This is because the car spends most of its life in a garage, but is used regularly so reducing the chance of flatspots and pressures are always maintained. It passes its annual inspection with no comment other than the tyres are dated 2003. Incidentally it also has the original battery, a Red Flash AGM which is connected to a battery condition charger in the winter.

[Craig]

Symphony is correct about the degradation of tyres and same principal could also be applied to the sail drive gaiter. UV degradation and tyres sitting for long periods of time creating a "memory" or flat spot are an issue but rubber kept out of the sun and without pressure differentials can last extremely long periods of time.

I tried finding information on failures of the saildrive gaiters about 5 years ago. I could not find any reference to any gaiter replaced that had damage. I've heard a few stories about lifting straps pushing the saildrive up and breaking the gaiter but can't even verify a case such as this. I can verify a case in Malta where a Bavaria in a race hit something so hard the engine mounts on one side broke and the engine turned 45 degrees. The sail drive gaiter remained intact and no water ingress resulted.

The tyres on a Flying Boat shot down near Broome, Western Australia during WW2 that had laid in the mud in 10 m of water since 1943 were recovered in perfect condition about 10 years ago.

I suspect that in the absence of UV or unusual stresses, the rubber gaiters will last indefinitely.

For private purposes I see no benefit in changing every 7 years because of the low risk of failure versus and high cost involved in changing. Insurance can only refuse to pay out a claim if the failure of the gaiter contributed to a loss. Unfortunately, any vessel used commercially will need the Volvo recommendation complied with.

Craig
"Shirley Valentine"
Gold Coast
Australia

[Yngmar]

The two digits inside the left dial appear to be the last two digits of the year of manufacturing, e.g. 98 = 1998, 00 = 2000, 02 = 2002. Not too sure what the numbers indicated by the arrows are, perhaps calendar week. On our new diaphragm, there is additionally a stamp to the right that simple reads "Year 2015" - much easier to decode

I've cut a small section of our old diaphragm out as souvenir after replacing it. It was in mint condition at 15 years age, but that doesn't mean the job shouldn't be done - there are other parts to this service task that can only be properly inspected when the saildrive is split in the process and those may not be in mint condition. This includes the water channels, mating surfaces and the painted steel clamping ring (which was in desperate need of some paint in our case).

[Tsb]

Hi All,

Thanks for the contributions. It's really helpful to hear your thorough and sensible comments.  Salty it's interesting that yours might be 2000. That would make mine a 2002 I guess. The boat is a 2003 which would make this the original seal of course.

Thanks Again