Why Change out diaphragms in a Yanmar SD20 Saildrive

[Tin Tin]

I guess Yanmar have to consider a case where SD is used heavily every day so the diaphragm gets worked everyday, this may wear the rubber and so in an abundance of caution that is why replacement time may be shorter than what a weekend user might prefer. However there can be failure reasons :
1 As noted above, any oil or solvents pooling in the diaphragm ring may cause the rubber to soften and split
2 A grounding may stretch rubber past its limit
3 A prop wrap around a mooring line will put a rapid side strain on the SD
4 Winter in water storage may cause brittleness in the rubber in freezing conditions
5. In tropical conditions the SD leg can get quite warm - so if your boat experiences the highs and low temperatures around the diaphragm it may perish more quickly.
6. A tired old sail drive rubber mount and or engine mounts will put excessive vibration on the diaphragm.


There may be more, these are the ones I could think of


If none of these apply, your diaphragms may last much longer

[ggray]

A couple of comments:

Cold can be deleterious to rubber, or just about anything, but winter in-water storage wouldn't be as cold as out of water storage.

Just as a data point: Many years ago I had to remove one motor from our catamaran. While the motor was out, I wanted to get out on the water. Sailed nearly 20 miles and back. I was a bit alarmed by how much the sail drive was moving around, lacking the support from the motor. So both diaphragms got a real workout without damage.

Originally Posted by Tin Tin

I guess Yanmar have to consider a case where SD is used heavily every day so the diaphragm gets worked everyday, this may wear the rubber and so in an abundance of caution that is why replacement time may be shorter than what a weekend user might prefer. However there can be failure reasons :
1 As noted above, any oil or solvents pooling in the diaphragm ring may cause the rubber to soften and split
2 A grounding may stretch rubber past its limit
3 A prop wrap around a mooring line will put a rapid side strain on the SD
4 Winter in water storage may cause brittleness in the rubber in freezing conditions
5. In tropical conditions the SD leg can get quite warm - so if your boat experiences the highs and low temperatures around the diaphragm it may perish more quickly.
6. A tired old sail drive rubber mount and or engine mounts will put excessive vibration on the diaphragm.


There may be more, these are the ones I could think of


If none of these apply, your diaphragms may last much longer