recommended service life of rudder

[unbusted67]

Hey guys, kind of an odd question here but does anyone know where I can find literature, maybe from Loyds or ABS, on recommenced service life for a vessel’s rudder. I run a T boat that has seen huge amounts of service and i’m wondering when we should think of rudder replacement as preventative maintenance.

[daletournier]

This is something ive thought about alot lately as I've just replaced my 18 year old rudder due to finding crevice corrosion in the shaft.

Personally I dont know how to answer your question other than saying the obvious, "rudders are extremely critical" and I dont think enough of us take a hard look at our rudders often enough.

If I hadn't of dropped my rudder 4 weeks ago to look I would never of known this corrosion existed. I posted about it here, and one Cf member said I was very prudent to of had a look, it was a compliment. But the reality is I should of dropped that rudder two oceans ago and had a good look rather than assumed all was ok, how long has the corrosion been there? How long would it of lasted? I don't know,maybe years? BUT in the middle of a dark stormy night 500nm from land I do not want to have the worry that it could break.

I think many are to complacent. I was looking at a old boat in the hard the other day that had lots of rusty water running out if his rudder, he wasnt concerned....I would be.

This year two boats lost rudders crossing the South Atlantic ,that I know of.

[barnakiel]

Lost my post.


Anyways, I think there is no such limit when the rudder is built to last.


Bearings are consumables.


b.

[daletournier]

Originally Posted by barnakiel

Lost my post.


Anyways, I think there is no such limit when the rudder is built to last.


Bearings are consumables.


b.

My argument to that would be, very few rudders dont eventually get water in them and SS doesn't like stale water.

[boatpoker]

solid SS rudder, hollow ss rudder, bronze rudder, FRP rudder with composite stock or ss stock or foam cored rudder with ss or composite stock ?

Gotta be a little more specific

[unbusted67]

Originally Posted by boatpoker

solid SS rudder, hollow ss rudder, bronze rudder, FRP rudder with composite stock or ss stock or foam cored rudder with ss or composite stock ?

Gotta be a little more specific

I believe it is ss stock, foam cored, with frp laminate.

[boatpoker]

Originally Posted by unbusted67

I believe it is ss stock, foam cored, with frp laminate.

There are no hard and fast rules but after just over 5,000 surveys I would expect to see some kind of issue after about 10yrs. but it's a progressive thing.

The so called "closed cell foam" that will not absorb water is a myth. It most definitely absorbs water and begins to decay and turns into a crumbly mess.

This is quite easily determined by percussive sounding. Moisture meters can be misleading as even if the core is saturated , if it has separated from the skin the meter may not see the moisture. Moisture meters measure capacitance not actually moisture. If there is no contact between the skin and the foam the meter cannot see it. A thernal imager will see it instantly.

The water in the rudder becomes stagnant. Stagnant water is de-oxygenated water. Stainless steel corrodes in the absence of oxygen.

Take a look at Moisture Meter Mythology and Flir thermal imager

[Qayaq]

I project manage Surveys on commercial vessels. Rudders and shafts out every 5 years. Inspect and repair if necessary and refit. In general we dont get rudder and shaft failures as the inspection interval picks up on any defects.
We have some fairly old vessels and some new ones. I would say that inspection stops failure and age is less of an issue than design or application of design in original build.

[unbusted67]

Originally Posted by boatpoker

There are no hard and fast rules but after just over 5,000 surveys I would expect to see some kind of issue after about 10yrs. but it's a progressive thing.

The so called "closed cell foam" that will not absorb water is a myth. It most definitely absorbs water and begins to decay and turns into a crumbly mess.

This is quite easily determined by percussive sounding. Moisture meters can be misleading as even if the core is saturated , if it has separated from the skin the meter may not see the moisture. Moisture meters measure capacitance not actually moisture. If there is no contact between the skin and the foam the meter cannot see it. A thernal imager will see it instantly.

The water in the rudder becomes stagnant. Stagnant water is de-oxygenated water. Stainless steel corrodes in the absence of oxygen.

Take a look at Moisture Meter Mythology and Flir thermal imager

Thanks for this.

Originally Posted by Qayaq

I project manage Surveys on commercial vessels. Rudders and shafts out every 5 years. Inspect and repair if necessary and refit. In general we dont get rudder and shaft failures as the inspection interval picks up on any defects.
We have some fairly old vessels and some new ones. I would say that inspection stops failure and age is less of an issue than design or application of design in original build.

Thanks, We will pull it out and have a look at it.