Pressure test a rudder ?

[Snowgoose-1]

I am currently repairing some nicks and scratches without having to open the rudder up. There was some seepage of seawater.

Anyone done a gentle pressure test ? Or perhaps some pressure applied to drive any water out ?
I note that ships pressure test rudders but they are made of steel.

 

[ash2020]

I think, if it's a GRP laminate, it's very unlikely that it would hold pressure. Not sure if it's worth the effort.

 

[rogerthebodger]

I pressure tested my rudder but it is steel. I then filled the rudder with old engine oil to prevent internal corrosion.

Never pressure tested a GRP rudder but it would be interesting to see what would happen.

I would not exceed more than 10 psi and immerse it in water to see where the leaks are if any

 

[Paul1962]

Suggest 2 PSI may be a better figure to test with

 

[Plum]

Suggest 2 PSI may be a better figure to test with

Agree 2psi and ideally submerged horizontally in water. If the blanking plug is above waterlevel you can do an occasional test while affloat although the outside water pressure at the bottom of your vertical rudder may be 2psi !

 

[rogerthebodger]

outside water pressure at the bottom of your vertical rudder may be 2psi !

That's why I suggested 10 psi so to exceed any possible water pressure

 

[Stemar]

What is the surface area of the rudder? If it's 3 sq ft. that's 432 sq ins. Even at 1 psi, that's a lot of force trying to split it apart

 

[Daydream believer]

Why bother in the first place?
Does your rudder need to be watertight?
Would there be a possibility that applying such pressure may break the bond between foam & outer skin?
Would the joint to the shaft of GRP & aluminium, or steel, at the top, actually hold much pressure & if broken, make leaks more likely?
Would the test weaken the joint between the 2 halves, such that later the rudder split in half?

 

[RivalRedwing]

I expect that most GRP rudders are wet inside and there is little one can do to fully prevent it, the shaft to GRP seal being the key point of leakage. I take the route of drilling a 6mm hole in the base of the rudder at haul out and filling that with epoxy again before launch. A little water drips out over the time on the hard and some fresh air enters which is probably beneficial for the stainless tangs.

 

[rogerthebodger]

I expect that most GRP rudders are wet inside and there is little one can do to fully prevent it, the shaft to GRP seal being the key point of leakage. I take the route of drilling a 6mm hole in the base of the rudder at haul out and filling that with epoxy again before launch. A little water drips out over the time on the hard and some fresh air enters which is probably beneficial for the stainless tangs.

This is why on any future boat I had would not have a GRP rudder as thy always leak water in and cause crevice corrosion on the tangs connection the rudder shaft to the rudder

 

[Snowgoose-1]

What is the surface area of the rudder? If it's 3 sq ft. that's 432 sq ins. Even at 1 psi, that's a lot of force trying to split it apart

Thanks for the replies.
Rudder is about 14 sq ft.

 

[Freebee]

be very careful even a small pressure on a large surface area is a lot of force and more likely to open up any weak seams or even blow it apart but I guess that would let the water out...............................or in!!!.

 

[RivalRedwing]

This is why on any future boat I had would not have a GRP rudder as thy always leak water in and cause crevice corrosion on the tangs connection the rudder shaft to the rudder

That rather reduces your boat options, but it is certainly your call. I opened mine a few years back out of interest, 1978 build, a bit damp inside, stainless steel tangs, no issues at all (including a dye penetrant crack check).

 

[Tranona]

This is why on any future boat I had would not have a GRP rudder as thy always leak water in and cause crevice corrosion on the tangs connection the rudder shaft to the rudder

One wonders why there are hundreds of thousands of GRP rudders in use round the world and no signs of an epidemic of failures! Rarely is crevice corrosion an issue but more commonly in older rudders it was the use of mild steel tangs that caused the problems. Now many production boats use aluminium stocks.

 

[lustyd]

That rather reduces your boat options

Carbon rudder stocks are relatively common these days and no reason the whole thing couldn't be carbon layup, which would make it entirely possible to remove any sources of leaks which usually start at the stock. This could easily be manufactured for any boat.

 

[RivalRedwing]

must admit that both aluminium and carbon give me the heebies as rudder stocks, probably totally irrational but give me a solid stainless rudder stock any day..

 

[Tranona]

must admit that both aluminium and carbon give me the heebies as rudder stocks, probably totally irrational but give me a solid stainless rudder stock any day..

Carbon (and laminated GRP) stocks have a chequered history with examples of early failure. US Hunters for GRP and Beneteau for carbon as examples.

Not sure how many builders actually use carbon now, but aluminium is pretty much universal in production boats and really does not give problems.

 

[Daydream believer]

Not sure how many builders actually use carbon now, but aluminium is pretty much universal in production boats and really does not give problems.

Aluminium can give problems. The main one being corrosion around the point between blade & bottom bearing becoming heavily pitted. Often due to issues such as contact with an incompatible antifoul paint, or some form of electrolysis etc.
The MyHanse web site shows cases where owners have had to replace them. I am sure that they are not isolated to those used by Hanse as many are Jefra, as used by other manufacturers. I would not point to Jefra being at fault either.
However, that being said, the overall saving in cost ( to a manufacturer) far outweighs the cost ( to the overall user base) of relative numbers replaced. Unless, of course, it is your one that is being replaced. Generally it is a matter of correct maintenance.

 

[Tranona]

Aluminium can give problems. The main one being corrosion around the point between blade & bottom bearing becoming heavily pitted. Often due to issues such as contact with an incompatible antifoul paint, or some form of electrolysis etc.
The MyHanse web site shows cases where owners have had to replace them. I am sure that they are not isolated to those used by Hanse as many are Jefra, as used by other manufacturers. I would not point to Jefra being at fault either.
However, that being said, the overall saving in cost ( to a manufacturer) far outweighs the cost ( to the overall user base) of relative numbers replaced. Unless, of course, it is your one that is being replaced. Generally it is a matter of correct maintenance.

Exactly. The issue of corrosion from antifouling took a while to emerge, but for at least the last 10 years the advice from builders and Jefa is to leave a 10cm ring around the lower bearing clear or use something like Trilux in that area. It is not just lower cost but a significant weight saving.

 

[Daydream believer]

This is why on any future boat I had would not have a GRP rudder as thy always leak water in and cause crevice corrosion on the tangs connection the rudder shaft to the rudder

Seems that your choices of yacht would be limited to somewhat older designs, along with all the accompanying disadvantages