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Old 12-09-2008, 23:06   #1
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Rudder Inspection

Planning to get back into sailing and looking at an older (1984) boat. Feel confident in doing preliminary survey on most major areas: hull, deck, rig, engine, etc but no idea on how one might (non destructively) check the integrity of the rudder and post. My main question is the condition of the rudder post and possibility of crevice corrosion and potential failure.

My only idea so far involves exploration by drilling or even grinding inspection hole(s) in the side of the rudder.

Any ideas, suggestions or experience with this?

Thanks
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Old 13-09-2008, 00:01   #2
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Could you provide more details of the construction please.
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Old 13-09-2008, 08:52   #3
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Might not work for you or your type of rudder construction but I dropped the rudder out and took to the local NDT blokes for eddy current and dye crack testing.

Also replaced the rudder stock tube and bearing for good measure while the rudder was off.
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Old 13-09-2008, 10:00   #4
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Quote:
Originally Posted by Wotname View Post
Might not work for you or your type of rudder construction but I dropped the rudder out and took to the local NDT blokes for eddy current and dye crack testing.

Also replaced the rudder stock tube and bearing for good measure while the rudder was off.

I am not sure I would go this far for a purchase consideration but it is indeed the only way to know for sure the condition. It may be something you would consider in your offer to purchase. drilling small hole is not going to tell you much except if water comes out you may need to get in a little deeper. The prospective seller may have an issue with any destructive testing.
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Old 13-09-2008, 17:57   #5
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More rudder details

Thanks for the replies. Thought from the context of my original post that the question was clear but upon re-reading perhaps it may be a bit fuzzy. So to clarify:

I am thinking about rudders that consist of blade constructed around a stainless shaft which is therefore enclosed in the finished structure. The shaft will have some method to prevent it from turnning inside the blade, perhaps tabs or wings welded to the shaft projecting perpendicular to the length of the shaft. The particular boat I am looking at has a skeg hung rudder but the issues that concern me would be the same for a spade rudder.

My main concerns center around the condition of that part of the stainless shaft inside the rudder itself where the metal is not visible and, if wet, could be subject to crevase corrosion. The failure modes I am aware of are the shaft itself breaking or failure of the tabs allowiing the shaft to turn inside the rudder blade.

So, without destroying the rudder how might one confirm that the hidden section of the stainless shaft is not corroded and ready to fail? How does a surveyor address this issue?
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Old 13-09-2008, 18:18   #6
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Skip, all that a surveyor will do is eyeball the rudder, out of water. All that you can reasonably do is eyeball the rudder, out of water. If there is no apparent damage to the rudder post or the point where it enters the rudder, and there are no cracks (not even a hairline that looks like "just a paint crack") in the rudder, and there's no weepage or repair to the rudder, it is presumed 100% good.

If you and the seller, are both very happy, sure, you can arrange to have it removed from the boat, sent out for xray or test holes, whatever you want--but I think the ordinary seller would say "Goodbye!".

Drilling test holes is problematic--they've got to be resealed. And they need to be all over. So go by the exterior, and if you buy the boat, then by all means take it apart for some expensive testing. Xray, ultrasound...you'll probbaly need to go to the aviation or pipeline industries to get that done. Boaters just don't do it, at the "ordinary sailor" level.
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Old 13-09-2008, 20:09   #7
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OK, what next

Well, so far it seems, as I suspected, that there is no easy (non destructive) answer to my original question.

So, a follow up question, am I being overly paranoid? After all, loss of steering at the wrong time could result in the loss of the boat. But, how likely is it that the rudder shaft of a well built 1984 boat would be corroded to the point of failure?

My current idea is to grind inspection holes at 2-3 points in the rudder to take a look, say at the top of the rudder and where the tabs are welded onto the shaft. If they pass inspection then of course seal the holes and go sailing.
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Old 13-09-2008, 20:33   #8
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Tap the rudder with the handle of a screwdriver. Listen for a high register, sharp response. Lacking that, drill some holes to check for infiltration. No water seeping?Grind the holes a bit, fill with epoxy putty, then bottom paint. This isn't rocket science. If there is water, suspect problems. No water, worry about something else.
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Old 14-09-2008, 00:24   #9
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Taking the rudder in both hands...

If it were me I would take the rudder in both hands and give it a light wriggle, feeling for any free play, any strange motion, any sounds other than the clunk and slosh to be expected if it is well mounted and sound.

Then, if all went well I would get a mate to turn the wheel in the boat through the normal range of movement, and as it moved I would push lightly against it to simulate the action of water, feeling and listening as I did it.

Then I would inspect the area round the shaft both externally and internally, as well as checking all pulleys, cables, hydraulics etc. looking for signs of corrosion or wear.

Of course this is all with perfect hindsight. When I brought Boracay I trusted the surveyor and forgot about the rudder completely. Still hasn't fallen off two years later.
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Old 14-09-2008, 08:24   #10
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Skip,

My rudder is a spade arrangement with a 1 & 7/8 SS stock. I agree there is no way I know of to check the condition of the stock or tangs inside the rudder itself.

My view is that the stock does not have a lot of forces on it inside the rudder. The forces are distributed across the stock, tangs and rudder material etc. However the forces are concentrated on the stock immediately where the stock leaves the rudder and enters the boat.

I dug away the rudder material for about a 1/2 inch at the top of the rudder and then had the exposed stock tested. After that it was resealed with an epoxy mix.

Who knows what is happening to the rudder stock and tangs inside the rudder but as there is no obvious water ingress in the rudder I trust it to be OK.

Interestingly, the SS rudder stock tube in the hull showed significant crevice corrosion where it was in contact with the hull material (wood). So much so that I estimate about half of the wall thickness was corroded in places, hence it was replaced. Still it had lasted around 30 years.
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Old 25-06-2010, 11:40   #11
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"I agree there is no way I know of to check the condition of the stock or tangs inside the rudder itself. "
Ultrasound or xray. Both almost unheard of for the mass market, but common for checking pipeline welds, aircraft...things that folks get real up$et about when they fail.
GE's advertising a new ultrasound machine that looks like a PDA with a big mouse attached to it...I wonder if that would be suitable, and affordable, for surveyors or yards to use?
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Old 25-06-2010, 13:01   #12
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The DUS-6 portable ultrasound from China sells for <$6,000.
Prices jump to $20,000 + from there.
Portable Ultrasound
I have no idea how effective any of these ultrasounds would be in examining rudders etc.
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Old 25-06-2010, 14:01   #13
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Dunno about the Chinese, GE hypes the new product as bringing ultrasound to places it never could be brought to, implying 3rd world bush clinics and all. And of course, the "medical market FDA approved" devices can easily be tagged at 10x what the same gizmo would cost on non-FDA markets, where megabuck liability concerns and insurance paybacks aren't an issue.

After all, a CT scan or MRI that "costs" $600 in the west goes for what, $50 in Singapore? (I've probably got the location and exact price mixed up, but one of the eastern countries that 'recently' adopted national health care, has in fact made that ten-fold price reduction happen.)

Heck, if Logitech or Apple sold it as an accessory...the technology ain't classified.<G>
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Old 25-06-2010, 14:16   #14
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How about a moisture meter?. Ultrasound would not work as any entrained air in the laminate will block ultrasound penetration. New boats are not always built with good rudders. Three Hylas 54's broke their rudders on the way to the Caribbean about three years ago. The lower third had no steel reinforcement and the rudders fractured at that point in normal sailing conditions. I don't know if they redesigned the rudders after that experience.
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Old 25-06-2010, 14:19   #15
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GE’s Vscan ultrasoubnd is currently priced at $7,900 per unit.
GE's Vscan puts ultrasound tech in docs' pockets | Health Tech - CNET News
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