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Cabin bilge steel pitting?


Crobot

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Hi Guys,

 

Just wondering if anyone had any thoughts on this..

 

We are currently in the process of drying out the back bedroom of our boat following a leak. I think the water may have been here for some time as there was a fair amount of rusty debris to remove.

 

Once we started clearing it out I noticed a funny circular notch where the steel was much more worn away than everywhere else (picture included). It seems a little strange to me to be so perfectly circular!

 

Any ideas? And furthermore any ideas on whether we should be looking to weld over it?

 

We are planning on treating the rest of the bilges with a rust inhibitor then painting it.

 

The base plate is 12.5mm.

 

Thanks for your thoughts!

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A plug weld?

 

With a 12.5mm baseplate would be more concerned about whether an asteroid is going to hit you than the rust pits.

 

 1mm of steel produces a rust bud 10mm thick, so how much do you think you have lost?

Edited by Tracy D'arth
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It's not pitting.

 

It looks like a bubble. Is it solid and is it definitely steel?

 

There looks to be a layer of rust across the top of the baseplate. Nothing to be alarmed about, I've removed loads off the top of my baseplate. The risk of the bottom rusting through from the outside seems to be a collective fear of narrowboaters in the same way the Gaulish villagers feared the sky falling on their heads. The reality is that it's far more likely to rust from the inside and folk don't think to check beneath their feet.

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Thank you both for your replies! 

 

They both made me chuckle!!!

 

Tracy, we scraped the entire floor of the bilges to remove all the flakey rust and gunk and at it's deepest the flakes were maybe 4mm/5mm which like you say and I've read, equates to about 0.5mm of the original steel.

 

Everywhere else on the floor is fairly level bar this odd little circle which at a rough guess may sink in deeper, maybe about 5mm?

 

Thanks Captain Pegg, I didn't think it was a pit but I didn't really know how else to describe it 😂 The hole itself seems to be very solid..we have scraped all the rust flakes away which covered the entire floor and so what's left is where it's drying out.

 

You are so right, I guess we just want to make sure we do the best we can to prevent any further deterioration and since we have ripped all the floor up might as well so it now!!!

 

I've attached a picture of all the manky rust that was there before. Admittedly not the best pic as it was before we lifted the floor so I took it through a tiny gap!!

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Must admit that on first viewing it looked to me like it protruded into the boat.

 

It's very odd, I think it would pay to have that area inspected from underneath when the boat is next out of the water. It seems to be deeper than the baseplate is thick or is that another optical illusion? 

 

Was something sat on that spot?

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Ahh what do you mean as in bubbled up rather than down? If that makes sense? To be fair my photos arent great. Il try get some better ones to give a better perspective next time.

 

Yeah that's a good idea.

 

I'm not quite sure I understand what you mean about it being deeper than the baseplate? Sorry?

 

As for something standing on it, it does appear that way but there hasn't been anything to my knowledge..

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16 minutes ago, Crobot said:

I guess we just want to make sure we do the best we can to prevent any further deterioration and since we have ripped all the floor up might as well so it now!!!

 

No time like the present!

 

Remove the loose rust, vactan it and paint it - topcoat not just primer -  before putting the floor back, and it will be better than nearly every other boat's bilge for years if not decades.

 

Do *not* waxoyl it no matter how many people tell you to.  It's upside down for waxoyl - great for underneath road vehicles, worse than useless inside a boat hull as it's semi- permeable so designed to let water through it.

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First, can you measure how deep it is?, pits and dents usually look much deeper than they actually are. Have a good scrape/wire brush in it and around it, then a good go with some course emery paper.

 

Get yourself a digital vernier caliper (a useful boat tool) and a little strip of brass about 3mm thick.  lay the brass across the "dent" and measure the depth using the "depth gauge" end of the vernier and subtract the thickness of the brass.

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Just now, dmr said:

pits and dents usually look much deeper than they actually are

 

Oh I dunno, this was yesterday's find.

 

I didn't have the micrometer handy so just used a watermate key as a reference.  2046247778_IMG_20210914_1333504342.jpg.8d367588cdac0f6fbb1e3cbd645a0b88.jpg

 

Microbially influenced corrosion, MIC, on a boat I know had a perfect hull 5 years ago when I looked at buying it.

 

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8 minutes ago, Crobot said:

Ahh what do you mean as in bubbled up rather than down? If that makes sense? To be fair my photos arent great. Il try get some better ones to give a better perspective next time.

 

8 minutes ago, Crobot said:

Yeah that's a good idea.

 

I'm not quite sure I understand what you mean about it being deeper than the baseplate? Sorry?

 

As for something standing on it, it does appear that way but there hasn't been anything to my knowledge..

 

I meant that from the photo it looks deeper than 12mm but as suggested above it probably looks deeper than it is, made worse by the lighting in the photograph.

 

Again as suggested above measure the depth. It may need some localised repair if particularly deep..

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3 hours ago, Crobot said:

 

Once we started clearing it out I noticed a funny circular notch where the steel was much more worn away than everywhere else (picture included). It seems a little strange to me to be so perfectly circular!

 

Any ideas?

IMG_20210915_142244_compress67.jpg

 

Have you had battery acid or something similarly corrosive dripping on this specific location, a small drip would eat a small area and end up being neutralized before it spread.

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32 minutes ago, TheBiscuits said:

Microbially influenced corrosion, MIC, on a boat I know had a perfect hull 5 years ago when I looked at buying it.

 

 

 

You know that the concensus of the Forum elders is that MIC doesn't exist and is just a scam to get boaters to spend more money getting their bums specially cleaned and treated.

 

Stop scaremongering !

 

More MIC pictures .........

 

 

 

 

Microbial Corrosion.jpg

MIC 2.png

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42 minutes ago, dmr said:

Get yourself a digital vernier caliper (a useful boat tool)

 

I much prefer an old style analogue one. The digital ones eat batteries!

 

I bought a lovely Moore and Wright vernier caliper on ebay for £20 recently. A delight to use compared to them horrible digital abominations. 

 

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Couldn't say what this is but corrosion can be nasty on the inside of a boat.  I've seen barrowloads of scale come out of a narrowboat and the same from a Dutch sailing barge. Also look at the join where the sides meet the bottom, that is vulnerable too.  When boats are built they should have good access to the bottom. It should be possible to get the floor up . It doesn't matter about the beautiful design or the brilliant fit out.  Thing is that it takes a lot of work  and money to do this and the customer seldom thinks about the stuff under the floor.  You should not just screw the floor down and build the rest of the boat on top of it as it is a hell of a job to get it up again. Anyway. It should be well painted inside, Mine is painted with bitumen paint, probably not the best choice but I had a budget and it is still fine but diesel and possibly Waxoyl will dissolve it. As ever the answer is paint and then even more paint and keep it as dry as poss.

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12 minutes ago, Alan de Enfield said:

You know that the concensus of the Forum elders is that MIC doesn't exist and is just a scam to get boaters to spend more money getting their bums specially cleaned and treated.

 

Stop scaremongering !

 

I've just spent two weeks in Wigan dry dock with two different boats, and both of them had it, one much more severely than the other 

 

Very aggressive grinding followed by very strong sodium hypochlorite left on for 24 hours then washed off.  Treating it early is the key, which is why I slip my boat every few years even though I use two pack.

 

The surveyor's short summary was "Keep doing what you're doing and I'll see you in five years" which is nice on a 1980's boat.

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Never seen anything like that on the inside of a baseplate but if it really has been wet for some time - and that initial photo does look bad - you might expect to see more than the "flash rust" that is typical of most narrowboat bilges.

 

I can't work out what's going on with the ballast - was this depression covered up by concrete/brick ballast and was the ballast resting directly on the base?

 

Whether it needs attention depends how deep it is, with a 12mm base you have a lot of headroom.

 

I like Owatrol for bilges, you can get it into spaces where there's poor access and it because it purges moisture you don't have to completely remove all traces of rust.  

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7 minutes ago, TheBiscuits said:

 

I've just spent two weeks in Wigan dry dock with two different boats, and both of them had it, one much more severely than the other 

 

Very aggressive grinding followed by very strong sodium hypochlorite left on for 24 hours then washed off.  Treating it early is the key, which is why I slip my boat every few years even though I use two pack.

 

The surveyor's short summary was "Keep doing what you're doing and I'll see you in five years" which is nice on a 1980's boat.

 

Microbially Induced Corrosion (MIC) is a highly unpredictable process but under the influence of micro-organisms, corrosion processes can be rapid, happening in a matter of months compared to the years it would take for ordinary abiotic corrosion to reach serious proportions. This phenomenon is well known in the oil, gas, water and mining industries but is little understood in the steel boating world.

MIC frequently occurs in areas with high nitrate content in the water – this particularly pertains to arable regions of the canal network and particularly to canals and rivers on the east side of the UK and where there is intensive crop farming using non organic chemical fertilizers with consequential phosphate, sulphate and nitrate run-off into the watercourses. Marinas fed by rivers are another risk area and, in salt water environments, it is well known that harbour muds are highly contaminated by sulphides produced by these creatures. Sulphide films are, by their very nature, highly corrosive and the identification of such very obvious. It is usually found under muddy and slimy surfaces, sometimes even behind paint coatings and a very careful visual inspection is necessary to locate it. It is not discoverable by non-destructive testing such as ultrasonic thickness measurement, eddy current testing or the magnetic method familiar to most marine surveyors. The bacteria are often found inside oxidised welds or in areas which contain physical defects such as porosity, overlap or lack of penetration. The microbes leading to this condition can both cause corrosion from beneath existing coatings or seek out pinpricks in the steel coating and cause the reaction to occur from the outside. MIC bacteria can be present under previous blackings and is not eradicated by simple pressure washing. Unless correctly treated, MIC can continue to thrive beneath the coating, emerging as major pitting

 

If a hull is found with evidence of microbial attack, it is necessary to deal with it to try to prevent it recurring. A simple solution is for the whole area to be washed with copious amounts of high pressure fresh water. When dry the area affected should be coated with a strong bleaching agent (sodium hypochlorite) diluted 1:4 with water and left for twenty four hours. Afterwards a second high pressure fresh water wash is necessary followed by recoating. This will probably remove around 90% of the microbes but the only real solution is to blast back to bare steel and to treat any inaccessible areas such as tack-welded rubbing strakes as best one can with the bleach solution before applying the next stage of the coating process. The main problem is that the microbes can continue to live beneath the existing paint coatings and once sealed in with a fresh blacking, the lack of oxygen and light is the perfect environment for them to thrive leading to a risk of corrosion from the inside out. No coatings are entirely proof against a microbial attack from the exterior. Minute pinpricks, mechanical damage below the waterline are all opportunities for the microbes to penetrate the steel and commence the process from the outside in..

 

WARNING SODIUM HYPERCHLORITE IS HIGHLY CAUSTIC AND TOXIC. IT MUST BE TREATED WITH GREAT CARE AND RUBBER GLOVES, WELLINGTON BOOTS AND EYE SHIELDS ARE ESSENTIAL

 

If the pressure washing has exposed areas of bare steel, it is recommended that a zincphosphate rust prevention system such as Fertan be applied. This should be allowed to work over a 24 hour period and MUST be thoroughly washed off with water and a brush to ensure that only the bare steel retains the Fertan before a top coat of Keelblack is applied. This is essential to ensure that any subsequent coating is properly attached to the hull. Nevertheless, the microbes can still live underneath adjacent prior paint coatings so the only certain way to remove the risk of future attacks is by blasting back to bare steel – an expense many owners may not wish to contemplate

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24 minutes ago, MtB said:

 

I much prefer an old style analogue one. The digital ones eat batteries!

 

I bought a lovely Moore and Wright vernier caliper on ebay for £20 recently. A delight to use compared to them horrible digital abominations. 

 

image.png.8299989ccb6fb97165b1cb4f1dd140d9.png

 

This is another one to discuss over a beer or three.

 

Good digital ones are quick, easy and a pleasure to use. Olde analogy micrometers (in particular) are really difficult with their "half binary" system and unless you use them often  its easy to make mistakes

My first digital vernier was great but died when the battery clip failed. My new more expensive one is crap and makes random zero offsets of about 5mm, I have now learned that this is a very common issue with the digitals. 5mm is fine cus I spot that but smaller offsets could really make life bad.

 

Once we get back oop Norf there is a good tool seller at the local street market so if I see a proper olde vernier I might well get it.

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Either slag inclusion in poor quality steel plate (very common) or SRBs, or both. Sulphate reducing bacteria occurs in low oxygen stagnant environments, and produces hydrogen sulphide which attacks iron and steel. Slag inclusion can lead to the formation of small galvanic cells due to the proximity of different materials in the steel. These in turn can give rise to galvanic corrosion and pitting. Galvanic corrosion can also be cause by faulty electrical equipment on the boat.

On the other hand it could just be a poorly painted area which has rusted a bit more than the surrounding material.

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