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baseplate to black or not to black

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2 minutes ago, Dorlan said:

Taken from last October's survey of our 35 year old boat:

 

A protective paint system applied after grit blasting is not "blacking the baseplate", which is what the OP was asking about. It's interesting, but not directly relevant.

 

 

 

Edited by Machpoint005

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29 minutes ago, Machpoint005 said:

A protective paint system applied after grit blasting is not "blacking the baseplate", which is what the OP was asking about. It's interesting, but not directly relevant.

 

 

 

The 'protective paint system' was a couple of coats of Comastic and they have obviously afforded a certain amount of protection to the base plate. It will be blacked again when its next out of the water.

 

 

 

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My narrowboat is almost 40 years old and I have owned it since April 1986. In my ownership I have always painted the base plate every two years . I am a member of a boat club that has a slipway with a trolley that enables me to walk under the boat one end and crawl under it the other . During my ownership I have  had to have two surveys for insurance purposes using two different surveyors and both commented on the advantages of painting the base plate . The most recent survey carried out in July this year concluded ' Troys ' hull below the waterline showed little general wastage and no indications of significant galvanic or electrolytic pitting within the sample areas inspected. For a vessel of her age this is considered exceptional and almost certainly due to the use of good quality original materials ,good initial preparation of the steelwork and regular maintenance over the years . I always use Sealex B130 Bitumen however this year I noticed it is much thinner and easier to apply than previous years . I am convinced that the reason base plates are not blacked is the majority of boatyards cannot get the boats high enough to be able to work underneath .  In another thread I mentioned  my most recent surveyor told me he surveyed  a Braidbar narrowboat  that had pits on the unpainted  base plate of 5 or 6 mm . I should perhaps add my boat is moored in the crystal clear waters of the River Nene , the steel shell was built by Peter Nichols and the boat is 12 volt only so no mains supply with the problems that can generate . 

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1 hour ago, Dorlan said:

The 'protective paint system' was a couple of coats of Comastic and they have obviously afforded a certain amount of protection to the base plate. It will be blacked again when its next out of the water.

 

 

 

Comastic was ace, unfortunately, it is no more.

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1 hour ago, Machpoint005 said:

A protective paint system applied after grit blasting is not "blacking the baseplate", which is what the OP was asking about. It's interesting, but not directly relevant.

 

 

 

I thought Dorlan's posts were very relevant to this topic. Are you suggesting that comastic or bitumastic is not a protective paint system?

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10 minutes ago, Troyboy said:

I should perhaps add my boat is moored in the crystal clear waters of the River Nene

 

This is perhaps more significant than the blacking, or lack of it.

 

 

7 minutes ago, PhilR said:

I thought Dorlan's posts were very relevant to this topic. Are you suggesting that comastic or bitumastic is not a protective paint system?

 

Blacking isn't usually referred to as "paint". It is a protective coating though.

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29 minutes ago, Troyboy said:

My narrowboat is almost 40 years old and I have owned it since April 1986. In my ownership I have always painted the base plate every two years . I am a member of a boat club that has a slipway with a trolley that enables me to walk under the boat one end and crawl under it the other . During my ownership I have  had to have two surveys for insurance purposes using two different surveyors and both commented on the advantages of painting the base plate . The most recent survey carried out in July this year concluded ' Troys ' hull below the waterline showed little general wastage and no indications of significant galvanic or electrolytic pitting within the sample areas inspected. For a vessel of her age this is considered exceptional and almost certainly due to the use of good quality original materials ,good initial preparation of the steelwork and regular maintenance over the years . I always use Sealex B130 Bitumen however this year I noticed it is much thinner and easier to apply than previous years . I am convinced that the reason base plates are not blacked is the majority of boatyards cannot get the boats high enough to be able to work underneath .  In another thread I mentioned  my most recent surveyor told me he surveyed  a Braidbar narrowboat  that had pits on the unpainted  base plate of 5 or 6 mm . I should perhaps add my boat is moored in the crystal clear waters of the River Nene , the steel shell was built by Peter Nichols and the boat is 12 volt only so no mains supply with the problems that can generate . 

My Teddesley built boat is now 40 years old. All the 7 mm (or maybe quarter inch?) plate is original. I have never blacked the base plate but the sides and uxter plate have always been blacked with comastic during my 23 year ownership. The last time this was done the base plate was coated with fresh water molluscs which I was advised to leave on! 

I have no 240 volt on board and I conclude that this + the quality of the old British steel is why it has survived.

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I've just blacked my boat. The base plate was interesting. Wire brushing produced clouds of orange dust  from a strip about six inches wide on both edges of the base plate. It was much worse midships compared with near the anodes. Clearly there is oxygen down there.

IMG_20200822_140219 (002).jpg

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31 minutes ago, PhilR said:

My Teddesley built boat is now 40 years old. All the 7 mm (or maybe quarter inch?) plate is original. I have never blacked the base plate but the sides and uxter plate have always been blacked with comastic during my 23 year ownership. The last time this was done the base plate was coated with fresh water molluscs which I was advised to leave on! 

I have no 240 volt on board and I conclude that this + the quality of the old British steel is why it has survived.

Environment and protection are the key to corrosion prevention. It’s the iron content in the steel that rusts and it does so because the specific type of alloy used to build almost all narrow boats (mild steel) has no specific formulation to prevent rusting. Iron is a universal element, British iron rusts the same as any other iron no matter the ‘quality’ of the steel.

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1 hour ago, Cheshire cat said:

I've just blacked my boat. The base plate was interesting. Wire brushing produced clouds of orange dust  from a strip about six inches wide on both edges of the base plate. It was much worse midships compared with near the anodes. Clearly there is oxygen down there.

 

 

(1) Not any more - it's iron oxide now.

 

(2) This may be more to do with how anodes work (or don't work) than any lack of a protective coating. We don't know.

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13 hours ago, mark99 said:

It's not real world practical. It' s one of the reasons baseplate is thick. The coating will get penetrated anyway soon after blacking unless you never ground the boat.

 

Consider electrolytic corrosion. Is it better to have a uniform metal loss across the bottom plate or concentrated in one or two spots where the coating has failed possibly leading to localised pinholes?

 

 

You spend time blacking the bottom, it gets scraped in a small location and you thus create a hot spot and possible pinhole.

 

Don't take my word for it - see below from the experts who spend their careers trying to protect buried steel. Holiday is the trade name for a break in the blacking/coating. This is re buried steel sitting in an electrolye/electrolytic corrosion so it a direct comparison to a boat in water.

 

 

 

 

 

"Compared with a bare pipeline in the same environment, a coated line can be expected to have fewer leaks during its service life; however, the coated line may have its first leak sooner because corrosion activity may be concentrated at the limited surface area of small holidays.

 

Under special circumstances, this effect can be even more pronounced. Suppose that after some years in operation a bare line develops a leak at the most aggressive location requiring repair or replacement. The corrosive environment would be compounded by the tendency of new steel to be more active (anodic) with respect to older steel, and the unfavorable ratio of anodic and cathodic surface areas results in a concentration of corrosion current and a greater corrosion rate.

 

The decision to avoid this predictable situation by coating the replacement piping actually makes matters even worse! Because the coating is not perfect, some new steel will be in contact with the electrolyte, and the remaining corrosion current is further concentrated at a small surface area where failures may occur in a short time"

Edited by mark99

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Some thoughts about this.

 

If the boat rarely comes out of a marina the blacking on the base plate might stay good much longer as it's not being worn off. If that boat is plugged into a shore line most of the time the blacking might protect the baseplate from corrosion due to galvanization.

 

If the boat is CC'ing most of the time, the blacking will wear off quickly, which is not good environmentally. However there may be less pitting due to the boat not being plugged into a shore line.

 

So perhaps it's worth blacking the base plate in the first situation but not the second?

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19 minutes ago, mark99 said:

 

You spend time blacking the bottom, it gets scraped in a small location and you thus create a hot spot and possible pinhole.

 

Don't take my word for it - see below from the experts who spend their careers trying to protect buried steel. Holiday is the trade name for a break in the blacking/coating. This is re buried steel sitting in an electrolye/electrolytic corrosion so it a direct comparison to a boat in water.

 

 

 

 

 

"Compared with a bare pipeline in the same environment, a coated line can be expected to have fewer leaks during its service life; however, the coated line may have its first leak sooner because corrosion activity may be concentrated at the limited surface area of small holidays.

 

Under special circumstances, this effect can be even more pronounced. Suppose that after some years in operation a bare line develops a leak at the most aggressive location requiring repair or replacement. The corrosive environment would be compounded by the tendency of new steel to be more active (anodic) with respect to older steel, and the unfavorable ratio of anodic and cathodic surface areas results in a concentration of corrosion current and a greater corrosion rate.

 

The decision to avoid this predictable situation by coating the replacement piping actually makes matters even worse! Because the coating is not perfect, some new steel will be in contact with the electrolyte, and the remaining corrosion current is further concentrated at a small surface area where failures may occur in a short time"

This is exactly what we saw on a number of workboats built in the late 70s/early 80s which we were surveyed here. About half had been epoxied from new, the rest had been blacked, and one of them had much love since.

 

The epoxied ones looked quite good at first glance, and the blacked ones quite scruffy. However the epoxied ones were peppered with deep pits and needed extensive steework. The blacked ones, whilst having a a very uneven surface had generally lost no more than 0.5mm and were fit for further service. Despite this, the owner opted to have them epoxied......

 

I think steel quality is the most important factor. As I'm typing this my feeet are being kept by a 1/4" thick steel baseplate that is 50 years old attached to iron sides that will be 85 years old at the end of this month. The last survey found nothing worse than 1.5mm seep pitting in the baseplate. When it finally does need replacing I'm thinking about trying Corten.

 

From a cost benefit point of view I suspect that it is generally not worth spending the money trying to prolong the life of the baseplate by coating the underside of it, but concentrate instead on keeping the inside of it dry. I have seen a lot of boats which have gone from the inside out - particularly ex-hire boats in the area around the bathroom.

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9 hours ago, Cheshire cat said:

I've just blacked my boat. The base plate was interesting. Wire brushing produced clouds of orange dust  from a strip about six inches wide on both edges of the base plate. It was much worse midships compared with near the anodes. Clearly there is oxygen down there.

It's not always about Oxygen.

 

There are increasing numbers of examples of Microbial corrosion on the inland waterways. I have a number of documents of the problem but they are all Pdf's so are not allowed to be posted on this forum.

 

Extract of one of them :

 

 

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.

 

MICROBIAL CORROSION TYPES 1. GALLIONELLA FERRUGINEA

Characteristically leaves a fairly shallow pit of approximately oval shape and a ‘rusticle’ made of ferrous and ferric hydroxide. This is a brown non-toxic insoluble powder with black streaks. It is not rust though a marine surveyor has described it in one of his reports by the curiously contradictory name of ‘living rust’. The name ‘rusticle’ was given to the detritus by Dr. Ballard when he found extensive amounts of the stuff on the wreck of the Titanic. It is commonly found on narrow boats and other canal barges in the form of an orange bloom or paste-like phenomenon, often in rings around deeper pits formed by the thiobascillus ferrooxidans corrosion (see (2) below. Being easily washed off, the orange corrosion is frequently considered to have been eradicated. Not so.

 

Marine Corrosion Solutions (@CorrosionMarine) | Twitter

 

2. THIOBASCILLUS FERRO-OXIDANS Often closely associated with the gallionella species, thiobascillus ferro-oxidans is a sulphur oxidizing bug (SOB). This leaves a similar pit to the gallionella species but with vertical stepped sides and the flat bottom covered with a hard silver-white substance. The latter is tetra hydrated ferrous sulphide and is non-toxic. It appears not to rust but will eventually start to discolour.

 

DEALING WITH A MICROBIAL ATTACK 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..

 

Microbiological Corrosion - an overview | ScienceDirect Topics

 

 

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We always paint the baseplate on Fulbourne, 83 years old and still on the original bottom!

 

 

3018 Aylesbury Dry Docking 5th April 2015.JPG

2007 Aylesbury Dry Docking 5th April 2015.JPG

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I think Cheshire cat's pic of a baseplate suggests a few things, first, that is not pitting, or that weird microbial stuff, the pic seems to show 'rust' and also it has not rubbed off. The theory that whatever you put on the bottom is a waste of time as it will be rubbed off is, in my experience, wrong. Phil R was advised to leave the growth of mussels on, they didn't get rubbed off and the shovels full of the damn things that were removed from our boat in Holland seemed quite happy to live upside down prior to jet washing. I have hit the bottom a few times really hard, maybe concrete or something as well as dragging along the bottom and scraping bricks, bikes and probably the usual selection of guns and knives and on the river Somme unexploded nasties yet when the thing is eventually lifted out the epoxy paint has hardly any visible damage.  I still think that if it gets wet - paint it.

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14 minutes ago, Bee said:

I think Cheshire cat's pic of a baseplate suggests a few things, first, that is not pitting, or that weird microbial stuff, the pic seems to show 'rust' and also it has not rubbed off. The theory that whatever you put on the bottom is a waste of time as it will be rubbed off is, in my experience, wrong. Phil R was advised to leave the growth of mussels on, they didn't get rubbed off and the shovels full of the damn things that were removed from our boat in Holland seemed quite happy to live upside down prior to jet washing. I have hit the bottom a few times really hard, maybe concrete or something as well as dragging along the bottom and scraping bricks, bikes and probably the usual selection of guns and knives and on the river Somme unexploded nasties yet when the thing is eventually lifted out the epoxy paint has hardly any visible damage.  I still think that if it gets wet - paint it.

The only sure way of detecting coating pinholes is via a "holiday detector".

 

A high voltage device that sparks and crackles when it detects a small pinhole as it detects an uninsulated pathway from metal to electrolyte.

 

A coating is both an electrickery insulator and a physical membrane/ barrier.

Edited by mark99

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I think that when you do hit the baseplate its only in a localised area and so not much of anything gets scraped off. We had a colony of fresh water mussels in the middle of the baseplate just aft of the bend for the bow . 

 

I wonder if Tim has got any photos of the baseplate before the new coat of blacking was applied to Fulbourne?

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11 hours ago, Machpoint005 said:

 

This is perhaps more significant than the blacking, or lack of it.

 

 

 

Blacking isn't usually referred to as "paint". It is a protective coating though.

Not as significant as quality of the steel. Midnight was moored at Ripon where the water is relatively clear for the first 7 years and that where the severe pitting happened. The hull sides were 2-packed from new and are still as good as ever. The baseplate was painted initially with Comastic then 2 years later sandblasted and 2-packed. I re-paint every  2 years and thankfully there's been zero deterioration. I was once told that paint on the baseplate would be scraped off in canals but I've seen very little evidence of that even though I've been grounded once and scraped along a few shallow canals.

'Blacking' in my experience usually means 'painting' with something er.... black 

Edited by Midnight

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Re small coating damage. Is it better to lose 10 grams of steel due to galvanic corrosion over 60 foot by 7 foot or 1/2" by 1/2 or smaller?

 

That can be the issue; the coating damage being small can concentrate the galvanic loss to that damaged holiday area.

Rather counter-intuitively the smaller the coating loss the bigger the potential issue in some cases. I will bet every single boat that has a blacked bottom fails a holiday detector test at the docking for recoating stage. Energy and utility pipelines ars rigorously coated and holiday checked prior to soft sand backfill and still are prone to pinhole corrosion even with impressed current cathodic protection.

 

Complicated subject with lots of variables so no hard and fast rules.

 

 

 

Edited by mark99

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6 hours ago, Tim Lewis said:

We always paint the baseplate on Fulbourne, 83 years old and still on the original bottom!

 

Too soon to tell then ;)

 

Mine gets checked every time it's out, but I didn't recoat it last time as it looked fine.  The sides had had enough epoxy scraped off that they got redone though.

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9 hours ago, Tim Lewis said:

We always paint the baseplate on Fulbourne, 83 years old and still on the original bottom!

 

 

3018 Aylesbury Dry Docking 5th April 2015.JPG

2007 Aylesbury Dry Docking 5th April 2015.JPG

 

Brilliant facility. It was just being finished when we guested at Aylesbury.

 

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If it's accessible and you can clean it properly and get underneath to paint it then do it. If you can't then don't bother.

 

The more paint you can get on a hull the better, but I've never painted my baseplate because the one dock where I could crawl underneath I couldn't angle the lance of the pressure washer to clean it properly, and as we know any paint job is only as good as the prep. However I always paint the upswept part of the baseplate at the bow. 

 

Partly I suppose it depends on how thick your baseplate is? If I was on a Springer with a 4mm V-base I'd definitely be painting it, but my unpainted 10mm basepate still looked fine last time I looked with a thin layer of light surface rust that brushed off by hand. 

 

Anyway, you're much better off getting rid of all the bitumen on your hull sides and painting it with a proper paint then worrying about the baseplate.

045.jpg

11 hours ago, mark99 said:

 

You spend time blacking the bottom, it gets scraped in a small location and you thus create a hot spot and possible pinhole.

 

Don't take my word for it - see below from the experts who spend their careers trying to protect buried steel. Holiday is the trade name for a break in the blacking/coating. This is re buried steel sitting in an electrolye/electrolytic corrosion so it a direct comparison to a boat in water.

 

 

 

 

 

"Compared with a bare pipeline in the same environment, a coated line can be expected to have fewer leaks during its service life; however, the coated line may have its first leak sooner because corrosion activity may be concentrated at the limited surface area of small holidays.

 

Under special circumstances, this effect can be even more pronounced. Suppose that after some years in operation a bare line develops a leak at the most aggressive location requiring repair or replacement. The corrosive environment would be compounded by the tendency of new steel to be more active (anodic) with respect to older steel, and the unfavorable ratio of anodic and cathodic surface areas results in a concentration of corrosion current and a greater corrosion rate.

 

The decision to avoid this predictable situation by coating the replacement piping actually makes matters even worse! Because the coating is not perfect, some new steel will be in contact with the electrolyte, and the remaining corrosion current is further concentrated at a small surface area where failures may occur in a short time"

But then one could make exactly the same argument for not painting the hull sides.

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30 minutes ago, blackrose said:

If it's accessible and you can clean it properly and get underneath to paint it then do it. If you can't then don't bother.

 

The more paint you can get on a hull the better, but I've never painted my baseplate because the one dock where I could crawl underneath I couldn't angle the lance of the pressure washer to clean it properly, and as we know any paint job is only as good as the prep. However I always paint the upswept part of the baseplate at the bow. 

 

Partly I suppose it depends on how thick your baseplate is? If I was on a Springer with a 4mm V-base I'd definitely be painting it, but my unpainted 10mm basepate still looked fine last time I looked with a thin layer of light surface rust that brushed off by hand. 

 

Anyway, you're much better off getting rid of all the bitumen on your hull sides and painting it with a proper paint then worrying about the baseplate.

045.jpg

But then one could make exactly the same argument for not painting the hull sides.

The hull sides have anodes fitted, so not a relevant comparison. 

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33 minutes ago, blackrose said:

If it's accessible and you can clean it properly and get underneath to paint it then do it. If you can't then don't bother.

 

The more paint you can get on a hull the better, but I've never painted my baseplate because the one dock where I could crawl underneath I couldn't angle the lance of the pressure washer to clean it properly, and as we know any paint job is only as good as the prep. However I always paint the upswept part of the baseplate at the bow. 

 

Partly I suppose it depends on how thick your baseplate is? If I was on a Springer with a 4mm V-base I'd definitely be painting it, but my unpainted 10mm basepate still looked fine last time I looked with a thin layer of light surface rust that brushed off by hand. 

 

Anyway, you're much better off getting rid of all the bitumen on your hull sides and painting it with a proper paint then worrying about the baseplate.

045.jpg

But then one could make exactly the same argument for not painting the hull sides.

No. There are two main types of corrosion at least.  Oxidisation in O2 rich area and electrolytic. I'm specifically talking about the 2nd. You are now talking re the first. I black the hull and sides to mitigate oxidation. 

Edited by mark99

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