Narrowboat replating.

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jakeroyd

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Apologies if this is not quite the right Forum for this question.

I am planning ahead for when the yacht becomes too much to handle and am considering narrowboats.

I understand the system used when the consruction is given as someting like 10/6/4 (10mm bottom , 6mm sides , 4mm top)

What i would like some guidance on please is replating.

I assume when surveyed the plating thickness can be measured by ultrasonics etc.

1) How much does a boat have to lose of the original build thickness before replating is required ?
2) How much on average is lost per annum from the bits in the water ?
3) What would an average cost be for rebottoming say a 58 footer ?
4) How does replating affect sale values?


And any other issues related.

Thank you in advance.................
 
I know a replated Narrowboat sank when trying to cross from South Dock to Limehouse. It was so low in the water it flooded through the engine vent and she foundered.
 
Ramage said:
I know a replated Narrowboat sank when trying to cross from South Dock to Limehouse. It was so low in the water it flooded through the engine vent and she foundered.
Click to expand...

The replating was only incidental - the real culprit was the air vent just above the waterline, popular amongst older NBs with aircooled engines (usually Listers)

You'll get more help on the canalworld forum where it is a perennial topic.
Personally I would do it - unless it was a small patch.
Usually on inland waters (no salt) a good quality hull with anodes should last 30 years. That would be one of a good quality specification 10/6/4 -baseplate / sides/ roof.
Invariably it's an old 'Springer' V-bottom hulled boats where the original skin was 3 or 5mm (later).
Costs vary from £2k to £6k depending on how much is needed and you may/will need to strip out a lot of the inside as well.
 
You have obviously been doing your narrowboat homework, but I can answer some of your questions, however I must warn you they are generalisations and may not necessarily apply to the vessel you look at.

The standard plate thicknesses for narrowboats of a reasonable quality is 10/6/4 and only the Springer built boats habitually used 5mm steel for the construction of the hull and unusually were vee bottomed. Although Springer boats do not have a great name for quality, they sold in the thousands and were the first boat for many proud owners. Today they can be picked up quite cheaply and for the size of boat, a real bargain. However, 2 or 3mm (or more) rust pits on a hull that will be at least 24 years old maybe the reason for the low price.

If you are considering spending more than just a few thousand pounds I would always recommend you get a hull survey from a competent surveyor who has experience with steel boats. Although some surveyors are good all-rounders, it is often horses for courses and there are surveyors who I would be delighted if they checked over a steel hull for me, but I would not ask them to go near a fiberglass vessel, and visa-versa. The hull survey should include an ultra-sonic map of the hull, anything less than 4mm is questionable and the surveyor should be able to advice you what work needs to be done. Please note that a survey report which has been commissioned by the owner, or another potential buyer may be interesting reading, but is no guarantee to the condition of the boat in question. The surveyor only has an obligation to the person who commissioned the report and not another third party.

If you were to drop a length of untreated steel plate into the river it will rust at a rate of approximately 0.1mm per year. From this you can understand why the bottom plate on most narrowboats is left untreated. However there are a number of factors which accelerates corrosion, oxygen is one factor. Look at a poorly maintained steel hull and you will see a band of rust around the waterline. This is where the oxygenated water is in contact with the steel as the water constantly laps the hull.

If the corrosion is sufficiently bad, this can be repaired by overplating a strip of plate around the hull. However in practical terms, it is easier to take the plate down to the chine where the bottom plate extends outside from the side plate and up to one of the rubbing strakes.

Electrolytic action between differing metals also causes corrosion. This is often in the form of pitting and can be quite local or over a wider area. It can affect just one side of a boat and even just one sheet of steel on a boat. It is accelerated in a stronger electrolyte, for example salt water or if there are stray electric currents passing through the water. Due to its more local nature, a plate appliqued over the affected area is usually sufficient.

In the most extreme case a complete hull can be overplated, but this is usually reserved for older narrowboats with 8 or even 6mm bottom plates, or our old friend the Springer. However, unless there is another important reason to retain the vessel it may not be viable with the cost outweighing the value.

A vessel which has been overplated should be examined to make sure the job has been carried out properly and to ensure there are no areas that have been missed but, assuming everything has been done correctly, it should not be detrimental and in some cases will enhance the value. Whatever the financial implications, it will always extend the life of the boat and although not a narrowboat, living in a vessel which is nearly 120 years old, I would be very nervous without a bit of overplating here and there...

I hope this is of help

Chris Hanley

N.B. If you do need any overplating work carried out on the Thames I would recommend talking to Big Dave at 4 All Marine near Chertsey.


jakeroyd said:
Apologies if this is not quite the right Forum for this question.

I am planning ahead for when the yacht becomes too much to handle and am considering narrowboats.

I understand the system used when the consruction is given as someting like 10/6/4 (10mm bottom , 6mm sides , 4mm top)

What i would like some guidance on please is replating.

I assume when surveyed the plating thickness can be measured by ultrasonics etc.

1) How much does a boat have to lose of the original build thickness before replating is required ?
2) How much on average is lost per annum from the bits in the water ?
3) What would an average cost be for rebottoming say a 58 footer ?
4) How does replating affect sale values?


And any other issues related.

Thank you in advance.................
Click to expand...
 
I made the transition in 2011 and bought a ten year old boat where the plates had corroded by...... Absolutely nil mm, still 10/6 on the hull and side to the gunwale. So you should have no trouble buying a boat up to at least 30 years old, which has no need of replating.

So this needn't be your biggest concern prior to buying a narrowboat.

Generally, when a 10mm plate gets down to about 3mm or 4mm, those who seem to know, seem to suggest replating.

I have frequented www.canalword.net since about 2010 and, between here and there, all my boating info is covered.,
 
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