Frequently Asked Questions About Narrow Boat Hulls Answered.
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Tue Jan 26, 2016 at 10:22am

At Whilton Marina we frequently get asked questions about steel narrowboat hulls. So in this article we will share these popular questions and give you the answers.

How Do I Know What Condition a Narrowboat Hull is in?

Generally speaking we don't know what the hull is like on the used boats we have for sale, unless the boat has had a recent hull survey carried out. This is why as a company we always recommend a prospective used narrow boat purchaser to commission a survey to be carried out on the boat before proceeding with the sale. 

How Thick Should the Steel be on The Hull?

For insurance purposes the minimum hull thickness must be 4mm.

The majority of modern narrowboats are built using 10/6/4mm plating or steel thickness specification, 10mm is the steel thickness on the hull base, 6mm the sides and 4mm the roof.

Why Do You Black The Hull?

Blacking the hull is a way of maintaining the condition of the boat and protecting it from rusting and should be carried out every 2-3 years. If Two Pack Epoxy paint is used then you are able to go 5-6 years before reapplying.

Can I do the Blacking Job Myself?

Yes if you want, but once you realise the time and effort that is required to complete the task you will appreciate that paying for this service is well worth every penny!

How is The Boat Taken Out the Water to Work on The Hull?

There are three different ways for getting the boat out of the water so that the whole hull can be inspected and treated if necessary.

  • Dry dock: where the boat is floated into a chamber and then the water is removed.
  • Cranin: but this can be an expensive option.
  • Slipway trailer: the boat is floated onto a trailer in the water and a tractor pulls the boat out. This is the most cost effective and popular choice.

What is used to black the hull?

There are two types of coatings which can be used to protect the hull, Bituminous and Two Pack Epoxy.

Epoxy paint is more expensive but it will last 5 – 6 years once applied and a Bitumen finished coating will last around 2 – 3 years.

When opting to use Epoxy the boat has to be grit-blasted to produce a perfectly clean surface before it is applied, this is why it is a more expensive option. However it will save you money in the future saving on the amount of dry docks needed.  

NOTE: You cannot apply two pack to a boat that has been blacked with bitumen previously. All east west narrowboats were blacked with two pack from new.

How Long Does It Take To Black a Hull?

It’s basically a long, messy and hard three day process.

Day 1; The boat is taken out of the water and pressure washed to remove muck and grime, the old blacking and debris like weeds, mud, and rust. The hull is now ready for the new application of paint. If the water line needs more attention, a machine can be used to work on this area. This machine is called a “scrubbler” if it is used during the blacking process it will usually incur an additional charge.

Day 2; Now the hull is cleaned it is ready for painting. The application has to be done manually with a small roller. The paint has a similar consistency as tar so has to be applied in small sections as the paint goes hard very quickly, therefore no machines are used and it is a timely messy job.

Day 3; Repeat day 2! The second coat gets applied and if required you can ask for an additional coat around the waterline (this may incur an additional cost). The boat is then left for 48 hours to dry before it is returned to the water.

How Much Does It Cost to Black a Hull?

We have supplied some estimated price examples using Bituminous paint on 3 different sized boats, each marina or contractor will have their own individual prices so please only use these costs as a rough guide;

Bituminous paint;
57 foot - £820
70 foot - £1000

Epoxy paint;
57 foot - £1,130
70 foot - £ 1,400

What Should I Do to Keep the Hull Well Maintained?

Unless you suspect a problem with your hull, or if you've just had a recent hull survey, then your boat does not need to be taken out of the water every year, but it should be preferably be taken out every two to three years.

Careful cruising will go a long way in protecting your hull! Crashing through ice will damage the paint protecting the hull, as will crashing into banks and locks, so responsible cruising will lessen the chances of the hull being damaged.

When the narrow boat is out of the water you can get the hull pressure washed to enable you to check the hull and stern gear. It is important to check for rust or pitting, particularly round the waterline.

The sacrificial anodes should never be painted over when painting the lower part of the hull as this would prevent them from working.

What Are Anodes?

The correct name for these important lumps of metal is a ‘Sacrificial Anode’ and they form a key part in the boat’s battle against corrosion. Put simply, they have a higher electrochemical value than steel, which means they corrode away faster. They are basically blocks of magnesium which are bolted to the hull at the bow or stern.

Why are the Anodes on a Steel Hulled Narrowboat Important?

The “sacrificial anodes” corrode in place of the metal of the hull and prop, thereby giving protection. So it is important to check the anodes, as their purpose is to prevent electolytic corrosion of the steel plate and the bronze stern gear. If the anodes are half wasted it is vital to replace them to prevent pitting and corrosion of the steel hull. If you do not do this then it can be a very costly mistake.

If the hull is corroded because the anodes are not doing their job properly it can be one of the most expensive things to put right, as it may mean that some re-plating needs to be done to the hull.

What is over plating/re-plating?

Over plating and re-plating are actually the same thing and a boats hull may need a full over plate, side plating, bottom plating or just patching. Quotes for over plating work can vary enormously due to the various degrees of work that may need to be carried out. Watch our video for more information...

Who Decides a Narrowboat Needs Over-plating/Re-plating?

A qualified marine surveyor is the ONLY person that can survey a boat AND then issue it with passed certificates.

Does the Condition of The Hull Affect my Insurance?

Yes! As mentioned above the hull should meet the minimum thickness of 4mm plating or steel thickness specification.

You will need to have a hull survey carried out by a qualified marine surveyor. During the survey the surveyor will inspect the hull (and other areas of the boat if you have a full survey) he will measure the thickness of the steel and check for damage and pitting.

If any overplating work needs doing to meet the 4mm minimum requirement he will recommend this in his report. Once the work has been completed the surveyor will return, check the work and if he agrees it meets the correct standards he will present you with a certificate.

We hope we have answered all your questions regarding narrowboat hulls but if there is anything we have missed, please give us a call or leave us a comment below and we will get back to you!  



Brian Hutchins | Thu Feb 18, 2016 at 2:46am
Is polyurea a viable hull coating for narrowboats? What sort of cost might this coating incur?
Whilton Marina | Wed Feb 24, 2016 at 3:31pm
Hello Brian, We have never come across a steel hulled narrowboat that has been coated with Polyurea. We believe the challenge with covering the steel in this product is that all rot, rust and corrosion must be removed and fixed before applying, such as it would with Epoxy coatings. The best thing to do would be to speak to a manufacturer or supplier of Polyurea who may be able to help you with this query.
Claire | Sat Dec 17, 2016 at 10:38am
Shell of narrow boat need metal thickness survey ? Approx cost please
Vic Hall | Sun Jan 1, 2017 at 1:11pm
Hiya and Happy New Year!Can you help me with a simple query? I am repainting my boat this Spring. Do I take the blacking onto the cheeks at the front (the parts that project from the hull that come into contact with lock walls etc)? At present the previous owner painted it with the standard gloss colour of the boat and stopped the blacking under the cheek. It seems to me to be easier to maintain the cheek in good condition if it is blacked. I intend to use Multiforte down the length of the boat to meet the blacking so it is only the front that I am concerned about.Thanks very much Vic
Whilton Marina | Wed Jan 4, 2017 at 12:28pm
Hello ClaireA hull survey costs between £400 and £500 depending on which surveyor you use. There is a list of surveyors local to our marina on our website in the Buyers info section, or copy and paste this link into a web browser to find our page on narrow boat surveys and surveyors:
Whilton Marina | Wed Jan 4, 2017 at 12:44pm
Hello Vic, I think you mean the rubbing strakes, (which are a steel reinforcing strip welded along the side of a narrowboat or canal boat’s hull, usually from one end to the other, to protect the sides of the boat from knocks and scrapes when mooring and in locks)We wouldn't normally black the rubbing strakes on a narrowboat, but obviously it is down to personal preference and is up to you if you wish to black them. Narrowboats are normally only blacked below the waterline for aesthetic reasons.
Mary | Thu Feb 16, 2017 at 6:50pm
Would appreciate a ball park figure to over plate 42 ft narrow boat including weed hatch, bitumen and anodes. Timeslots available for this year would be appreciated. Boat built 1989 by brummagem
Whilton Marina | Mon Feb 20, 2017 at 3:13pm
Hello MaryUnfortunately due to the amount of narrowboats we sell, we do not have the capacity to take on any overplating work on other boats.
David Obrien | Mon Apr 3, 2017 at 5:27pm
Can you take a wide beam boat on the open water
Whilton Marina | Tue Apr 4, 2017 at 3:34pm
In general, narrowboats and widebeams have been designed for inland use, i.e. on canals and river navigations.Most can also handle estuaries and lakes, provided the waters are reasonably protected and care is taken about tides and other currents. The engine may not be powerful enough to make headway against fast flowing water.However, it is possible to take one across the English Channel, or for a short coastal journey. But (very important!) only with careful preparation, appropriately skilled crew, the correct equipment, and the right weather. You should also check your insurance policy as it may not be valid.
Joseph | Wed Apr 5, 2017 at 12:27pm
Is there are minimum number of times a boat can be overplated? Does this affect the chance of getting insurance?
Pat Craven | Fri Apr 14, 2017 at 3:39pm
I am looking to buy a canal boat and am very interested in one that the owners do not know who the builder was. Should this be a problem?
Whilton Marina | Tue Apr 18, 2017 at 1:17pm
Hello Pat, Narrowboats usually have a plate somewhere on the boat with the builders name. However if you can't find a plate and don't know the builder it should not be a problem, and does often happen with older boats.
Whilton Marina | Tue Apr 18, 2017 at 1:31pm
Hello JosephI think you mean maximum, and not minimum, when you asked the question "is there a minimum number of times a boat can be overplated and does it affect the insurance"A narrowboat can be overplated for a second time. The first lot of plating would be removed and re plated once again. However if the first lot of re plating, once removed showed excess wear on the original hull, it could mean that the boat may not be able to be replated again and would mean the end of the boats life.For insurance purposes any re plating work should be checked and signed off by a suitably qualified marine surveyor, the insurance company would want to see written evidence that the work had been done to a satisfactory standard.
Dave | Tue Apr 18, 2017 at 9:30pm
Hi are all hulls built as one space or are they separated into sections? So if I have a leak into the front (e.g.from fresh water tank) will the water flow to the back of the boat as it is lower and where I can inspect it from a hatch?
Whilton Marina | Mon Apr 24, 2017 at 11:58am
Hello DaveNarrowboat hulls are built in sections which are called bulkheads, however potentially any water leak could fill the whole of the hull. There are inspection hatches to enable sight of inside the hull to check for water.
Hannah | Wed Jun 28, 2017 at 6:23pm
Is it okay to purchase a second hand boat that has been entirely over plated? The one in question has been surveyed and is in good condition, but will this effect the re-sale value in, say, 5 years?
Whilton Marina | Mon Jul 17, 2017 at 2:48pm
Hi Hannah, We would always advise to have an independent hull survey done when buying a used narrowboat, this especially applies to ones that have been over plated. If the overplating has been done correctly and was signed off by a surveyor at the time the work was done, and a current hull survey was undertaken with a satisfactory outcome, there is no reason not to buy a narrowboat that has been over plated. The re-sale value in five years time will obviously depend on the condition of the boat and the market at that time.
phil | Wed Jul 19, 2017 at 5:47pm
Hi I have a new widebeam boat brought from New 2years ago. The fresh water tank filler under rear deck has cracked & broke away we had no way of telling this so over time the hull filled with water when we did find this out we pumped out over 100gallons of water. We got back to company we brought from they will deal with water tank & hopefully any damage to wood panelling inside. Could you tell if there will be long term damage in future to the hull. As the company assures there won't be. Will I need marine surveyors report to say there will be no corrosion from this leak in the future. It's peace of mind for me incase I have to go legal against the company as the boat cost over £100000. THANKYOU.
Tony | Fri Jul 21, 2017 at 1:38pm
Does the hull have to be 4mm think to get 3rd party insurance ?
Whilton Marina | Tue Jul 25, 2017 at 11:18am
Hello Phil, If you are worried that there could be long term damage to the inside of your widebeam hull, we would advise you to talk to a qualified marine surveyor who will give you independent advise about this.
Whilton Marina | Tue Jul 25, 2017 at 11:33am
Hello Phil,Yes that is correct the minimum thickness of a narrowboat hull is 4mm to get third party insurance.
Norman Almond | Thu Aug 10, 2017 at 3:57pm
Thinking about anodes and welding them to the hull., Is there a fire risk inside the boat if it is spray foam insulated. Do you have to gain access and remove insulation or other flamable material before welding. I agree there should be more than two at the bow and two at the stern.
Whilton Marina | Mon Aug 21, 2017 at 4:22pm
Hello Normand AlmondWe recommend welding two annodes at the front of the boat, one either side of the bow which is not a problem due to the water tank being in situ, and two annodes fitted to the outside of the engine bay where the engine is situated. This won't cause a fire risk because of where they are situated. (We do not recommend fitting of annodes midships due to the fact that they might get fouled up in narrow locks)
Morgan | Fri Sep 1, 2017 at 11:09am
Hello I've had my narrowboat sand blasted and blacked by a boat builder company 6 months ago and my hull has lots of rust spots appearing all under the water line is this due to poor workmanship by the boat builder or could there be another reason for these rust spots ??
Whilton Marina | Mon Sep 11, 2017 at 2:33pm
Hello Morgan, It's not easy for us to comment on your query re possible rust spots on your narrowboat hull. We would recommend that you go back to the company that did the work and ask them to look at it.
Adrian | Sun Sep 24, 2017 at 11:22pm
Has anyone mounted a rising platform/turntable for a small car anywhere on a narrow boat?
Whilton Marina | Mon Sep 25, 2017 at 1:07pm
Hello AdrianWe are not aware of any narrowboats with car decks on board. Probably not a good idea due to the weight of a car being on board and could make the boat very unstable. Best to tick with bikes aboard.
Mike | Thu Jan 4, 2018 at 5:27pm
I plan to have some welding done on my elderly narrow boat soon and would appreciate advise on what electrical systems and equipment needs to be disconnected to protect them - many thanks.
Whilton Marina | Tue Jan 9, 2018 at 12:54pm
Hello Mike, the only system we recommend is that you disconnect the battery's, this should make it safe to start welding.
Mark Jones | Wed Feb 28, 2018 at 10:53pm
If a narrowboat is to be over plated is it common practise to fill the boat with an inert gas to stop any flammable material catching fire during the welding process. Secondly, after over plating is there a requirement to remove some of the ballast to counter the increased weight of the boat, and stop the boat sitting low in the water.
karen goode | Mon Apr 9, 2018 at 5:22pm
hi I'm looking to purchase a 1925 converted bantock it's 70ft and needs a new base plate what is the cost involved to do this and would it be worth it
Colin evans | Tue Apr 17, 2018 at 10:17pm
Hi, not a question: I just wanted to say many thanks for the really helpful expert knowledge & info on your websiteCheers
Whilton Marina | Mon Apr 23, 2018 at 3:35pm
Hi Colin, we are pleased that you found our website information useful!
Whilton Marina | Mon Apr 23, 2018 at 4:06pm
Hello Karen (a few questions above) It would cost somewhere in the region of £12,500 including VAT to overplate the base plate on a 70ft boat. This would give the boat a new life for several years. However it depends on what you are paying for the boat as to whether it's worth it. A surveyor would be able to advise on a value for the boat once the overplating work was completed.
Richard Brennan | Tue May 1, 2018 at 9:26am
My boat is 10/6/4 but what should the 'counter' thickness be?
Reg H | Fri May 11, 2018 at 2:05pm
Before repainting metal narrow boats, there seems to be several methods of removing rust and paint.. Sandblasting, Grinding down and Shot blasting get most mentions. There is also something called 'scabbing'. What is it and which method is best for a complete repaint?
Reg H | Fri May 11, 2018 at 5:00pm
Apologies. The process I queried about in my previous comment should have read 'scabbling'!
Whilton Marina | Mon May 21, 2018 at 12:17pm
Hello Reg, Scabbling can be used to remove paint and rust, but are not the easiest method to use on the hull, which is probably why it's not often mentioned. However scabbling is sometimes used on the roof of a narrowboat to strip it back to bare metal in preparation for a repaint. Care needs to be taken and goggles and safety equipment worn.
Whilton Marina | Tue May 22, 2018 at 3:51pm
Hello Richard (a couple of questions above) Counter thickness is usually the same as the base plate on a narrowboat, so in this instance it should be 10mm
julie devereux | Wed Oct 10, 2018 at 9:28am
I had a survey done on my boat 2 years ago when I brought it but was wondering how often I should get it done. How often should the hull be checked?
whilton Marina | Mon Oct 15, 2018 at 2:37pm
Hello Julie, The hull of your narrowboat will take the brunt of the elements. This means it should undergo regular inspection to avoid leaks and other damage. It’s best to keep an eye on rust, corrosion and pitting, and don’t forget to have the inside of the hull checked over too. Since the hull is normally out of view, you will need to organise regular inspections by a professional. You will be required to take the boat out of the water in order for a marine surveyor to carry out a review of the state of the hull. As a rule of thumb, this should be done every three to four years – or more often if you’ve sustained any accidents. A qualified marine surveyor can inspect cruising damage, hull build quality, outlets and penetrations, and plate thickness
Lois | Tue Nov 20, 2018 at 6:31pm
hi, im thinking of buying a narrow boat but hope to get it surveyed before, im told it has poured concrete in the hull, if it requires replating does this have to be removed first because I cant see how it would be possible, ive done some research, some say its a good thing the concrete and others bad, its a V bottom too, please can you advise? thanks
Whilton Marina | Wed Nov 21, 2018 at 1:41pm
Hi Lois, you do not need to remove the concrete in order to over plate your narrowboat, the only time you may need to is if it sits to low once plated this will be the only way to remove weight to re ballast.
Colin J | Sat Sep 7, 2019 at 7:32pm
Currently looking at buying a narrowboat/widebeam and have done lots of research etc. However was quite alarmed recently at the number of boats that had sunk (stats via internet). The standard of the new boats seems excellent and my plan would be to buy new however I was almost put off the whole project by seemingly how easy these boats can take on water and sink. Am I being overly alarmist. I just imagine water suddenly coming up through beautifully laid flooring and fittings!
Whilton Marina | Mon Sep 9, 2019 at 3:04pm
Hello Colin, taking into consideration the sheer number of narrowboats on the UK's waterways, sinking is not common. A well maintained narrowboat will not sink. It is important to make regular bilge checks, pumping out any water, especially during wet weather. Installing boat covers will also greatly help to keep the boat dry. We advise to get a hull survey done before purchasing a used narrowboat and get it surveyed every few years thereafter. (this may be required for insurance purposes anyway) We also advise to learn how to use the boat especially when going through locks to avoid catching the boat on the lock cill.
Mark | Tue Sep 17, 2019 at 1:16pm
With the advancement in manufacturing, can I ask what maybe a silly question. Why still manufacture hulls in Steel, is there not a rust proof alternative?
Whilton Marina | Tue Oct 1, 2019 at 2:52pm
Hello Mark, Seaotter make aluminium narrowboats, however they are very costly compared to a steel narrowboat. So maybe it's a question of cost, and traditionally narrowboats have always been made in steel.
Christine H | Sun Nov 3, 2019 at 9:49am
Hi. A friend of mine is looking at 2 different cruiser stern boats. One built by Eggbridge and the other by colecraft. Regarding the hulls, which is better in you opinion. Both have been blacked in the last year.Thanks
Whilton Marina | Fri Nov 22, 2019 at 4:32pm
Hi Christine, Thank you for your comment, Colecraft is a very well known boat builder and to this day they are still building boats, Eggbridge is not as well know, although the quality of the hull will depend on how well it has been maintained over the years.
Tony Sail | Tue Dec 3, 2019 at 9:12pm
The bare metal floor that we can see on our 50ft narrowboat, when looking under the floor boards, is always damp. (We do spend most of our time living on it). Is this normal or have we a slow leak somewhere keeping it all damp. Thanks. Bought a lovely perfect condition 30ft narrow from you six years ago and when i have looked at the metal floor of that one it was dry...but we don't stay on that one for long periods.
Whilton Marina | Mon Dec 9, 2019 at 3:31pm
Hello Tony, The dampness is more than likely due to condensation caused by heating aboard the narrowboat during the winter time. Which would explain why your other boat which was not regularly lived in didn't have the same issue.
Matthew | Sun Jan 3, 2021 at 7:41pm
Hi there,When I got my boat blacked the people at the dry dock said I should get Anoids on the boat. Nearly everyone said they are beneficial, however this one person advised me not to get them. Any idea why?ThanksMatthew
Robert Ware | Thu Jan 7, 2021 at 7:59pm
We live on a narrowboat in a marina. We are connected to shore power and protected by a galvanic isolator (it's one with a pass/fail gauge and I test it regularly). We had new anodes fitted two years ago although the previous ones (at least 4 years old) are also in place and still quite chunky. The new anodes look a bit grubby but seem to be close to the original size. Am I right in thinking that a significant issue with stray current corrosion would result in faster deterioration than expected?
Whilton Marina | Thu Jan 21, 2021 at 12:52pm
Hi Robert, Yes you are right by saying the stronger the current the faster deterioration. The anode absorbs the current, therefore if the anode isn't deteriorating the boats hull will be fine.
Whilton Marina | Thu Jan 21, 2021 at 12:57pm
Hi Matthew, we couldn't comment on why the one person said they needed replacing, was he a hull surveyor? I would always follow the advice of a professional than the general public.
HM | Sat Mar 20, 2021 at 8:22am
Hi there, do you need to have regular surveys of a narrowboat once bought? I.e after a pre-buying survey is complete, would you re-survey every few years? Thanks
Whilton Marina | Mon Mar 22, 2021 at 10:55am
Hi HM, you would only survey your boat pre purchase, unless you've had a collision with the boat or you have concerns about the hull.
Jodonald | Thu Apr 8, 2021 at 12:41pm
Hello. I am a prospective narrowboat owner. I have read a lot of useful information about steel hulls and all the steps on their use , repair, life expectancy, standards, treatments and more but have not seen any data on steel quality standards. Is there a preferable type of steel used in the construction of narrowboats? Is there a test for steel quality included in any testing.
Adrian | Sat May 22, 2021 at 6:31pm
Hi. I've spent half a day, trawling through used narrowboat ads and I'm fine with most of the terminology. However, I've just happened upon an ad which states that a 47ft boat has a "blue water quality hull".With little context, can you explain what this means please? Thanks.
Dave | Wed Dec 15, 2021 at 10:31pm
Hi. I like the question section!Hull construction. Why is the baseplate made so thick at 10mm as it generally has no contact with anything other than water. If the minimum hull thickness for boat insurance is 4mm, why do they make the sides 6mm thick instead of 8mm , for example? 8mm thick sides would give a lot more working life, right?
John Evans | Mon Feb 14, 2022 at 5:35pm
As a prospective owner (possibly later this year) I much appreciate the valuable advice given here. It has answered a lot of concerns I had.
Whilton Marina | Tue Feb 15, 2022 at 12:41pm
Hi John, Thank you for your kind comments.
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