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Hull Blacking Process 2017-05-30T15:52:15+00:00

HULL BLACKING PROCESS

A maintenance task loathed by many narrow boaters but a necessity to maintain and protect the hull of your narrowboat

A narrowboat needs to come out of the water every 3-4 years for hull blacking
Pitting on a narrowboat hull is a sign of galvanic corrosion
The narrowboat hull needs thorough preparation before re-blacking

Hull Blacking… The Process!

The key is preparation, as with so many things.

Firstly the narrowboat has to come out of the water. There are three main ways this is done depending upon the marinas’ facilities.

One is lifting by a crane, the other is by dragging the boat out on a bogey up a slipway and finally there is the dry dock. Here the boat is floated into a dock and the water is pumped out leaving the boat “dry” and resting on supports.

Dry docks and slipways are often the most expensive and complicated items for a boat yard to install as they require planning permission and construction.   As a cheaper and much simpler option ‘floating dry docks’ are available in some boat yards. A ‘tub’ container is sunk to the canal bed; a door opens allowing  the boat to sail in; the door closes and the water is pumped out so the boat is now dry and ready for maintenance.

What method you choose may be determined by price, location or personal preference. Check with marinas and boat yards in your area and visit facilities to be sure of getting the best deal for you.

Once the boat is out the fun begins and here the key to the job is preparation.

Preparation

Don’t be alarmed by lots of bright pitting along the hull sides and on the base plate. Some pitting is perfectly normal and is evidence of galvanic corrosion. This is why we have protective anodes.

Look closely at those pits. It’s into all of these you will need to force the new coating to stop the rot. Very deep pitting will indicate an issue either with your  on board electrics, the mooring electrics, your neighbour’s electrics and/or your anode protection scheme. Sort it, blacking the boat will not stop it, only slow it down. Deep pits can be filled with weld or by specialist liquid metal coating systems.

Pressure washing is the preferred method of removing the initial crud that has built up on the hull over the previous two of three years.
Heated pressure washing is even better and the only way to be really effective is with industrial spec washers. Driveway models just don’t cut it.

It’s useful to have helpers at this stage. If possible, by far the best method at this stage is to have someone immediately following the pressure washer and mechanically removing any stubborn bits of weed or loose material. We can’t stress enough here how it is so much easier with a hot high pressure washer and a big scraper to get the stuff off.

Pressure washing and scraping, no matter how good, will not suffice if the job is to be done properly as there will still be some organic matter in the form of weed and inevitably some loose bits you missed.

Sanding

Now it’s time to break out the abrasive wheels.

Some use sanding discs, some use wire discs. The challenge with these products is that they soon clog up as the coating heats up with the friction and starts to melt. This can turn an already difficult, dirty and time consuming job into a real chore.

The ideal solution is a high speed revolving “chipping” wheel that removes the coating with revolving tungsten teeth. Innovative products are available that perform this task and the finish is nearly akin to bare-metalling the hull.

Now, if you’re really game, you can attack the base plate. Why not. Well because it’s hard, not normally quoted for in marina menu pricing and because someone once said it wasn’t worth it. If there’s an older boat out of the water, go and have a look at the base plate. There will be pitting as on the hull sides, it’s just that it’s not so noticeable. Oh, and it doesn’t really matter down there because a) the steels thicker, b) it’s dark,and c) it’ll get scraped off!

Just because the steel is thicker doesn’t mean it won’t corrode. It’s dark! and yes some will get scraped off, but hardly any in reality.

So hull sides at least fully prepared and you have a choice. Now is a good time to have the anodes replaced. Do not paint over the anodes. In any case at this stage inspect all seams, base plate joins, propeller and shaft and any underwater grilles protecting mud boxes or bow tubes.

Rectify any issues such as evidence of cavitation or excessive corrosion.

Remove all debris from the prop and give it a clean & polish.

Primer (Optional)

Some people like to apply an adhesion promoting marine primer coat at this stage too. If you do use primer, ensure it is a specialist marine product suitable for underwater applications. Ordinary primer is porous and you will be wasting your time.

Refer to the manufacturers instructions regarding number of coats and drying times.

Top Coats

Then it’s time to lay on the top coats. Usually at least two are recommended with a third around the water line.

If using standard bitumen products, use a thinner product for the first coat. It will be easier to work it into any hull pitting and you do need to work the first coat in.
Use a brush not a roller. Using rollers for the first coat means that they often slide the coating over the top of the deeper pits, leaving the very bottom of the pit uncoated. Unless you coat the metal, it will continue to corrode. There are no weekends or days off for corrosion!

Having laid down the base coat, working the product into the nooks crannies and pits, refer to the manufacturers re-coat time. This will usually be between 12 and 24 hours depending upon temperature and humidity.

Apply the second coat, this time maybe a bit thicker if using bitumen. Let it cure and apply the third. The third coat need only be applied to slightly above the waterline down to the base plate if you want but it won’t hurt to do the whole lot.

Reckon on at least 5 litres of primer, 20 litres of hull protection, 3 or 4 rollers and as many discs as it takes to do the job properly for an average 57 foot narrowboat sides, plus a tin or two for the base plate if you decide to do it.

With reference to the coatings manufacturers product recommendations, regardless of brand, it will take around 3 days to apply 3 coats. In fact a coat goes on in a couple of hours, it’s the drying and re-coat time that needs to be allowed for.
Add a days preparation, and another fiddling about with the prop, touching up the paintwork and chatting and drinking tea, then factor 5 days for a proper job. Question any company who promises a proper job in a weekend.

If you do the preparation, there is no reason why your investment should not be protected for the next three years.

Hull Blacking Process

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