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Cleaning of hulls?

Hello, We are moving from sailing on the sea onto the canals. Every year we clean off, scrub and anti-foul the hull. This makes a big difference to the speed, commonly going from 5.5 to 6.5 knots at the same engine revs. We notice that, on the canal, many hulls are weedy and rough and never cleaned. The speeds on the canal are between two and four knots so the drag must be quite high with a surface area of about 715 sq ft on a full size boat. I know that many are now having smoother epoxy on the bottom but still no-one seems to scrub off.
Do narrowboaters notice a big difference after blacking? If so, why do they not spend an hour or two scrubbing the fouling off?
Baffled, Andrew and Val.

Asked by: Andrew Durrant  | 10.09am, Tuesday 6 July

WW says:

Interesting point- it must be said that on rivers, you can notice a difference- though most boats that sport a significant weed growth are based on river navigations, or hardly move...!
When on canals, abrasion in narrow locks, contact with the side and, frequently, the bottom of the canal means that weed doesn't hang around for long!
I once spent two weeks in summer moored up on the River Soar, the weed around the waterline was horrendous- however, few locks along the Trent and Mersey canal, and it has all but been scraped off!
Mainly fouling on narrowboats is limited to just around the waterline, as light penetration is fairly low in most canal environments- although slime is quite common, as is a general biofilm. If boats move regularly, fouling does not seem to be a big issue- even for GRP boats on canals. Also the time and effort for scrubbing off, plus not being able to use intertidal scrubbing points, as you might in a south coast marina, preclude most owners from bothering. Some canal water conditions are also far from ideal for weed growth anyway!
I am sure other readers, and WW writers, will have an opinion!

Mark Langley  | 11.24AM, Tuesday 6 July

Generally, fouling after winter seems to be minimal- certainly on most canals. Bitumen (and its derivitives) does have some properities which restrict growth.
As for fouling on the bottom plate, I have never seen a dry-docked boat with any weed growth on the baseplate- infact, nothing more than about 6 inch below the waterline, unless it has been static for many many months, over a hot summer!
Once on rivers, I agree fouling can be more of a problem, but even some metal boats on the Broads, Sea Otters, for instance, remain fairly weed (and zebra mussel!) free until very late in the summer.
If you come alongside a bank, you will probably scrape any remaining weed growth off as you approach the bank- or in locks, as I mentioned earlier! If you see how easily hull paints are scraped off, you can see that plants don't really stand a chance!

Mark Langley  | 3.29PM, Tuesday 6 July

Readers say:

Hello again,
Thanks for the reply.
I was thinking more of tying up just off the bank and using a stiff broom under the water. A special cranked one with a float attached could be used to scrub the bottom plate, like the one made by Kiwiproducts. As you rightly point out, a regularly used boat will stay reasonably clean but many boats must be badly foulded after the winter.
Cheers Andrew and Val.

Andrew Durrant  | 1.51PM, Tuesday 6 July

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