Weed filter in French canals

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pcatterall

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We are planning a lengthy get away through the canal system. My mate has read about a yacht that had loads of blockage problems, they resorted to 'back flushing the system daily'
I don't really understand what is entailed in that? remove/clean impellor etc?
What stratagies for keeping the system clean have you adopted ( we have a Perkins 4108)
Thanks as ever.
 
we did the somme, marne and seine route last year and did not really have any problems but I did check the raw water strainer every few days and took quite a bit of weed out. I carry a handpump purchsed from liddles with varios attachments one of which fits perfectly on strainer inlet pipe. 3 pumps of handle sends a bolt of air down. Used this in salcombe with great success for clearing blocked seacock also useful for sinks toilets etc. I think Grehan has adapted a dinghy foot pump to do same. (apologies if it is not you Grehan).
 
pcatterall said:
I don't really understand what is entailed in that? remove/clean impellor etc?
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The weed shouldn't get as far as the impellor - it should all be caught in your strainer. Presumably you know how to clean/empty that. The extra bit for really weedy areas is in clearing the pipe from skin fitting to strainer - either with a stick if it's all mounted in a straight line, or with a pump as described above.

Pete
 
We took our previous boat through the Forth & Clyde canal twice every year from 2000-2009 (apart from 2004). There was a huge amount of duck weed in several places in 2000. At one point we were turning the engine off and back flushing every lock in a series of locks. The weed not only blocked the strainer but also choked the metre long pipe leading from the strainer to the skin fitting.

It would have been a big problem but I was lucky to have something on board to make flushing easy. My really old dinghy foot pump fitted inside the filter and close to the inlet . So I took the cover off, pulled the filter and cleaned it. Then I used the pump to blow air back and could feel pressure building before a sausage of duck weed blew out under the hull.

I improved the design for following year by using a stirrup type pump and better seal over the inlet. The weed problem vanished after a few years once the canal was being used regularly so didn't need the pump after 2002.

This works well if the problem is very fine weed and I think that's the main problem. Coarser weed is mostly stopped by strainer on the outside of the hull (assuming you have one). So only fine duck weed gets through into the pipe.

Certainly worth making up something that seals over the inlet inside the strainer and connects to a dingy pump.
 
We also went north to south through the canals and rivers (Calais-Port St Louis) and only cleaned the filter once. Motor boats with water inlet mounted shallower were clearing their raw water strainer twice or three times a day. All depends where the pickup is situated I guess. Dont let it put you off, it is a fabulous journey and one you wont forget ! :)
 
I have done the canal trip through France twice each way, once in 1988 and once in 1997, both times heading towards the Med in March/April and returning in September. Weed was an ongoing major problem, especially if the maintenance staff had been cutting it nearby! It's essential to have a good, accessible strainer that you can quickly get to and clean. For some reason, most blockages tended to occur just when it was least convenient to stop, Sod's law in action! Another problem was polythene bags, which easily got sucked into the cooling inlet - the best method to get shot of them was to remove the top of the strainer and fit an Avon dinghy footpump hose - the hard plastic nozzle is a good fit for the top of my strainer - and jump on it - the resulting air blast was always effective in clearing the blockage.
 
I intend to do this journey in the next couple of years. I know what it is like to have the inlet blocked and the engine start to overheat and I dread to think of the consequences of dealing with commercial barges/locks when the intake blocks.

I was wondering whether to fit a second water intake with the old-fashioned type of filter that screws onto the skin fitting (not a vetus plastic bowl job), and a three way valve. Not a difficult modification and then if one intake gets blocked you just turn to the other which would be on the opposite side of the hull.
 
I wouldn't make another hole in your hull just for this trip - however, you could consider fitting a 'T' piece in one of your cockpit drains or your sink drain, if either would be suitable, with an inline strainer and changeover valve as suggested.
 
pcatterall said:
So back flushing refers to just the filter/sea cock and we need to get/adapt some device to do that.
Click to expand...

It depends on where your filter is located, if it is easy to get at, then just taking out the strainer and cleaning it may be easier or even buying a spare strainer so you can just swap and clean at leisure.

The time of year is a significant factor, i.e. when grass is cut and dumped in the canal (I had to go over the back a few times to get weed off the prop) also late in the year when the water has warmed up and there is a significant amount of algae bloom.
 
weed

Had nothing in the filter at all on the Marne route in April/May 2003
Must be as others say, a time of year thing! (saildrive with Vetus Plastic inlet strainer above engine)
 
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