How to stop the wa­ter from get­ting in

Canal Boat - - Back Cabin: -

QIs there a cer­tain height that the ex­haust out­let should be from the wa­ter­line? I have heard on the grapevine that it is 250mm or ten inches.

ALAN THORN­TON, via email

ATONY REPLIES: This seems an easy ques­tion but it is far from that: it de­pends on the age of the boat; whether it was built to com­ply with the Recre­ational Craft Di­rec­tive (RCD); whether it is a hire or pri­vate boat.

I can­not get in­volved in RCD mat­ters: the pa­per­work refers to a great stack of ISO stan­dards which are ex­cep­tion­ally ex­pen­sive to buy. If this is a new build to RCD stan­dards, con­sult a sur­veyor. How­ever I sus­pect the 10in/250mm would be the min­i­mum height.

As far as I can see there are no Boat Safety Scheme de­mands about hull open­ing heights for pri­vate boats, but for hire boats they must be a min­i­mum of 10in/250mm above the nor­mal laden wa­ter­line – so best prac­tice is to stick to the 10in rule for any class of boat.

But things are not quite as clear as spec­i­fied above. Given that the rea­son for min­i­mum height is to pre­vent flood­ing when the boat heels or gets over­loaded, you can re­duce it (or even have out­lets below the wa­ter­line) pro­vided cer­tain other con­di­tions are met, such as a re­li­able shut-off valve on the skin fit­ting and suit­able pipework. This mainly con­cerns things such as sink drains, but if the pipework (a metal ex­haust pipe, for ex­am­ple) sweeps up to a swan neck and back down to the hull out­let, then as long as the swan neck is 10in above the wa­ter­line it meets best prac­tice. Ex­haust pipe runs are crit­i­cal be­cause the ex­haust man­i­fold is of­ten below the wa­ter­line, and if wa­ter gets into the man­i­fold you could be look­ing at a new en­gine or costly re­pairs.

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