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Distance Above Waterline For Hole?


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I'm about to fit a second bilge pump to my boat. Before I drill a hole for the waste pipe is there a regulation as to how far the hole should be from the waterline, as a minimum? If not, what is a suitable distance?

 

Thanks

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I would be aiming for around 10in or more if it fits, our kitchen sink is less, but over 10" to the too of the sink.

 

Not that I have ever had it checked, but its common sense imo.

 

 

Daniel

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250mm I think (10") to satisfy Certificate of compliance. However: When building mine I wanted the sink to drain directly but there wasn't enough height for this to happen. No problem said my surveyor, as long as you use marine-grade hose (i.e. half decent pipe with that helical reinforcing will do) and use double SS jubilee clips between it and the sink drain then the top of the sink effectively becomes the height above the waterline.

 

If it is just to satisfy the BSC then I think 100mm (4") is the accepted height.

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For a bilge pump I would make the outlet as high as possible. Maybe fit a non-return valve too.

 

Imagine that the boat was taking on water but the bilge pump stopped working with the outlet below water level. Water could then syphon into the boat and sink it.

 

Alan

Happend to my one time friend's butty.

I agree as high as poss.

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It's my hire boat. The existing pump is manual only, I thought it prudent to fit an automatic one as a back up, particularly a it's basically an open boat. The existing bilge pump's waste is around 14 inches above the water line. Drilling the new one a few inches lower would make it easier to fit the waste pipe to the skin fitting but I'll take the advice on board, and drill it at the same height.

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Could you not use a "Y" adaptor and use the same hole?

 

It would be great if I could but not sure if it's possible. My new pump has 19mm hose the existing is bigger, 25mm maybe. If one pump was working, would it not tend to simply push the water out of the other pump, gravity and all that?

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For a bilge pump I would make the outlet as high as possible. Maybe fit a non-return valve too.

 

Imagine that the boat was taking on water but the bilge pump stopped working with the outlet below water level. Water could then syphon into the boat and sink it.

 

Alan

I would use a vented loop that's mounted high instead of a non return valve.

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Don't forget to route the hose above the outlet and then dropping back down to the outlet.

 

That's certainly more important than the outlet height and standard marine practice. Probably no need to have it vented if the pipe is of reasonable bore, but the top of the loop ideally should be at least a couple of feet above waterline when underway.

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That's certainly more important than the outlet height and standard marine practice. Probably no need to have it vented if the pipe is of reasonable bore, but the top of the loop ideally should be at least a couple of feet above waterline when underway.

 

It's the height of the "vent" that's important (the loop still needs to be higher than the water level at heel), if that's the skin outlet or via a loop vent (you can get loop vent's with remote vents) then the higher the better - more important on rough water and sailing boats than canal boats tho.

Edited by Robbo
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I still think the outlet height above the waterline is important. For example, if a skin fitting near the waterline gets knocked off in lock then you've just got a hole in your hull.

And this. We have only a fiting removed once on 24years, but it happens.

 

Unless you go for a welded steel afair.

 

 

Daniel

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Why do you say that?

 

Daniel

 

Because it stops the possibility of water backing up the pipe into the boat. The loop or gooseneck can cause siphoning however so a break vent is sometimes needed at the highest point particularly if outlet is below the waterline, as in the case of a seagoing marine toilet. In that case though a ball valve would be needed adjacent to the through hull fitting should a hose let go.

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When I had the BSC done on my boat, the guy picked up that the engine 'ole cooling air vents were only about 5 inches above the waterline, and his comment was along the lines of them complying with the rules for private vessels on a canal, but if I was planning on going onto a river, he'd like to see 10 inches or so for safety. Nothing else is less than 10 inches above the waterline. He also mentioned in conversation that 5 inches was acceptable for private vessels, but not for commercial vessels.

 

Now I don't need such good ventilation in the engine 'ole, I'm planning to get at least 10 inches freeboard there by welding plates over the existing vents, leaving enough area for the engine to beathe.

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