Bilge pump outlets - height, etc.?

[LittleSister]

Going to be fitting new bilge pump outlets to our 26ft 'project' boat (1 x 15mm, 1 x 38mm), and wondering whether to mount the outlets
(a) higher, so less risk of flooding if a fitting fails but likelihood of staining the old white gelcoat with dirty dribbles, or
(b) lower.

I'm wondering about putting the bigger one at the top of what I would call the boot topping (anti-fouling carried up above the waterline), like the existing exhaust outlet, but this would be only about 6" above the waterline at rest. Want to avoid the cost of a seacock if possible.

Also wondering whether any advantage/disadvantage to transom (fairly steeply sloping facing downwards) mounting versus side of hull.

None of the choices make much difference to the height the water has to be pumped, or the length of run of pipe after the pumps.

What does the team think (before I start drilling holes in the hull)?

 

[sailorman]

Going to be fitting new bilge pump outlets to our 26ft 'project' boat (1 x 15mm, 1 x 38mm), and wondering whether to mount the outlets
(a) higher, so less risk of flooding if a fitting fails but likelihood of staining the old white gelcoat with dirty dribbles, or
(b) lower.

I'm wondering about putting the bigger one at the top of what I would call the boot topping (anti-fouling carried up above the waterline), like the existing exhaust outlet, but this would be only about 6" above the waterline at rest. Want to avoid the cost of a seacock if possible.

Also wondering whether any advantage/disadvantage to transom (fairly steeply sloping facing downwards) mounting versus side of hull.

None of the choices make much difference to the height the water has to be pumped, or the length of run of pipe after the pumps.

What does the team think (before I start drilling holes in the hull)?

fitting it low give a nice loop up & then down to the fitting to avoid back filling.
The Vetus site has good info

 

[BrianH]

I have a very deep bilge sump where I needed to site my automatic pump so the height that I had to lift the water was important on the pump performance. I chose the shortest route by venting into the cockpit where the large drains could easy clear any output and it avoided another hole in the hull.

Another advantage was that anyone in the cockpit is immediately warned of activation without the need of an alarm - it doesn't do to be unaware the ship is filling with water, even if it is being cleared. If below the sound of the pump is warning enough.

 

[Salty John]

On or just above the boot stripe with a loop on the inside to prevent back siphoning.

 

[sailorman]

I have a very deep bilge sump where I needed to site my automatic pump so the height that I had to lift the water was important on the pump performance. I chose the shortest route by venting into the cockpit where the large drains could easy clear any output and it avoided another hole in the hull.

Another advantage was that anyone in the cockpit is immediately warned of activation without the need of an alarm - it doesn't do to be unaware the ship is filling with water, even if it is being cleared. If below the sound of the pump is warning enough.

My bilge sump is similar, i have a water witch sensor & a diaphragm pump in the lazeratte some 12 ft away & a strainer above the bilge sump. No wires in the bilge water

 

[BrianH]

My bilge sump is similar, i have a water witch sensor & a diaphragm pump in the lazeratte some 12 ft away & a strainer above the bilge sump. No wires in the bilge water

With my pump (Johnson Ultima) the “field effect” sensing system is integrated within the pump body - reportedly superior to external (or even internal) mechanical float switches - and thus necessary to be sited in the potential draining area. The wires are, presumably, immune to submersion and where they enter the pump appear to be well sealed.

 

[fisherman]

On or just above the boot stripe with a loop on the inside to prevent back siphoning.

plus anti syphon valve, about £10

 

[LittleSister]

Thanks all.

I chose the shortest route by venting into the cockpit where the large drains could easy clear any output and it avoided another hole in the hull

I'm doing this to get rid of the current unsatisfactory arrangement which vents into the cockpit drains, and splurges dirty water up into the cockpit when you pump, and involves an appalling mess of pipes, multiple t and y fittings, jubilee clips etc.,

On or just above the boot stripe with a loop on the inside to prevent back siphoning.

plus anti syphon valve, about £10

Is siphoning really much of a risk? When you finish pumping it'll be largely pumping air; even at 6" the outlet will be above the water line at least intermittently even if the stern is squatting at speed. (The pumps themselves are well above the waterline.)

 

[john_morris_uk]

I am going to respectfully disagree with several suggestions.

Into the cockpit is forbidden on a coded boat. In survival conditions where the boat is being swept by waves and the cockpit is being swamped from time to time, you don't need the bilge being pumped into the cockpit as well.

I am not convinced that close to the waterline is best either? The disadvantage of higher is that one is adding to the pumping height so the loop up will be a compromise anyway.

Anti siphon loops just add to the resistance where you don't need it.

All IMHO...

Edit: I didn't mean to write anti siphon loop in the above I meant to write anti siphon valve! My apologies. Loops are good, valves are not so good and add unnecessary resistance. IMHO

 

[Salty John]

I like anti-syphon loops because they allow you to make a nice smooth turn of the pipe back down to the exit point without danger of kinking the pipe, and their smooth interior wall will give less resistance.

 

[sailorman]

I like anti-syphon loops because they allow you to make a nice smooth turn of the pipe back down to the exit point without danger of kinking the pipe, and their smooth interior wall will give less resistance.

My electric diaphragm pump outfall is tee`d ( + a 90 deg bend looking up the flow) into the hand pump outlet pipe on the downside of the loop so both have a loop

 

[Salty John]

You mean like this? This is how I like to put two pumps into one outlet - with or without siphon breaks in the loops.
View attachment 36108

 

[Talulah]

You mean like this? This is how I like to put two pumps into one outlet - with or without siphon breaks in the loops.
View attachment 36108

That's the same way our main heads and holding tank pump out. One pipe from the heads, one from the holding tank pump. (Except the outlet is below the water line ;-) )

Equally our deck drains and hand bilge are the same as your diagram. The top pipe is the deck drain. The lower pipe from the manual bilge pump. I did on one occasion connect the manual bilge pump to the holding tank as the holding tank pump was blocked. At the same time the seacock was closed. As I was pumping away stood inside the cockpit locker it took a few unpleasant moments for me to realise I was pumping the sewage up the drain pipe and on to the deck immediately above me which then started to drip down into the cockpit locker where I was stood.

 

[sailorman]

You mean like this? This is how I like to put two pumps into one outlet - with or without siphon breaks in the loops.
View attachment 36108

Yes

 

[LittleSister]

What do people mean by a siphon loop, as opposed to a syphon valve? (Both my bilge pumps are above the waterline, by the way.)