Bilge pump levels

[blackrose]

I'm installing a second bilge pump in the engine bay with a separate float switch because I don't want to rely on a single pump with potential for failure like sticky float switch, blown fuse or whatever.

 

So the question is, if the first bilge pump is at the lowest level (a square recess under the stern gland 2" lower than the rest of engine room floor) where should I install the second pump?

 

I've seen drawings showing bilge pumps at different heights but I've never really understood why? Should I install the second pump/float switch at the same place as the first or slightly higher on the engine room floor? Or doesn't it really matter?

 

Edited August 25, 2023 by blackrose

[Iain_S]

Doesn't really matter, although the blurb under your picture gives the reasons.

 

The lower pump can be a small capacity one, which will draw less current when running and will probably be able to get more water out than a larger one. The second, higher, pump can be a bigger one, as it will only come on in an emergency, such as failure of, or a leak sufficient to overwhelm, the first one.

[Alan de Enfield]

 

I'm not sure that the BSS, or a surveyor would be over enamoured with the height of the skin-fitting, and even with the swan-neck it only looks like it is about 150mm (6") whilst the recomendation is 10" minimum.

 

A slight bit of heel and you'd have water running back into the boat down the bilge pump pipe.

 

Maybe thats the idea - water runs into the boat via the 'high' bilge pump and as it fills the lower part the 'low' pump kicks in and pumps it out - perpetual motion ?

[Kudzucraft]

I see no reason not to put it as low as you can. If they both run at the same time thats not a problem.

 

It could be argued putting a second up higher for emergencies but I prefer a dry bilge on my boat.

[blackrose]

22 minutes ago, Alan de Enfield said:

 

I'm not sure that the BSS, or a surveyor would be over enamoured with the height of the skin-fitting, and even with the swan-neck it only looks like it is about 150mm (6") whilst the recomendation is 10" minimum.

 

A slight bit of heel and you'd have water running back into the boat down the bilge pump pipe.

 

Maybe thats the idea - water runs into the boat via the 'high' bilge pump and as it fills the lower part the 'low' pump kicks in and pumps it out - perpetual motion ?

 

I agree with you on the height of the skin fittings. The rest of the diagram isn't necessarily meant to be to scale so I don't think we can infer anything from that.

39 minutes ago, Iain_S said:

Doesn't really matter, although the blurb under your picture gives the reasons.

 

 

Yes I read the reason but as I said, I didn't really understand it because it doesn't seem that logical to me. As Kudzucraft says, why wouldn't you just put them both as low as possible?

Edited August 25, 2023 by blackrose

[Paul C]

Personally I'd do a 2nd bilge pump as a COMPLETELY separate install, including running from the engine/start battery (assuming the first bilge pump runs from the domestics). For that reason, it makes sense to have the 2nd slightly higher than the first, so the anticipated duty is 0% under normal operation, with the first doing the lion's share of the work. Only when large quantities of water, or a failure of the 1st occurs, would it be activated (and drain the engine/start battery in the process).

[blackrose]

Ok thanks. I was going to connect the second pump to the domestic batteries.... They're both charged from solar so I'm not sure that's going to make too much difference but I have more faith in the domestic bank.

[Jen-in-Wellies]

With bilge pumps, if one fails, how do you tell? The second one will carry on fine, until it fails. The way I'd do it would be to do a separate install, as @Paul C suggests, with the second mounted above the first, then have an indicator light that tells me when the second has come on. This would let me know that the first has failed and needs attention.

On my boat I've just got one bilge pump, but there is a gadget I made to let me  know if it has ever run. My boat has a Volvo dripless stern gland, so the bilge having any water in it at all is an unusual event, so I want to be informed. You could use a similar thing on your backup, higher level bilge pump to let you know that the primary pump has either failed, or been overwhelmed by the water flow rate coming in.

A typical three wire auto bilge pump has a ground wire, an always on 12V wire, going to the level detection switch and a manually switched 12V override wire. When the float switch turns it on, the override wire also becomes live. Connect this to a 12V latching relay, that drives an LED, or warning light. When the backup pump turns itself off, the warning light will still be lit and remain so, to you reset the relay with a push button. That way, you are warned that the primary pump has failed. Simple and cheap to make and consumes no power in normal use.

My warning panel that tells me if my bilge pump has run. LED and reset button. I test it every so often.

Jen

[blackrose]

I don't understand what you both mean when you say separate installations? They are separate pumps so of course they will be separate installations. I won't be tapping the second outlet hose into the first if that's what you were thinking. It will have its own skin fitting.

8 minutes ago, Jen-in-Wellies said:

With bilge pumps, if one fails, how do you tell? 

 

I regularly test my bilge pumps.

 

I have a water level alarm under the stern gland so if I'm out cruising and there's an accumulation of water I would get an early warning. But the main point of an automatic bilge pump is to drain water in the event of a leak when one isn't on the boat, so I wouldn't be around to tell if a pump fails.

12 minutes ago, Jen-in-Wellies said:

 

My warning panel that tells me if my bilge pump has run. LED and reset button. I test it every so often.

Jen

 

Ok. I just test the pumps themselves. I also have other bilge pumps in the cabin

[Jen-in-Wellies]

10 minutes ago, blackrose said:

I don't understand what you both mean when you say separate installations? They are separate pumps so of course they will be separate installations. I won't be tapping the second outlet hose into the first if that's what you were thinking. It will have its own skin fitting.

I was copying what Paul C said.

 

10 minutes ago, blackrose said:

I have a water level alarm under the stern gland so if I'm out cruising and there's an accumulation of water I would get an early warning. But the main point of an automatic bilge pump is to drain water in the event of a leak when one isn't on the boat, so I wouldn't be around to tell if a pump fails.

If one bilge pump fails, while you are away, and the other works, you won't know the first is duff till you next test it. This is a way of finding out. If you have a regular test schedule then this is fine. I simply offered what I have installed as something to consider. No problem if you are happy with what you already do and may suit some one else reading this thread.

[Sea Dog]

10 minutes ago, blackrose said:

Ok. I just test the pumps themselves. I also have other bilge pumps in the cabin

Nowt wrong with a bilge pump, a back up bilge pump and then more bilge pumps, but it has prompted me to wonder what comes next in the following sequence:

Belt, braces and.... 

[Puffling]

So the majority of bilge flooding events occur while one is underway? I'd have thought so, with weed hatch cover leakage or stern gland failure being highest on the list of culprits.

 

I installed two bilge pumps on my boat but each is manually switched. I figured the risk of accidental actuation of a float switch is significant, and a drained battery bank while away from the boat is a big expense.

 

My second pump is in the cabin bilge, but can be lifted out and settled into the engine bilge fairly quickly in the event it is required. To alert me to flooding, I have an audible (very loud) flood alarm in each bilge, with the sensor fixed 5mm above the baseplate and shoeplate steels.

 

This wouldn't be suitable for someone wanting to protect their boat over long periods when it is unattended, but it suits me living aboard. Like @Jen-in-Wellies I have a dripless stern gland (Vetus) and the engine bilge is usually rather dry.

 

Do you have a third, emergency bilge pump - namely a wet vacuum cleaner? I think one of these is probably the easiest way to cover most flooding cases, plus the generator to power it when batteries are submerged 🙄

[blackrose]

Ok thanks. One can install all sorts of gadgets. I know someone who gets a text message whenever any of his bilge pumps activate, but personally if I was away for work and unable to get back to the boat I'd rather not know. 

 

In the 18 years I've lived in this boat none of the 3 automatic bilge pumps I've got has ever activated. The bilges are bone dry and they're just an insurance policy.

[Puffling]

4 minutes ago, Sea Dog said:

Nowt wrong with a bilge pump, a back up bilge pump and then more bilge pumps, but it has prompted me to wonder what comes next in the following sequence:

Belt, braces and.... 

Salopettes?

[blackrose]

12 minutes ago, Sea Dog said:

Nowt wrong with a bilge pump, a back up bilge pump and then more bilge pumps, but it has prompted me to wonder what comes next in the following sequence:

Belt, braces and.... 

 

Well I've got one in the bow under the bow thruster, one in the back of the cabin and one under the stern gland. Adding a second in the engine room is as you say belt & braces, but no more than that.

11 minutes ago, Puffling said:

Do you have a third, emergency bilge pump - namely a wet vacuum cleaner? I think one of these is probably the easiest way to cover most flooding cases, plus the generator to power it when batteries are submerged 

 

Yes and it's been very useful for various jobs, but not much use of I'm not around to operate it.

11 minutes ago, Puffling said:

I installed two bilge pumps on my boat but each is manually switched. I figured the risk of accidental actuation of a float switch is significant, and a drained battery bank while away from the boat is a big expense.

 

 

Float switches don't usually activate accidentally. It's normally the other way around and they stick and don't activate when they should which is why they should be regularly tested. 

 

As well being operated by the float switch my engine room bilge pump can also be manually activated.

Edited August 26, 2023 by blackrose

[Quattrodave]

3 hours ago, Jen-in-Wellies said:

That way, you are warned that the primary pump has failed. Simple and cheap to make and consumes no power in normal use.

My warning panel that tells me if my bilge pump has run. LED and reset button.

 

I have my bilge pumps set up with an electromagnetic counter so I can also tell how often they have activated, you can always reset them to zero so you don't have to remember numbers...!

 

Something like these:

https://www.amazon.co.uk/Electromagnetic-Counter-Six-digit-Electronic-Leaning/dp/B09BG82WGR

[Chewbacka]

6 hours ago, Jen-in-Wellies said:

I was copying what Paul C said.

 

If one bilge pump fails, while you are away, and the other works, you won't know the first is duff till you next test it. This is a way of finding out. If you have a regular test schedule then this is fine. I simply offered what I have installed as something to consider. No problem if you are happy with what you already do and may suit some one else reading this thread.

But if the back-up pump is higher then when you look in the bilge if the level is ok for the first pump, the first pump is not faulty, but if the water level is too high and the second pump is doing the work the first pump is faulty.    Just a quick look is all it takes.

[Paul C]

Or install a (once again, separate) bilge alarm.