Are manual bilge pumps useless?

[PaulRainbow]

But the corollary is that if you switch the negative then the pump and all its wiring will be at 12V (unless it is running). Switch the positive and it is only the switch itself (and its connections) that are at 12V

Since I am just about to rewire my bilge pump I am keen to get this right.

At the moment I have two positives from the switch panel, one for automatic and the other for manual, the manual is connected to the pump supply and the automatic switch connects the automatic and manual together. I intend to add waterproof connectors (or put Waco type in a gel box).

A) Negative switched...... Single positive to the pump, live at all times, cannot be isolated via the panel switch (because it isn't wired to it). Should be fused at the supply end.

B) Positive switched....... Positive wire to the pump from the manual setting of the switch, not usually live. Another to the bilge switch, usually live, but can be isolated via the panel switch. Both the manual and auto wires should be fused, so you fit the fuse before the panel switch.

IMO, switching the positive is the correct way. Switching negatives can cause confusion. I would connect the negative to pump, this is usually fitted with long enough wires to get well clear of the bilge. If the bilge switch wiring is not long enough to get the connections clear of the bilge (usually it isn't) extend the wires with glue lined crimp to get clear of the bilge. You should then have the pump positive and the bilge pump switch wires clear of the bilges to make the connections, with only two waterproof connections below the cabin sole.

 

[fisherman]

not talking about a pump, just an alarm. The pos goes from battery to warning light, the neg goes via the bilge switch to the warning light.

 

[PaulRainbow]

not talking about a pump, just an alarm. The pos goes from battery to warning light, the neg goes via the bilge switch to the warning light.

You have a separate switch for the alarm ?

 

[fisherman]

You have a separate switch for the alarm ?

No, an inline fuse on the battery pos, because it bypasses the main isolation switch.

 

[PaulRainbow]

No, an inline fuse on the battery pos, because it bypasses the main isolation switch.

You've lost me

You said

not talking about a pump, just an alarm. The pos goes from battery to warning light, the neg goes via the bilge switch to the warning light.

What bilge switch is the negative going to ? Is it the switch that activates the pump, or a dedicated alarm switch ?

 

[geem]

Our alarm is wired with the main bilge pump. If the pump runs, the alarm goes off. We only panic if alarm doesn't stop running....

 

[fisherman]

You've lost me

You said

[/I][/COLOR]What bilge switch is the negative going to ? Is it the switch that activates the pump, or a dedicated alarm switch ?

Dedicated alarm switch. For pump operation you need bigger capacity and pos switched. For alarm only the pos goes from battery via fuse to panel light/sounder. The neg goes from battery to bilge float switch to panel light/sounder. Of course having waterproof connections down below is important, but you rely on the integrity of the switch itself.

 

[fisherman]

I see the confusion: if the float switch is only for an alarm it can be the £8 low current reed switch. To run a pump you need a higher capacity mercury switch which has a delay before switching, otherwise your pump would be constantly toggling on/off.

 

[PaulRainbow]

I see the confusion: if the float switch is only for an alarm it can be the £8 low current reed switch. To run a pump you need a higher capacity mercury switch which has a delay before switching, otherwise your pump would be constantly toggling on/off.

Got you now :encouragement:

It's more usual to connect the alarm to the positive to the pump. So the negative goes straight to the alarm and/or light, the positive comes from the positive that goes to the pump. If the pump runs, either because the manual switch has been closed or the auto switch in the bilge has closed, the alarm goes off. But if what you have works for you, fine :encouragement:

 

[fisherman]

All i wanted was an alarm that passers-by could see or hear, as well as me at sea. It can easily be wired to an external light visible from afar. I also rigged a light/sounder to the pump as I forget to turn it off, don't like auto pumps.

The only time I had a call I told the chap to find the key and look below, he described a lot of water, so asked him to fire up the pump. Later enquiries revealed someone had tied me to a ladder at low water, using my 1in dia mooring warp. The security guard had called out the HM at midnight, the deck was 3ft under water at the stern, water got in through a disused pump suction connection which was not well capped. They had to tape a knife to a pole and cut the rope from above. Disappointingly they didn't phone me on the spot as the alarm was sounding then.

 

[AntarcticPilot]

A typical small manual bilge pump will output around 20 gallons a minute. A typical small engine pump will output around 15 gallons a minute. If you do a search, you'll find previous threads on this subject, eg http://www.ybw.com/forums/showthread.php?268953-Raw-water-pump-as-emergency-pump

And it varies a LOT from engine to engine. My Volvo 2003, running perfectly normally, pumps very little water out the exhaust; a few litres a minute at most. In fact I can probably estimate it - I guess, judging from the volume of the pump, that it pumps at the very most 6x5 cc per revolution. The pump runs on a gearing from the cam shaft; I don't know the ratio, but looks like a reduction gear. So, lets assume it runs at about engine revs. At 3000 rpm, it will pump 90 litres per minute, pretty close to the 20 gallons a minute quoted above for a manual bilge pump. However, that's optimistic - first, I think I've overestimated the volume pumped per rev - it may be as little as 6x1 cc. Further, the reduction gearing may be 4:1, not the 2:1 I've assumed. Using these minimal assumptions, the rate drops to 9 litres a minute, and it's also pumping through a network of narrow pipes that restricts it further. EVen 9 litres a minute (call it a bucket a minute!) looks like a lot compared with what actually comes out the back, so even my minimal assumptions may be too high. My manual bilge pump can easily keep up with a hose running into the bilges (I've done it to clean the bilges out!). How long I could keep it up is another matter! But on these figures, I reckon even a bucket chain could easily beat my engine water pump, and the manual bilge pump will do better more ergonomically!