andyball
New member
I'm sure we all agree that a typical, or even several large bilge pumps won't save a boat with a major leak; by which I mean a 2" hole, say 2' below the waterline. But a 1" hole...same depth shifts maybe 1500 gallons per hour, which on a boat with 2 largeish pumps is surely sustainable until the batteries run low.... indefinitely with shorepower....is that pointless to have?.
Do all sinkings due to leaks happen only with major leaks? what about one that lets in say 150 gallons per hour on average? many boats would sink if that continued for a day or so (few would escape some water damage,I imagine), but even a small pump, combined with shorepower & a charger (many boaters do have this luxury), would cope with it.
Thorough & detailed tests of small (as in not great commercial things) bilge pumps are thin on the ground....they're not exactly scintillating reading, so even if carried out, few would be fully published in magazines.
Based upon my own experience with a "2000 US gallon per hour" pump actually making 1200 imperial gallons p/h at 12.4V (a modest lift & length of pipe by boat standards, but normal for a 22' sportsboat) .....75% or less of claimed output is normal.
A huge & thorough-sounding test by West marine in '99 found some that made 92-104 % of their claimed rating, with 3' lift & 6' of pipe, which is rather better than mine, although only 50% of those tested managed 75% of claimed output.
The same test also looked at efficiency; & although details are sketchy, the summary in their 2002 catalogue claimed a flow (with lift,pipes & skin fitting) of between 13 and 30 US gallons per hour for each measured Watt of pump power.....so an imaginary "toy town" pump pulling say 2 Amps (25Watts'ish) might pump 325 to 750 US gallons per hour. A test in PBO June 2002 claimed results between 10 and 20 imperial gall's per hour,per Watt,which sounds very broadly similar; although this was based upon claimed current draw, not measured Amps.
Assuming that West Marine were exaggerating (no reason,just assume it) I'll say just 200 imperial gallons per hour, although the reality might be much larger according to west marine.
Take an imaginary boat with one of these imaginary (but based on west marine's tests ) pumps that pull's 2 Amps or there abouts......the pump will draw 2AH from a battery if it runs for an hour & pump 200 gallons in that time.
Same imaginary boat has a "spare" 40AH of useable battery capacity ( made up notionally by assuming a fully charged 90AH battery that's lost a bit of it's capacity ....quite a (very?) small amount by many boat standards ?. The pump would run for roughly 20 hours before the battery was flat & in that time remove maybe 4000 gallons of water. (The west marine tested pumps drew less current & pumped less water at low voltages, but became more efficient, so the gallons vs Amp Hours figure should stay similar,even though the battery voltage would drop steadily)
" a pint of water weighs a pound and a quarter " I was taught ?...so a gallon must be 10lb's & 4000 gallons must be 40000 lbs or 18 tonnes 'ish.....easily enough to sink a small boat & do plenty of damage to many larger ones if you waited 'til you arrived at the boat to pump it out. This is 640'ish cubic feet of water....similar to a 10' square, 6' deep swimming pool.
Even if you scoff at only 3' lift & 6' of pipe in the west marine test & therefore & halve the amount pumped, not having 9 tonnes of water inside your boat seems reasonable enough.
<font size=1>Actual tests not completed...your mileage may vary.<g></font size=1>
If you get a big leak & don't check the boat for ages; it'll sink regardless of a tiny bilge pump. But...many boats have rather more than 40AH of useable battery capacity, and pumps rather larger than my imagined one are available, and you could fit more than one.
With a proper leak & no shorepower/charger, you're still underwater ; but very many boats do have these ....& many are berthed in staffed marinas who might notice a warning buzzer/flashing light/constant pumping & investigate.
If you're absolutely certain your pride & joy will only ever get really big water leaks, or none at all.....auto-bilge pumps are a waste of money.
So: some big assumptions? based on a test I haven't got all the details of, using (by 35' boat standards) a shortish amount of hose & very modest lift,ignoring inefficiences caused by starting/stopping with the float switch & water running back down the hose when the pump's off. All worthless then?.
I took the figures from the least efficient pump west marine tested, based the figures on the smallest pump generally available (500gph/25W'ish ),reduced even those figures by about 30%, & assumed a quite minimal battery capacity. Take the figures & halve them again for good measure & they still suggest 9 tonnes of water could be outside a boat, rather than in it. Halve them once more, it still looks worthwhile.
Enough imagining! do real life boats,reasonably well maintained -or not, given that even the best make mistakes-ever leak "modest" amounts of water (talking up to 2 gallons a minute here, which may not look modest when you lift a hatch). Ever had a leak that wasn't there when you left the boat ?....how big?. What about smaller leaks, un-noticed over a week or more away from the boat? Don't seacocks, skin fittings ,shafts, rudderstocks etc ever leak unexpectedly?. Or is a disastrous hole that'll sink her in 15 minutes the only way these things work?.
If boats are like cars & bikes (fixed many more of those), then sometimes, even with the best of intentions & maintenance, things can go wrong unexpectedly.
I only mention all this because (apart from insomnia,of course, it's 4.30AM !), auto-pumps, esp with warning lights/buzzers, seem quite useful & practical to me, even with modestly-sized pumps/battery capacity.
PS :if I've missed a decimal point or two & come up with ludicrous figures......it's the late hour - I'll laugh too.
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Do all sinkings due to leaks happen only with major leaks? what about one that lets in say 150 gallons per hour on average? many boats would sink if that continued for a day or so (few would escape some water damage,I imagine), but even a small pump, combined with shorepower & a charger (many boaters do have this luxury), would cope with it.
Thorough & detailed tests of small (as in not great commercial things) bilge pumps are thin on the ground....they're not exactly scintillating reading, so even if carried out, few would be fully published in magazines.
Based upon my own experience with a "2000 US gallon per hour" pump actually making 1200 imperial gallons p/h at 12.4V (a modest lift & length of pipe by boat standards, but normal for a 22' sportsboat) .....75% or less of claimed output is normal.
A huge & thorough-sounding test by West marine in '99 found some that made 92-104 % of their claimed rating, with 3' lift & 6' of pipe, which is rather better than mine, although only 50% of those tested managed 75% of claimed output.
The same test also looked at efficiency; & although details are sketchy, the summary in their 2002 catalogue claimed a flow (with lift,pipes & skin fitting) of between 13 and 30 US gallons per hour for each measured Watt of pump power.....so an imaginary "toy town" pump pulling say 2 Amps (25Watts'ish) might pump 325 to 750 US gallons per hour. A test in PBO June 2002 claimed results between 10 and 20 imperial gall's per hour,per Watt,which sounds very broadly similar; although this was based upon claimed current draw, not measured Amps.
Assuming that West Marine were exaggerating (no reason,just assume it) I'll say just 200 imperial gallons per hour, although the reality might be much larger according to west marine.
Take an imaginary boat with one of these imaginary (but based on west marine's tests ) pumps that pull's 2 Amps or there abouts......the pump will draw 2AH from a battery if it runs for an hour & pump 200 gallons in that time.
Same imaginary boat has a "spare" 40AH of useable battery capacity ( made up notionally by assuming a fully charged 90AH battery that's lost a bit of it's capacity ....quite a (very?) small amount by many boat standards ?. The pump would run for roughly 20 hours before the battery was flat & in that time remove maybe 4000 gallons of water. (The west marine tested pumps drew less current & pumped less water at low voltages, but became more efficient, so the gallons vs Amp Hours figure should stay similar,even though the battery voltage would drop steadily)
" a pint of water weighs a pound and a quarter " I was taught ?...so a gallon must be 10lb's & 4000 gallons must be 40000 lbs or 18 tonnes 'ish.....easily enough to sink a small boat & do plenty of damage to many larger ones if you waited 'til you arrived at the boat to pump it out. This is 640'ish cubic feet of water....similar to a 10' square, 6' deep swimming pool.
Even if you scoff at only 3' lift & 6' of pipe in the west marine test & therefore & halve the amount pumped, not having 9 tonnes of water inside your boat seems reasonable enough.
<font size=1>Actual tests not completed...your mileage may vary.<g></font size=1>
If you get a big leak & don't check the boat for ages; it'll sink regardless of a tiny bilge pump. But...many boats have rather more than 40AH of useable battery capacity, and pumps rather larger than my imagined one are available, and you could fit more than one.
With a proper leak & no shorepower/charger, you're still underwater ; but very many boats do have these ....& many are berthed in staffed marinas who might notice a warning buzzer/flashing light/constant pumping & investigate.
If you're absolutely certain your pride & joy will only ever get really big water leaks, or none at all.....auto-bilge pumps are a waste of money.
So: some big assumptions? based on a test I haven't got all the details of, using (by 35' boat standards) a shortish amount of hose & very modest lift,ignoring inefficiences caused by starting/stopping with the float switch & water running back down the hose when the pump's off. All worthless then?.
I took the figures from the least efficient pump west marine tested, based the figures on the smallest pump generally available (500gph/25W'ish ),reduced even those figures by about 30%, & assumed a quite minimal battery capacity. Take the figures & halve them again for good measure & they still suggest 9 tonnes of water could be outside a boat, rather than in it. Halve them once more, it still looks worthwhile.
Enough imagining! do real life boats,reasonably well maintained -or not, given that even the best make mistakes-ever leak "modest" amounts of water (talking up to 2 gallons a minute here, which may not look modest when you lift a hatch). Ever had a leak that wasn't there when you left the boat ?....how big?. What about smaller leaks, un-noticed over a week or more away from the boat? Don't seacocks, skin fittings ,shafts, rudderstocks etc ever leak unexpectedly?. Or is a disastrous hole that'll sink her in 15 minutes the only way these things work?.
If boats are like cars & bikes (fixed many more of those), then sometimes, even with the best of intentions & maintenance, things can go wrong unexpectedly.
I only mention all this because (apart from insomnia,of course, it's 4.30AM !), auto-pumps, esp with warning lights/buzzers, seem quite useful & practical to me, even with modestly-sized pumps/battery capacity.
PS :if I've missed a decimal point or two & come up with ludicrous figures......it's the late hour - I'll laugh too.
<hr width=100% size=1>
