Every boat over 24 +/- feet with a bilge & cabin should ideally have a
dual pump configuration. I have been harping on this for years but folks rarely go for it.
Pump #1 for a 30 footer would be a 2000GPH+ centrifugal style "
oh $hit" pump with the bilge switch mounted slightly higher than the primary nuisance water pump.
The nuisance water pump should be a diaphragm style pump for dealing with nuisance level water. Diaphragm pumps can use check valves but don't normally need them as they tend to self-check.
Premium bilge switches like the Ultra Pump Switch Jr. or Sr. should be used with both pumps.
These problems are generally related to a number of issues:
#1 Poor bilge switch chosen for the task - Ever since the removal of mercury from the Rule etc. float switches the reliability has been about as good as a Yugo and they tend to last about as long as a bag of Doritos at a Grateful Dead concert.. How to Rx? Don't buy unreliable products. The switches from Ultra Safety Systems are about as reliable as they get.
#2 Inadequate bilge pump system design - A good bilge pump system makes use of a "
nuisance pump" which is a diaphragm style and a second emergency pump or oh $hit pump which is a high capacity centrifugal type. The nuisance pump does all the routine work and the oh $hit pump is used only in emergency situations and the switch is mounted slightly higher in the bilge. As a bonus a manual "gusher" style pump should be installed with a cockpit handle..
#3 Improper system design and install - Centrifugal Rule type pumps should not have check valves installed in the outlet hose. Check valves are a band-aid at best and owners and even builders often choose them over a
proper installation but should not. They are flat out dangerous at best, and battery killers at the very least. It's one of the number one causes of destroyed battery banks other than cheap bilge switches I see. Centrifugal pumps should also use smooth walled hose, utilize a siphon break and have as few bends as possible. The discharge should always be above max heeled waterline in a well designed system. Wire should be sized for the least voltage drop to maximize performance. Centrifugal pumps will never pump anywhere close to their rating "as installed" so the biggest capacity
oh $hit pump you can fit is the best choice.
Best bet to avoid these issues:
Install a well designed bilge pumping system utilizing a nuisance pump (diaphragm type). Use quality bilge switches such as those by Ultra Safety Systems, use sufficient wire for minimal voltage drop, use water proof splices for all wiring terminations, make all terminations above bilge height when ever possible, fuse the pumps per manufacturers recommendations and do not use a check valve on any centrifugal type pump. Check valves are fine on a diaphragm pump but a very bad idea on a centrifugal bilge pump...
Sadly the best bilge switch ever made was discontinued because boaters refused to pay for the technology and reliability. I bought an extra before they ran out....
That said I have yet to have or see an Ultra Safety Systems bilge switch fail....
Misleading Marketing:
Bilge pumps are some of the most grossly misrepresented items we use on boats today and many of us in the industry believe this is borderline
criminal.
We have three major items that inhibit the performance of your pump.
Friction Head Loss
Static Head Loss
Voltage
These pumps are
rated at what is commonly called the "
open bucket rate" or ZERO HEAD and they are rated at charging voltages of 13.6V.
Fair? Hardly...
In a University of Virginia study, they found most pumps delivered 15-33% less than what the manufacturer claimed even when tested as they rate them at "open bucket"..
One 2000GPH pump that was tested claimed 2000GPH at zero head. Testers found it delivered just 1500GPH at 12V and zero head. This is 500 GPH below what the pump maker lied to the consumer about on the box and we've not even installed it yet to realize head losses. They also claimed the pump to be capable of up to 18' of head, and it could only muster 14' of head at 12V... If voltage drops below 12V the performance gets even worse. That 2000 GPH pump at 10V could only produce approx 420GPH at 7' of head. Seven feet of head is fairly common on a sailboat. Bump that to 12V and we get approx 720GPH. Course this is just
static head and does not include for friction head (fittings etc.) and voltage..
Lets look at some actual test data for a 600GPH pump.
600GPH Manufacturer Label (assuming it actually performs at that rating)
Running Pump at 12V = Loss of 141 GPH
3' Static Head = Loss of 179 GPH (3' is NOTHING on a sailboat)
10' of 3/4" Corrugated Hose = Loss of 114 GPH
1 3/4" Thru-Hull Fitting = Loss of 11 GPH
In a typical installation a 600 GPH pump (on a power boat with only 3' of static head) will only deliver 155 GPH "
as installed". Now add a check valve, and a sailboats static head, and you are well below 100 GPH for a typical sailboat running a 600GPH pump.
I would urge all boaters:
Do not share hoses
Do not share thru-hull fittings
Do not use check valves on centrifugal pumps
Do not use corrugated hose
Do not allow any
dips/water traps in outlet hose
Do not fuse the pump at beyond the manufacturers suggested size
Do not use any 90 Degree fittings
Do use smooth walled hose
Do buy the biggest pump you can fit
Do use quality bilge switches
Do use waterproof splices
Do keep all terminations out of bilge water
Do use wire that results in the least voltage drop
Do use a dual or tri-pump configuration
Do install a high water alarm
Do use a siphon break
