Dual bilge pumps

Stu Jackson · Oct 19, 2015

Abe,

No, don't do it, UNLESS you manage to run BOTH at the same time ALWAYS.

From an engineering perspective, one pump, if off, will have the other pump pumping into and through it, and right back into the bilge!!!. If you add a check valve to stop this (commonly done on industrial pumps pairs) you introduce something that ABYC doesn't suggest: check valves in bilge pump lines can get clogged.

Recommendation: run a separate hose to a separate thru hull, and you'll be in business with two pumps.

victorhoisington · Oct 19, 2015

After considering everything Stu said, I'll modify my resposne

2 pumps and the wiring is adequate to handle the extra load you should be OK.. Don't forget to upgrade the wiring (don't forget the fuse/circuit breaker) to handle the extra load in and, don't try to overload the electrical If you do you could blow a circuit (no pump) or cause an overload on the circuit you have leading to overheating and...

You don't want to end up as a story in the current feature forum.

Good luck and safe boating.

Gunni · Oct 19, 2015

Bad idea. If you want to go this way set up two independent bilge pump installations, power, hose, thru-hull.

Kings Gambit · Oct 19, 2015

atwhite2 said:
Just a theoretical question...

When I purchased my Tartan 30, the bilge pump did not work, the short term solution was to replace it. I replaced it with a 800gph pump. I took the old pump home and have since brought it back to working condition. There is only one bilge hose installed... but is there any issue with re-installing the now working old bilge pump and connecting it with a hose "T" to the current bilge hose. The thought being, the more GPH the merrier? This would add an additional 800 gph (1600 gph total).
Is there a flaw in my logic, or would one pump not work and the other pump work all the time? They would each have their own independent connection to the same power source.

Thanks

-Abe

Too late now, but you might have asked this question b/f getting the replacement pump. If you care about pumping capacity, then a replacement pump with higher (2x) capacity would have been a better replacement, probably. Small boats may actually need higher relative capacity than large ones b/c ultimately they will sink sooner than a larger boat on an equivalent amount of water.

centerline · Oct 19, 2015

Gunni said:
"set up two independent bilge pump installations, power, hose, thru-hull.

I agree.
the ONLY way to get both pumps to discharge the highest volume of water in the most efficient manner is having two completely independent systems installed.
there is no sense in having two bilge pumps if they are both on the same circuit... if the single circuit fails, you lose the ability of both pumps.
but then, it may also be argued by those that dont know any better, that it really doesnt matter because if you lose the battery/charge you will lose both pumps anyway.... but no matter how you argue it or why, its recommended to have a manual pump in addition to the electric one.... the manual pump will always be more dependable in ALL conditions.

but in addition to what Stu Jackson said, if you were to install a check valve in an attempt to run two pumps on one discharge line, even if it didnt clog, it WILL restrict the water flow considerably in normal operation... about 40% on most installations.

depending on how much head you are pushing from the pump and assuming the hose and wiring installation is near perfect, the efficiency will be closer to 75-80% of the pumps rated capacity. never expect 100% of what it says it will pump.

mitiempo · Oct 19, 2015

I agree with Stu and the others above - 2 totally separate systems each with their own outlets and circuits.

I think the best solution is a small pump as low as possible for normal de-watering and a larger capacity pump mounted a bit higher for those times it is really needed. The small pump can either have a check valve or its hose size can be reduced to minimize flow back into the bilge when it shuts off, it that is a problem. The larger pump should not have a check valve. Hoses should be smooth walled inside so as not to restrict flow.

JamesG161 · Oct 20, 2015

atwhite2 said:
Just a theoretical question...

When I purchased my Tartan 30, the bilge pump did not work, the short term solution was to replace it. I replaced it with a 800gph pump. I took the old pump home and have since brought it back to working condition. There is only one bilge hose installed... but is there any issue with re-installing the now working old bilge pump and connecting it with a hose "T" to the current bilge hose. The thought being, the more GPH the merrier? This would add an additional 800 gph (1600 gph total).
Is there a flaw in my logic, or would one pump not work and the other pump work all the time? They would each have their own independent connection to the same power source.

Thanks

-Abe

There is nothing wrong with the concept, if applied with the thoughts of others in this post, even with the same thru hull. We used to call this in the "industry" an Installed Spare.

You only need each pump to have a discharge isolation valves or a 3 way valve ( for two) on their discharge ( not the thru hull seacock).

I would much rather have an Installed Spare than have a backup to install in an emergency.

Industrially, we would need the Installed Spare and find it not functional, so we had a rotation schedule, A to B, then B to A, to insure continuity of operations.

BTW I have shower grey water bilge pumps that I leave on as backup. I may have more water in boat than the bilge , but it wouldn't sink.
Jim...

Kings Gambit · Oct 20, 2015

JamesG161 said:
There is nothing wrong with the concept, if applied with the thoughts of others in this post, even with the same thru hull. We used to call this in the "industry" an Installed Spare.

You only need each pump to have a discharge isolation valves or a 3 way valve ( for two) on their discharge ( not the thru hull seacock).

I would much rather have an Installed Spare than have a backup to install in an emergency.

Interesting idea. What about having a "high capacity" manual (diaphragm) pump as an installed spare on the existing through hull in case the impeller pump fouled, or the battery went dead?

JamesG161 · Oct 20, 2015

Kings Gambit said:
Interesting idea. What about having a "high capacity" manual (diaphragm) pump as an installed spare on the existing through hull in case the impeller pump fouled, or the battery went dead?

I have that on my boat and the pump handle is at the helm, but the pump is above the water line, making its discharge check valve more reliable.

BTW I like the 3 way valve better, since it is A or B.
Jim...

mitiempo · Oct 20, 2015

Kings Gambit said:
Interesting idea. What about having a "high capacity" manual (diaphragm) pump as an installed spare on the existing through hull in case the impeller pump fouled, or the battery went dead?

Best that all bilge pumps have their own dedicated outlet. You never know when you will need all of them working at full capacity.

Kings Gambit · Oct 20, 2015

mitiempo said:
Best that all bilge pumps have their own dedicated outlet. You never know when you will need all of them working at full capacity.

Understood, but it does not have to be either-or. Could have a manual installed spare backing up the electric pump, plus another manual on its own thru-hull. For most boats, that would mean three manual bilge pumps aboard. One installed on the boat originally orperated from the cockpit, one to back up the electric on the same discharge as an installed spare, and one on a new thru-hull discharge. So, at any one time, the boat would have always have 3 three pumps dewatering through 3 separate discharge thru-hulls (assuming you have 3 crew members available to pump).

Lengthy (and thoughtful) discusssion on this topic in here last year.

http://forums.sailboatowners.com/index.php?threads/plan-to-save-or-to-abandon-the-ship.165801/

mitiempo · Oct 20, 2015

Kings Gambit said:
Understood, but it does not have to be either-or. Could have a manual installed spare backing up the electric pump, plus another manual on its own thru-hull. For most boats, that would mean three manual bilge pumps aboard. One installed on the boat originally orperated from the cockpit, one to back up the electric on the same discharge as an installed spare, and one on a new thru-hull discharge. So, at any one time, the boat would have always have 3 three pumps dewatering through 3 separate discharge thru-hulls (assuming you have 3 crew members available to pump).

2 electric pumps with one manual worked from the cockpit is a good solution.

Kings Gambit · Oct 20, 2015

mitiempo said:
2 electric pumps with one manual worked from the cockpit is a good solution.

Not if the batteries are dead and the engine can't be started, etc. See post #13 above yours.

Gunni · Oct 20, 2015

No batteries required.

mitiempo · Oct 20, 2015

Kings Gambit said:
Not if the batteries are dead and the engine can't be started, etc. See post #13 above yours.

It is a rare boat that has 3 manual pumps. Most have 1, some 2. Combining outlets for a manual and an electric pump or 2 electrics is a bad idea needing either valves which have to be switched or check valves which limit flow.

Maine Sail · Oct 20, 2015

atwhite2 said:
Just a theoretical question...

When I purchased my Tartan 30, the bilge pump did not work, the short term solution was to replace it. I replaced it with a 800gph pump. I took the old pump home and have since brought it back to working condition. There is only one bilge hose installed... but is there any issue with re-installing the now working old bilge pump and connecting it with a hose "T" to the current bilge hose. The thought being, the more GPH the merrier? This would add an additional 800 gph (1600 gph total).
Is there a flaw in my logic, or would one pump not work and the other pump work all the time? They would each have their own independent connection to the same power source.

Thanks

-Abe

Abe,

The major flaw in the logic is believing the lies the bilge pump maker tells you.. Bilge pumps are some of the most grossly misrepresented items we use on boats and many of us in the industry belie 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 "open bucket rate" or ZERO HEAD and at charging voltages. Fair? Hardly... On top of that, 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..

One 2000GPH pump that was tested claims 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 you about on the box and you'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 sailboat static head and you are well below 100 GPH for a typical sailboat running a 600GPH pump.

I would urge you:

Not to share hoses
Not to share thru-hull fittings
Not to use corrugated hose
Not to use any 90 Degree fittings
To use smooth walled hose
Buy the biggest pump you can fit and count on half that rating at best!!

JamesG161 · Oct 20, 2015

Main Sail, well done!

The thread started as a "back up" since he had 2 pumps.

Back up = Reliability
Two+ independent pumps = Capacity
Manual + Power = Safety

I did a minor Safety analysis of my boat within 2 months after seeing the entire system.
This may be more complicated than the thread, but I did a WICL type review with includes the above 3 points.
https://www.osha.gov/SLTC/etools/safetyhealth/mod4_tools_methodologies.html for the adventurous.

I ended up with my failure mode being the loss of 1 through hull. Not a collision, not a rogue wave or big storm.

As Main Sail clearly pointed out, Bilge pumps, off the shelf types, are for minor management of interior flow.

I found that 50% of the my Bilge rated capacity would handle a single broken thru hull line failure, basically giving the crew time to pound in and wire off a tapered wooden plug to stop the leak. I have a screw driver, rubber mallet, wire and wire ties in a kit near the bilge (Safety).

I back up my main bilge with 2 shower grey water bilge pumps = 1.5 main bilge. These back ups do (Safety/Capacity/Reliability). These are on the house batteries versus Main Bilge on Starter Battery (Reliability). Plus one hand pump at the helm.

So my point is...

Pick your needs to define your system!

I think an installed spare gives Abe = Reliability. If done as A or B. There is friction loss in a "Y" or Wye but not too restrictive.
Jim...

StephenD · Nov 29, 2015

It's probably somewhere in here that I found this, but it's a thoughtful look at bilge pumps through the eyes of the experienced surveyor and insurance claims investigator David Pascoe. Enjoy, hope you can sleep afterwards!! (I can now, but only because my 27 gets put on the hard tomorrow).
http://www.yachtsurvey.com/bilge_pumps.htm

Dual bilge pumps

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SBO Weather and Forecasting Forum Jim & John

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SBO Weather and Forecasting Forum Jim & John

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