Sizing bilge pumps

[bcooke]

With my cabin sole out, now is the best time to put in an electric bilge pump. I was wondering about how big a pump to get. It seems like the next bigger is pump is just another $20 more and the next is just another $20 more and the next... you get the idea.

Is there any reason why I shouldn't just get the biggest pump that will fit in the bilge?

-Britton

[Tim]

You might want to consider a couple things:

1. How about a small pump deep in the bilge for routine dewatering, with a larger emergency pump slighly higher.

2. Deep bilges present problems for pumps because of the length of hose required to exit the bilge--this water will tend to backflow when the pump shuts off, meaning that there will always be water in the bilge (best case) or (worst case) you could have a pump that continually cycled trying to rid itself of this water. Check valves seem like the answer, but are historically unreliable.

The best pump for this situation (or just about any) is an impeller or diaphragm pump, located remotely, with a suction in the bilge. These cost a lot more than the junky centrifugal pumps, but because the pump is located well above and outside of the bilge (and away from moisture), and because of their more robust construction and design, they'll probably last forever. You can wire these into a float switch like any other pump.

I would use one of these for my routine dewatering, and install the big emergency pump (which can be a regular centrifugal bilge pump) somewhat above the bottom of the bilge, just in case. If you can fit one of those 3500 GPH Rule pumps as your emergency, why not indeed.

And remember, of course, that the pumps rated output is, in practice, extremely optimistic, and that these pumps typically generate about 1/2 the rated flow depending on the head (vertical distance) of the installation, the length and size of the hose, etc.

[bcooke]

Good info.

I have heard the dual pump theory before. What surprised me though is when I went to the catalog I noticed that the 3500 gph Rule pump draws 15 amps while the 300 gph Rule pump draws 2 amps. 12 times the pumping ability for 8 times the draw. By my math, the bigger pump is more efficient and would actually draw less power to get the same amount of water out of the bilge (because it would do so much quicker).

I wondered about check valves but when I read about the Glissando setup it seems the check valve didn't last very long and it isn't missed much. With my deeper bilge I might have more of a problem with backflow so maybe I should just keep spares around and make them easily accessible.

I also have a manual pump from the PO in the cockpit so I was thinking I would stick to the manual pump for routine removals and use the electric on a float switch for emergencies and when I am away from the boat for a while. One advantage of the manual pump is that once the routine is established of giving the pump a try every day, any increase in seepage will become immediately apparent. Or I might splurge and have two electrics, along with a manual in the cockpit and the waste pump connected to the bilge with a Y-valve. And of course I always keep a bucket on board as well.

While purusing the catalogs I also came across an electronic float switch that had no moving parts and was setup to avoid the quick cycling from the backflow. Cost was about $60 which didn't seem too bad for something that should work without a hitch for a very long time. Anyone tried one of these?

-Britton

[JonnyBoats]

In the March/April 2006 issue of Good Old Boat on page 78 there is an article titled "Bilge pump spy" detailing how the athor turned a $4 pedometer from Wall Mart into a bilge pump counter.

The advantage of a counter is that it will tell you how many times your bilge pump has cycled on and off. This allows you to detect small leaks before they turn into big ones.

[Tim]

A counter is a good idea. I just can't figure out why I would waste my time reconfiguring a pedometer when you can buy counters all set to go.

I think the author was just showing off, frankly. I looked at that article and just shook my head. I'll buy one, thanks.

[CharlieJ]

Saw something some while ago- A guy wired a regular engine hour meter into the circuit so when the bilge pump ran the hour meter did too. Then he knew how long it had run in between visits.

[s/v Faith]

THis is from a post I made on the Sailfar.net site earlier this year. My system has evolved as I installed it, the first part (above the line) was from June.


Bilge pumps

After a good storm on the Chesapeake earlier this year, I was reminded of the value of a good bilge pumping system.
Of course we know there is no better bilge pump then 'a scared Sailor with a bucket', but I am not a huge fan of that system since it is tough to sail and bail at the same time.

The boat I was on had a small (500 GPH) electric pump in the bilge, and a manual pump mounted where it could be operated from the cockpit. The leak was not a big one, but when I discovered it the floor boards were floating, so there was a fair amount of water to get rid of.

Issue 1). Electronic switches.
The electric pump?s automatic switch was one of the fancy ?solid state? ones. It of course failed. It was the second failure of one of these ?foolproof? solid state switches I have personally delt with. The first was on an Alberg 30 I have been keeping an eye on. For my boat there will be nothing but good old mercury float switches.

Issue 2). Redundant redundancy.
The smallish electronic bilge pump was not able to remove the water fast enough for my liking. I have a similar sized pump on my boat, and it works fine for normal underway splashes that wind up in the bilge, but it was out of it?s league. Even if it were larger, the manual switch had taken it out of the running. It also eventually clogged while clearing the bilge (you just have to turn it off, and the backflow of water mostly clears it). The manual bilge pump, a Bosworth Guzzler, (400 I think) had nearly cleared the bilge when the flapper valve either failed or was jammed with debris.

The ?thirsty mate? slide type pump then had to be used to finish clearing the bilge.The Guzzler is a good pump, but like anything else it can (and will) fail when you need it. I was glad that the thirsty mate pump worked, since it would be hard to get a bucket into the narrow bilge access.
The plan for my boat was to be set up like this one had been. I have now decided add another pump (triple redundancy, quadruple if you count the thirsty mate pump). I will keep my < 500 GPH pump at the lowest point of my bilge. I will also add a >1000 GPH pump at a higher place in the bilge to take over if the first pump becomes clogged, overwhelmed or fails. I have already purchased a ?plastimo 925? manual pump that I will mount in the cockpit.

If you have an inboard, you might look at using the cooling pump as an extra means of removing water. Consider this carefully though, as running your motor dry, or sucking debris into the cooling system might complicate your situation.

Issue 3). Bilge hygiene.
Both of the pump failures I experienced were the result of trash in the bilge. I hose my bilge out regularly on ?Faith? but it is easier to keep clean since it is well glassed and accessible.

Issue 4). Awareness.
Of course this would not have been as pressing a problem if I had known earlier that the bilge was filling. This boat had a high bilge water alarm, but it failed. I plan to wire an extra float switch to the ?test? button of a smoke detector, to notify me if the water rises. The smoke alarm will still function, so it will do double duty. It should also be loud enough that if it went on while the boat was at the dock and I was not present, someone might hear it and know something was wrong. It would also work to keep the bilge access open if you are in bad wx, but that might present a hazard to crew going below.

I know this is a long post, but floating floor boards are enough to ruin your whole day. My First mate did great through the storm, the waves and wind did not seem to phase her, even the lightning did not bother her all that much. Looking below and seeing all that water was a bit much, and I will admit it is something I would rather not repeat myself. Maybe this will remind someone to re-visit your dewatering system.
__________________________________________________________________
Update;

Since starting this thread, I ended up going with a little different set up.

First is an Atwood Sahara 750 GPH pump. It is mounted at the lowest point of the bilge with an internal float switch. It handles the normal splashes that come into the bilge. It draws 2.8a running under load, and with the >3' head pumps an honest 450 GPH.



Second, I looked at a bunch of pumps for a larger capacity back up... Ended up with a Rule 'Gold' 2000 GPH pump. It was pricey, but I liked the way it was built. It is mounted just aft of the Atwood, and slightly higher. It is also pumping a head of >3' so I get something like 1500 GPH out of it.


These two pumps running together should go for something like 10 hours on my current battery. I would more realistically expect something less then that but plan to double the capacity of the battery bank next spring.

Then there is the Plastimo 925 manual pump that I will mount in the cockpit. It is rated at 60 GPH, but I guess that has more to do with how fast I pump it. It wants a 1? hose, which I am having some trouble finding in the crush resistant hose?. but I will work out something.


[sub]Slightly different model, looks the same though[/sub]

Then there are two of the Thirsty mate pumps aboard. (one of the 18? and one of the 36?)


They don?t take up much space, and are easy to grab and run to go help someone else out.

Then there is always my ?Bacon & associates? 7l Rubber bucket. (I love this thing, has a great handle, and slightly flexes?.. wonderful bucket!)

[Capn_Tom]

I really like the looks of the plastimo. Nice clean mount. I was a bit puzzled by your reference to it's GPH until I followed the link and discovered you meant 600. Unless like me you need to rest for 50 minutes following 10 minutes of pumping.