The ultimate boat maintenance mystery

[Roger Long]

There is definitely a cyber Tee shirt in this for somebody. It’s also the best example of Longs Law* that I’ve ever encountered.

My boat has a small, secondary bilge sump which is just a recess in the main bilge. Into this goes all the grey water which is pumped out by an Atwood Sahara 750 bilge pump along with stuffing box drip, condensation, anchor rode drip, etc. It’s a great system BTW. Zero odor (I just spend a day with my head stuck in the sump so, I’m sure). All the galley sink waste, soap, oil eating bugs, etc. just cancel each other out with the help of the generous ventilation.

The pump itself came from the Atwood shower sump I installed in 2005 and moved to this sump in the rearranged bilge a couple years later after I installed a second fuel tank in the bilge. It has and integral float switch and has always worked flawlessly with only one float switch jam that I can recall.

I left yesterday on a four day cruise and this morning heard a strange sound coming from the bilge. On investigation, I discovered that the grey water pump was stuck on. I wiggled the float switch with the little knob on the pump housing and it would turn off if I turned it but came right back on again.

I pulled the pump off it’s strainer mount and fished it up out of the sump (working at arm’s length in on those situation where you can’t see your hands or what you are doing). The combination of oil eating microbes I put in the bilge after spilling some fuel last spring and the soap and kitchen debris had made a solid gel about the consistency of Jello that completely filled the float switch housing. I scooped out the worst of it and put the pump back. Didn’t fix it.

Next, I cleaned the whole pump to like new condition, sticking paper towel twists into every crevice and wiping out the strainer basket as well as the whole bilge sump. No Joy.

I pulled the pump again and, by careful manipulation of the float switch discovered that a mechanical resistance had developed in the internal switch that the float activates. If you dropped the float switch, it would go off, however, if you very carefully let it down, as the falling water level does, it would catch in the ON position. I touch would turn it off with a small click.

Well, with a two week cruise coming up in a week and no time to fiddle with the boat in between, I decided to cancel this trip and go back for a new pump. With dangerous thunderstorms in the forecast, it wasn’t the worst thing to do anyway.

I motored back to Portland, rode the dinghy ashore and went to Hamilton Marine for a new pump. They only had the 500 GPM model instead of the 750 but the cases and strainers are identical. The difference wouldn’t be critical for these small water amounts.

I went back out to the boat and installed the new pump (with on long row back to shore, and walk back up to the house for the heat shrink connectors I forgot that I took off the boat) which snapped right into same strainer basket screwed into the bottom of the bilge.

It does EACTLY THE SAME %$@^*((^)&% THING!

OK, dried out the bilge with the manual pump that goes into an even smaller sub – sub sump and is used for stripping the bilge dry. Checked the strainer basket, no blockages, cracks, breaks, or obstructions, it looks exactly like the day I put it in. Only other common item is the bilge line. I disconnected that and blew through it, absolutely no resistance or obstruction.

I put everything together and took it apart a couple of times. The pump simply starts sucking air before the water level is low enough to turn off the float switch. It isn’t the well known back flow problem because the pump never goes off. It just sits there sucking away. Good thing this happened while I was on the boat or I would have lost two expensive AGM batteries.

For now, I’ve pulled the fuse to the float switch supply and will be using this as a manual grey water pump. Damn it, I could have done that with the old one and saved 50 bucks.

I’d sure like to solve this but I’ve run up against something even the person who figured out the “Titanic” break up can’t solve. Everything about this installation is exactly the way it has functioned for three years now. I haven’t touched a thing except to clean the sump in all that time. I’m completely buffalo’ed.


* Long’s Law is too complex to express fully here with its numerous algorithms, proofs, cites, and underpinnings of topological restricted set theory. However, it can most simply be described this example: If you computer won’t start and you look under the desk to discover that the plug has been kicked out of the wall, that won’t turn out to be the problem.

 

[butchrobbins]

I may have missed something, but you described a problem with the float, not the pump and then talked about replacing the pump, not the float.

 

[woodster]

if you indeed changed the float and the pump i would trace my wireing all the way back the the power source and make sure there is no damage to the wire and that all the connections are solid and sound and then ck the switch and make sure it is in good working order...some switches do go bad......

regards
woody

 

[Roger Long]

I may have missed something,

You did. This pump has an integral float switch. Normally, it's not ideal because you can't replace one without the other. However, this one lasted longer than pump or float switch I ever had and it's a good solution for a very small sump where there isn't room to work or install a separate float switch.

 

[Roger Long]

i would trace my wireing all the way back the the power source

Why? Pump runs like crazy. So did the old one. Re-read my post.

 

[Monty Miller]

Check the switch at the electrical panel. Is it a 3-way switch, off-on-test? It might be defective or wired wrong.

 

[Ross]

Has something knocked it out of plumb? That could place a segment of the strainer higher than the float switch. Can you get a camera down in there and take a picture? you stated that it is a blind installation. Or is it a case of "I can look at it or I can work on it but I can't do both at the same time?"

 

[kpgraci]

Square One

So the pump continues to run when the water gets too low to suck up. OK. Sounds like a flat adjustment problem. Sure...its disturbing that the old pump had the same symptoms, but that was most likely due to the 'sticky' float switch.

So I would start over - forget what you think you know about the problem.

I've seen this many times - we get an idea in our head about a problem and don't realize we are making some assumptions that are incorrect, and those assumptions will prevent us from solving the problem until they are corrected.

 

[Roger Long]

Sounds like a flat adjustment problem.

It's dead flat because it's sitting on fill that was poured and self leveling when the boat was hauled and level. Still, if I can get in there, putting some washers under the float end of the strainer / mount to raise the float switch is the first thing to try. The hoses for the emergency bilge pumps, which are on a higher level, and a bunch of others stuff have to be removed to do anything like that. It's a major job that will probably have to wait for winter.

Someone on the Wooden Boat forum suggested adding a bit of weight to the float switch. That's the first thing I'll try. Fortunately, I can use the old one to experiment with and find the amount that won't hold the switch down permanently. Now that it's been in the greasy bilge water, it will be a challenge to glue it on though.

 

[Johnb]

Is there a little chamber for the float that is not emptying out? Can you ntry it in a bucket of water?

 

[woodster]

Why? Pump runs like crazy. So did the old one. Re-read my post.

i know it is running ....but the wires could have been cut or shorted out sence you have three wires running to your pump and the manual wire could be shorted out with the automatic wire thuss making it run all the time....

regards

woody

 

[Roger Long]

i the manual wire could be shorted out with the automatic wire thuss making it run all the time....

No, because it works exactly right when I manipulate the float switch with my fingers.

 

[Maine Sail]

Someone on the Wooden Boat forum suggested adding a bit of weight to the float switch. That's the first thing I'll try. Fortunately, I can use the old one to experiment with and find the amount that won't hold the switch down permanently. Now that it's been in the greasy bilge water, it will be a challenge to glue it on though.

Roger,

If this is a mercury switch simply epoxy a nickel to it or my preferred a 5/16" nut. Fixed a few Rule switches like that and they worked for a good long time after that. The extra weight closes it so the mercury rolls better inside. This is a very common problem with the mercury type floats they sometimes don't "float down" fast enough to roll the mercury inside. Have not cut one open in a while and they may not even be using mercury anymore but a little weight may do the job.

PS if it is for gray water why not just use it manually. My shower sump and ice box sump are both manual and work very well that way..

 

[Lee Coller]

I would say you replaced one pump with a defective float switch with another with a defective float switch.

 

[Roger Long]

If this is a mercury switch ...

It's not. It's mechanical

The first one clearly developed too much mechanical resistance because I could reproduce the problem with the pump pulled up into the cabin. Can't complain about something that worked since 2005 in those harsh conditions. The switch problem can't be reproduced in the second pump.

PS if it is for gray water why not just use it manually.

That's what I'm doing now by just pulling the fuse to the float switch supply. I already had a panel breaker wired to the float switch bypass.

Now, if I had only though of that this morning, I would have had a great day of sailing and be anchored out there right now in the thunderstorms that didn't happen instead of typing on this damn computer. I forgot that pulling that fuse only disabled the float switch and not the whole pump. Forgetting a system detail cost me a whole day and night of cruising.

I'm going to end up frigging with it tomorrow because it's going to drive me nuts until I figure this out.

 

[Don12364]

Hysteresis in the float switch?
Lifting the float brings the pump on but when the water level reduces to the point the pump sucks air the switch has not yet been turned off. All microswitches have this feature and so do most mercury ones.
This means the bilge can never be pumped dry and I have often thought of fitting a timer to the switch so that it keeps the pump running for, say, another ten seconds or so until the pump does suck air. This being the point that the pump cannot get any more water out.
In your case, as the switch is part of the pump, it might also be that the float switch is not level which could increase the likelihood.

 

[Bill Roosa]

Clearly bilge gremlins

Sorry to inform you Roger, but I believe you have bilge gremlins. A blood sacrifice is required in most cases to, at a minimum, appease them. I'm betting that you did not cut yourself during any of your rummaging in the bilge spaces. Alternately use some one else's blood or buy a bilge rat to keep him company. Just make sure you don't feed him during the daytime.

Oh yea, one more thing, he will no doubt just set up shop somewhere else so you might want to think about attracting him to a system that you can stand to have a gremlin in. I've managed to get mine into a cabin light fixture that I don't use much. Course the final solution is to raft up with someone you don't want as a friend and then do bloodless maintenance. They tend to migrate to a new boat when you do that. BEWARE, he may have gremlins too and the cure could result in more gremlins on your boat. Your best bet is to heard them into a cabin light or such.

 

[Roger Long]

A blood sacrifice is required in most cases

Due to numerous hose clamps and fiberglass edges, let me assure you that enough blood has been shed and pumped overboard to appease the gremlins of a whole Yacht Club.

 

[Roger Long]

OK, I’m back waiting for epoxy to cure after a couple hours of bilge crawling when I should have been sailing and cruising on a gorgeous day.

Adding weight (four ¾” # 12 S.S. sheet metal screws) to the float switch did the trick but that still doesn’t explain the sudden onset of the problem.

Here is the general layout:

Photo:

You can see the hose connections to the emergency bilge pumps on the upper level at the bottom of the photo. The plastic hose coming from the top left is the sink drain with a plastic strainer basket stuck over the end. Head sink and shower drains come in bottom right. The smooth hose in the top center is the manual bilge pump line that goes to into the smaller sump with a check valve on the end.

The grey water discharge goes from the pump and exits top right. Big hoses on left are fuel vent and fill for bilge tank.

I verified that the pump is dead level by looking at the waterline around the housing. After filling and let it go into endless sucking mode, I also verified that I could push the float switch down with the knob and the pump would stop. I then started experimenting with weights on the float.

Here is my best theory:

The float switch on the original pump did go bad. I think the jelly that was forming in the float chamber slowed the action of the switch so that arcing roughened the contacts enough to let the float start hanging up. I verified this hang up again this morning

Atwood has (this is just the theory) a whole production run of pumps in which the manufacturing tolerance on weight has drifted to the low side or, perhaps, it is just this pump. It could have been something like the Chinese switching from lead to pot metal for the ballast inside.

There is some funny new stuff in the pump documentation. It now says, (despite the package label) that it is not a bilge pump and is only intended to deal with standing water and not leaks or emergency situations. There is also a goofy sketch with an explanation that the discharge line must run straight out through the transom with no upward run. Evidently, they never heard of sailboats or powerboats with a bilge lower than the waterline in which case their diagram would sink the boat. In another section, it does talk about the discharge line running up to the through hull without any high spots that could create air locks. The goofy stuff appears to be an addition. I wonder if it was easier to just write new manuals than to chuck an entire production run of pumps.

 

[Ross]

Roger, remember that instructions from companies in China are probably written by someone for whom english is not a first language. Sometimes they truly mangle a sentence.