Bilge Pump Discharge Arrangement

[DCMY #92]

My neighbor has a late model non-Hatteras MY. It has a 2" PVC pipe manifold running along the inside of the hull on both sides. All A/C circulating water discharge, sink drains, A/C condensate drains and bilge pump discharge is routed to one of these drain manifolds. Each manifold discharges through a 1-1/2" through hull fitting just above the waterline.

He noticed that one of his 4 bilge pumps was cycling regularly. Investigation revealed a good stream of seawater entering the bilge through the aft most bilge pump. Turning off the A/C stopped the flow. It turns out that the drain manifold to which this pump is connected was clogged near its outlet with mussels and oysters, causing A/C cooling water to backflow through the bilge pump.

The drain manifold has been cleaned and the blocked portion replaced. This has solved the problem - if the system is cleaned often enough to prevent clogging again.

A call to the boat dealer revealed that this is not uncommon if the drain manifolds are not cleaned regularly. If fact, they said an identical model partially sank recently due to this same problem. I suggested that all the bilge pumps should have a separate through hull discharge filling and should not be tied into the drain manifold. The manufacturer agreed to make this modification at their expense if the owner insists, but said the didn't recommend it was a weaker arrangement than their design.

I suspect that their response is based on the desire not to acknowledge a design problem and their willingness to pay for the modification if the owner insists is due to their behind the scenes view that independent discharges are actually safer. Frankly, I am surprised that manufacturing standards and guidelines allow bilge pump discharges to be combined. I also suspect that bilge pump capacity is reduced when combining the flow from 2 pumps with A/C cooling water and trying to pass it all through a single 1-1/2" fitting.

My neighbor is interested in comments from this group regarding the best way to arrange the bilge pump drains, what design standards allow, etc. Thanks in advance for your thoughts.

 

[MikeP]

On our 53 there is a manifold in each eng room. The ac seawater pump (port side) and bilge pumps on both sides discharge into them. There are "cleanout" plugs on top of both so you can poke around with a stick or whatever and get rid of any deposits. I think the manifold is a better design than additional holes in the hull but I have to admit I have never even removed the plugs...maybe I should.

 

[captddis]

There was a thread about this problem a few months back where I talked about the same problems with Ac units discharging into the tubes. The only safe solution is to have a seperate discharge for the AC units.


Is the boat a Viking?

 

[bostonhatteras]

you mentioned that the outlet of this manifold arrangement was clogged with mussels, etc. therefore it must be underwater. does you friends boat have a seacock on that throughull? it must for safety. also 1 1/2" for all discharge? the lenght and many tee fittings, couplings etc would introduce so much restriction that it might as well be 1". I cannot imagine how that arrangement could ever be superior to a single outlet with proper riser loop and ABOVE the water line for each device discharging water. but then again in today's world aesthetics win out over function all the time. just the ability to discharge into the boat through another device should be enough to make a surveyor condemn the system and state the boat not seaworthy. buyer beware!

 

[Avenger]

On mine the bilge pumps either discharge directly, or to a sea chest with the outlet above the water line. However, the A/C cooling water discharges to a seperate sea-chest with an outlet below the water line. Probably to eliminate the constant splashing noise.

As usual Hatteras' example seems to make good sense.

 

[Traveler 45C]

My ER bilge pumps and the A/C circ pumps directly into a seachest. It's clogged up a few times from mussels growing in there. I don't have a clean out plug on mine. Mike, got a picture of yours?

This is definitely something to keep an eye on if your away from your boat and leave the A/C running. If your batteries should get low and water is back-flowing through your bilge pumps then...she'll slowly sink.

 

[MikeP]

Here's a pic - perhaps my calling it a "cleanout" is a bit generous but you can put a stick or rod in the opening and/or attach a hose with some chosen chemical in it to do whatever.

 

[Brian Degulis]

If your friend wants to make the existing setup safer he could ad check valves to the bilge pump discharge lines. You would still be relying on the valves and I don't like the setup but I would improve it an awfull lot.


Brian

 

[DCMY #92]

".....this manifold arrangement was clogged with mussels, etc. therefore it must be underwater"

The discharge from the drain manifolds is just above the waterline. There is no valve. The mussels apparently grew in the tube due to the constant flow of A/C cooling water.

Regarding check valves in the bilge pump discharge lines: I would think that a check valve would further reduce the pump's capacity.

 

[Pascal]

check valves on bilge pumps are a recipe for disaster. It's not a matter of if but when they will get stuck... and they do reduce flow some. it's a bandaid to a poor installation (my opinion and the opinion of 2 surveyors i discussed that with)

Hatteras MYs (older ones) had those seachests mike mentioned on the hull sides, 5 i believe on the 53MY for instance (at least on my 1970). i've never heard of any issue BUT the outlet isnt' that big... i dont' think they're over 1 1/2". seems to work though, I know my AC outlet plus a one bilge pump discharge on one side and it's never back flowed. about 5000gph total

teh 70 footer i run has a 2" pipe (or maybe 2 1/2) on each side of the hull, collecting just about everything except Air Con cooling water and water maker brine, those go straight overboard. sumps, bilge pumps, sinks, etc... go thru those drains which exit 12" above water line in the swimplatform. obiovulsy barnacles wont' be an issue.

either system is a way of reducing the number of thruhull, which isnt' a bad idea. but sending that below water line is not a good solution.

 

[GJH]

Hmmm. My 56 is quite different. Every pump and every drain has its own through hull. Lots of holes in the boat: not counting vents, 24 above the water line, 7 active below the waterline. There are 3 more BTWL that have been decommissioned since the conversion to fresh water toilets and from-holding-tank-only waste discharge.

The three shower sumps are designed as high water back-ups, most directly for the forward bilge and starboard bilges, indirectly for aft and port.

 

[Traveler 45C]

Thanks Mike.

I'm gonna' have to modify mine so I can get in there, something a little bigger than that.

Ya' think chlorine tablets in the A/C strainer would keep these critters from growing?

 

[MikeP]

I'm gonna' have to modify mine so I can get in there, something a little bigger than that."

Seems like a good idea - woudn't be much work to use a hole saw to cut a fair size opening in the top then use a large plug fitting - kind of like the big fitting on top the fuel tank - and plug there.