Limber holes

[pmagowan]

Is the only benefit of limber holes to reduce the number of bilge pumps you have? Would it not be better to have a pump for each section of the boat and then no limber holes. This way water would be isolated to one section and it would assist in identifying the source of any leak. Each pump could have an alarm on it so that activation of any pump would immediately alert you to the section of the boat that was flooding. My limber holes block very easily which is a pain and, being a wooden boat, introduce the possibility of rot deep within important timbers.

If you did have multiple bilge pumps what would be the best way to arrange them to avoid multiple discharge through hull fittings?

 

[Bob Stay]

I've been thinking similar. You need one way valves if you want to discharge more than one bilge pump through the same hole. Otherwise you're just moving it about, not getting rid of it.
But then, imagine if 3 bilge pumps were all trying to pump out through the same hole, at the same time, it might cause a big restriction?
I think adding the extra skin fittings seems the way to go, should not be a problem, (each must have a cock, easily accessible.)

 

[bedouin]

I think adding the extra skin fittings seems the way to go, should not be a problem, (each must have a cock, easily accessible.)

A seacock on the output of a bilge pump?

Not sure everyone would agree with that

 

[Norman_E]

If your boat has a sump above the keel the limber holes will eventually get any water to it. If you block them and fit pumps in each bilge section you would need about a dozen pumps on my boat, but mine is Fibreglass and the wood in the stringers is protected by a waterproof coating. What you could do is fit some pumps in bilge areas which might flood, and pipe the output through existing limber holes to a big pump in the lowest area of bilge, with a single overboard output.

 

[ghostlymoron]

It's a good idea to keep the bilge under the engine seperate to avoid contaminating all the compartments with oil/grease. You can then store food products such as wine and beer in the 'clean' compartments.

 

[Tranona]

The idea of limber holes is to prevent water collecting in inaccessible areas and causing rot (in wooden boats). Of course they have to be kept clear and often they are too small and block easily.

In modern construction it is easier to isolate specific collection areas or to ensure limber holes are easy to keep clear. There is a lot to be said for draining into one sump, particularly if there is a deep cavity above the keel, and then ensuring a free flow of water into it. However one of the great things about modern hull construction is that there should be no water in there in normal use - the bilge pump of my Bavaria died because of lack of use after 10 years!

If you do want to have multiple pump sumps then discharging through a manifold to one through hull makes sense. Personally I would arrange for one sump with a pickup for a manual and electric pump and forget about it - except chck they both work every year or so.

 

[Len Ingalls]

I like bilge pump discharge thru hulls above the normal heeled waterline but that's just me. / Len

 

[lw395]

It's a good idea to keep the bilge under the engine seperate to avoid contaminating all the compartments with oil/grease. You can then store food products such as wine and beer in the 'clean' compartments.

Very true.
Also true for the section under the stern gland.
Good to keep the two separate, then you can deal with any drips from the stern gland separately from wiping up a few drops of oil or diesel from under the engine.
I think bilge pump systems need to be kept simple, but keeping one or two bulkheads without limber holes should not be a problem.
In my view, the less water lying in the bottom of an enclosed yacht, the better. One or two sumps you can check and dry with a cloth would be my ideal.
I also race open boats where there is generally water flowing around, that is a different problem. I would think some wooden yachts are between the two.
Likewise a yacht that is in regular heavy use, like racing with lots of wet people aboard for extended periods is a different game to a family cruiser.

 

[Seajet]

On the hotel motor barge I worked on on the French Canals one season, a chap did come along and fit about 10 bilge flooding alarms along the length, with corresponding pumps and lights on the open bridge; that was to fulfil a new regulation though which seems fair enough when professionally carrying passengers and the thing was 38 metres long.

On my 22' sailing boat I have closeable limber holes with 3 bilge pumps, 2 manual - 1 in saloon, 1 in cockpit, and an auto electric job.

The manual pump below has a long roving hose coiled next to it, to reach to either end.

I also have captive bung type limber holes to the cockpit lockers, so I can drain them into the bilge to pump out should i ever want to.

In normal sailing all internal bilge limber holes are open and the cockpit locker ones closed, but it's nice to be able to control where water goes if something nasty happens, with particular regard to trim;

for instance allowing the aft sections to flood so the cockpit coamings were being washed over might well mean ' Goodnight Vienna ! ' so the stern lockers are all subdivided, a hole punched in one bit should not risk the boat and will be drainable once the cause is sorted.

I have been able to end up with a system like this through simply having the boat a longer time than most people keep boats, I am perfectly happy with this one and knowing every millimetre is a big bonus; I can still always see room for improvement to details though...

 

[pmagowan]

Interesting replies. I think for my current boat I might try and make the limber holes a bit bigger. She is prone to water in the bilges anyway and being of carvel construction in mahogany with the minimal electrical system multiple bilge pumps are probably a bad idea. In my next boat I intend to have 3 main sections that are watertight as well as aft and stern crash bulkheads. This obviously leaves me with a multi-pump solution or at the least a multi-hose solution unless I have limber holes which can be closed. I like the idea of a single manifold to reduce the number of through-hulls (I don't like through-hulls of any kind). This does decrease the flow, of course, if I was to have multiple pumps running at once. The crash bulkeheads might not need a pump as you could easily bail them out at your convenience after they have fulfilled their function.

Currently I just wiggle some clothes hangar wire in the limber holes from time to time but it is a pain. I wonder is it possible to make the cabin sole watertight? Just a thought!

 

[Poignard]

An old technique was have a few inches of small size chain through each limber hole, with some sort of home-made handle at each end. This was pulled back and forth every once in a while to keep the limber hole free.

 

[Seajet]

Interesting replies. I think for my current boat I might try and make the limber holes a bit bigger. She is prone to water in the bilges anyway and being of carvel construction in mahogany with the minimal electrical system multiple bilge pumps are probably a bad idea. In my next boat I intend to have 3 main sections that are watertight as well as aft and stern crash bulkheads. This obviously leaves me with a multi-pump solution or at the least a multi-hose solution unless I have limber holes which can be closed. I like the idea of a single manifold to reduce the number of through-hulls (I don't like through-hulls of any kind). This does decrease the flow, of course, if I was to have multiple pumps running at once. The crash bulkeheads might not need a pump as you could easily bail them out at your convenience after they have fulfilled their function.

Currently I just wiggle some clothes hangar wire in the limber holes from time to time but it is a pain. I wonder is it possible to make the cabin sole watertight? Just a thought!

If the cabin sole was watertight - without inspection / pump access hatches, how would you know there was a leak until maybe too late ?

Personally I have no time for ' flooding alarms ' like ships, I want a pump to start up when water approaches it, on my boat I could hear this unless I was motoring, so an lED ( not a hooter as battery power may be precious if flooding ) in circuit when it's running would be ideal.

Such LED's, rather than set at easily ignored shin level like a lot of boat engine instruments, could be beside the companionway sliding hatch near eye level.

Miltary aircraft have warning lights in just such a place, when they light up one looks to the master warning panel to see what's the problem.

Not for nothing are the primary lights by the coaming officially known as ' Attention Getters ' ...

 

[prv]

Is the only benefit of limber holes to reduce the number of bilge pumps you have?

Probably. Once upon a time a bilge pump was a substantial investment, and a boat would only have one:

There's certainly some benefit to separate pumped sections, but I think only if the partitions between them are usefully high. In our boat there's only three or four inches between the hull and the sole boards, so subdivisions would make no meaningful difference to safety, having to check and pump out multiple sections would be a faff, and the bulk of hoses and pumps would not be trivial either.

In my opinion separate bilge pumps require separate skin fittings. Otherwise you either have an absurdly large pipe and hole somewhere, or the pumps can't all work at their full capacity at once. In your subdivided scheme you'd also end up with some very long pipe runs, as the forepeak suction for instance ran back to the manifold instead of discharging somewhere near the bow. Long pipe runs reduce pumping capacity.

Pete

 

[pmagowan]

If the cabin sole was watertight - without inspection / pump access hatches, how would you know there was a leak until maybe too late ?

Personally I have no time for ' flooding alarms ' like ships, I want a pump to start up when water approaches it, on my boat I could hear this unless I was motoring, so an lED ( not a hooter as battery power may be precious if flooding ) in circuit when it's running would be ideal.

Such LED's, rather than set at easily ignored shin level like a lot of boat engine instruments, could be beside the companionway sliding hatch near eye level.

Miltary aircraft have warning lights in just such a place, when they light up one looks to the master warning panel to see what's the problem.

Not for nothing are the primary lights by the coaming officially known as ' Attention Getters ' ...

I said watertight, not 'without access'. You can have plenty of access in a watertight sole. I just wonder if a watertight sole might be a good idea or are there downsides?

Flooding alarms can be buzzers, LEDs, both, and can be linked to pumps. The key is to know immediately that a leak has occurred because stoping it early is easy. Stopping it late might be impossible.

 

[pmagowan]

Probably. Once upon a time a bilge pump was a substantial investment, and a boat would only have one:

There's certainly some benefit to separate pumped sections, but I think only if the partitions between them are usefully high. In our boat there's only three or four inches between the hull and the sole boards, so subdivisions would make no meaningful difference to safety, having to check and pump out multiple sections would be a faff, and the bulk of hoses and pumps would not be trivial either.

In my opinion separate bilge pumps require separate skin fittings. Otherwise you either have an absurdly large pipe and hole somewhere, or the pumps can't all work at their full capacity at once. In your subdivided scheme you'd also end up with some very long pipe runs, as the forepeak suction for instance ran back to the manifold instead of discharging somewhere near the bow. Long pipe runs reduce pumping capacity.

Pete

There are issues. I will need to think harder. Of course the problem regarding multiple pumps running at once is a good problem to have since having only one pump means your capacity is limited anyway.

 

[knuterikt]

Have anyone been able to find a bilge pump that can remove all water?
Having many small compartments with 5 mm or more water left don't sound tempting.
Imagine opening up each one to sponge out the rest...

 

[pmagowan]

Have anyone been able to find a bilge pump that can remove all water?
Having many small compartments with 5 mm or more water left don't sound tempting.
Imagine opening up each one to sponge out the rest...

I think the plan is to have no water in any of them unless there is a significant problem. In that eventuality then mopping up a few mil of water is not too big a chore.

 

[Bob Stay]

A seacock on the output of a bilge pump?

Not sure everyone would agree with that

I was thinking it might be needed to avoid down flooding in the event of beaching, with the boat lying on her side. It happenned to me recrntly and I had to climb out and bung the outside of the bilge pump outlet, to ensure the sea didn't enter when the tide came back in.

 

[Bob Stay]

I like bilge pump discharge thru hulls above the normal heeled waterline but that's just me. / Len

And if possible, above the waterline when she is lying over on the beach and the tide comes back in, which would be when you want cocks on the bilge pump outlets to avoid the sea coming in where it's meant to go out!

 

[prv]

I was thinking it might be needed to avoid down flooding in the event of beaching, with the boat lying on her side. It happenned to me recrntly and I had to climb out and bung the outside of the bilge pump outlet, to ensure the sea didn't enter when the tide came back in.

A diaphragm pump (manual or electric) shouldn't back-flood because it has valves. A centrifugal pump will do, so I fitted a one-way valve in the outlet of mine. I know valves are sometimes frowned upon as restricting the flow, but this is a rubber tricuspid valve that opens very easily and to full-bore size.

I can see some value in a ball valve on the outlet for belt and braces, if routinely left open unless needed.

Pete