Of Bilge Pumps and Float Switches......serious...

[boatone]

Now THAT is being silly....how many boats are fitted with a fax machine?

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[Deleted User YDKXO]

The best engine bilge pump arrangement I've seen is a 2 pump arrangement, a very small lower pump with its own float switch small enough to be located right down in the vee of the bilge and designed to deal with stern gland drips or the like and to clear the bilge of as much water as possible. Then right above it another much larger pump with its own switch designed to deal with much larger leaks. Both pumps were wired to different breakers with their own audible and visual alarms with the alarm for the bigger pump being much louder. If I remember correctly, there was also an engine driven pump with it's own pick up hose and outlet
However, fab though this may sound, I do wonder how useful even a system like this would be in the event of a catastrophic failure like an engine intake hose or seacock failure or the log transducer failing, all of which would result in a massive flow of water into the bilge. The trouble is that submersible bilge pumps are actually very inefficient and their flow capacity drops significantly if they have to lift water up even a small height or if they have to pump through a restricted outlet pipe. So, even the biggest bilge pump is going to be quickly overwhelmed by a major leak which of course is an argument for having a bloody loud alarm

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[halcyon]

It is around 7 seconds ( there appear's to have been no moans ) to cover small amounts of water or boat rocking, simple and cover's most of the problem. The same as everything with OE equipment, value for bucks spent.
We are currently working on a monitor that shows pump load, with blocked pump alarm, pump dry alarm and pump turn off option, plus some other areas are possible.
What do you want ?

Brian

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[Wiggo]

It occurs to me that if a seacock (or similar) fails catastrophically, unless you happen to have a man standing nearby with access to the keys and a pump, it's going to sink anyway.

A failed seacock on the raw water intake will open a hole of about 2-3 square inches a foot below the water line. From memory, according to the RNLI handbook, that will let in something like 30,000 gallons an hour, or 500 gallons a minute. That's (roughly) 2500 litres, or 2.5 tonnes per minute. So your 10 tonne motor cruiser will sink in 4 minutes. With a pump capable of handling 200 gallons/minute, you delay the sinking to 10 minutes.

A standard bilge pump might shift 1000 gph, so even 10 of these wouldn't shift 200gallons/minute, less as the boat gets lower in the water.

If the seacock fails underway, you can at least try to plug it to prevent the sinking, but if it fails while you're away (and 4 out of 5 sinkings are in a marina/berth), an alarm is only going to help if the marina has 24x7 security, and they can respond in minutes, with a very big portable pump.

Save the money you would spend on the alarm and spend it on servicing seacocks/hoses and/or insurance, IMHO.

<hr width=100% size=1>Nihil curo de ista tua stulta superstitione.

 

[Deleted User YDKXO]

Excellent post and some sobering statistics. I've been trying all afternoon to remember some fluid mechanics theory from way back in order to work out the flow through a 2" hole 3ft below the waterline (any fluid mechanics engineers out there?) and it seems the info is in the RNLI handbook. Doh!
I'd spend some money on a good liferaft as well

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[mjf]

What ever happened to that idea of a large floatation bag that when activated keep the boat afloat?

I recall we discussed this when that Fairline hit the Buoy in the solent and sat on the sand.

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[Its_Only_Money]

Re: Of Bilge Pumps and Float Switches......serious

Of most interest to me is the "flooding while underway" scenario, including sudden failures at any time when she can be moved, at least you have a chance of putting her on the mud etc to potentially avoid a total submersion. Consequently I'd give most time to an loud alarm to the effect that there was unexpected water in the bilges rather than having the unattended boat automatically manage the situation. Worst case you get more warning of having to abandon!

Of course this will be different depending on boat/moorings/usage etc etc

I guess in theory man doesn't need keys (I'd rather he broke in but more to the point would he??), or pump (stopping the ingress is the aim, not removing it), just a wood plug of an appropriate size and a mallet to seat it. Of course we all keep those by the engineroom hatch in any case right?? /forums/images/icons/wink.gif He also needs to be made of stern stuff as he is about to break into (therefore there can't be anyone on it), a boat he suspects is sinking!

So you only actually need a loud alarm and someone willing to (slightly) damage your boat to save it.......hmmm

Of course if you are friendly with your marina staff you could individually prepare them with a "if this enormous klaxon goes off then I don't mind at all if...." speech??

<hr width=100% size=1>Rgds

Simon
Its Only Money
Fairline Sprint
Solent-based

 

[Wiggo]

Re: bloody lunatic

you'd have to be to try and seal one of our seacocks:

Open lazaret
Remove junk in front of access panel
Climb into lazaret
Remove panel
Climb under cockpit floor
Stick head and shoulders through access panel
Get hit in face by fire hose effect from seacock
Try to hammer in bung while not getting fouled up on saloon floor/gearbox/exhaust

Life raft for me, I think...


<hr width=100% size=1>Nihil curo de ista tua stulta superstitione.

 

[boatone]

Whoa guys.....\'ang on a mo......

......this is all getting a tad ridiculous now in relation to my original post.

Cost of an extra floatswitch and a bit of wire to connect circuit to horn etc is really pretty much petty cash territory. For that relatively small outlay you would have the earliest possible warning that summat was amiss. I accept that a catastrophic ingress of water might well be beyond the capacity of pumps but the operative words here are EARLIEST POSSIBLE WARNING. Whether you or anyone else is able to do anything will then depend on the specifics of the actual situation.

Please return to earth and allow the KISS principle to maintain momentum......

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[clyst]

Re: Whoa guys.....\'ang on a mo......

Hows about this for KISS ---wire a B&Q smoke alarm (by-passing the smoke detection bit) across the float switch that should be nice and audible and extremely cheap plus you still have the smoke detection bit as a bonus.
Cheers

Terry

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[Its_Only_Money]

Re: bloody lunatic

So I guess they don't get opened/closed/cycled very often then?? /forums/images/icons/wink.gif

<hr width=100% size=1>Rgds

Simon
Its Only Money
Fairline Sprint
Solent-based

 

[Its_Only_Money]

Re: Whoa guys.....\'ang on a mo......

Yes but you wouldn't know whether you were on fire or sinking (I accept that the first may lead to the second in short order), I mean you have to be able to brief the crew on whether the buckets should be filled in the bilge and chucked over the side, or filled over the side and chucked in the bilge /forums/images/icons/smile.gif

<hr width=100% size=1>Rgds

Simon
Its Only Money
Fairline Sprint
Solent-based

 

[boatone]

Re: Whoa guys.....\'ang on a mo......

Thats actually quite funny..../forums/images/icons/laugh.gif





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[clyst]

Re: Whoa guys.....\'ang on a mo......

Good point I slipped that one in to see if anyone would spot that!! Seemed a good idea at the time though! Oh well back to the drawing board . Do I get any marks for trying??

Cheers
Terry

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[Its_Only_Money]

Re: Whoa guys.....\'ang on a mo......

A for effort but C- for result IMHO of course!

<hr width=100% size=1>Rgds

Simon
Its Only Money
Fairline Sprint
Solent-based

 

[plombier]

Heard over the weekend of a boater in the Southampton area whose auto bilge pump was activated by a leak in one of the diesel fuel tanks and promptly dumped the lot in the oggin. The boat owner was prosecuted for serious polution offences.


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[andy_wilson]

Is that the one that ripped the deck off as she sank?

Flotation never caught on except for little dinghies cos it takes up too much room, is difficult to protect from chafe before and after deployment, and needs hugely strong lashings to prevent decks parting from the hull.

And would you like to sleep on a berth with auto-inflation bags beneath you?

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[jfm]

autoinflate under the bed

No but I have sat on a flybridge bench seat with a hinging locker lid and some autoinflate LJs tightly packed in, and when one of those goes off randomly you do have a "WTF" moment

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[Wiggo]

Re: bloody lunatic

Every time we go out, but I wouldn't try it knowing the compartment was flooding...

Look, it's a boat. Half the jobs on board need an ambidextrous dwarf contortionist.

<hr width=100% size=1>Nihil curo de ista tua stulta superstitione.

 

[hlb]

Yep but in most cases and luckily I was one of them. The pipe or whatever, does not totaly brake, so hopefully only a bit more water comes in than usual.

<hr width=100% size=1> No one can force me to come here. I'm a volunteer!!.

Haydn