Bilge Emergency Pump Idea

[mcarling]

Originally Posted by Kettlewell

After an experience many years ago in the Bahamas I am of the school that basically believes you're going down if you get a hole in the hull somehow.

I agree. Back in the days of monohulls, my grandfather was a sailor/racer and naval architect. He told me that redundant bilge pumps were for the purpose of trying to save the boat in the event of a thru-hull failure (hose clamp, corrosion, etc.) and that all but the tiniest hull tears would send any sailboat to Davy Jones' locker.

As a boy I suspected my grandfather might be exaggerating the point in order to instill fear of grounding. As I grew up, learned physics, and saw and heard about sunken sailboats, I understood that he had not been exaggerating.

I've never seen a monohull sailboat that I thought could survive a significant hull tear. I'm impressed that Kettlewell and others were able to save that trawler under ideal circumstances (in a marina with many people at hand to help, the fire department right there, a diver in the vicinity, etc.). Without the compartmentalization found in military ships, cruise ships, or the amas of a trimaran, saving a vessel with a hull tear of any large fraction of 1% the length of the vessel is virtually impossible. In an uncompartmentalized 40' monohull, a 4" x 1/2" tear is unlikely to be recoverable with any set of bilge pumps I've ever seen on a personal vessel.

<hat off to Kettlewell>

[HopCar]

"The reason I'd want to protect the engine is that as long as it's running I have a source of power to run high capacity bilge pumps and save my boat. The raw water pumps on most engines are pretty feeble compared with purpose made bilge pumps. If you're worried about bilge pumps failing, get a spare bilge pump. "

Ziggy, we're just going to have to disagree. It is my opinion that there is very little danger of stopping the engine by running bilge water through it. If the engine goes underwater, it will stop. Your point about the small capacity of engine cooling pumps is true for small sailboat engines. Most will only move four or five hundred gallons per hour. Still that additional four or five hundred gallons an hour might just buy enough time to save the boat. On boats with bigger engines it makes even more sense to have the option. It is just an option and you don't have to use it, but if your engine is about to go under water, don't you think you might want to try it? If you're ever in the position I've just described and you think to yourself, "Damn that HopCar was right! I should have installed those valves." Your intake seacock is underwater now so just close it and slash the hose. Let's hope that neither of us gets into a position where we'll find out who is right.

As for the folks that carry a gas engine crash pump, think about converting it to propane. If it sits for a long time without being run, it's more likely to start on propane. Also carry a can of starting fluid in case you need to encourage it to start.

Daz, I'll buy the second round.

[Pelagic]

Perhaps one of the biggest culprits in loosing a sinking boat is that many bildge alarms are not loud enough or daylight visable in the cockpit when everyone is outside and pressing hard

[Dockhead]

Originally Posted by Kettlewell

After an experience many years ago in the Bahamas I am of the school that basically believes you're going down if you get a hole in the hull somehow. A large trawler was backing away from the fuel dock in Marsh Harbor and hit something on the back of its keel. The water quickly rose above the floorboards and by the time I arrived the boat was seriously listing. My wife took the children onboard back to our boat so they would be safe and I worked with other cruisers and the owners to try and keep her afloat. The Hopetown fire and rescue eventually showed up with several large gasoline pumps. With five gasoline pumps going, one a five incher and the others three inchers, we were just barely able to stay ahead of the water until a diver showed up and located the hole in the back of the keel. He stuffed something in the hole, about the size of his fist, and that slowed the water enough so that we were able to make Man O'War and get an immediate haulout. It was creepy working down below in the cabin with water sloshing about above my knees, the boat listing heavily, while trying to keep the pumps from clogging up, which they did with regularity. Then it would be a mad scramble disassembling the pump or clearing a strainer. First one than another would jam with something that used to be useful but was now detritus: underwear and socks, a sewing kit with spools of thread, charts, toilet paper, you name it. The boat's own pumps were next to useless. The engines were knocked out of commission early on. Until you experience it, it is very hard to believe the quantity of water that comes in through a very small hole when it is under pressure. There is no way the average cruising boat's pumps would stay ahead of any significant hole.

That's very much the way I imagine it

And that's why I have two life rafts, and kept up to date, and a grab bag. At sea, without divers and rescue services, it doesn't take much of a hole to sink you, I think. How will you find the leak to plug it? How will you keep the pumps you have unclogged, even if you have a lot of pumping capacity?

I've said it before, but I think cruising boats over 45' ought to have watertight bulkheads. I love, love, love the Sundeer setup with three watertight compartments and no throughhulls at all in the middle one -- that should be basically unsinkable, nearly, anyway.

My boat has got a watertight bulkhead in the forepeak, and the hull is Kevlar forward of the keel to help prevent holing in case of a collision. So far so good. But the bloody lazarette communicates with the main bilge -- bad idea. And I have something like 14 holes in the bottom, and a corresponding number of rubber hoses. So I consider the risk to be pretty significant.

I don't count on the built in pumps to stay unclogged or keep up, so for me a Honda trash pump it is. I can power it with the genset (which lives far above the waterline), the inverter, or the Honda backup generator. It will not prevent a sinking in case of a major holing but might just allow me to find and plug a more minor leak -- just maybe.

Manual pumps are fine for a little drip, but forget about manual pumping any kind of real leak. They are even worse than electric in the sense that someone who could be unclogging intakes is busy pumping. Of course you need a manual pump in case you're in a big storm, have been rolled, lose electrics, and have water in the boat but no breach of the hull. That's what manual pumps are for. But they are more or less useless in case of any kind of leak, bigger than a drip.

[Wotname]

As several posters have suggested, the "standard" recreational boat bilge pump (manual or electric) is only intended to remove small amounts of water from the bilge.

As an example, I removed the hose from an 1/2" seacock and opened it. After getting a couple of inches of water into the bilge, I tried to keep up to the ingress with the manual bilge pump. It wasn't to hard to keep up and I slowly got ahead of it. With two pumps (and two people) going it was much easier.

Then we tried it with a 3/4" seacock open and flooding the bilge. With both manual pumps going (two people), we could just keep up but could not get ahead of the ingress.

Just for fun (), we tried with the 2" seacock open and flooding the bilge - didn't take long to be convinced to shut it. No way could we even get anywhere near keeping up.

Try it yourself when you have nothing better to do than experimenting in sinking your own boat

[Stumble]

I have posted this before, but of you go to Flowrate Calculation for a Draining Tank you can run the numbers to see how much water will come in a given size hole at x depth below the water. Figure a 2" hole 24" below the waterline lets in 110 gallons/minute, or 6,600gallons an hour.

My normal recomendation is that a boat should at a minimum be able to pump out at least double the amount of water that the largest thru hull would let in if it failed completely. Not that this is proof against a significant gash, but you have to put some limit of pump capacity.