May 22, 2012

Can your pumps cope?

IT’S A SAD FACT, but most bilge pumps cannot keep up with the inflow of water from a reasonably small hole in your hull. So, if you hit a rock, the first thing to do is try to stop the flow of water somehow, either by stuffing cushions or towels in the hole, or by covering the hole from the outside with a collision mat.

Unfortunately, it’s difficult to get to the bare hull on many boats because of built-in furniture and liners, so you should also have at hand a suitable ax with which you can hack away the beautiful varnished teak.  Don’t worry, you won’t feel a single twinge of remorse while you;re hacking to save your life.

Stuffing things in the hole should slow down the flow enough to enable your pumps to cope while you make more permanent repairs, but it’s as well to bear in mind that a suprisingly small hole will sink your boat in short order, and the smaller the boat the bigger the pumps you need.

This is the formula that gives you the rate of flooding from an underwater hole:

Incoming gallons per minute = D x square root of H x 20, where D = the diameter of the hole in inches and H = the height in feet to which water must rise to reach the outside level — in other words, the depth of the hole below outside water level.

If I haven’t frightened you enough already, take note that a mere 2-inch diameter hole 3 feet below the waterline will let in 69 gallons a minute, or more than 4,000 gallons an hour. A high-capacity power pump is rated at 3,000 gallons per hour.

Today’s Thought
Great floods have flown from simple sources.
— Shakespeare, All’s Well that Ends Well.

“I hear old Bill got addicted to brake fluid.”
“Yeah, that’s right.”
“How’s he doing?”
“Oh, he’s okay. He says he can stop any time.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)


Anonymous said...

Yikes! What is the solution to this?

Anonymous said...

Perhaps the solution is a judicious application of low density marine foam.