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When I first did the calculations several years ago, I was surprised at the results. I also came to the conclusion, they were very few hand or electric operated bilge pumps which could match the flow of water entering a boat, should she be holed unless one could stem the flow of water. The largest hand pump commonly available is rated at 30 gallons per minute and the largest electric pump is rated at 62 gallons per minute. These rating are with very little hydrostatic head pressure (back pressure). If these pumps could be fitted, then total pump capacity is 92 gallons per minute. Because of frictional drag in the hoses and head pressure (back pressure), the pumps must be derated to let's say 25 gallons per minute and 50 gallons per minute flow rate, respectively or a total of 75 gallons per minute. Now let's derate the in-flow rate for my estimate for a 2" diameter hole 2' below the waterline from 120 gallons per minute to 100 gallons per minute. Simple arithmetic shows the boat is now taking on 25 gallons per minute (~200 lb. of sea water per minute). Unless the flow of water is stopped, the boat is going down. True, we have "bought" some time but ............... These calculations are sobering. We must also ask ourselves how many boats are lost at sea, very few. How many boat hit containers, very few. Although I believe I am well read and have a few miles under the keel, voyagers such as the Pardey's and Hiscock's, tell us time and time again, practice prudent seamanship, know where you are, pick your weather window and have a well maintained, well found boat under foot.
Fair Winds and Following Seas,
Rod Bruckdorfer
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An eye opener, eh?
This is exactly why you should know where every
thru-hull on you boat is and how to get to it in the
dark or reaching into a couple of feet of water to
find it.
Unless you litterally hit something in the water, the
only holes that can let in the ocean are the ones you
put there. Better be sure you can reach them quick and
the valves work.
Stan R. “Waxwing”
— Rod Bruckdorfer <seagypsy@att.net > wrote:
When I first did the calculations several years ago,
I was surprised at the results. I also came to the
conclusion, they were very few hand or electric
operated bilge pumps which could match the flow of
water entering a boat, should she be holed unless
one could stem the flow of water. The largest hand
pump commonly available is rated at 30 gallons per
minute and the largest electric pump is rated at 62
gallons per minute. These rating are with very
little hydrostatic head pressure (back pressure).
If these pumps could be fitted, then total pump
capacity is 92 gallons per minute. Because of
frictional drag in the hoses and head pressure (back
pressure), the pumps must be derated to let’s say 25
gallons per minute and 50 gallons per minute flow
rate, respectively or a total of 75 gallons per
minute. Now let’s derate the in-flow rate for my
estimate for a 2" diameter hole 2’ below the
waterline from 120 gallons per minute to 100 gallons
per minute. Simple arithmetic shows the boat is now
taking on 25 gallons per minute (~200 lb. of sea
water per minute). Unless the flow of water is
stopped, the boat is going down. True, we have
“bought” some time but … These
calculations are sobering. We must also ask
ourselves how many boats are lost at sea, very few.
How many boat hit containers, very few. Although I
believe I am well read and have a few miles under
the keel, voyagers such as the Pardey’s and
Hiscock’s, tell us time and time again, practice
prudent seamanship, know where you are, pick your
weather window and have a well maintained, well
found boat under foot.Fair Winds and Following Seas,
Rod Bruckdorfer
====Stan Roeder & Barbara Wall
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