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West Wight Potter Mailing List maintainer
dfarrell@ridgecrest.ca.us
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Recently there's been discussion of drain hole sizes for flooded boats.
Here's some data that may help you decide about drain holes.
This is the water flow rate through various drain hole diameters. The flow
is in gallons per minute, drain diameter in inches. This is for 6 inches of
water head. In other words if your boat had 6 inches of water above the
drain hole, this is the rate it would flow out into the air. This also works
for water flowing into the boat (sinking). From the chart you can see that
the water flowed into the P-15 in the brochure at 45.4 gpm (two 1.5" holes
at bottom of hull). Question - after how many minutes would the lady be
swimming?
0.25 inches .63 gpm
0.5 inches 2.52gpm
0.75 inches 5.67 gpm
1 inch 10.08 gpm
1.5 inch 22.7 gpm
2 inch 40.34 gpm
2.5 inch 63 gpm
3 inch 91 gpm
3.5 inch 123 gpm
4 inch 161 gpm
The formula used is:
Flow rate (cubic inches/second) = 0.74 x Area x square root (2 x g x h)
g = 386 in/sec/sec
h = head in inches at any instant
gallon conversion: 235.2 cubic inches to the gallon
Multiply flow rate by 60 and divide by 235 to get gpm.
Simplifying:
Flow rate (gpm) = .1889 x Area x square root (772 x h)
This formula DOES NOT take into account length of drain pipe. More viscous
fluids, such as oil, would drain much slower. Someone please check the
calculations and formula. Thanks,
Jim Nolan P-19 #426 Panache
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