Sizing bilge pumps

[rogerbum]

On another board the topic bilge pump sizes came up so I did some poking around. I remember this coming up here before and finding a few of these links but am not sure if they were posted before.

http://www.yachtsurvey.com/bilge_pumps.htm
http://www.boats.com/content/boat-articles.jsp?contentid=1893
I like this link titled "Why do boats sink?" . It has statistics on the most common reasons for sinking both while at a dock and while underway. It also has a nice table that gives water flow rates through different size holes at different depths below the water. From the table you'll see that a 1" hole (e.g. the drain plug size) leaks at a rate of 14gallons/minute at 6" below the water line. That's 840 gallons per hour! Hence assuming that your pumps are not operating at the full rated capacity (a good assumption), you need a pump rated for 1200-1500 GPH to keep up with what leaks through the drain plug.