"If a small boat sits 12 inches in the water from water line to plug, the flow velocity is 8.5 ft. / sec. When the plug is 3/4" dia., that clear hole will allow a maximum of 702 gal. / hr. to enter the boat. This flow should be easily handled by a single bilge pump of 1200 g.p.h. capacity. At at 2 feet submerged head, the flow is greater so now 990 gal. per hour are coming in. (The good news being that the pump will have less head and so discharge rates will increase.) The boat sinks quicker as the water puts the boat deeper in the water. David Pascoe ( http://www.yachtsurvey.com/bilge_pumps.htm ) suggests that even small vessels should have 2 pumps with a total capacity of about 3000 g.p.h. With a smaller pump, sinking will be a slow event. Even slower with an excited crew member on the bailing bucket! lol Once again, good battery management and maintenance are critical to the safe operation of any vessel. Perhaps check the pumps and switches now-and-again, as well."
I have always been a fan of Rule centrifugal pumps and presently have 3 on board - one forward and two near the transom totalling 4350 gph. (My brother-in-law manages maintenance for a small charter fleet and has found centrifugals very reliable on smaller boats.) All 3 are fused, switched and wired independently. The smaller ones - 750 and 1100 gph, are for routine pumping. The larger, 2500 gph unit is for a disaster. The pumps depend entirely on: 1. well charged batteries with the capacity to do the job. 2. adequate wiring to provide full current, reliably to the pumps (heat shrink connectors and 12 ga. wire for the largest pump.) 3. large pumps, considering their actual output may be only 50% of the rating; 4. large diameter, smooth bore discharge hose and clamped fittings. (Discharge ~2' above the water line). - do not use the cheesy, cheap corrugated stuff. 5. - maintenance: check the pumps and switches every once-and-a-while.
My opinion is that 1 - 5 is more important than the brand. Bilge alarms work if someone is listening (we usually ignore car alarms - unless it's ours). And remember the plug!