There aren't many regulations for pleasure craft pump capacity. We can refer to the ISO 15083-2003 (categories A,B and C recreational boats) and AS1799 standard for some guidance.

GPM - gallons per minute

LPM = litres per minute

ISO boats less than 19.6ft (6m): = 2.6 GPM ( 10 LPM or 600 litre per hour)

AS1799 boats less than 33 ft (10m): = 17.44 GPH (66 LPM or 3960 litres per hour)

As you can see, there is quite a variation in minimum bilge pump capacity requirements.

ESTIMATING FLOODING RATE FROM HULL DAMAGE:

The minimum recommendations for bilge pump capacity seems to low. We can check the minimum required pump capacity against the approximate flooding rate from a rather small hole in the hull below the waterline. The following is a reasonable approx formula for flooding rate:

GPM = 5.56 x d^2 x (sq.rt)H

Or

LPM = 2.08 x d^2 x (sq.rt)H

d = approx opening diameter, in or cm

H = depth of opeing below the waterline (head), in or cm

Example:

Let's assume a simple puncture of approx 2" (50mm) diameter located 6 in (152 mm) below the waterline for a power boat or yacht.

5.56 x 2 inches^2 x (sq.rt) x 6 = 54.47 GPM

2.08 x 50mm^2 x (sq.rt) x 15.2 = 203 LPM

If you were unlucky enough to get an impact 1.5 ft down ( 457mm) with the same hole diameter, then the amount of water pouring in would be approx 94 gallons per minute or 351 litres per minute !

Whoops - unless you have some form of foam flotation or sealed air compartments, your going down, unless your boat is made from wood. Even still, you would still want to have the capacity to pump the boat out faster than the water is coming in !

You can quickly see however, that even a hole of modest size (and not all that deep) will quickly exceed the minimum bilge pump capacity required above. There are practical limits to how large a bilge system you can and should install, but I recommend more than the minimum requirements given by the standards above.

SIZING UP A BILGE PUMP FOR THE REAL WORLD

Many manufacturer's bilge pump capacity ratings aren't all they ought to be. Most manufacturer's rate their pump capacity with no hoses attached and with no lift (head). Those that do rate for head state this clearly, and it's usually a nominal 10-ft of 3-metre head or height. However, not a boat in existence operates a bilge pump with no lift or hoses attached.! Also, the friction in 3 to 6 feet (1 -2 metres) or more of hose and pipe commonly found in all bilge systems cuts the flow rate, and the batteries are seldom delivering full oomph.

Manufacturer's rate capacity in gph (gallons per hour) or gpm (gallons per minute); or in metric lph (litres per hour) or lpm (litres per minute) Unfortunatly, that shiny new pump rated at, say, 1,500 gph (5,700 lph) in the catalog will seldom deliver more than half that in a real- sevice installation. Indeed, 40 percent of rated capacity is about the norm. In other words, the real flow out the thru-hull outlet from this 1,500-gph (5,700 lph) pump will be about 600 gph (2,280 lph)

Allowing for this loss in flow rate, what's the minimum pump capacity that should be installed? The following will give sensible results.

Pump Capacity (gph) = 1000 + (100 x displacement in long tons)
Or
Pump Capacity (lph) = 3,785 + (372 x displacement in metric tons)

Example:

Assuming a boat has a displacement of 2200 lbs (998 kg or .998 metric tons)

Long Ton = 2240 lbs

2200 lbs / 2240 = .982 long tons

1000 + (100 x .982) = 1098 gph or 1098 gph / 60 minutes = 18.3 gpm

Or

3,785 + (372 x .998 metric tons) = 4156 lph or 4156 / 60 minutes = 69.27 lpm

This is the minimum power-driven pump capacity (manufacturer's rated capacity; we've allowed for 40 percent efficiency) that should be fitted. If you have less capacity, get a bigger pump or an additional one.

To avoid large amperage draw on the batteries, install the larger high capacity pumps on pads to lift them about 5 inches (125mm) above the lowest point in each bilge compartment, with each pump's automatic float switch up on the same level. Small -capacity submersible pumps are located right at the lowest point in the bilge sump in each compartment, with their auto foat switches at their level. In this way the smaller, low powered pumps handle the vast majority of routine bilge pumping. This reduces battery draw. In the event of a serious flooding situation, the water rises high enough to trip the upper-capacity bilge pumps.

Hope this helps out.

Have a good one