[octopus]

Most boats use one or more electric bilge pumps that are wired directly into the boat’s electrical system. Automatic bilge pumps have a sensor or a float switch that turns the pump on if it detects rising water. Bilge pumps with automatic sensors usually turn off when the water goes below a certain depth. A pump can also be activated via a switch on the dashboard. There are also manual bilge pumps available that are good to have on board as a backup means of removing nuisance water in the event the electric pumps fail, or can't keep up with the amount of water coming into the bilge, or if the batteries are not working for some reason. [links]

[buck]

How are bilge pumps rated? Bilge pumps are rated to pump a certain number of gallons per hour (gph) or gallons per minute (gpm). The gph ratings for bilge pumps from manufacturers such as Jabsco, Rule, and Attwood are measured at the bilge pump itself and don't consider such elements as the distance the water must be pumped upward to the thru-hull fitting above the waterline, dips in the voltage supply, or drag created by corrugated hose, or other elements. Bearing these factors in mind, understand that these electric pumps typically work at about 60% of their rated capacity. For example, a pump rated at 1,000 gph will actually pump about 600 gph.

[Alex8844]

The bilge pump is just one component of the bilge system on a boat. There's also the hose and the thru-hull fitting, and you have to position the discharge opening where it best suits your needs. For safety reasons, many boat owners choose to install more than one bilge pump. So what is a bilge pump, why do you need one, and which one should you choose?

[X0nic]

Here are some suggested pump capacities based on boat length. Understand that though t hese numbers may seem high, in the event that you need a bilge pump for an emergency, it's better to have more bilge pump capacity.

[chaord]

A standard electric, submersible centrifugal pump that can move 500 gallons per hour (gph) sounds as if it should be able to handle nuisance water easily, and even be capable of dealing with bigger problems. After all, 500 gph is just over 8 gallons per minute (gpm). That's the equivalent of just over one-and-a-half jerry cans of water every minute. But chances are, that pump is not even moving half that volume. To get an estimate of your pump's real-world pumping ability, figure out how much each of the following might be reducing its rated capacity on your boat.

[5bernardorios2]

If you have any boat larger than a small runabout, chances are you have an electric bilge pump somewhere aboard. That bilge pump is not intended to keep your boat afloat in the event of a hull breach, but simply to remove "nuisance" water — including, among other things, small amounts of spray or rainwater that come in when the companionway is open, drips from the stuffing box, or leakage or seepage from a deck fitting or port light that's not quite watertight. Though those bilge pumps are not intended for hard duty, the BoatUS Marine Insurance claim files show that in many cases, sinkings have been delayed and even avoided because a bilge pump kept up with a small leak and allowed time to fix it before it became a large leak. Conversely, many sinkings involve a bilge pump that has been ignored for weeks or months as it cycled increasingly frequently, or one that has run the battery flat in a relatively short period of time when the volume of water entering the boat led to continuous running of the pump.

[MrFlibble]

Most manufacturers rate their bilge pumps while running off 13.6 volts of DC power. But bilge pumps will only rarely see 13.6 volts in the wild. Batteries will only deliver that kind of power while being charged through shore power or with the engine running; they'll deliver considerably less when they're not being actively charged. In addition, the voltage at the battery will not be what reaches the bilge pump six or a dozen feet away in the bilge. Bilge pump wires are sometimes undersized, and connections are often corroded (it is the bilge, after all). All of this can decrease the voltage actually reaching the pump by 20 percent or more, and can easily result in a 20-percent drop in capacity. To maximize voltage to the pump, clean all connections regularly, and check the wire-gage recommendations for your pump size. If that wire's undersized, up-size. And if you decide to install a higher-capacity pump after reading this article, make sure to put in a new, larger wire.

[assdewqq]

Most manufacturers also rate their bilge pumps when pumping water horizontally. But bilge pumps are located in the bilge — below the waterline. Water is going to have to be pumped UP to reach the outlet, and it will have to go even higher if the outlet hose includes an anti-siphon loop above the waterline, as it should on most boats. Therefore, in the wild, all bilge pumps have to lift the water some amount of vertical distance — called head — from the bilge to the top of the anti-siphon loop or to the outlet. Head is expensive in terms of pumping capacity. Three feet of head height, as might be found on larger powerboats, decreases the capacity of that 500-gph pump by about 30 percent. Six feet, as could be necessary on a large sailboat, decreases capacity by more than 40 percent. Assuming the anti-siphon loop is appropriate for your boat, there's no way around that loss of capacity. If you want to move a lot more gallons per minute than you are right now, you'll have to up-size the pump.

[da2ce7]

Tips to help you choose the right bilge pump for your boat.

[osjak]

The ideal bilge-pump system does not exist. Boats come in all sorts of sizes and are put to all sorts of uses in a variety of different environments. However, after decades of boating I have developed a few prejudices, offered here as a sort of buyer’s guide to bilge pumping.

[motherhumper]

Total Capacity
I recommend the following total-bilge-pump capacities as rules of thumb. Boats less than 20 feet: 1,000 gph; 20 to 25 feet: 2,500 gph; 25 to 32 feet: 4,000 gph; 32 to 36 feet: 6,000 gph; 37 to 45 feet: 8,500 gph.

[Btcm]

Pump Ratings
The number embossed on the pump is optimistic. There are formulas for calculating actual gph versus rated gph based on hose diameter, the height that the water has to be lifted (the "head") and voltage. I simply count on an actual capacity of 60 percent the advertised rating.

[HopeFlynn7x]

While your boat may not need an â automatic⠝ bilge pump switch, it definitely needs an adequately sized bilge pump — or multiple pumps, if your bilge is divided into separate watertight compartments. Far too many boats have undersized pumps. Get a pump that is capable of pumping out more water than could possibly come in. The amount of water that might come in can be easily determined by finding the largest through-hull in each compartment; then, you can size your pump to suit the flow that would be generated if that through-hull broke off. Most small pleasureboats donâ t have through-hulls larger than 2 inches, and most through-hulls are at the turn of the bilge, which is less than a foot below the waterline. So, for the sake of simplicity, we will size a pump to suit those conditions. Consider that a 2 inch hole, from a broken-off through-hull fitting a foot below the waterline, will allow 79 gallons of water per minute to flood into the hull. That can fill the average 30 foot hull and sink it to the deck in about 30 minutes. So, we need to pick a pump that will deliver around 100 gpm to the bilge pump discharge, which is above the waterline. It is important to remember that the pump will have to move the water up 3 or 4 feet to the bilge overboard. Pump engineers call the friction caused by the water flow through the pipe â friction head⠝ and the distance the water has to rise to its discharge â static head.⠝ Together, they refer to them as the pumpâ s â head.⠝ Unfortunately, when you look at bilge pumps in the marine store, they are not rated for the quantities they can pump against any head. Instead, pumps are rated for the very high outputs they can achieve when operated with an open discharge. What this means is that the pumpâ s listed capacity shows only what it can pump with no discharge piping attached. When you add a length of discharge piping and an uphill climb to the bilge overboard, you may reduce the pumpâ s capacity by as much as two-thirds. Now, if that werenâ t enough to confuse the issue, the pump sales industry has thrown us another curve. It rates bilge pumps in gallons per hour (gph), making the units sound much bigger than they are. In other words, that bilge pump with the number 1,500 (gph) on its housing will only pump 25 gpm. Coming back to our example, what we REALLY need to overcome our 79 gpm of water flooding in from our broken 2 inch through-hull is three or four of those 1,500 gph pumps. When we also consider the discharge head from the static rise, and the piping run, we will find we need about six of them to push that much water overboard. The biggest bilge pump in one of the most popular national marine discount center catalogs is a 3,700 gph unit (62 gpm), with no head. Add a 3 foot rise to the overboard discharge, and its actual capacity may drop to only 30 gpm. Consider that this 3,700 gph pump only has a 1 1/2 inch diameter discharge pipe. Yet, we are expecting it to pump more water through that 1 1/2 inch pipe than will be coming in through our larger 2 inch hole. Once, I was using a standard bilge pump rated at 1,500 gph, with a 1 1/8 inch discharge hose to pump out a 30 foot boat. I routed the loose discharge hose up the companionway ladder and over the cockpit coaming. The total rise from the bilge to the coaming was just over 6 feet, but nothing was coming out the end of the hose — even though this brand-new pump was running full blast. So, instead, I routed the hose to the galley sink — a mere 4 foot rise from the bilge — and I began to get a trickle of water.

[KyleBles87]

[jack8logan]

[aisnake]