Bilge pumps. Those things everyone who owns a boat talks about, knows they’re supposed to have one, that it lives….somewhere down there in the bilge, and nine times out of ten it’s dark, wet and dirty.
To start let’s look at the function of a bilge pump system. One of the things I often here when rescuing a boat from the bottom is the assurance that, "The bilge pump was working when we left it." In most cases I’m sure it was running but, contrary to the theory that a bilge pump is made to prevent sinking, bilge pump systems are not designed for that.
In center consoles and small to mid-size sail & power boats, bilge pump systems are designed to rid the bilges of nuisance water, a weeping stuffing box or rudder post, rain water making its way to the bilges from poor hatch seals, potable or salt water leaks, tankage leaks, all of which collect in the bilge. Given that a 1” hole three feet below waterline will let roughly 2000 GPH of water into the boat, those 500 GPH to 800 GPH pumps which you find on most 20’ – 30’ production boats will only handle small amounts of water in the bilge. This is the most common bilge pump system we encounter.
(It is important to note here that any of the above water intrusion sources can and do sink boats when left unattended for long periods of time. Unless left on a charge source, batteries are finite so eventually the pumps stop working. If you need to leave a boat unattended on a mooring it’s a good idea to have someone checking on it regularly.)
There are three types of bilge system designs, the first being the system described above. Its primary function is to keep the bilges de-watered from nuisance water intrusion. The second type is the high water system which is designed to work in tandem with the nuisance system. Again, the purpose of the high water system isn’t to prevent sinking, but rather delay it.
If your center console is set up with a 500 GPH bilge system, the high water system would be a 1500 to 2000 GPH pump (or more) installed to activate when the nuisance system was overwhelmed. The general scenario would a beautiful day until a raw water hose let go, or those rocks did jump up and attack the bottom of your boat and you have that 1” (or bigger!) hole. The idea is to take an event which might sink the boat in fifteen minutes and turn it into 30 or 40 minutes. This gives you more time to locate and mitigate the leak, more time to get to shore, or worst case scenario a bit more time to get out a distress call and get help.
The third type of system, which is seen in offshore vessels and commercial vessels, is a crash pump system. These can be simply be a self-driven (gas) high volume trash pump. If you have onboard AC generators they can be AC driven and either can be built in or portable. These systems are designed to give as much time as possible in the event of a catastrophic moment. That said, if that moment tears a 6’ – 10’ breach in the bottom of the boat, even these systems only give you time to respond. On most 20’ – 30’ boats space to build in or store such a system simply isn’t practicable.
So those are the three basic system designs. For most of the small to mid-sized boats we recommend a primary bilge pump system with a good high water system equipped with audible alarms.
Given all the choices, what type of pump should you have? We’ll explore pump types, advantages and disadvantages in the next installment. Stay tuned.