You will never sink if your bilge system is good enough
At a minimum, every boat and every compartment in a boat should have redundant pumping systems. These systems should be configured with a primary / backup arrangement and tested regularly. Every boat should also have a high water alarm system and/or an indicator that tells that the pump has been running constantly for a period of time.
There is no maximum amount of bilge pump capability however, the following table can be used as a guide for sizing bilge pumps. The primary pump can be smaller than the secondary pump. That will allow it to be replaced more often since the secondary pump should never be used except for extreme situations.
Boat Length # pumps Capacity (GPH)
16 – 22 2 5,000 – 5,500
21-26 2 6,000 – 6,500
27 – 35 3 7,500 – 8,500
36 – 42 3 9,000 – 10,000
43 – 49 4 10,000 – 12,000
50 – 59 4 11,000 – 13,000
60+ 5 + 12,000
Bilge pump installation – Every boat should have more than one bilge pump. The redundancy should also be extended to each compartment within reason.
When any bilge pump is installed the output hose should be looped up to the top of the gunnel. This will protect from water infiltration in case of a break in the hose. without the loop any break in the hose would result in the hull connector being a hole in the hull. With a loop installed a break in the hose before the top of the loop would not result in any disadvantage based on the through hull connector (see the following figure).
Every boat must have redundant and properly installed bilge pumps.
A friend rented a 40 foot sailboat with a couple of other friends. The idea was to take the boat on Lake Ontario from Henderson Harbor to Kingston Ontario during the evening. They were moving at a good clip with the boat keeled over to the port. Someone went below and discovered water in the cabin. They had discovered a leak. A frantic search uncovered a break in the bilge pump hose at the starboard bilge pump. The redundant pumps were configured to pump out the opposite sides of the boat, i.e. the port pump exited the starboard gunnel and the starboard pump the port gunnel. The hoses were not installed with a loop and so when the hose came off the starboard pump and the boat was leaning to port, they essentially had a leak in the port side hull. Had the pump been installed with a loop up the gunnel, there would be no leak. but only a bilge pump that wouldn’t pump. A much less serious problem.
Bilge Pump Switch
There are several different types of automatic bilge pump switches. Each type has its problems but all of them are adequate if you take proper care in the installation and maintenance. All Bilge pump switches are wired and therefore require proper wiring. By proper wiring we mean neat, protected and properly sized.
High Water Alarm
I read about a 30 something foot boat last summer that sunk close to shore in a river. The captain’s account of the situation was that he heard a thump but didn’t think much of it at first. A short while after hearing the thump he went below for something else and noticed water on the floor. The water was above the lower deck and rising. This is not the ideal way to find out that you are sinking. You should have some type of monitor or high water alarm that would give you an indication of high water or large leak. This monitoring will provide precious time to prepare for the emergency.
High water alarms are simply a audible indication connected to a float or other type of switch that goes off when the bilge water gets over a certain level. The level should be well below the cabin floor. In addition to the high water alarm, it would always be a good idea to add an emergency bilge pump along with the high water alarm.
Bilge Pump Monitoring
Bilge monitors tell you when the bilge pumps has been on for more time than usual, indicating a large leak. Another friend of mine had a slow but steady leak in his shift cable boot. I noticed the bilge pump coming on once every three minutes or so. The operator of the boat had no idea that there was a potential problem because he had no indications that the bilge pump was automatically activating. A bilge pump monitor would have given him an audible and/or visual alert every time the bilge pump came on. He would have noticed that it was coming on often and been able to fix the problem. As it turned out his boat kept afloat due to a good bilge pump system but it could have been disastrous.
In the previous high water alarm example the boat didn’t have adequate bilge pumping for an emergency. The only thing he could do was to maneuver to shallow water, get everyone in life jackets and abandon ship. Had the boat been equipped with an emergency pump he could have maneuvered to a marina where they could have hoisted his boat ashore and fixed the problem with no collateral damage. As it was the boat went under which experts indicate will cost 40 percent of the original cost of the boat. How much would an emergency pump have cost?
- You should have enough bilge pump capacity to overcome a complete failure of your largest through hull fitting or drain plug. This is just a minimum. We cannot specify a capacity that will be enough for any situation. The more capacity you have the less chance you will have of sinking. You must trade off the cost vs. capability.
- Inspect and test your bilge system often. Include float switch, wiring, junk in the bilge …
- Use redundant bilge pump systems. 2 completely separate systems would be a minimum.
- Always have a high water bilge alarm. Redundancy here would also be good.
- Bilge system monitoring provides an indication that something is wrong in the bilge faster that your standard high water alarm
- Emergency gasoline powered pumps are a good idea
More reading about keeping your boat afloat