Flood - De-watering (Bilge Pump System) Reliability

The Panther was a small sightseeing boat used in the Florida Everglades. It was poorly operated and poorly maintained. The boat had a shaft tunnel that protected the propeller and allowed the boat to navigate shallow waters. It was common for these types of boats to run aground. However common it might have been, it should not be OK to run aground without inspection and maintenance afterwards. The Panther was running in a damaged state for an extended period without repair. The boat was taking on water regularly. The bilge pumps masked the symptoms, and the problem got worse until the final day. Adding to the potential problem was a corroded and inoperable bilge high water alarm. Additionally, the starboard bilge pump did not work.

The Panther was on its third tour of the day. The operator, who indicated that the boat had been operating fine, noticed no problems. One of the passengers, while waiting to board, noticed that the port bilge pump was pumping out water on a regular basis. He estimated 3 or 4 gallons every 30 seconds. The passenger said nothing until after the voyage.

About halfway through its last tour, the Panther listed to the starboard. So much water spilled over the sides that the Master stopped the boat and flagged down a passing crab boat for assistance. As soon as the crab boat pulled along side, the Panther swamped and sank right out from under the passengers.

The Panther had been operating in a damaged state. The section of the hull that held the propeller strut was broken, rotted, and leaking water. As it got worse, the leaking increased. Only one of the two bilge pumps was working and the high water alarm was not operable.

Even though no deaths resulted, the accident should have been avoided.

The boat should never have been allowed to operate using the bilge pumps to mask a serious hull leak. Similar things can happen to you, for example:

Table 1 shows the reasons that boats sink while under way according to Boat US Seaworthy website [17]. According to the US Coastguard, in 2002, 559 boast capsized, 348 boats swamped and 335 boat sunk for a total of 1242 sinkings. Imagine yourself with a dinky little manually operated bilge pump with no indication about the level of water in your bilge.

Table 1 Why Boat Sink from the Seaworthy Website [17]

These situations happen often. If you have young or old people aboard that are weak swimmers, the situation is even dangerous. Adequate pumping capability is crucial. How much is enough and how much is too much. The answer here is simple; you cannot have to much emergency pumping. What is the minimum requirement is a harder question to answer. You must answer the answer for your boat and the way your boat is used. If you have an open bow and take it offshore 25 miles or more, you will need more that the person who has a closed bow and who only travels around an inland lake when the weather is nice. Even the inland boat must be prepared for an unexpected storm. Many boats have multiple compartments. Each of these is treated separately with its own bilge pump system.

The bilge pump system is your life-line and in many cases is more important than a life raft. Don’t take it lightly. Let’s talk about what can and does happen that might require you to want a good bilge pump system. Even though most sinking is at the dock, the bilge system should be designed for the worst case at sea not the best case at the dock.

Leaks can occur from several different components on board the boat. According to the Boat US Seaworthy Web Site[17], boats sink because of Water over the gunwales, leaky through hull fittings, leaks from the raw water cooling system, leaks in out drive boots, rain, snow and sleet.

Repair or replace Leaky through hull fittings immediately. In some cases the through hull is not being used and could be removed. Obviously, fill the hole with something, either fiberglass repair or a dummy fitting.

According the ABYC every below water through hull fitting must have a seacock. However, just because you have one does not mean that it is in working condition. You must actuate them often to make sure they are working and not leaking. Take each seacock apart, inspect it, and lubricate it as part of your yearly maintenance. Replace any worn seals and parts, lubricate with a good water resistant grease and generaly make sure the valve is in good operating order.

Raw water-cooling system is another major area that can cause excess water in the bilge. Raw water coming from a faulty exhaust system can fill the bilge and sink the boat before you know it. In many cases, the exhaust boot comes off or splits causing large amounts of cooling water to enter the bilge. This happens many times as a result of engine backfiring. Inspect all of the flexible components of your raw water cooling system. Keep the engine in good running condition so you won’t get any backfiring. Use double stainless steel clamps on all raw water fittings including the flexible exhaust hoses.

One of the most important things to know is; at what rate is your boat taking on water, and is the rate increasing. Most boats leak some amount of water. You need to know what is normal and what is abnormal. Whether you know what the actual rate is or if you know how often the bilge pumps turn on, you should have some type of monitoring.

The sinking of a boat will accelerate as it goes down. The lower the boat gets the more above water fittings and scuppers are underwater with the potential greater intake of water.

Consider a 2 inch hole in the bottom of your boat as a design goal. Figure 1 shows how much water will come in through a 2-inch hole at various depths. Two inches is about the size of a through hull Sonar transducer. For example if your hull bottom is 1 foot below the surface, you can expect to fill a 55-gallon drum with water every minute from the 2” hole in the hull. That translates to 55*60 = 3300 GPH.

Figure 1 Leak Rate from a Two Inch Hole

Add this all up and you have a disaster coming at you and the faster you respond the less impact it will have.

You need ample bilge pump capacity, advanced indication of an emergency and properly installed and inspected through hull fittings. Fifty-five gallons per minute is the same as 3300 gallons per hour. Therefore, 4000 gallons per hour should be the least bilge pump capacity that you should have in a boat that can expect a 2-inch hole a foot below the surface. Twice this rate should be a design goal of a good redundant system. In other words, this situation should have two independent 4000GPH bilge systems.

I know of a situation where the boat owner took out his through hull SONAR transducer for inspection. After inspection he decided he would leave it out until a latter date. Of course he forgot about the lack of the transducer the next time he launched the boat. It was a large trailer boat so he didn’t realize that the boat was taking on water at a rate of 55 gallons per minute until a couple of minutes had passed. This owner (name withheld) had already parked the car and disengaged the large trailer when he returned to the boat to see water on the deck. Rushing back to get the trailer hooked up he neglected to latch it properly. He barely got the boat on the trailer so it was cantilevered on the end. He pulled the boat out and as soon as he stopped, the trailer popped off the hitch, swung on the safety chains smack into the back of the SUV smashing in the back door. The boat was now resting, full of water, on the 2 bronze propellers. I understand it took 6 – 10 big men to get the trailer back on the hitch since the boat was hanging off the end.

This person was lucky. No permanent damage to the boat, but his pride needs a little more time to recover fully.

One of the most often occurrences of bilge flooding for trailered boats is forgetting to put the drain plug in. I have done it more that once, almost everyone who trailers their boat at some time forgets this silly little plug. Certainly as a bare minimum, you should have enough pumping capacity to handle fully the loss of the drain plug. See Figure 2 for the rate of a 1” diameter leak. As you can imagine, the one-inch hole is quite a bit less than the 2-inch hole. If you meet the 2 inch hole criteria you will have this covered.

Figure 2 Rate of a leak vs Head (depth) from a One Inch Hole

Leak Rate Calculation [30]:

Q = 25*A*K*sqrt(h)


Bilge Pump system failure

The Miss Majestic [25] was a small military vessel converted for commercial sightseeing. It was built by the military for rough duty and could remain afloat even if battle damage caused considerable leaking. This robustness was mostly due to an over sized bilge pump that received its power from the main engine.

The converted bilge system consisted of 3 small electric bilge pumps with a total pumping capacity of 2500 GPH and the oversized engine driven bilge pump with a capacity of 15,000 GPH. The total bilge system capability was a respectable 17,500 GPH. This vessel could have taken a several bullets through the hull and still make it to shore safely.

The practice of the operator on the Miss Majestic was to turn on the electric bilge pumps before entering the water and turn them off when exiting. Since only one of the electric bilge pumps had an automatic float switch, two of the pumps were on all the time.

The boat had a shaft cover that was below the waterline. It was made of rubber and secured on each end by a single hose clamp.

The shaft cover somehow came off while in route with a full complement of passengers aboard. Water gushed in through a significant sized void. No one knew anything was wrong until the boat listed to one side. Almost immediately the stern went under and the boat went to the bottom, stern first. The boat sank so fast that the passengers could not all get on life jackets and the operator did not even get out a May-Day message.

This was a failure to properly configure, monitor, and maintain. Proper configuration would have provided double clamps for the shaft cover as well as proper bilge system. Monitor the amount of water in the bilge, the amount of water being pumped out and the condition of the bilge system. Maintain the bilge systems as well as the vessel itself.

As it turns out;

This catastrophe could have been avoided if:

More time could have been provided to allow the vessel to get ashore, better prepare passengers for the emergency:

This was a tragic account that could have been prevented with proper configuration, monitoring, and maintenance.

Whenever you have a continuous, significant leak, get it fixed. Do not rely on the bilge system. Most boats have small leaks that are considered normal. As a rule of thumb, a small normal leak should be less 1/10,000th the capacity of a redundant bilge pump system. For example, assume you have two redundant 1000 GPH bilge pumps. That gives you 2000GPH but only 1000 redundant GPH. 1/10,000 of that would be .1GPH or 2.4 Gal per day. Even if you left your boat unattended for 2 weeks, you would only have 33 gallons of extra water in the bilge. Most likely it will not be a problem as long as you maintain your battery, you don’t get huge rainfall and the leak stays small.

Monitoring the leak will give you an indication of how large the continuous leak is and if it is increasing. There are several devices on the market that tell you how many times the pump has turned on. or some actually give you the amount of time the pump was on.

Keep your bilge pumps in constant working order. Test them regularly. I’m sure the operator of Miss Majestic had no idea that the bilge system was going to be called on for special duty on the day of that last voyage.

Bilge pumps are usually inexpensive plastic pumps that work pretty well most of the time. However, they have many failure modes with many causes. The motor jams due to contamination in the bilge, the hoses can be come clogged due to junk in the bilge, the bilge float switch can become stuck by floating debris, the hose can crack or leak at the joint, just to name a few. The chances of your bilge pump system failing is great. Therefore you need redundancy and enough pumping capacity to overcome a large leak.

Many boats have minimal bilge dewatering capacity. The capacity should be a function of the size of the boat as well as the size of your through hull fittings. If you have 4 - 2” through hull fittings, you should have more pumping capacity than a boat that has as single 1” through hull fitting.

Inspection and testing of the bulge system is also important. A friend of mine took out a bareboat charter for the weekend. It was a fairly new 35 foot sailboat. As long as they were keeled over on the starboard side they had no problems. But after a couple of hours into the sailing they came about and keeled over on the port side. After a little while they noticed water on the floor of the cabin. The boat had two bilge pumps one on the port and one on the starboard side. The port side exited the starboard aft and the starboard side exited the port aft. The hoses were armored with stainless steel braid but each one ran through a stowage compartment. Apparently, the hose on the port side had broken right at the through hull fitting. When keeled over to the port, water gushed in faster than the port bilge pump could pump it out. Once they determined the problem they realized that they could only sail keeled over to the starboard. This would not allow them to get back home until they fixed the problem. While underway, they made the repair and were good as new. However, the person that designed such a situation … should be flogged. This is just one example of what can happen. Had they not been on their toes the situation might have been worse.

They could have used an emergency bilge pump if they had one. These systems are usually powered by gasoline and provide an extra amount of bilge pumping for an emergency. One type uses the boat’s main engine to turn a large impeller that will pump if water gets near the top of the oil pan. The more usual emergency pump is a reliable gasoline powered 200+ gallon per minute standalone pump. Of course you must be sure it is working order and that you have the proper type of fuel onboard.

The captain should be aware of the condition of his bilge dewatering system. It should be tested frequently and any problems fixed.