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How NOT to
Sink! What you need to know about bilge pumps and keeping your boat afloat - 99% of boats do NOT have adequate bilge pumping capacity (and that likely includes yours).
Your Bilge Pump Is Inadequate. Really. A one and a half inch hole two feet below the waterline will flood a boat with 3,720 gallons of water per hour (GPH). Typically boats under 30 feet will have 500 to 2,000 GPH of rated bilge pumping capacity. Does anybody see a problem here?
3,720 gallons per hour rushing in versus 2,000 gallons per hour pumping out
Actually the situation is much worse than that because most systems are not capable of pumping their full rated output in real world conditions. For instance, look at the specs listed on the Rule instruction sheet for their 1,000 GPH pump. According to their own figures, with a laboratory perfect 13.6 volts and pushing the water though a 1 meter head, output will be only 720 GPH! Almost 30% less than its rated pumping capacity!
Actually It's Worse Than That But it gets worse. The above figure is capacity at 13.6 volts, pretty much laboratory perfect battery conditions. The typical boat is not likely to be getting that voltage to the pumps because of weak or undersized batteries, undersized wiring and corroded connections. Add in backpressure from corrugated bilge hose and you could well end up with only 40% to 60% of rated pumping capacity. And from what we've seen snooping around on boats, even those figures might be optimistic.
My neighbor's boat
A neighbor's boat - see photo above. This old woody was notoriously leaky and was literally being kept afloat by the bilge pumps. The bilge system was, to put it mildly, less than robust (pretty stupid given the hull's leakiness). The owner left town one weekend and to no one's surprise, the batteries died. Once that happened, it was a foregone conclusion that the boat would sink within hours. Which it did.
Most Pump Far Less Than Advertised Bottom line - in real world conditions, most bilge pumps are probably pumping somewhere between 40 and 60% of their rated GPH!
Bilge Pump Setup On Our Boat Since we can't cover every possible boat and how it should be rigged, we thought it might prove helpful to detail how we rigged the bilge system on one of our boats, a 27-foot Ocean Master center console. Feel free to steal any ideas that make sense for your particular situation.
The Bilge Pumps: We employ three pumps totaling 7,300 GPH of pumping capacity (2,000 main, 1,800 and 3,500 as back-ups). We use three pumps for simple reason of redundancy. If you only have 2 pumps and one fails, you are down to a single pump. Never a good idea. Is this overkill? Maybe, but because of the issues raised above, you should factor in a large safety margin. Over the past 8 years we have personally witnessed 6 boats that were sunk at the docks. Just this past weekend we were treated to the sight of a 32 foot center console sunk at the docks. Mind you this wasn’t some beat up old boat, it was a $100,000, 4 year old boat from a well know manufacturer. Call us crazy, call us paranoid, but we prefer our boat on top of the water, not under it…
Bilge Pump Float Switches: For activation redundancy we use float switches on two of the pumps while the third pump is electronically activated (it cycles on every 2 minutes, runs and shuts off quickly if it senses no water being pumped*). On the two float switch activated pumps we use Rule Super Switches which are a step up from their regular switches. They seem to have better wiring and construction. We also don’t use covered switches for one simple reason - every time we head offshore we manually lift each of the float switches to make sure they are not stuck and that they trigger the pump properly . You can’t do this with covered switches.
Bilge Pump Hose: Do not, any under circumstances, use that cheap corrugated hose that you see in every marine store (and on a number of production boats). Those corrugations cause backpressure, which further reduces pumping capacity. In addition, we question how long that stuff will hold up in the marine environment. We prefer Trident series 147 or 148 smooth walled hose. This is beefy stuff that is expressly designed for critical below the waterline connections. Another thing, hose runs should be well supported, otherwise as the boat bounces, they will put strain on the connections at the bilge pumps and at the thru hull discharge fittings.
Bilge Pump Hose Clamps: Obviously we all know you're supposed to employ 2 clamps below the waterline. Unfortunately, many bilge pumps do not have a nipple big enough to fully support two clamps. Talk about dumb product design. In some cases the best you can do is one clamp fully secured while the second is lightly snugged up but not fully tightened.
As to the clamps themselves, you want to make sure they are 100% 316 stainless (not just a 316 ss band). These will last much longer than the all 304 or 316 with 304 nut. Better yet are the all 316 stainless the clamps by Scandvik that have a non-perforated band. Without the perforations the band is likely to be stronger and have less cracks and such for corrosion to start. We swear by these clamps. They really do seem to corrode less than even good 100% 316 stainless perforated clamps.
Keep Bilg Discharge High - Riser Loops: Here’s an eye opening experiment. Put a garden hose with water running against one of your bilge thru hull discharges. You’ll notice the water flows directly into the bilge almost unimpeded. So what does this mean? Well, if you are out in rough seas, say drift fishing, each time a wave comes up the side of your boat and covers a thru hull it is likely pouring water into your bilge. Or if the thru hull discharge becomes submerged for some reason, water could come pouring in and give you a one way ticket to the bottom.
For these reasons your discharge point (where the bilge discharge thru hull exits the boat) should be adequately high off the water. In our mind 24 inches is good. If your discharges are lower, then you should add a riser loop to the discharge hose. Because our boat came with bilge discharge thru hulls close to the waterline, only 12-18 inches, we added a nice sized riser loop in the hose (and adequately supported it). And yes, a riser loop may decrease pumping capacity somewhat - another reason to have plenty of bilge pumping capacity onboard. You can never have too much!
Making Good Wire Connections To Your Bilge Pumps: OK, here is where we veer off into obsessive / compulsive. The bilge is an incredibly corrosive environment and plain old crimps just don’t cut it. We make my connections as follows.
We use Ancor adhesive lined, heat shrink crimp connectors. Ancor also sells a special ratcheting crimper that releases when the proper crimp has been made. It costs about $40 but allows you to make first class crimps with a little practice. Once the connection is crimped, you then use a heat gun to shrink the tubing and melt the adhesive which seals the joint. So far so good. But to be doubly sure, before we do the first crimp, we slide a piece of slightly larger heat shrink tubing down the wire. Then, after we make the first heat shrunk crimped connection, we let it cool, then slide the larger heat shrink tube over the connection and heat shrink again. Viola, crimped, double heat shrunk connections. But we’re not done yet. We then fully tape the connection with good electrical tape for additional abrasion resistance. The final connection ends up being a little bulky but it is one we have a high confidence in.
The Wire: All wiring should be supported by clamps or zip ties every 6-12 inches and should not lie loose in the bilge for obvious reasons. This keeps the connections out of the water and prevents the wiring from jamming the float switch either open or closed. Again, common sense.
For marine applications, the appropriate wire to use is multi-strand, tinned, marine rated wire. We use the insulated duplex wire which has 2 insulated wires in a white, protective sheath. The wire should be sized for a 3% voltage drop if possible, but in no case for more than a 10% voltage drop. There is a very simple chart which shows the proper size wire to use for each of these voltage drops based on the length of the wire run and the amperage of the electrical device. You can find this table in any decent marine electrical book, in the West catalog, or on some product websites (Ancor, Blue Seas etc). Visit www.ancorproducts.com and then go to the technical Information menu, choose Conductor Sizes - then choose tables for 3% and 10% voltage drop.
Voltage Drop Tables To Calculate Proper Wire Size Based on these tables, if you have a long run (say from batteries in the console to the pumps in the rear of the boat) and large capacity bilge pumps, you will need some HEFTY wire to meet the 3% voltage drop. This may not be practical, but go as large as you can and in no case smaller than the wire needed for a 10% drop.
Thru Hull Discharges On Bilge Pumps: Its sad that I even have to say this, but you should be using bronze or chrome over bronze thru-hulls for the bilge discharge, not the plastic ones. Remember the weight of heavy hose can cause a lot of strain on the fitting as the boat bounces up and down on waves (another reason to make sure your hoses are well supported). Common sense, go with the metal fittings. If appearance is really important to you, thru-hulls are now being made in 316 stainless steel.
Batteries To Power Your Bilge Pumps: OK, now we have adequately sized bilge pumps, properly sized wiring, good electrical connections, 316SS hose clamps, heavy duty hose (with riser if necessary), metal thru-hulls for discharge and all wiring / plumbing is well supported by zip ties or other clamps. Almost done.
Only thing left is the batteries. Whole books could be written on this subject. Suffice to say you absolutely must have high quality, high capacity marine batteries. Otherwise all the above effort is meaningless. On our boat we run a group 31 deep cycle house battery plus 2 group 27 starting batteries. We will probably add a second group 31 battery to the house bank. Even better would be a single 4D house battery with 2 group 31 starting batteries. Remember, a properly sized bilge system uses a lot of juice. Also, buy a good quality 3 stage charger to make sure your batteries will stay in peak condition
Wiring Up the Bilge Pumps Bilge pumps should be wired direct to the appropriate batteries with the right size circuit protection. In our case we used in-line fuses that are readily accessible near the battery - not buried somewhere in the bilge. If your bilge pumps are wired AFTER the battery switches you have a problem. When you turn the battery switch to off as you leave the boat, you no longer have working bilge pumps. A sure recipe for disaster. By wiring them directly to the batteries, with circuit protection, you will have working pumps regardless of how the main battery selector switches are set.
Bilge Pumps And How Not To Sink - A Summary A boat builder once looked over our bilge system and joked that we didn't have a sportfishing boat, we had a firefighting boat with all my pumping capacity. We took that as a compliment. To put together the system described above might cost $400 to $800 dollars more than the typical installation. But considering the cost of the boat, and the very high value we place on my own life, we consider it a bargain. Not too mention the peace of mind when 30 miles offshore or somewhere in the islands with no other boats in site.
* note, If you employ electronic bilge pumps that cycle on every few minutes, and they are wired direct to your battery, you could run into a situation in which over time your batteries are drained. The amperage used as these pumps cycle is really small, but you must factor it in to your equation. If your batteries are constantly hooked up to a charger, this shouldn't be a problem. If not, you better estimate the drain over time versus your battery capacity. In addition, if you store your boat in dry storage or on a rack, why have a bilge pump constantly cycling for no reason? In these cases, what you can do is rig a dedicated switch to the electronic pump so that when the boat is out of the water the pump does not cycle on and off. For these reasons we use these types of pumps in conjunction with traditional float switch activated pumps.
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