Designing a bilge-pump system for your boat

 

The Problem

You’re bilge pump system has to handle two situations – pumping out the normal accumulations of water from stern gland, condensation and minor leakage, and pumping out a large influx of water in an emergency.

The most likely causes of a catastrophic leak in a displacement boat are:

  1. The loss of a seacock – either the hose becomes detached or the seacock itself breaks off the through hull.
  2. Loss of a through hull transducer.
  3. A disintegrating drive shaft stuffing box or stern gland.
  4. An overheating engine which melts the exhaust system components and pumps water into the bilge.

Holes in the hull caused by grounding or collision, and flooding by waves could be any size; it’s unrealistic to design for such freak occurrences.

Simple fact: A 1½” hole (such as an open seacock) located 2’ below the waterline will let in around 60 US gallons (230 litres) per minute. That’s 3,600 gallons per hour. That water weighs nearly 30,000 lbs. If you were so inclined you could calculate the amount of water your boat could accommodate before she sank. It isn’t many hours for the size of boat most of us sail.

So, ideally, you need an emergency bilge pump system to handle around 4,000 gallons (15,000 litres) per hour. You also need a supplementary system to keep the bilge dry.

Types of pump and how to drive them.

We can power our bilge pumps in three ways:

Mechanically, off the engine.

Electrically, from the batteries.

Manually, by a crewmember.

Think about these options a little. To drive the pump mechanically the engine must be running; to drive the pump electrically there must be juice in the batteries; to drive the pump manually a crewmember must be available.

To cover all contingencies the bilge pump system will need to be a combination of pump types.

Capacity ratings

Now, before we select the appropriate pumps, let’s consider the pump capacity rating. I’m going to try and make this as simple as possible because not everyone wants to plough through charts and graphs and extrapolations to calculate the precise capability of a bilge pump.

An electric pump with a rated capacity of 2,000 gallons per hour will only do this if there is no hose connected and the batteries are bulging with volts. But in real life the pump has to lift the water out of the bilge and push it uphill to a discharge point. Furthermore, it has to push this water through a pipe, and various bends and probably a seacock. This combination of the uphill battle and the resistance in the system is known as the pressure head and it must be applied to the pump’s rated capacity to get the real-world capacity.

My rule of thumb for calculating pressure head in a typical 25’ to 45’boat installation is to measure the height from the pump to the highest point of the pipe run and double this figure to give total pressure head. So, if you want a pump to move 2000 gph vertically 5’ your total pressure head is 10’ Now look at, for instance, a Rule 2000 electric pump which has an open flow rating of 2000gph and apply the 10’ pressure head on the manufacturers chart; you will find that this pump does a little under half of the open flow rating at this pressure head.

So, my second, and simpler, rule of thumb is – down rate electric pump capacity to 40% of rated capacity. And be aware that this requires the batteries to be fully charged; depleted batteries and dodgy wiring will further degrade performance.

Your 2000 gph pump will actually handle around 800 gph.

Mechanical and manual pumps usually give the capacity at a particular pressure head so their selection is less confusing, but the rule about total pressure head stands.

The biggest manual pumps, such as the Edson 30, will pump one gallon per stroke and the Whale Henderson Mark 5 about half that rate. Although some manufacturers give pump capacity at hugely optimistic pumping rates, (70 strokes per minute, for instance), 30 strokes per minute is hard work; if you can manage that you’ll get 1800 gallons per hour from the Edson. These are physically large pumps and can be challenging to house on a small boat. Lower capacity pumps take up less room.

Types of pump.

Every boat should have at least one manual bilge pump. Manual pumps are diaphragm pumps and the best type are double acting – they pump on both forward and backward strokes of the handle. Think about its location and how easy it will be to operate in an emergency. A long handle that can be operated in a standing position is best; kneeling in the cockpit is less good. Do what you can.

Electric pumps are, most often, of the submersible, centrifugal type. Such a pump would form the basis of your non-emergency maintenance system – to keep your bilge dry under normal conditions. Equipped with a level switch it will cycle on and off as needed to keep nuisance water from building up. Float switches are notoriously unreliable so check them frequently; electronic switches with no moving parts, such as the Water Witch, are usually a better choice.

You may wish to add a second, higher capacity pump as an emergency pump and it should be designed to come on if the smaller pump isn’t coping. It should have a level switch located higher in the bilge than the maintenance pump. This switch should operate an audio/visual alarm to tell the crew it has operated. You must be able to override the automatic function and force the pump to run if the switch fails.

If your boat can accommodate it the best of all pumps is a mechanical clutch pump, belt driven off the engine. A Jabsco Series 51270 engine driven pump will handle 4,100 gph at 10’ total pressure head but is physically large and nearly impossible to house on smaller boats.

Your engine already has a pump on it, the cooling water pump, and some advocate that this be plumbed in such a way that by switching a valve it will draw its water from the bilge instead of outside. I’m very sceptical of this advice – the engine pump doesn’t move an awful lot of water, and I’d hate to be jeopardising my engines cooling system when I already have an emergency on my hands.

So, to sum up: A typical bilge water management system will comprise a 12v submersible pump to handle normal seepage, one or two larger electric pumps to handle larger influxes and a manual bilge pump to supplement the electric pumps or replace them when the batteries are flat. An engine driven pump would be a very desirable addition.

Oh, and a baling bucket is a vital component of any leak management system.

Installation considerations.

It will be clear from the discussion of pump capacity that keeping the total pressure head as low as possible is important. The pump in the bilge should be located as close to being vertically in line with the discharge hole as is feasible so that the length of horizontal run is minimised. The maximum lift height will be determined by the distance between the pump outlet and the discharge point, or the top of any loop, vented or otherwise, in the line. Sharp bends should be avoided. The pipe should have smooth interior walls. You’re trying to make it as easy as possibly for the pump to move the water – don’t put obstacles in its way.

You’ll want the bilge pump discharge hose to be well above the heeled waterline. If you can’t achieve this you’ll need to consider a vented loop. Try hard to avoid that need.

Consider installing your electric pumps and their switches on a common base; I use a piece of Plexiglas. If your bilge is very deep you can attach a handle or lanyard to this base plate to allow you to lift the whole assembly within reach for maintenance and repair.

*

OK, those are my thoughts on bilge pump systems, but let me say right now that I have never had a boat in which the bilge pump system could evacuate 4,000 gph. In smaller boats it’s just impractical to achieve this capacity, as you may have gathered from the above. Top priority, therefore, is to avoid a situation that would require such a capacity:

Prevention and preparation.

Minimise the number of holes in your boat. Use a manifold or seachest where appropriate to combine several functions into one seacock. Use suitable seacocks – bronze, stainless or Marelon. Use quality hose and double clamp it. Maintain your seacocks, engine stuffing box and rudder bearings scrupulously and regularly.

You have to be able to get to all your seacocks easily and quickly even when they’re underwater. At each seacock you must have a soft wood or rubber bung of the appropriate size. Tie it to the seacock with a lanyard. Have a contingency plan for stemming the flow from a hull breach, stuffing box failure, displaced rudder or other catastrophe. Keep your cockpit drains clear and, if your boat doesn’t have a bridge-deck (companionway sill) keep the lower companionway hatch board in place if there’s a chance of shipping a wave.

It’s a good idea to have an exhaust temperature monitor on your exhaust pipe. A melted exhaust pipe will allow the engine to pump its raw cooling water into the boat. Melting of exhaust components can occur before the normal engine block temperature alarm sounds.

Note: In the forgoing discussion I’ve used US gallons and (litres) because that’s what most pumps are rated in and it saves me making conversions. If you want figures in Imperial gallons multiply the US gallon figure by 0.83 or divide the litre figure by 4.5.

Storm preparation – keep it simple

On a small boat in really heavy weather the only thing most of us want to do is lie in our bunk wishing it would all go away. If you’re seasick it must be ten times worse.

Going on deck to take action to secure the survival of the boat is a frightening proposition. It’s easy at this point to convince yourself that you should wait until it’s a bit calmer before putting in that reef, or hoisting the storm jib, or securing the dinghy which is beginning to come loose in its chocks. Of course you can’t succumb to that inner voice; you have to put on the harness and lifejacket, get yourself out into the maelstrom and get the job done.

If you’ve never been there you can’t imagine just how hard it is to operate under the conditions you’re likely to find on deck: The banshee wail in the rigging, the constant deluge of spray and solid water, the violent motion threatening to hurl you overboard. Even the strongest crew can become exhausted in a frighteningly short time.

One hand for the boat and one for yourself is the rule, although for much of the time it’s two hands for you and that leaves none for the boat which is why it’s so terribly hard to perform tasks that seemed so simple when it was calm.

This is why my mantra is simplicity in all things. That huge sea anchor with a complex bridle of rope and chain which you bought for just this occasion is going to defeat your attempts to deploy it, unless you have a large, strong and un-seasick crew. Even putting in the third or fourth reef with your single line reefing system with miles and miles of line is going to be a challenge if you’ve left it a bit late.

In my experience, if conditions are such that you can successfully deploy drogues, sea anchors and the like you probably don’t need them. By the time conditions are bad enough that you might benefit from such devices you’ll probably be unable to deploy them successfully without the possibility of damage to the boat or the crew. Heaving-to or running off will be your best tactics.

So, analyse your systems again and ask yourself how easy it’s going to be to get the boat snugged down and safe when the going gets tough. Can you get the sail plan sorted quickly and efficiently? Can you heave-to? Can you secure the helm? Is there any chance of items lashed on deck coming loose?

If you plan ahead and prepare the boat for bad weather before it arrives you probably can lay snuggly, and smugly, in your bunk until the storm passes. Assuming your lee cloths are properly designed and tested, of course, and your lockers have good catches and the floorboards are screwed down. And, vitally, you’ve given yourself enough sea room.

Intra-boat communication

Accurate communications between skipper and crew are vital but, at times, difficult – no more so than when the skipper and crew are operating at opposite ends of the boat. Like when you’re docking or anchoring.

The really slick teams have sorted out a series of hand signals that allow them to carry out these functions noiselessly, as if communicating by ESP. The helmsman and foredeck crew work in silent harmony to arrive precisely at the mooring buoy, the crew triumphantly grasping the ring with the boathook and getting a line attached effortlessly.

I have seen teams using headset walkie-talkies – a great idea as long as you stay calm and enunciate properly. If the crew switches off the headset and can still hear the captain screaming at her, little has been achieved.

Strangely, in ninety percent of man and wife crews the foredeck work is undertaken by the wife whilst hubby stands behind the wheel spitting out commands. We do it ourselves. It seems illogical but it appears to work for most people. One of life’s little mysteries.

Shouting is one form of communication that simply doesn’t work – it leads to a terrible atmosphere when the anchor is finally secured and drink is being taken in the cockpit.

The other method I would strongly recommend you avoid is one we witnessed in the Allen’s Cay anchorage in the Bahamas one dark and windy night. A large modern boat with him-and-her crew crept into the anchorage and began an anchoring saga of epic proportions. They were communicating intra-boat by vhf radio – she with the handheld on the foredeck, he on the fixed set back at the helm. They chose to use channel 16. In an anchorage full of boats monitoring channel 16. I have to say it was very entertaining but if it were a movie it would have had an X rating for language.

Apparent wind

Right, lets get back to basics – apparent wind, what’s that all about?

The concept of apparent wind is largely unknown to non-sailors but if you sail a boat it’s a fundamental fact of life: apparent wind is what you sail in.

Apparent wind is the wind you experience when the boat is moving – it’s the true wind modified by the boats motion. A 15-knot breeze coming at you from 45 degrees off your bow when you’re stationary becomes a 20-knot breeze at about 35 degrees off your bow when you’re moving forward at around 6 knots. The boat speed adds to the true wind speed, and modifies its angle of approach.

Conversely, when the wind is from behind its speed is reduced by the speed of the boat. A 15-knot breeze from dead astern is an apparent wind of just 9 knots when the boat is moving at 6 knots.

When you’re sailing you don’t really think about apparent wind – it’s the wind you’re sailing in and that’s that. However, there is a time when you really need to consider the effects of apparent wind and that’s when you change from a course off the wind to a course on the wind. If you’re running downwind in 20 knots true wind it might feel like a perfectly manageable 14 or 15 knots apparent. But as you slow and turn onto the wind things will become a bit more of a handful, unless you’ve anticipated it.

Apparent wind – the wind you sail in.

Bondage

No, no, I’m not referring to activities in the book 50 Shades of Grey and nor do I mean forming meaningful relationships; I’m referring to the connecting together of your boat’s non-current carrying metal components to form a common ground for your DC electrical system.

Bonding, that’s the word.

The bits we’re talking about are the engine, gear box, fuel tanks, water tanks, the external casings of pumps and motors and so on. Typically, in a bonded boat these items would be connected together with copper conductors to a common bonding conductor which usually runs fore and aft down the boat. Not bonding your boat means leaving all those big chunks of metal isolated from each other.

The idea is that bonding everything together with appropriate copper conductors provides a large common ground for the electrical system, it provides lightning protection and it controls corrosion.

There are some who prefer not to bond. These isolationists aren’t necessarily anti-social; they just think that bonding leaves the boat vulnerable to stray-current corrosion outside the hull even though it is protected from stray current corrosion within the boat.

An important issue is the question of whether or not to connect your through hulls into this common grid. Personally, I prefer plastic (Marelon) through hulls and seacocks so, for me, it’s a moot point. But with metal through hulls you have to decide whether to connect them to the other components or to leave them isolated to look after themselves. The predominant view is that you should leave them isolated.

So, research the subject and make your choice – to bond or not to bond, that is the question. Bondage, that’s something else.

Troubleshooting your VHF antenna system.

It’s that time of year when some boat owners realise their vhf radio or their AIS unit is not performing up to scratch. The boating forums are full of appeals for help and some of the responses are good, some a bit fanciful. Here’s a link to some advice on troubleshooting your antenna system:

Troubleshoot your antenna system

I hope this helps.

Note that I wrote this in 2011 when we’d been the Metz UK and European agent for six years, we’re now in our thirteenth. My, how time flies.

Comments etc.

Have to turn off comments for a while – life’s too short to spend time deleting idiot spam comments. Back later, I hope, when the spammers move on.

While I have your attention, remember Sailing Snippets is still available to download for FREE. You’re welcome.

Here’s a picture of a fleet of racing boats: