Powerboating - Part Seven

Like most boatowners, it didn't take me long to realise that if I wanted to keep boat maintenance costs to an acceptable level, I would have to learn to do a lot of the work myself. So this month it's off with the electrician's hat and on with the plumber's overall!

FRESHWATER PLUMBING
The advent of small DC voltage pressure water pumps has made life a lot simpler for extended stays onboard.

The style I prefer has three or four chambers which each contain a small diaphragm. A rotating cam pulsates each of these diaphragms in turn and this causes suction. The water is pushed out of each chamber through a non-return valve and thence down the delivery pipe. A switch that senses pressure is mounted on the end of the housing and is wired to the motor.

Installation is simply a matter of connecting the inlet and outlet hoses and joining positive and negative wires.

This style is self-priming and capable of delivering around 13.5lt per minute, although larger models are available.

Low current draw (around 6amp) and quiet operation, coupled with high reliability and low cost, has seen these pumps fitted to just about all new boats on the market today.

One last thing in their favour is that they can be run dry without damage. If your boat still has manual pumps, either foot of handle, and you have been thinking of upgrading, then I can recommend this type.

In Fig One we've shown a typical freshwater plumbing system for the average boat. Additional heads will of course mean additional shower and sink sets.

There is an accumulator directly in the output side of the pump. The purpose of this is to stop short-cycling of the pump if a tap is only slightly turned on. When this happens in a system without an accumulator, the pump will rapidly cycle on and off, which is not good for the pump's motor as it tends to heat up rapidly under these circumstances.

If you find this occurring too frequently, go to the expense of an accumulator. This is simply a pressure vessel with two chambers separated by a rubber membrane (See Fig Two).

The top chamber is pressurised with air, generally with a bicycle pump, and the bottom chamber allows the water to flow through. If a tap is turned on slightly, it will be some time before the pressure in the system drops sufficiently for it to be sensed by the pressure switch in the end of the pump. When it does cut in, it will run until the pressure is restored in the accumulator. The overall result is the elimination of short-cycling of the pump.

PIPING HOT
In the standard hot water system (HWS), the cold water enters the container at the bottom and pushes the hot water out at the top. A relief valve is mounted on the side, and as the water heats up and expands, the container comes under pressure. The valve opens at a predetermined temperature and relieves the pressure by venting excess water to the bilge.

The disadvantage of this type of HWS is the cold water is mixing with the hot, reducing the overall temperature of the water.

A better design is the mass transfer system shown in Fig Three. The container is first filled by operating the relief valve's lever at the top. This admits water through the uppermost outlet (A) of the valve until water flows out of the overflow.

After turning the hot water system on, the water heats up. (This heat is typically supplied via a heat exchanger from the engine's cooling water). When a hot water tap is turned on in the boat, cold water enters a heat exchange coil through outlet B of the relief valve, picks up heat from the mass of the hot water in the container and thence travels to the open tap.

There is no mixing of the hot and cold water, so the storage of heat lasts much longer than in the standard system. An additional advantage is that the container is not placed under any pressure; as the water expands it simply flows out of the overflow.

The container is kept topped up with water by the action of the relief valve opening at a predetermined temperature.

It is a good practice to 'burp' this valve every so often to clear the seat of the valve of any debris that may accumulate and cause it to weep. (Note: For the sake of clarity I have omitted the engine water heating coil from Fig 3.)

IN GOOD TASTE
The type of hose and fittings to be used on fresh water systems is a matter of personal preference. Over the years, plumbing has undergone some radical changes in both domestic and marine applications. Various companies now make hose and fittings that simply push together and seal with an O-ring system and these are becoming increasingly popular for their cheapness and reliability.

A further advantage is colour-coded hose, making it is possible to instantly recognize hot, cold and saltwater [Ed: read on] plumbing by the colour of the pipe.

If using the old-fashioned method of hose clamps, etc, make sure the hose used is food grade to eliminate the dreadful taste of plastic in the water.

On the subject of taste in the freshwater system, there are a variety of water purification and conditioning agents that can be added to the water supply if a taint is apparent.

In Fig One, note that just before the cold water outlet at the sink we have included a carbon filter. These devices have a disposable granulated carbon filter that can be replaced every few months or so.

Not entirely necessary on new craft, these devices do trap a lot of the gunge that builds up in water tanks over time and certainly add a freshness to the water.

If your tanks are older (with inevitable algae build-up), then it is worth considering the fitting of a pump filter just before the inlet of the pump. These are cheap and screw undone to reveal an easily cleaned stainless steel screen.

GREY WATER
As far as the drainage of all this water is concerned, it is generally piped overboard from above the waterline into the ocean. To distinguish it from sewage, this waste is generally termed 'grey' water.

Because of the design characteristics of the average powerboat, most sinks will drain through gravity and not require any assistance from a pump. However, this is almost never the case with the shower, as the drain is generally well below the waterline, and this water will need to be pumped overboard.

If only it was just water! Unfortunately this shower waste usually has a lot of fats and oils mixed in as well as a fair amount of human hair, all of which combine to produce one of the most intractable plumbing problems on the boat.

Some manufacturers makes a sump to solve the problem of removing waste water when it is below the waterline. This sump is shown in Fig Four and Five and consists of a sealed box inside of which is a small pump operated by a float switch. The waste water flows into the sump box through a strainer, and when the level reaches a predetermined setting, the float switch actuates the pump and the water in the sump is pumped overboard.

If the water is relatively free of contaminants, then the sump and pump will operate with little trouble. Iin my experience these set-up is not satisfactory when used as a shower sump. The inlet strainer is not capable of screening back all of the fats and human hair that are washed down with shower water. The hair winds around the impeller of the pump and can slow the operation to almost a standstill, while the fats build up around the float switch and prevent it working. Both also build up around the inlet of the pump to further compound the problem.

Of course, the damn thing only ever gives trouble when you have a boat full of people and you're are halfway through your shower. The options are to ignore the problem and flood the shower recess, or terminate the shower and get a screwdriver, take the lid off the sump, clean the inlet screen, de-cake the gunge from around the pump and float switch, unwind the hair from the impeller and chew on two valium to keep the stress level below life-threatening limits!

It's perhaps no surprise then that one of my happiest days afloat was when I smashed that bloody sump into a million bits and threw it in the bin... For there is a better way!

There are on the market today pumps which operate on the diaphragm principle, like the manual bilge pumps of old. The beauty of this design is that there are no rotating parts, so this eliminates the problem of hair becoming entangled. This style develops enough suction to drag anything down the plug hole, they can be run dry, and draw moderate current under load.

Such pumps (gulper pumps) are simply connected directly in line between the floor waste and the overboard discharge (see Fig Six). I have had one installed in my boat for the past three years, I use the shower every day and the pump has never given any trouble, nor has it ever blocked.

Are there any disadvantages? Well, it's difficult to make the system automatic - I simply have a waterproof switch in the shower marked 'Pump'.

Nobody will ever forget to turn the thing off either, because here is its biggest failing - it's noisy! When someone is using the shower on my boat, it sounds as if they are having a major asthmatic attack as the pump wheezes and sucks the water from the shower.

I can live with it. Especially after all the nonsense I went through with the BLOODY sump.

FULLY TANKED
The he most common question people ask when discussing water on a boat is 'how much is enough?' Well, in my opinion you can never have too much, but tanks take up a lot of room and water weighs an awful lot.

The ideal would be 100lt per person per day, although with careful use most people can get away with half of this.

The problem can be overcome when the boat is moored close to a shoreside supply and the fitting of a shore water connector with regulator allows the use of unlimited water when onboard.

The purpose of the regulator is to reduce the pressure from the utility supply to a much lower level that the hoses on the boat's plumbing can accommodate. Never try to connect the hose to the vessel's system directly, as leaks will inevitably occur and could result in a sinking if this were to happen while the boat was unattended.

Shutting the tap to the nearly off position will not reduce the pressure - only the flow.

The regulator is connected into the plumbing after the accumulator.

This does not solve the problem of maintaining sufficient freshwater when away from the shore supply. For that we may need to increase the water tankage or fit a watermaker. Or both.

Increasing the tankage is not as difficult as it sounds. The answer is flexible tanks. These are simply bladders made from PVC or similar and come in a variety of sizes and shapes.

When a location is found on the boat to suit their installation, check to make sure they will not be subject to chafe as they move around with the movement of the boat. It is a good idea to glue outdoor carpet down before fitting the tanks. Generally they come with hold-down points sewn into the corners and these can be used to locate them firmly in position.

Vessels configured in the sedan style can often find space in the lazarette, but remember that ideally they should be mounted higher than the pump. I fitted two 200lt tanks in this location on my boat and they have never given any trouble. The plumbing is straightforward and most flexible tanks come with full installation instructions.

When it comes to fitting a watermaker, I strongly recommend that you closely follow the manufacturer's instructions. There are many kinds on the market and nearly all operate on the reverse osmosis principle.

Watermakers require a regular service if they are to operate efficiently. Polluted water can ruin the delicate membranes and they should only be operated in clear, clean seawater, unfortunately not always found in our favorite cruising spots.

In all cases be guided by the manufacturer's recommendations.

SALTWATER PLUMBING
Plumbing of saltwater through the boat should almost be considered a necessity since the advent of the small, low-cost pressure pumps described in freshwater plumbing.

Although special deck wash pumps are manufactured, these are considerably more expensive and I do not really think they are worth the cost unless large volumes of saltwater are required (such as on the deck of a sportsfishing boat, when an engine-driven pump is also a viable alternative.)

The actual plumbing is simplicity itself, and in Fig Seven I have drawn three outlets although there could be more if necessary. The outlet over the sink is a big saver of freshwater if this is used to clean the sink, etc.

Note that there is provision to draw saltwater off the strainer for other equipment such as refrigeration pumps, etc. The advantage of this is a reduction in the number of skin fittings in the vessel. (Note, however, that the engine saltwater should be dedicated for that purpose alone.)

The type of hose and fittings to use on the circuit is a problem best dealt with in discussion with your supplier, as the range and array of these items is extensive to say the least.

Use only the best quality, and recommend a rubber compound for the strainer-to-pump section with double hose clamps, as this is below the waterline and could sink the boat if it were to fail.

For the remainder there are some ingenious systems that greatly simplify the installation.