Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

PART SIX:PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION

creating unpleasant smells. Every shower

sump should drain into a dedicated and fully

enclosed, properly vented gray-water tank.

This tank should have its own dedicated

pump, with an auto float switch, to empty it.

Remember also that the shower sump is usu-

ally well below the waterline. If so, the

pumpout line must rise well above the water-

line to a vented loop and then back down and

overboard. Follow the recommendations in

Chapter 7 and as discussed in Chapter 18 (see

Figure 18-3).

The alternative is that each shower sump

be deep enough to hold a fair amount of

water under its grate and have a dedicated

pump for emptying it directly overboard.

Essentially, this makes each shower sump a

small, individual gray-water tank.

Gray-Water Tanks

Discharge from sink and shower drains is

termedgray water. This is different from dis-

charge from heads (sewage), which is black

water. In most areas, gray water can be

discharged overboard, but not in all areas. Be

careful; check the local regulations. If a boat

will operate in 100 percent no-discharge wa-

ters (no-discharge zones or NDZ), then it

needs a much larger gray-water tank—as large

or even larger than the black-water (sewage)

holding tank. In this case, instead of draining

overboard, all the sink and shower drains

must empty into one or more gray-water

tanks. These are pumped out from deck fit-

tings at the dock just like a head holding tank,

or they can be emptied overboard through a

Y-valve when you’re no longer in an NDZ.

Running Pipe

Twenty or thirty years ago, almost all this

“piping” was made from whatever was

handy, frequently from inexpensive hose.

Such hoses can crack or tear. They can im-

part a bad taste to the water and may not be

certified as safe for drinking water. Hose is

still fine, of course, but be sure that it’s good-

quality hose certified safe for potable water.

Drain hose only needs to be tough and long-

lasting, as I doubt you’ll be drinking from it.

Hose is often the best solution for drain

lines.

Plastic-Tube Piping

Freshwater plumbing, though, is better made

from purpose-manufactured plastic tube

(not hose). My personal preference is the

standard for plumbing in many homes. It’s

light, corrosion free, inexpensive, fully

approved for use with drinking water, and

available off the shelf at Home Depot,

Lowe’s, and such. It is PEX tubing (cross-

linked polyethylene, Figure 20-5) connected

with Flair-It connectors. The tubing is easy

to cut and bend, and the many Flair-It con-

nectors and valves will meet virtually any

need. Attaching the tubing to a Flair-It elbow,

tee, valve, and so on is a snap. You just cut

the tube to length, slide the crimp ring onto

the tube, press the tube on the fitting’s tube

barb, slide the crimp ring back up to the fit-

ting, and screw it tight. No special tools are

required and no sealant, plumber’s dope, or

plumber’s tape is needed. Companies such as

Whale, Sea Tech, and others also make a

complete line of marine plumbing fittings

and tubing. These, too, are designed for

quick tool-free and sealant-free connections.

My experience with some of these is that the

fittings will start to leak after you have

disconnected and reconnected them a few

times. PEX doesn’t have this problem. Of

course, you can still use all hose for your

Figure 20-4. Hose
drain trap