Cruising World – May 2018

may 2018

cruisingworld.com

70

MONTHLY MAINTENANCE

A

boat owner recently asked me about

a design she was working on for a

raw-water manifold, one that was to be

made from PVC pipe. My advice: “If you

can’t stand on it, it’s probably not robust

enough.” While that test method is less

than quantifi able (for example, I weigh

145 pounds, so what works for me might

fail for others), it generally addresses the

issue of raw-water plumbing, which in far

too many cases simply isn’t properly de-

signed or installed, at least not in a man-

ner that imparts the level of durability and

reliability required for such components.

Apart from seacocks, which I’ve

covered in previous columns, raw- water

plumbing includes any means by which

seawater is supplied to, or discharged

from, a range of equipment, such as en-

gines, generators, watermakers and

air-conditioning systems; deck, sink and

shower drains; and sanitation discharge

systems. For the most part, if it will re-

sult in fl ooding if it fails, it falls into the

category of “raw-water plumbing.”

Hoses used for this application must

be specifi cally rated for raw water (for in-

stance, “marine wet exhaust” or “SAE

J2006R”). While those examples refer

specifi cally to engine applications, in fact,

they are far broader in their coverage. In

other words, if the hose is good enough to

carry exhaust discharge, and is rated and

labeled for this use, it’s rugged enough for

most other raw-water applications.

Typically, hose of this sort is either

EPDM-based (this can be black or white

rubberlike material) or silicone, which is

usually blue or red. It’s critically import-

ant that the hose labeling include the

words “wet exhaust SAE J2006R.” In the

absence of this label, the hose’s suitabil-

ity for this purpose is unknown. Clear

PVC hose, sometimes called “red trace”

because of the red fi ber some versions

contain, is not designed to be used for

raw-water applications, and yet I encoun-

ter it on a near-daily basis in this role.

While silicone offers certain attri-

butes, it’s not always more desirable than

EPDM hose. Silicone is extremely fl ex-

ible, and thus well suited for absorbing

movement and vibration; for that rea-

son, it’s often used in exhaust systems.

However, it’s also more expensive and

less resistant to chafe, kink and crush

damage. For the majority of raw-water

applications, where extreme fl exibility is

not necessary, a high-quality EPDM hose

makes the most sense.

Metallic plumbing used in raw-water

applications must be both rigid and corro-

sion resistant. Bronze is the most popular

material; however, it’s available in a dizzy-

ing range of alloys, some of which are not

suitable for exposure to seawater. Gener-

ally speaking, copper alloys must contain

less than 15 percent zinc (the less the bet-

ter) in order to be safely used with seawa-

ter. Under no circumstances should brass

be used. Its high zinc content, typically

45 percent or more, makes it susceptible

to “dezincifi cation” and structural fail-

ure. While there’s no defi nitive means of

determining zinc content outside of lab

testing, the more yellow a copper alloy,

the more zinc it contains.

Because of its lack of tensile strength

and modulus of elasticity, the use of PVC

is frowned upon where raw water is con-

cerned, with very few exceptions. It is

occasionally and successfully used in

air-conditioning systems, for distribution

and return manifolds. When used in this

raw-water role, it must be schedule 80,

and fully supported and protected from

loose gear and misplaced feet. Hoses

must not impart excessive strain on PVC

plumbing components, and PVC plumb-

ing must never be directly attached to

seacocks, strainers or other below-the-

waterline gear.

Finally, remember that step-on-it test.

If you have doubts as to whether it will

stand up to this measure, it’s probably not

robust enough.

Steve D’Antonio offers services for boat

owners and buyers through Steve D’Antonio

Marine Consulting (stevedmarineconsulting

.com).

5 PLUMB CRAZY

When it comes to raw-water plumbing protocols, there are

certain standards and procedures that must be met.

BY STEVE D’ANTONIO

While at fi rst glance it looks similar

to bronze, because of its tendency to

“dezincify,” brass should never be used

for raw-water applications (top). This

unsupported seawater distribution

manifold is far too fragile for such a

critical role (above). Clear PVC hose,

even when wire reinforced, is unsuited

for conveying raw water. Rigid pipe

is more durable than hose, but it’s far

less fl exible (right). Long, unsupport-

ed overhanging sections are an invita-

tion to leverage-induced failure.

STRESS TEST

When it comes to raw water

manifolds fashioned from PVC pipe,

my advice is pretty simple: If you

can’t stand on it, it’s probably not

robust enough.