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Over the
years, I have been struck by how little attention so many people
in our industry seem to pay to the hoses in their boats. I have been as guilty of this as
anybody. Eighteen years ago, I bought the various hoses for my own boat--cockpit drains,
engine raw-water circuit, toilet, and bilge pump hosts primarily on the basis of price
rather than quality. Soon after the boat was launched, I spilled some acetone in the
cockpit, and it ran down the cockpit drains. Suddenly, water was flooding into the boat.
The acetone had eaten straight through the cheap, spiral-reinforced PVC "cockpit
drain hose" that I had installed. I was pretty badly shaken. By nightfall, I had
those drains plumbed with heavy-duty hoses, which, although not impervious to acetone, at
least stood some chance of resisting a spill. I also took all the acetone off the boat.
(In fact, acetone and hoses simply don't mix; I have subsequently heard reports of U.S.
Coast Guard-approved fuel hoses that developed leaks in service because the boat builder
cleaned them down with acetone at the time of installation.)
Then there was the time the raw-water screen for the engine-cooling water got blocked. The
raw water pump put a vacuum on the raw-water suction hose, collapsing the hose and causing
the engine to overheat. Out went the cheap heater hose that had come from the local
automotive parts store, and in went a good quality hose. Some months later, I was standing
in front of the engine when the same heater hose, this time on the siphon-break circuit,
blew, giving me a hot saltwater bath. I then finally replaced all of it.
Over the years, I have been forced to upgrade most of the hoses on the boat. It's been a
frustrating and expensive way to learn that hoses are a rather specialized item, and that
on a boat--where hoses are essential to keeping the boat functional and afloat, there is
no substitute for a quality product designed for a specific purpose. In what follows, I'D
like to look at the principal tasks that hoses must handle, and the quality standard that
a hose should meet to carry out those tasks.
Exhaust Hose
Exhaust hose requires a heavy-duty, fabric-reinforced construction. Until recently, there
were no standards governing these hoses, but good-quality hose was invariably labeled as
'Type Certified Marine Exhaust Hose," or something similar. This has now changed with
the Society of Automotive Engineers- (SAE) new standard for marine exhaust hose, SAEJ2OO6.
Adopted by the American Boat and Yacht Council (ABYC), this standard includes the
requirement that the hose be able to withstand a total loss of cooling water for two
minutes with the engine running at full power, and still not suffer a loss of integrity,
-a pretty tough test. The few hoses that meet this standard will say so on the hose
itself, and can be counted on to give good service.
Exhaust hose comes with or without wire reinforcement. The former is known as
"hard-wall;" the latter, "soft-wall." Manufacturers commonly recommend
that hoses longer than four to six times the inside diameter of the host (most exhaust
hoses), or those with relatively tight curves, be wire-reinforced for added support. The
objective is to prevent the hose from chinking on bends, sagging on long horizontal runs,
and "panting" (also called "pulsing") from the constant pressure
changes that occur in an exhaust.
There are, however, disadvantages to wire reinforcement. The wire is formed from spring
steel which, if exposed to the atmosphere, will rust, weakening the hose--a particularly
likely scenario if the hose has poor adhesion between its layers. (J2006 has stringent
adhesion requirements.) There have also been cases where the wire became the path for
stray galvanic currents, causing devastating corrosion; or for short circuits, resulting
in a fire. Also, the wire is nasty stuff to cut, often leaving a razor-sharp piece of
metal sticking out of the end of the hose. And if the hose isn't a perfect fit on its
nipple, the wire makes it difficult to get the hose to seal.
Many times, when a hose is adequately supported and has no tight bends, the reinforcement
isn't necessary. But in the case of exhaust hose, the support is critical. Exhaust
hose--particularly the soft-wall variety--should never span open spaces or be hung from
deck beams, because panting will cause chafe at the supports or hangers. If necessary, the
hose should be given a "bed" to sit on. If you need long exhaust-hose runs, you
can avoid having to use hard-wall hose (and save money) by splicing in lengths of
UL-approved fiberglass marine exhaust tubing. But, this tubing is not as effective as hose
at absorbing exhaust noise.
ABYC P1, Installation of Exhaust Systems for Propulsion and Auxiliary Engines, calls for
double-clamping all exhaust hose connections, with a minimum band width (for each clamp)
of 1/2": in order to minimize the chances of carbon monoxide and water leaks into the
boat. The standard also states: "Clamps used for this purpose shall be entirely of
stainless steel; clamps depending solely on spring tension shall not be used"
(A22-1.7.10). I would like to see the standard extended one step further, and require that
the hose clamps be of all-300-series stainless steel. This would eliminate the commonly
used "all-stainless" hose clamps that have a 400-series stainless steel screw
that rusts almost as soon as it comes into contact with salt water.
For larger-diameter exhaust hoses, "T-bolt" hose clamps are far more dependable
than regular hose clamps. Note, however, that although many industrial T-bolt clamps have
stainless steel bands, the bolts are often carbon steel, which rusts in the marine
environment. A few manufacturers have their clamps specially made with 300-series
stainless bolts, which are longer-than-normal to accommodate varying hose thickness'; plus
a lock nut to prevent loosening from vibration.
Engine Raw-Water Hoses
The engine manufacturer generally installs heavy-duty, fabric-reinforced hoses between the
raw-water pump and the heat exchanger (including any oil coolers in the raw-water
circuit), up to the point of the water-injection elbow on the exhaust. But, all too often
the engine installer will use a light-duty rubber or plastic hose (such as automotive
heater hose) to connect the raw-water seacock to the raw-water pump, plumb in a siphon
break, and make the connections to a hot-water heater.
Although heater hose is generally designed to tolerate temperatures as high as 2100F, and
pressures to 60 psi, it is relatively thin-walled and soft. If the raw water screen on the
outside of the boat or the raw-water filter becomes clogged, the vacuum pulled by the
raw-water pump will collapse heater hose, and most other non-wire-reinforced hose,
starving the engine of water. What's more, heater hose-primarily because it is
thin-walled, has relatively poor abrasion resistance. If the hose is in contact with some
part of the engine bed or supporting structures, and is not itself firmly supported, the
engine vibrations that are invariably transmitted to the raw-water suction hose will soon
cause it to wear through.
Good-quality marine water hose, on the other hand, is thicker than heater hose, and is
reinforced with different synthetic materials, commonly, polyester yarn in two or more
layers, or plies.
All Below-the-Waterline Hoses
Similar considerations govern the selection of below-the-waterline hoses. In fact, the
same hose that's used for engine raw water hose is often an appropriate choice for cockpit
drains, sink drains, and toilet suction lines. The common properties here are a certain
minimal strength, a broad tolerance of chemicals, resistance to abrasion, and in the case
of bilge-pump and toilet suction hoses, the ability to withstand the maximum suction
pressure of the pump without collapsing. What's called for is a fabric reinforced rubber,
or heavy-duty vinyl (PVC), hose. What's often installed, though, is some variant of a
flexible, reinforced, thin-walled rubber or PVC hose that even the manufacturer or
wholesaler may label as "not recommended for below the waterline use." Says Bill
Shields of Trident Marine (Canonsburg, Pennsylvania), "Anything attached to a
through-hull is an extension of the hull. It must have an integrity as close as possible
to that of the hull."
If a hose is reinforced it may be smooth walled on the inside, in which case it can be
directly slid over, and fastened to, a suitable smooth pipe stub or hose nipple.
Sometimes, though, the inner wall contains a spiral rib that makes it next to impossible
to achieve an effective seal without adding special adapters. These adapters, which are
sometimes called cuffs, must have the appropriate thread (left-handed or right-handed) and
thread spacing to match the direction of the reinforcement in the hose. In other words,
you should buy them from the hose supplier at the same time you buy the hose. You must
also apply a sealing compound between hose and cuff; consult the manufacturer to find the
correct sealant.
Regarding the through-hull connection for below-the-waterline hoses, ABYC H27, Recommended
Practices and Standards Covering |
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