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Seacocks, Through-Hull Fittings, and Drain
Plugs, calls for the installation of a seacock on "all piping, tubing, or hose lines
penetrating the hull below the maximum heeled waterline.. under all normal conditions of
trim" (H27-27.4, emphasis added; note that the standard contains one or two
exceptions for boats with built-in flotation and self-draining cockpits). Many people
recommend double hose clamps on all below-the-waterline hose connections; but if the
connection is watertight, with a good-quality clamp, a second clamp adds little security,
What's more, there is often insufficient room to properly space two hose clamps; as a
result, one is halfway off the end of the fitting, and may damage the hose.
Sanitation Hose
If you run a clean rag up and down the discharge hose on many marine heads and then sniff
the rag, you may notice a foul odor--even if the hose seems to be in good shape. This is
because all hoses including some of the heavy/duty variety, are minutely porous, and in
time will allow the contents to seep through. Accordingly, toilet-discharge hose must be
of a special impermeable type, generally labeled "Sanitation Hose." There are
two choices: some variant of PVC; and heavy-walled tube sanitation hose. The PVC hose is
considerably cheaper-less than half the price--but more prone to problems.
To increase its resistance to moisture absorption, PVC sanitation hose must be specially
formulated, or "compounded," from a high-density material with a greater
than-normal wall thickness. Ultimately, however, any flexible PVC hose that is permanently
filled with effluent will absorb enough moisture to begin to smell. The reason for this is
that in order to make the hose flexible, the manufacturer must add a plasticizer, which
creates a larger molecular structure that is minutely permeable. Rigid PVC pipe, which is
what's used for household effluent, does not contain the plasticizer, and as a result
makes an excellent choice--in certain cases--for marine-sanitation purposes. But, it is
more difficult to run than hose, and has a tendency to develop leaks at the joints as a
result of the constant flexing on a boat.
PVC sanitation hose is relatively stiff, and may therefore be difficult to fit tightly to
any hose barbs. If the barb is undersized, the clamping pressure needed to seal the hose
to the barb will cut into the hose, and cause it to develop microscopic cracks (creating
hard-to-trace leaks) at the edge of the clamp. If, on the other hand, the barb is too big,
and the hose has to be stretched over it, the hose will work-harden and once again develop
microscopic cracks where it has been stretched.
Rubber Sanitation hose is more tolerant than PVC hose of poor hose-barb fits. It also has
greater flexibility, and, thanks to its heavy-wall construction, resists permeation much
longer. In fact, says Bill Shields, it's resistance to permeation is directly related to
wall thickness. With rubber hose, thickness rules ".
When installing sanitation hoses-either PVC or rubber, avoid creating low spots that will
retain effluent. If that's not possible, advise the boat owner to flush the head
sufficiently after each use to clear all the effluent out of the line. You should also
warn the owner not to use alcohol-based antifreeze, petrochemicals, and most toilet bowl
deodorizers--all of which contain chemicals that will destroy the moisture-absorption
resistance of the host.
Whichever sanitation hose you choose, it should have a smooth wall on the inside. This
will minimize the chances of clogging. Nevertheless, when choosing sanitation hoses, bear
in mind that over time, the inside of the hose will slowly plug up with calcium deposits.
At some point, the owner or a boatyard may have to remove the hose and beat it on the
dock, to break the calcium loose. If the hose isn't rugged enough to take this beating,
it's not suitable for the job. ( better yet just replace it. Who's got time or money to
redo a hose replacement.)
While we're on the subject of sanitation hoses. it's worth noting that Federal regulations
(33 CFR 159.87) mandate pumpout fittings "of either 1 1/2" or 4" nominal
pipe size." A nominal 1 1/2" pipe has an actual outside diameter of around 1
7/8",; a nominal 1 1/4" pipe has an outside diameter of 1 1/2" Many waste
fittings currently on the market are marked as being 1 1/2" fittings, which seems to
refer to the outside diameter of the hose barb on the bottom of the fitting. The caps
themselves are generally 1 1/4" pipe thread, which is not legal.
Federal regulations have nothing to say about the size of vent fittings on holding tanks,
they say only that these tanks must 'be vented or provided with a means to prevent an
explosion or over pressurization as a result of the accumulation of gases;' (33 CFR
159.95(a)2), and that vents must be designed and constructed to minimize clogging by
either the contents of the tank or climatic conditions such as snow or ice;; (33 CFR
159.01). The U.S. boat building industry seems to have settled on 9/16," inside
diameter (ID) or 5/8" ID hose as a suitable vent size, but in Europe the latest draft
of the ISO standard requires one of the following:
1.) that the vent
line has a 1 1/2" (38 mm) ID: or
2.) that there be multiple vent lines of at least 16mm, which together add up to an
equivalent area; or
3.) that there be a vent line of at least 12mm, combined with a vent valve on the tank,
which has an opening of 38mm, and a notice close to the pumpout fitting on the deck
stating that the valve must be opened before pumping.
To prevent overfilling of holding tanks, the federal regulations require that "each
sewage retention device must have a means of indicating when the device is more than
three-quarters full by volume' (33 CFR 159.83). This is another legal requirement that is
frequently violated. Various level indicators are available at a cost of $20 to S60. so
compliance is neither difficult nor expensive.
Fuel-Carrying Hoses
Fuel fill and fuel-line hoses are a very special item, particularly on gasoline engines.
These are the only hoses on a boat whose construction must by law, comply with certain
U.S. Coast Guard standards, which are based upon fire resistance and permeability.
Fire resistance is determined by the "two-and-a-half-minute burn test," of which
there are two levels. Hoses that pass the more stringent test are classified as Type A;
hoses with slightly less fire resistance are classified as Type B. There are also two
types of permeability test. Of the two; the more demanding imposes limits on
gasoline-vapor migration through the hose under test conditions to less than 100 g/m2 of
interior hose surface per 24 hours. Such hose is classified as Class 1. Hoses with
somewhat higher permeation rates (up to 300 g/m2 per 24 hours) are classified as Class 2.
Two other standards that apply in this field, and which are referenced in the Coast Guard
regulations, are SAEJ1527DEC85, and a similar standard of Underwriters" Laboratories.
UL 1114. In 1993, SAE J1527DEC85 was superseded by SAE J1527JAN93. The updated version is
referenced in the ABYC standards. but not in the Coast Guard regulations.
We end up, then, with four classes of hose referenced in the Coast Guard regulations :
USCG Type Al, USCG Type A2, USCG Type B1, and USCG Type B2. To qualify for any of these
categories, the hose designation, date of manufacture; and the name of the manufacturer
(or a registered trademark) must be written on the hose. Otherwise, it is not legal in
those systems-primarily inboard gasoline engines, and inboard/outboards that must comply
with these regulations.
The regulations state that for inboard gasoline engines and inboard/outboards, any hose
run as a fuel line between the fuel pump and the carburetor must be classified as Type Al,
This also applies to fuel lines from the tank to the "inlet connection on the
engine," unless the maximum loss of fuel, if the fuel line were cut is less than 5 oz
in 2 1/2 minutes. In that case, Type B1 may be used. This exception applies mostly to
those systems with anti-siphon valves.
Similarly, vent or fill lines must be Type Al or A2, unless the maximum loss of fuel if
the hose were cut is less than 5 oz in 2 1/2 minutes, in which case, Type B1 or B2 may be
substituted. This effectively allows B2 hose on all self draining fill hoses (fill hoses
that do not remain full of Fuel once the tank has been filled, which includes most fill
hoses). Nevertheless, to my knowledge, all fuel fill hoses currently on the market are
Type A2.
ABYC H24, Gasoline Fuel Systems, outlines a similar standard to the Coast Guard's, except
that it requires Type A2 hose on all fill hoses inside engine compartments. It also covers
outboard motors (requiring B1 or better hoses), which the Coast Guard does not. ABYC H33,
Diesel Fuel Systems, goes a step further than the Coast Guard, by extending similar
standards to inboard diesel engines, which are not covered by federal regulations. ABYC
includes a modification that allows any of the four classes of hose to be used for fill
and vent hoses.
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