The following article came from Professional BoatBuilder
The Whole Story on Marine Hose - by Nigel Calder
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
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.
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 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.
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
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.
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.
The National Marine Manufacturers Association (NMMA) Handbook for Boat Certification
, uses the exact same language as the ABYC.
Both the Coast Guard regulations and the ABYC standards specify maximum acceptable tolerances between fuel-line hoses and any nipples to which they are attached; require a bead, flare, or serration on the nipple (but do not allow installation of hose over a pipe thread); and require a hose clamp that does not "depend solely on the spring tension of the clamp for compressive force" (33 CFR 183.560d). Double clamps are required on fuel-fill pipes, each with a minimum band width of 1/2" ABYC requires the clamp to be "beyond the flare or bead, or fully on serration where provided, and at least 1/4" (6mm) from the end of the hose" (H24-24.11.6).
Fill pipes are required to have a minimum 1 1/2" ID; vent pipes a minimum 9/16". ID ABYC states that they must be self-draining (that is; not normally full of fuel), but this is not included in the Coast Guard regulations.
LPG, CNG, and Drinking-Water HOSES
For drinking water
ABYC and NMMA standards state that the entire system should be plumbed with hose or tubing manufactured from Food
and Drug Administration (FDA)-approved materials, with the hoses or tubing so labeled. The FDA, in turn, requires PVC hoses to be manufactured from virgin, rather than recycled, PVC and textile reinforcement. Compliant hoses are stamped "FDA approved." Although such hoses are commonly clear plastic, this has never made much sense to me, since the light that gets into the drinking water
promotes the growth of algae. It is far better to use opaque FDA-grade hose or pipe, and in fact must household-style PVC water pipe is ideal. If this is combined with opaque water tanks, so that no light gets into the system, water will stay clean and drinkable almost indefinitely. (Note that PVC pipe from the hardware
store is rated for cold water; CPVC pipe is required For hot-water systems.)
LPG (propane) or CNG (compressed natural gas) hoses, which either constitute the supply line or make the flexible connection from a copper supply line to a gimbaled galley stove
, are clearly a critical safety
item. For LPG systems, ABYC Al, Marine Liquefied Petroleum Gas/LPG/ Systems, requires that the hose should be marked as complying with "UL 21 LP Gas Hose"; while A22, Marine Compressed Natural Gas /CNG/ Systems, states that CNG hose should be marked as complying with "NFPA (National Fire Protection Association) 52." In both cases, the standards call for end fittings to be permanently attached. Swaging is one acceptable method of attachment; a hose clamp is not.
The two standards also specify that every appliance should be served by a continuous fuel line (that is, one with no joints or connections) from the gas cylinder regulator
to the appliance or, in the case of gimbaled stoves, to a length of flexible hose connecting to the appliance. This means that if a boat has more than one gas appliance, it is unacceptable to run a common supply line, and then tee off this line to the devices. Any connections or tees must be made inside the gas-bottle locker which, if designed according to the standards, will be sealed to the accommodation spaces and vented overboard
. This will keep any gas leaks from the connections or tees out of the boat.
Choosing a Supplier
It must be clear by now that the business of building a quality hose for a specific purpose is more complicated than first meets the eye. On the face of it, most hoses are round and black or white, with a hole in the middle--but that's where the similarity ends. Even with two hoses that look identical, there may be all sorts of differences in the chemicals that have gone into compounding the hose, the type of fabric
reinforcement, the skill with which the hose has been laid up (much hose is still hand-built), and the quality of the adhesion between different layers in the hose.
Hose manufacturing is a worldwide cottage industry, with factories scattered all the way from the Far East to Turkey
, and the United States. Almost none of the handful of wholesales or retailers of marine hoses in this country actually make their own hoses. Unfortunately, some pretty awful hose finds its way into the marketplace from time to time, making the boat builder
or consumer very much dependent on the wholesaler or retailer. Consequently, it's best to buy from a recognized dealer, and to make sure that the hose is manufactured to recognized standards (UL, SAE, CG, and ISO--the European standards setting body).
Even with high quality, properly installed hoses, there is always the potential for an unforeseeable failure. Many boat owners leave crucial seacocks open from one season to another, and never look at their hoses and hose clamps. After a year or two, the valves become frozen in place and the hose clamps are covered in rust The boat is an accident
waiting to happen.
Or, consider a completely different problem: A rat once made its way aboard some friends' boat, and it chewed through the flexible connection to their propane galley stove
. Luckily, being safety
conscious cruisers, they always close the tank valve after using the stove-otherwise, the rat might have killed them. Once they realized what was going on, they had the foresight to close their seacocks--which was fortunate, because before they finally cornered it and bludgeoned it to death, it took a bite out of half the hoses on the boat!
Encourage your customers to inspect the hoses on their boats on a regular basis. Any kind of below-the-waterline hose failure has the potential to sink the boat.
About the Author: Nigel Calder is a contributing editor of Professional Boat Builder. Also, Nigel wrote the definitive book for general boat repair.
If you like this type of in-depth article, and want to go to the source of some of the best technical information about boats, their design, and construction, get yourself a subscription to Professional BoatBuilder
. It's worth every penny. ( No, I don't get a kickback*)
*I believe that Nigel does accept various forms of “manufacturer support” - nonetheless, he remains a popular & respected “authority” on all things marine.