The Whole Story on Marine Hose    by: Nigel Calder

   The following article came  from Professional BoatBuilder Magazine. If your a Marine Mechanic and are not getting this magazine, you are missing some of the most up to date information available to the marine repair business.
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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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