It's a case of "out of sight, out of mind" when most people consider their exhaust and fuel hoses. Buried deep in your engine compartment, running under your decking, or winding from an invisible exit pipe to a pump, they're part of a system that keeps your boat running right and safely. For this reason alone, they warrant regular inspection and, when needed, rapid replacement.
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Your exhaust system is constantly subjected to massive changes in temperature. This is particularly true of wet-exhaust systems, where water is used to cool the hot gases from your engine. We recommend rubber or silicone hoses for exhaust systems, because of their durability, flexibility, and strength. Rubber is more flexible, and is able to stretch and shrink repeatedly. However, it will eventually weaken and split. Silicone hoses are considerably stronger, and can last six times as long. They are much more expensive, but we think they're worth it. Fitting a pricey hose may seem pointless, but it will save you money and hassle in the long run.
Vibrations from the running engine can shake the clamps holding the various pieces of hose together. While exhaust hose is reasonably flexible, each separate connection represents a potential weak point in the system. We recommend that you use good quality stainless steel clamps. These are corrosion resistant and may actually last longer than the hoses they're holding together. We also suggest you use "hump" hoses at every connection possible. Simply a piece of hose with an additional "hump" of hose material, they provide more flexibility, absorbing much of the damaging vibration from your engine.
The best advice we can offer anyone fitting an exhaust hose system is to fit the best quality hose you can afford and inspect it regularly. Having your hose burst or split is not only inconvenient but dangerous too. Carbon monoxide poisoning or fire can result-a high price to pay for something relatively cheap to do right.
The same guidelines we suggest for exhaust hoses also apply to your fuel lines. Obviously, anything carrying explosive material has to be strong and durable. Three types of hose are normally found on marine engines: flexible hose (A1, A2, B1, and B2), steel lines (on the engine), and copper tubing. What concerns us is the flexible tubing, since this is the part of the system most likely to fail. The metal hoses can be checked when servicing your engine, but the flexible hoses need constant monitoring. Due to vibration, it is a legal requirement that metal fuel lines be connected to the engine with flexible hose. You should check all joints for leaks at least twice a season. Use your fingers, and look out for stains on or around the fitting. For hoses without permanent end fittings, use stainless steel clamps.
Wipe your hoses with a dry rag and see if you smell gasoline. This is a sign that your hose has disintegrated and needs replacement. Hoses deteriorate more quickly if your engine uses gasoline blended with alcohol. Fuel blended with methanol makes fuel lines brittle, while an ethanol mixture makes them soft. This means that the best way to avoid alcohol damage is to use alcohol-free fuel. All flexible fuel lines must be USCG approved SAEJ hose, which is resistant to alcohol.
So, which hose should you go for? Well, fuel lines use a standardized lettering system. This initially seems a little confusing, but is very simple. Of the two types available, A and B, A is more fire resistant, and has to be used at the fuel pump and carburetor where more than five ounces of fuel could spill if the hose is cut. Type 1 has less permeation loss than Type 2. This makes Type 1 the better hose for all applications. Therefore a hose marked A1 is a stronger, more leakproof, fire-resistant line. It is also more expensive but, as with the silicone exhaust hoses, we think the cost is worth it.
Our Marine Insurance Department frequently deals with boat fires. Leaking fuel hoses are a major cause. By checking your hoses regularly and you may spot a potential problem before it happens. After all, replacing a hose is a lot cheaper than replacing a boat!
By Tom Burden, Last updated: 7/11/
Consider what can happen when a hose bursts. If you are lucky, you will only have nuisance repairs to electronics, engine or interior. If fate has it in for you, a defective hose can cause a stink if it&#;s the discharge of the head, cause a fire if it&#;s part of a gas line or even sink your boat if it&#;s connected to a thru-hull fitting. That&#;s why we recommend spending a little more on a high-quality marine hose that offers more durability and better performance in critical applications and why you should inspect your hoses frequently for signs of deterioration.
Your application will determine what kind of hose to purchase. Our selection of hoses encompasses most applications and is available in any length from a foot up. The following is a guide to match hose and application.
Raw water intake hoses ingest water from outside a boat to cool an engine, flush a toilet, cool an air conditioner or provide a fresh supply of water for fish in bait tanks. Use only hose recommended for &#;below waterline&#; connections. Depending on the application, raw water intake hose will have fabric, PVC or stainless steel spiral reinforcement that resists kinking and prevents the hose from collapsing when for example, an engine pulls a vacuum due to a clogged water intake screen. For engine raw water intake, we recommend Shield's Series-250 or Series-252 hose, both of which are reinforced with a metal wire helix to prevent collapse. For engine coolant circulation, Shields Series-135 hose, which is reinforced with polyester yarn spirals can be a good choice&#;however care must be taken not to exceed the minimum bend radius and the temperature rating of the hose. For an overview of hose applications, see the hose application tables below.
Drainage hose for cockpit, sink or shower needs to be flexible with strong walls and resistance against kinks and abrasions, but since they are under positive pressure, they generally don't require helical wire reinforcement..
Potable water hoses must be made of FDA-approved, non-toxic materials so they won&#;t cause bad taste in drinking water supplies. Pressurized freshwater systems must use reinforced hose to withstand pump pressure (approx. 40&#;60PSI). For fill and vent hoses in water tanks, extra-heavy-duty sanitation/water hose should be used, while reinforced rubber hose is the best choice for hot water up to 140°F.
Alternatively, you may use a reinforced vinyl hose reinforced with nylon braid. Examples include: Series 162 (polyester reinforced clear PVC hose), FDA approved; Series 140 VAC Standard (steel wire reinforced PVC hose); and Series 148 Multi-Purpose (vinyl helix hose) FDA approved, ideal for critical drain and fill applications.
Bilge pump hoses typically use corrugated polyethylene with molded cuffs because it is flexible, economical and resists oil, solvents and other waste that collects in the bilge. For better flow you should choose a hose with a smooth bore, abrasion-resistant cover and good anti-kink flexibility. Examples include: Series 148 Multi-Purpose (smooth-walled vinyl helix hose) FDA approved, ideal for critical drain and fill applications, and Shields Multiflex Hose (Series 141). Of the corrugated hoses, the best is Shields VAC Standard (Series 140) and Bilgeflex (Series 120).
Sanitation hose has to be tough, flexible and resistant to odors and toilet chemicals. Choose hose with a smooth bore, heavy wall and specifically labeled for marine sanitation use. There are two choices: white vinyl hose and sanitation hose. Both will eventually smell. We recommend only smooth interior wall hose because corrugated types trap waste and restrict flow. Rigid PVC does not pass odors but is stiffer and more difficult to route and does not connect directly to pumps and thru-hulls. Still it is possible to plumb part of the system with rigid PVC, switching to hose where necessary.
For more information, please visit marine wet exhaust hose.
Reinforcement: Many hoses have reinforcement in the walls for strength and rigidity, and to prevent collapse or expansion under pressure. The reinforcements can be wire, yarn spiral or PVC/vinyl helix.
Burst strength: Hose used for discharge lines has to resist pressure. This so-called burst strength, measured in pounds per square inch (psi) depends on product design and diameter; small diameter hoses have greater burst strengths. Hose with multiple plies or helical reinforcement has greater pressure limits, which is important for pressurized water or exhaust applications.
Vacuum rating: Hose on the intake side has to withstand suction, a property that is measured with a so-called vacuum rating. Intake hose should have a vacuum rating of 20 or higher.
Temperature range: Mostly critical for engine cooling hose, but might also be important for pressurized hot water systems.
FDA-approval: Hose used in potable (drinking) water systems must be constructed from safe, non-toxic materials that are contamination- and corrosion-free.
Bend radius: For proper installation a hose should not be bent more than the minimum bend radius recommended by the manufacturer to avoid kinks and breakage. Especially important for sewage lines and bilge pump applications.
Sometimes a lubricant is needed to install a hose onto a fitting.
Hoses are sized by their inside diameter (ID). Hose fittings are labeled based upon the ID of the hose they fit. In other words, the outside diameter of a 1/2" barbed elbow is liable to measure slightly greater than 1/2", but it will fit 1/2" ID. hose just fine. Smooth bore hose is recommended for all applications, since corrugated hose can reduce flow by as much as 30%. Hose needs to be matched to the fittings on pump, through-hull, deck fill, tank, etc. See below for some sizing guidelines. Some popular diameters by application:
Marine hose clamps are stainless bands that compress hose around barbed fittings. They can be made from a variety of metals, but quality ones are all stainless steel, including the screw, band, and other parts. T-Bolt hose clamps are much stronger and have a 360° clamping surface. They are used in applications with high pressure, heat, vibration, or other severe requirements, like exhaust systems. Two clamps are recommended for below-waterline connections. Thru-hulls, hose lube & sealant, etc. may be necessary to make a hose fit and complete your marine plumbing system.
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