Marine Exhaust and Fuel Hoses
Revised by BoatUS editors in April 2012
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.
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 SAEJ1527 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.