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FINDINGS LIBRARY · ENGINE AND FUEL

Marine exhaust hose: cracks, heat damage, clamps and how surveyors write it up

UPDATED 9 NOVEMBER 2026 · 3 EXAMPLE FINDINGS · 4 SOURCES

How wet exhaust hose fails, what to look for at the clamps and along the run, why a cooling failure cooks the hose before the engine gauge moves, what a surveyor checks and three example findings graded A, B and C.

AT A GLANCE
Exhaust hose
USUAL GRADE
A for a leak of exhaust gas or water, a split, or hose that's been overheated. B for cracking, soft spots, bulging at clamps or corroded clamps. C for single clamps where double clamping fits, or unmarked hose
FOUND WITH
Following the whole run from the injection elbow to the transom with the engine off and running, feeling for soft spots, reading the hose markings, and looking for soot, water stains and discoloured sections
JUDGED AGAINST
Hose marked for marine wet exhaust, per Southern Boating. Wire reinforcement on all but short runs, and double clamps where the fitting allows
REPAIR COST
Hose and clamps by the length of the run. Power & Motoryacht notes good wet exhaust hose is typically rated for only 350°F, while exhaust gas can be twice that hot

A wet exhaust uses seawater to cool the exhaust so it can run through rubber hose. That's fine as long as the water keeps flowing. When it stops, or when the hose ages, the exhaust system leaks water into the bilge or carbon monoxide into the boat.

How a surveyor checks it

The whole run. Follow the hose from the injection elbow to the transom outlet. Southern Boating's list: leaks, kinks, chafe, bulging at the hose clamps, cracks and other signs of deterioration. Power & Motoryacht adds discoloured sections, which can mean overheating, worn spots where the hose rubs on structure, and broken hangers.

Engine off and running. Southern Boating notes some leaks only show with the engine running. Sail magazine's tip for gas leaks: look for black soot.

Feel it. Squeeze along the hose for soft spots, especially near the elbow where it's hottest.

The markings. Hose should be labelled for marine wet exhaust. Southern Boating says anything more than a short run, four times the inside diameter, should be wire reinforced, and every connection should be to a rigid component. Hose slipped over hose and clamped is not acceptable.

The clamps. Power & Motoryacht: replace corroded clamps with 316 stainless, screw included, and double clamp every hose. Southern Boating notes double clamping only works where the barb is long enough.

The muffler. Drain plugs on waterlift mufflers sometimes back out after winterising, letting water and exhaust into the boat. Check they're in and tight.

What decides the grade

Gas or water escaping, or a hose cooked by a cooling failure, is an A: the engine shouldn't run. Cracking, soft spots and corroded clamps are B. Clamping and marking points on sound hose are C.

Exhaust hose: example findings

The same defect written up at each grade, the way Axsail writes it from what the surveyor says on board. The grade follows what was found, so use these as wording, then grade what you see.

ENGINEA
Exhaust hose, main engine

Soot and water staining on the hull lining beside the exhaust hose aft of the waterlift muffler. Hose split for 4 cm at the outlet of the muffler. Engine room smells of exhaust with the engine running.

Recommendation: Do not run the engine until the exhaust hose has been replaced. Test the carbon monoxide alarms.

ENGINEB
Exhaust hose between injection elbow and muffler

Hose surface crazed like an old tyre, soft when squeezed near the elbow, and bulging beside one clamp. Clamp screws rusted.

Recommendation: Replace the exhaust hose and clamps with marine wet exhaust hose and 316 stainless clamps within 12 months.

ENGINEC
Exhaust hose connections

Hose in good condition. Single clamps at each end where the fittings have room for two. No markings visible on the hose.

Recommendation: Double clamp each connection where the fitting allows, and confirm the hose is rated for marine wet exhaust when it's next replaced.

ASafety. Safety or compliance deficiency. Fix before the vessel is next underway.
B12 months. Deficiency that needs timely attention. Fix within about 12 months.
CRoutine. Note or observation, cosmetic or maintenance. Routine maintenance at the owner's convenience.

Why the gauge doesn't warn you

Power & Motoryacht's point: if cooling water is cut off, by a failed impeller or a plastic bag over the intake, the temperature in the exhaust hose climbs faster than the engine's. Wet exhaust hose isn't rated for uncooled exhaust; even premium hose is typically rated for 350°F, and exhaust gas can be twice that. It recommends a pyrometer on the exhaust. After any overheat, look at the whole exhaust run as well as the engine.

What replacement involves

Part Notes
Wet exhaust hose Marked for marine wet exhaust, wire reinforced except on short runs, Southern Boating
Clamps 316 stainless including the screw, T-bolt type preferred by many mechanics, Power & Motoryacht
Silicone hose Can last six times as long as rubber, at a higher price, BoatUS

Photos to take

The full run, each connection and clamp, any soot or staining, discoloured sections and the hose markings. With Axsail, describe what you feel along the hose as you photograph each section.

Writing it up

Say where the defect is along the run, what you saw and felt, the clamps, and whether the hose is marked for wet exhaust. With any leak, say "do not run the engine" and recommend the CO alarms are tested.

Frequently asked

How often should a marine exhaust hose be replaced?

Replace it when it shows cracks, soft spots, bulging at the clamps or leaks, or after a cooling water failure has overheated it. BoatUS notes rubber hose will eventually weaken and split, and silicone hose can last six times as long at a higher price.

What hose should be used for a wet exhaust?

Hose labelled for marine wet exhaust, able to stand heat, the weight of water, pressure, oil and acids, per Southern Boating. It says anything longer than four times the hose's inside diameter should be wire reinforced.

Why does a wet exhaust hose melt?

If the cooling water stops, the exhaust in the hose heats up fast, faster than the engine temperature. Power & Motoryacht notes even top-quality wet exhaust hose is typically rated for 350°F, while exhaust gas can be twice that hot, and recommends a pyrometer on the exhaust.

Should exhaust hoses be double clamped?

Power & Motoryacht says every exhaust hose should be double clamped, with 316 stainless clamps, and many mechanics prefer T-bolt clamps. Southern Boating adds that double clamps only work where the fitting is long enough, with each clamp at least 1/4 inch from the hose end and fully on the barb.

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Standards it's judged against

ABYC A-24

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