Hull and Engine Room

Marine exhaust systems, tanks and ventilation

This category brings together three systems that share a single principle: moving fluids and gases around the boat without them ending up where they shouldn't. Exhaust and ducting, fuel and oil tanks, vents and breathers, blowers, water strainers and hose clamps.

They are unglamorous items, but they are directly tied to safety: most fires and explosions on leisure boats start with inadequate engine room ventilation or a leak in the fuel system.

Product families in this category

• Elbows and Bellows (147)
• Fuel Tanks (41)
• Hose Clamps (43)
• Tank Fittings (39)
• Water Filters and Accessories (32)
• Gas Extractors (9)

For silencers, waterlocks and gas/water separators, see the dedicated Silencers category.

Exhaust systems for boats

A marine exhaust carries away the combustion gases and, in a wet exhaust setup, the water that has cooled the engine as well. Its components: the exhaust elbow (where the water is injected), the exhaust hose reinforced with textile or wire cord, connectors and adaptors, elbows, AISI 316 stainless steel hose clamps and the topsides or transom outlet.

Common diameters run from 40 to 152 mm. Never reduce the bore specified by the engine manufacturer: every restriction increases back pressure, fuel consumption and exhaust gas temperature.

Exhaust hose is a consumable with a shelf life, even if it doesn't look like one. Check it every season for cracks, blistering or areas softened by heat, and replace it on age every 8-10 years.

Engine room ventilation

An engine room needs ventilation for two reasons: to feed air to the engine for combustion and to clear fuel vapours, which are heavier than air and collect in the bilge.

On petrol-engined boats, a blower is mandatory and must be run for at least four minutes before starting the engine. Its intake should sit at the bottom of the compartment, which is where the vapours gather. This is one of the most effective and most ignored safety measures there is.

Vents and breathers must be of adequate cross-section and designed to keep green water out in heavy seas. Tank vents must be above the waterline and fitted with a flame arrester.

Tanks, water strainers and hose clamps

Tanks. For fuel, oil and water. Fuel tanks must be made of approved material, bonded to earth on petrol installations, and fitted with a vent, a watertight filler neck and, ideally, an accessible level sender.

Raw water strainers. Fitted between the thru-hull and the cooling pump. This is the component that stops weed, sand and plastic bags from reaching the impeller. Check it often in areas with a lot of suspended matter: a blocked strainer will overheat the engine exactly like a shredded impeller.

Hose clamps. Always use AISI 316 stainless steel, screw included (many cheap "stainless" clamps have a carbon steel screw that rusts within a season). On every connection below the waterline, use double clamps.

Delivery in 24-48 h to mainland Spain and the Balearics, 3-5 days to the Canary Islands and the rest of the EU. Orders placed before 14:00 ship the same day. Returns within 14 calendar days, plus technical advice by phone and WhatsApp.

Frequently asked questions about marine exhaust and ventilation systems

What components make up a marine exhaust system?

The exhaust elbow where the cooling water is injected, the reinforced exhaust hose, the connectors, adaptors and elbows, the silencer or waterlock, the AISI 316 stainless steel hose clamps and the topsides or transom outlet. On a wet exhaust there is usually a gas/water separator at the end of the run as well.

How often should the exhaust hose be replaced?

On age, every 8 to 10 years, even if it looks perfectly fine. Check it every season for cracks, blistering or areas softened by heat. An aged hose lets go without warning and fills the engine room with exhaust gas and hot water.

Is a blower mandatory in the engine room?

On petrol-engined boats, yes, and it must be run for at least four minutes before starting the engine. Its intake should be positioned at the bottom of the compartment, because petrol vapours are heavier than air and collect in the bilge. It is one of the most effective and most ignored safety measures on board.

What is a raw water strainer for?

It is fitted between the thru-hull and the cooling pump and stops weed, sand and plastic from reaching the impeller. It is worth checking often in areas with a lot of suspended matter, because a blocked strainer will overheat the engine exactly like a shredded impeller.

Which hose clamps should I use on a boat?

AISI 316 stainless steel ones, making sure the screw is stainless too: many budget clamps sold as stainless have a carbon steel screw and rust within a season. Every connection below the waterline must have double clamps.

Can I reduce the exhaust diameter if it doesn't fit?

No. Reducing the bore specified by the engine manufacturer increases back pressure, and with it fuel consumption, exhaust gas temperature and wear on the valves and turbo. If space is tight, change the routing or use tight-radius elbows, but never choke down the diameter.