Marine diesel exhaust checks

Most marine exhausts are water cooled, with water from the engine’s raw water cooling system used to cool the exhaust gas. The water and exhaust gas mix together in the injection bend, where it turns into steam before cooling and condensing back into water which then makes its way out of the hull via the exhaust system.

Exhaust system inspection

With the boat ashore, it is wise to inspect the exhaust system for corrosion damage, especially around the injection bend:

Injection bend – this is where the raw water cooling system meets up with the exhaust gases to in order to cool the gases enough to prevent the flexible rubber sections of the exhaust from melting. Check the condition carefully, looking for any signs of corrosion.
Exhaust piping – look for external signs of deterioration in the flexible rubber piping, connections and clips, checking the condition of the double clips all along the system. Any signs of white crystals indicate there have been sea water leaks.

Smoking exhaust

If you have noticed the engine exhaust smoking a lot during the sailing season this can indicate a number of potential problems with the engine that may need to be rectified. It is normal for an engine exhaust to smoke until it is warmed up so you only need be concerned if the exhaust is smoking after the engine has fully warmed up.

The colour of the smoke can be a guide to what might be wrong. White, blue or black smoke from a diesel exhaust indicates there is a problem. White smoke has two general causes: overcooling where proper combustion is not taking place or worn piston rings. Blue smoke comes from burning oil. It can be caused by worn valves or piston rings. Black smoke typically indicates partially burned fuel, worn injectors or clogged air filters. The chart below looks at possible causes and solutions. To help solve the mystery you may need advice from your boatyard mechanic.

White exhaust smoke
Possible cause	Solution
Blocked injectors	Service the injectors
Water or air in the fuel	Defective seals, possible leaking head gasket
Check the breather pipe is clear and not obstructed	Remove and clean out
Reduced cooling water flows	Check the raw water system
Blue exhaust smoke
Engine oil level too high	Check the oil dipstick. If too high, pump out some of the oil
Worn valve guides and seals	Replace oil seals
Piston ring and bore worn, giving a low compression	Get compression checked by a boatyard pro
Leaking turbocharger seal	If fitted, get the turbocharger checked by a boatyard pro
Black exhaust smoke
Blocked air filter element	Inspect and replace
Inadequate ventilation in engine compartment	Check the ventilation isn’t blocked
Blocked or damaged exhaust hose	Check the exhaust hose isn’t blocked or restricted in any way; internal inspection may be required as inner layers of exhaust flexible hose can collapse
Malfunctioing fuel injection	If the airflow is unobstructed and the engine not overloaded, poor injection could be the problem.
Over pitched propeller – engine will not reach its full rpm	Check the engine will reach full rpm in neutral; if it does not get the propeller checked / re-pitched if necessary
Accumulated debris on hull	Inspect and clean if required

First Aid Afloat – fish spine injury

First Aid Afloat - Here is what to do if somebody stands on a fish spine: • Check for dangers. Is it safe for you to enter...

Navigating Through Rough Waters: Tips for Handling Adverse Weather Conditions in a Sailboat

Navigating through rough waters in a sailboat requires skill, preparation, and a good understanding of both your vessel and the environment. Here are some tips for handling adverse weather conditions including Preparation, Techniques, Safety and much more..

Sail care and maintenance – Part 1

When thinking about the care, maintenance and repair of sails it helps to have some understanding of the properties of the ever growing range of modern sailcloth and the fibres they are made from, as opposed to the traditional canvas sails of the past.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Getting to the Start

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the start of a 10-part post where solo sailor, Bernie Branfield, shares his first hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

Dripless shaft seals

Dripless shaft seals are designed to completely stop water from entering a boat’s hull via the stern tube. There are two main types of dripless seals known as face seals and lip seals which many boat manufacturers now fit to production boats.

ColRegs Nav Lights & Shapes, Rules Of The Road and IALA Buoys Apps

ColRegs Nav Lights & Shapes, Rules Of The Road and IALA Buoys Apps Make Learning Rules on iPhone, iPad, iPod and Android...

Repairing a leaking hull-to-deck joint

If you suspect a hull-to-deck joint has failed, then being absolutely sure where the actual leak is occurring is of prime...

Tools and spares for your boat

Tools and Spares to take to sea!

You won’t regret taking a look at our essential tips and checklist to make sure you’re prepared for routine maintenance and those unexpected jobs that come up whilst you’re afloat!

Essential Boat Safety Briefing

Skippers Responsibilities Skippers are obliged to give a safety briefing to the crew even if they are a regular crew. At...

DIY boat upgrades: Budget-friendly projects to enhance your (older!) boat

DIY projects that can enhance both the functionality and aesthetics of your boat. In this article, we’ll explore a variety of DIY boat upgrades that won’t break the bank but will significantly enhance your boating experience.

Keel maintenance and Repair – Part 2

If you have ever witnessed a boat colliding with a rock or other submerged obstacle you will know that there is an almighty thump and the whole boat shakes and judders. While such hard groundings seldom result in catastrophic keel failure, something has to give and even the sturdiest keels can easily be damaged by such an impact.

Boat Engine Failure – what to check

Engine failure If your engine fails or is overheating there are a number of things to check immediately: • Air filter...

Essential boat engine checklist

Boat engine checklist Engine oil level check Even if you have checked it previously, confirming the engine oil level is up...

Crew Overboard Drill – Updated

How to respond to crew overboard A Man Overboard (MOB) drill is a crucial safety procedure that every boater should practice regularly. It simulates...

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 7 – Motivation

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the seventh of a 10-part post where solo sailor, Bernie Branfield, shares his first-hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.

The give-way hierarchy at sea – who gives way to whom?

Whatever their size or type, all skippers have a responsibility to avoid collisions with other boats at sea. It is...

Rudders and steering systems – Part 3

In the third of our three blog articles on rudders and steering systems, we look at how to replace rudder bearings and repair a water-saturated core.

Jester Challenge 2022 – Sailing single handed from Plymouth UK to the Azores: Part 3 – Preparations

Jester Challenge – A modern experiment in old-fashioned self-reliance, self sufficiency, and personal responsibility. This is the third of a 10-part post where solo sailor, Bernie Branfield, shares his first hand account of his single-handed, 2022 Jester Challenge, from Plymouth, UK to the Azores, in his 26′ Invicta Mk2, Louisa.