Tips & Advice Category

Engine Cooling System Maintenance – Checking the Anodes in your diesel’s cooling system

If you have a diesel engine in your boat it is most likely kept cool by a closed cooling system integrated with a sea water circulated through a heat exchanger (or exchangers).

This setup requires the same maintenance that is required for any vehicle cooling system, (fresh clean water and suitable antifreeze additive), as well as the need to care for the raw water components that feed salt water through heat exchangers.

The most common heat exchangers on cruising boats are the tubular variety. The external shell looks a bit like a pipe; inside is a series of tubes that resemble drinking straws, which are surrounded by coolant. Seawater passes through the tubes, absorbing heat from the engine coolant. It’s a simple arrangement that allows engines to be filled with coolant rather than seawater, thereby reducing corrosion and increasing efficiency. Engines that are cooled directly by seawater must operate at a lower, and therefore less efficient temperature to prevent salt from precipitating and accumulating within the cooling passages.

As simple as heat exchangers are, they are far from fool proof. The mixture of hot coolant, cold seawater and dissimilar metals makes for a stressful life where the metal is concerned.

Most heat exchangers are equipped with sacrificial anodes, which must be replaced regularly

This is probably one of the most critical (and also most forgotten) aspects of engine maintenance.


These are usually pencil type anodes screwed into the heat exchanger via a brass threaded plug.

Their consumption rate varies with conditions, use, water temperature and salinity. While many users simply replace them seasonally, it’s best to initially remove them monthly for inspection, to determine their rate of consumption.

In some cases, they can be replaced annually; in others, every two months.

If they are allowed to deteriorate too far, they can drop off into the heat exchanger where they can pile up, blocking water flow in the process.

If you remove the anode plug and there’s no remnant of a pencil anode attached, it most likely has fallen off – your replacement interval is too long; they rarely erode away completely without separating from the plug.

This brings us to the second potential issue with your heat exchanger- obstructions and blockages

Clean your diesel’s cooling system.

To more mechanically capable boat owners, removal and cleaning of heat exchangers is not too daunting but you need the right tools and equipment as well as a degree of care as the tubes can be easily damaged.

An easier method of cleaning, especially if done regularly, is to use a chemical flush/descaling agent. Common brands are Barnacle Buster and Rydlyme.

These products can be used to flush the whole raw water system and will dissolve any scale build-up in heat exchangers etc. They will also dissolve any old anodes that might remain so its important to remove all anodes before starting the flushing process

Nearly half of this heat exchanger’s tubes are restricted by debris, marine growth and depleted zinc pencils.

A nice clean Yanmar intercooler exchanger!

A proper regular maintenance routine will keep your engine running at the right temperature and your cooling system in top condition, with much reduced chance of failure (which often comes at the most inconvenient time)

There are some great instructional videos on YouTube or come in and have a chat.


BAY OF ISLANDS ANCHORAGES – Here’s our top five


Oke Bay is our favourite bay to drop anchor. There is a sandy beach and the bay has a good depth of water with a sandy bottom, good holding and there’s usually lots of room. Good meeting place on a hot summer day.
There is good shelter in most conditions, but there can be a bit of a roll if there is a swell outside.  Oke Bay is also great for snorkelling for the kids or walking onshore with great walking tracks leading out to the Peninsula.  Be careful when going ashore as the waves hitting the beach can be quite strong and we have experienced a very embarrassing exit from our dinghy and an unplanned swim!



PIPI BAY (Awaawaroa)

Awaawaroa Bay is known as Pipi Bay.  It has great anchorage with a reasonable depth of water and good holding in a muddy sandy bottom.  It provides good shelter from most wind directions.  It is very popular during the summer holidays so it can become quite overcrowded.  The cicadas are deafening in the summer time and Tui’s will wake you in the mornings.
Beautiful Pohutukawas line the bay




Omakiwi is a great and very popular anchorage, sheltered from North East to South East and provides good holding and plenty of room.  There is a good beach with a pine forest above it with interesting walks and is close to the road for picking up extra crew.



ARMY BAY (Waiwhapuku)

Waiwhapuku is commonly know as Army Bay because during the Second World War there was a defence base there.  There are still concrete remains of the hut floors and also the gun emplacements from where you can get magnificent view of the Bay of Islands.  It has good protection from Westerly winds. Anchoring can be marginal on a hard bottom – not recommended for overnight in a blow, however winds from the west often drop off at night.
Army Bay gives access to great walking tracks on Motorua Island, but remember no animals are allowed onshore.




Assassination is one of the most popular anchorages as it provides excellent protection in gales.  It can become quite crowded during peak holiday times.  There is good deep water right up to several bays which all have good holding.  Opunga Cove has a lovely sandy beach and Orokawa is great for a stroll past the baches.
During the spring when the Kowhai Trees are flowering, the Tui’s become intoxicated on the nectar and become very rowdy.



ANTIFOULING – Everything you’ve ever wanted to know, and things you didn’t know you wanted to know

Fouling, or more accurately ‘biofouling’, is the build-up of plant and animal life that occurs on all submerged structures, from rocks to oil-rigs – and of course, boat hulls.
These are generally split up into two subdivisions; microfouling and macrofouling.
Microfouling is made up of microscopic bio-organisms, such as slime, bacteria and other small algal life forms.
Macrofouling is the bigger stuff that us boaters tend to get worked up about, such as barnacles, mussels, oysters, fanworm and seaweed.





Why should I worry about it?

Because any significant growth of fouling has an immediate effect on your boat’s performance and its fuel efficiency.
On planing powerboats even a light build-up of fouling can knock a few knots off your top speed and increase fuel consumption by 30%.  Heavier growth may prevent a boat from planing altogether.


Does fouling vary from place to place?

Absolutely – from place to place and even year to year, according to the water temperature, its salinity, the level of sunlight, the quality of nutrients and countless other factors.
Generally speaking, the higher the water temperature, the greater the growth, hence the reason fouling is so bad in areas like the Mediterranean.  There are big variations in Northland harbours, with local boaters invariably claiming that their haunt is the worst.


Has it always been a problem?

Yes! and it was arguably even more of a problem to the lumbering sailing ships of yesteryear.  Heavy fouling or the lack of it could be a matter of life or death during the slow-motion  naval battles that they engaged in

How did they cope?

In the early days careening was the preferred method  This involved tipping the ship on its side, lighting small fires under the hull, then scraping off the softened pitch and fouling by hand.
Pitch, tar and even whale grease were favoured by the likes of Christopher Columbus and Sir Walter Raleigh.  The introduction of metal sheathing, first with lead and then copper and zinc, didn’t happen until the 1700’s.


What other types of antifouling were tried?

You name it, someone has tried it.  Patent records have been filed for everything from ground to arsenic, red lead, sulphur and even guano!
History doesn’t relate which ones were the most effective, suffice it to say that bird poo doesn’t feature on many chandlers’ stocklists these days!.



The two main categories of biocidal antifouling are hard and ablative:

1. Hard
Hard Antifouling delivers  biocides through ‘contact leaching’ – it is contact with water which causes the biocides to leach out and protect the hull.  As a result the protection is not constant, it starts out high and then wanes as the biocides deplete, leaving behind a buildup of hard film.  They also lose their antifouling ability if kept out of the water, so they cannot be hauled and relaunched without repainting.  They are not affected by erosion and so are commonly used on speed boats and racing vessels.

International Ultra 2 is ideal for the racing yachtsman that regularly cleans the bottom of his boat.





2. Ablative Antifouling

Also known as self polishing antifouling, the delivery mechanism for this antifouling type is erosion.  The paint either wears away due to the friction of moving through the water and so releases biocides, or there is a chemical reaction at the surface of the coating which releases biocides.The release is controlled and so they provide linger and more consistent protection than hard film antifouling.  As it is only active in water, the boat can be hauled and relaunched without loss of protection.  Altex No: 5 is a popular choice for Northland Boaties.

All Marine carries good stocks of all antifoulings including Carboline Sea Barrier 3000.  This is a good commercial version of Altex No: 5 and considerably cheaper!



What type of antifouling should I use on aluminium?

Antifouling paint used for aluminium should not contain cuprous oxide biocide as the high copper content can lead to corrosion problems unless the hull is expertly painted and protected using sophisticated impressed current protection systems.

Antifouling formulated using cuprous thiocyanate are better used as this material is more compatible with aluminium.  However, it is crucial to apply the correct primers at the correct film build thickness to provide a barrier between the antifouling and the aluminium surface.  Altex Petit Vivid and International Trilux 33 are good options. 

An advantage of products formulated using cuprous thiocyanate, is the ability to produce bright clean colours including clean whites.

ALL MARINE Staff are always on hand to answer any of your questions, so feel free to pop in for a chat and some friendly advice.





GRUNT’s Amazing Cleaning & Polishing Products

Dave had a bit of a project restoring his Cat (Polyester Fibreglass boat with gelcoat finish) to its former glory.

After a basic hose off and wash, he used WATERLINE STAIN REMOVER,
then GRUNT EMER-GEL Rust, Stain & Oxidation Remover
(Dave calls it “Elbow Grease in a Can !) to remove the stubborn stains.


Followed by a polish with GRUNT SUPAWAX, Lagoon Hopper came up as good as new !