Marine diesel at Applecross
Swan River berthing, close to central Perth, in water that is brackish for much of the year and behaves nothing like the ocean fleet’s.
The river is a different electrolyte
This is the defining fact about keeping a boat here. The Swan is brackish upstream and increasingly saline towards Fremantle, and the balance shifts with rainfall, season and river flow.
A boat that stays on the river and a boat that runs down to the ocean regularly are in materially different corrosion environments, and the anode alloy should reflect that:
- Magnesium is for fresh water only and wastes rapidly in salt
- Zinc passivates in brackish and fresh water and stops protecting
- Aluminium spans the range and generally suits a river boat that goes out
An owner whose anodes last far longer than expected is not saving money — a passivated zinc protects nothing. See why anodes matter.
River water in the raw water circuit
The Swan carries more suspended material than the ocean, and after winter rain considerably more. Strainers fill faster than an ocean-berthed boat’s, and heat exchangers collect what gets past.
The water is also warmer than the ocean through summer, which gives the cooling system less margin than a Fremantle boat has.
A flat-water fleet
River boats do a great deal of low-load cruising in sheltered water. That is pleasant boating and it is the pattern that glazes bores and builds carbon.
Running the engine up under genuine load — which on the river means deliberately, or on a run downstream and out — is the mitigation, and it needs to be a habit rather than an accident.
Going out the river
A boat running from Applecross to the ocean passes through a changing electrolyte, transitions from flat water to Indian Ocean swell, and meets the afternoon sea breeze on the way home. The fuel-stirring failure that defines this coast applies, and it applies to a tank that has been sitting in flat water undisturbed.
If the boat rarely goes out, deal with the fuel before a trip rather than discovering the tank’s contents in the swell.
Frequently asked questions
What anodes should a Swan River boat use? Usually aluminium for a boat that moves between river and ocean. Zinc passivates in brackish water and magnesium is fresh-only.
My anodes last ages. Is that good? Not necessarily. A passivated zinc in brackish water protects nothing while looking healthy.
Does river water affect cooling? It carries more suspended material than the ocean and is warmer in summer, so the raw water side needs attention on a shorter cycle.
Is flat-water river cruising bad for the engine? Prolonged light loading glazes bores. Run the engine up under real load deliberately.
What should I do before a trip outside? Deal with the fuel system. A tank that has sat in flat water gives up its contents in ocean swell.