Max,
I am a marine engineer and worked on big motor ships much of my career.
The simple fact is that this would not be practical for anything less
than a megayacht with a large hired crew.

Any heavy fuel equipped ship not only has heating coils in the tank to
warn the fuel so it softens enough to be pumped out, but then also has
specialized fuel heaters that are used underway to heat the residual
(what is left over when everything they actually want is gone) fuel oil
(the current name for bunker oil) fuel to near 300F for either diesel
injection systems or atomizing burners in a stream generator (boiler).
In the engine spaces of a motor ship that runs heavy fuel is also a set
of crud catchers, strainers, filters and even centrifuges to get the
fuel clean enough to prevent damage to the injection equipment.

There is also a "burn time" issue with residual fuel oils. Back when
big engines (greater the 18'(.5m) bore were low speed engines they could
get away with it, but as they are now medium speed engines (this is
piston speed not crank speed) they are now haveing trouble there. The
story was that the low burn speed could cause conditions where the fuel
would squirt all the way across the bore to stick on the far side
without burning at all. New injection hardware has cured some of this,
but that new technology is also less crud tolerant.

Out here on the great lakes (where I last worked) they don't even bother
with trying to use heavy fuel in diesels, but a long run here is three days.

Matt Colie
Lifelong Waterman, Licensed Mariner and Perpetual Sailor

wrote:
Howdy group,
All the yachtsmen I know who run a diesel use only 'diesel fuel', which
is light and expensive. However, in the merchant navy we use bunker
fuel whenever we're going to be running the engine for a long time,
without varying RPM.

It's thicker than molasses at room temperature, but when suitably
heated, it runs enough to be used in a diesel engine. It also costs a
fraction of regular 'diesel fuel' (aka "Champagne"). The engine is
started with light diesel fuel until it's running hot enough, then the
fuel mixture is gradually changed over to bunker. If the ship comes to
manoeuvering conditions, then the mixture is switched back to light
fuel. They always go back to light fuel before shutting off the engine,
too, to 'clean' the insides for the next start-up.

Now I'm wondering why we don't do this in cruising yachts, where the
engine is running constantly for days, especially considering the fuel
prices of late. All one would need is a heated holding tank and a way
of adjusting the fuel mixture. Then again, I'm not a marine engineer.
Am I missing something?

Regards,
-Max