Page 25 - WestlawnMasthead20_Dec11

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ince so much of my yacht design work has focused on
displacement-speed boats the “single versus twin argu-
ment” has always been one of the first questions asked and
answered. Obviously fuel economy becomes a dominant
concern particularly for boats that are intended to cross
oceans. Historically one big engine has been more fuel-
efficient than two. Big ship builders know this and usually fit
the fewest engines necessary except when higher speeds
are an issue. But economy of a single engine doesn’t mean
just fuel consumption. It also means the savings when you
buy, install and maintain one engine instead of two. That
also means one driveline, one propeller, fewer thru hulls and
on and on.
A single engine has generally been my system of choice, but
not in all cases. When draft becomes an issue sometimes it
is difficult to fit as large a single propeller as you might want
and twins become a better option. Sometimes stepping up
to a larger engine simply makes the size of the engine too
big to accommodate. Most low speed engines have a tru
or industrial background where size and weight are not a
huge issue. That’s not the case in a confined engine roo
Also, in spite of the dependability traditionally shown for
diesels, there are owners who have heard all of the argu-
ments, but still feel safer knowing they have twins. I’ve
never tried very hard to change that decision.
This has been my general rationale for the 30-plus years.
Today, however, the equation is even more complex. Wit
the increased use of engine-mounted electronics modern
engines are significantly more efficient and likely to be m
durable as well. Pods, azimuthing drives, etc. complicate
efficiency issue even farther. And while this new level of
technology is here to stay and will likely to be a boon for
boaters it does cause some concern particularly if you ar
an owner thousands of miles from shore with a single wo
horse diesel.
Thoughts on Installing Single or Twin Engines in
Voyaging Motorcruisers
By Chuck Neville