T&T: Diesel or gas

[Richard Cook]

Here's another perspective on fuel efficiency, weight, and slowing down:

Our boat is only 26', with a relatively slow planing hull, 260hp diesel, 
and sterndrive.  We used to cruise at 18 knots on plane, getting 1.75 
nmpg.  The boat weighs 11K lb loaded with full tanks on the water 
(exceptionally heavy build for a 26).  If it were a couple of thousand 
pounds lighter, like most other 26's, it would cruise several knots 
faster and get 25-50% better mileage.  It's weight puts it on the knee 
of the efficiency curve - lots of power required to keep it on plane.  
Operating on plane, weight is very significant.  We went to great 
lengths to avoid carrying stuff we didn't need, and to take lightweight 
approaches to the stuff we did carry.

We now cruise at 6.5 knots, and get close to 4 nmpg (if I could keep my 
engine warm enough going slower, I would).  Going slow enough to stay 
near hull speed rather than planing makes a HUGE difference.  At this 
speed weight matters little.  30-50 miles a day most days is enough, and 
we see more, have less noise, less worry about floating wood, etc. 

Richard Cook
New Moon (Bounty 257, Volvo KAD44P)


Randy Pickelmann wrote:
> Marc,
> Thanks for the great question.  It causes us to rethink why we do what we do.
> It was interesting to read Arild's post this morning about slowing down,
> followed shortly after by  Jim's post about his Monk 36 doing 8.5 mph while
> burning 2.2-2.4 GPH.  By slowing down just one knot your fuel economy will
> increase dramatically, as will your range.  On my 36' Manatee we can cruise at
> 6.5 kts. (just shy of 7.5 MPH) and burn about 1.25-1.5 GPH.  Granted that part
> of the equation is hull form but most of it boils down to choosing at what
> speed you wish to travel and how much fuel you are willing to buy.  That means
> that if we plan to cruise 50 miles per day, Jim will be at the marina or
> anchorage about 45 minutes before me.  Its all a personal choice.