Boat - 1985 Wellcraft Californian with twin Cat 3208 NAs.
I've already developed my fuel/range curve for running on twin engines - I
get aroune 1.2 nmpg to 0.85 nmpg over the range of speeds from 8.5 to 15
knots. With a 35 foot waterline, the hull speed is about 7.5 knots. Flat
out, the boat will run 17 knots at 2500 rpm. Our usual cruise with twin
engines running is 13.7 knots at 2250 RPM (0.9 nmpg).
Interesting Data:
On both engines, to run 7 knots takes 1200 rpm and yields a (calculated)
nmpg of 1.8.
On a single engine, to run at 7 knots takes only 1500 rpm. Using my
figures from Caterpillar, this makes for 3.5 nmpg and thus about doubles
the range of the boat. Under a single engine, the boat can only turn 2100
RPM and reach 9 knots. At around 8.5 knots the fuel burn is equal - above
that it is cheaper to run both engines.
The Caterpillar manual says to run the engine in neutral for 5 minutes
every few hours when it's freewheeling the prop to lubricate the transmission.
At least on paper, this extends our range at 7 knots / one engine to over
1000 nmiles!
Also on paper, at 9 knots, the boat has about 100 miles LESS range on a
single than by running both engines.
I am interested if anyone else has developed similar data for twin engine
boats and what their real-world experience has been running on a single.
-JimB
Jim Baumgart
<")))>><
(760)749-4257 San Diego
Boat - 1985 Wellcraft Californian with twin Cat 3208 NAs.
I've already developed my fuel/range curve for running on twin engines - I
get aroune 1.2 nmpg to 0.85 nmpg over the range of speeds from 8.5 to 15
knots. With a 35 foot waterline, the hull speed is about 7.5 knots. Flat
out, the boat will run 17 knots at 2500 rpm. Our usual cruise with twin
engines running is 13.7 knots at 2250 RPM (0.9 nmpg).
Interesting Data:
On both engines, to run 7 knots takes 1200 rpm and yields a (calculated)
nmpg of 1.8.
On a single engine, to run at 7 knots takes only 1500 rpm. Using my
figures from Caterpillar, this makes for 3.5 nmpg and thus about doubles
the range of the boat. Under a single engine, the boat can only turn 2100
RPM and reach 9 knots. At around 8.5 knots the fuel burn is equal - above
that it is cheaper to run both engines.
The Caterpillar manual says to run the engine in neutral for 5 minutes
every few hours when it's freewheeling the prop to lubricate the transmission.
At least on paper, this extends our range at 7 knots / one engine to over
1000 nmiles!
Also on paper, at 9 knots, the boat has about 100 miles LESS range on a
single than by running both engines.
I am interested if anyone else has developed similar data for twin engine
boats and what their real-world experience has been running on a single.
-JimB
Jim Baumgart
<")))>><
(760)749-4257 San Diego
