Some Background: Last year I launched my pocket trawler with a Perkins 4.107
engine coupled to a Borg Warner Velvet drive at a 2:1 reduction and a 16 X 9
three blade propeller. The trawler weighs around 8000lbs and has a waterline
length of 22 feet. Late in the season I developed some engine trouble and
replaced the drive system with a Sabb H2 (18hp) coupled to a 19" two blade
controllable pitch propeller.
The Perkins 4.107 is 107 cubic inches of displacement, weighed 520lbs with the
trans and develops 46 hp @ 4000 rpm. Coupled to the 16 X 9 propeller and the
Velvet drive transmission the engine would turn up a maximum of 2400 rpm. I
don't have power curves but I would estimate this to be around 25 hp output.
This engine would drive my boat to hull speed at around 1700 rpms ( probably
around 14 or 15 hp. In real world cruising the average fuel burn was 0.82 gph
for a speed of 6.0 knots. Converted to MPG this works out to 7.3 nmpg.
The Sabb H2 is 70 cubic inches of displacement and weighs in at a hefty 480
lbs for only 18 hp. That 18 hp is developed at its maximum rpm of 2200. The
Sabb drive system is a controllable pitch propeller. The gear reduction is
2:1 and is integral with the engine. You have drive and neutral. Reverse is
by reversing the pitch on the propeller blades. The Sabb drive system drives
the boat to 6.0 knots at a power setting of 1375 rpm. According to the power
curves this is about 9 hp or so. Fuel burn this year averages 0.59 gph for a
mileage of 10.1 nmpg.
The boat is heavier this year and uses more electricity. Last year the boat
was probably run in larger waves for comparison. Both engines have a 150 amp
alternator and sea water pump.
Any way you look at it the Sabb drive system is much more fuel efficient than
the conventional system. I realize that a two blade larger diameter prop is
more efficient than a smaller three blade propeller whether it is controllable
or not and the Perkins was a larger cubic inch displacement. My calculations
work out to 38% better mileage. At the very outside a controllable pitch
propeller probably delivers 20% to 30% better fuel economy.
Some Background: Last year I launched my pocket trawler with a Perkins 4.107
engine coupled to a Borg Warner Velvet drive at a 2:1 reduction and a 16 X 9
three blade propeller. The trawler weighs around 8000lbs and has a waterline
length of 22 feet. Late in the season I developed some engine trouble and
replaced the drive system with a Sabb H2 (18hp) coupled to a 19" two blade
controllable pitch propeller.
The Perkins 4.107 is 107 cubic inches of displacement, weighed 520lbs with the
trans and develops 46 hp @ 4000 rpm. Coupled to the 16 X 9 propeller and the
Velvet drive transmission the engine would turn up a maximum of 2400 rpm. I
don't have power curves but I would estimate this to be around 25 hp output.
This engine would drive my boat to hull speed at around 1700 rpms ( probably
around 14 or 15 hp. In real world cruising the average fuel burn was 0.82 gph
for a speed of 6.0 knots. Converted to MPG this works out to 7.3 nmpg.
The Sabb H2 is 70 cubic inches of displacement and weighs in at a hefty 480
lbs for only 18 hp. That 18 hp is developed at its maximum rpm of 2200. The
Sabb drive system is a controllable pitch propeller. The gear reduction is
2:1 and is integral with the engine. You have drive and neutral. Reverse is
by reversing the pitch on the propeller blades. The Sabb drive system drives
the boat to 6.0 knots at a power setting of 1375 rpm. According to the power
curves this is about 9 hp or so. Fuel burn this year averages 0.59 gph for a
mileage of 10.1 nmpg.
The boat is heavier this year and uses more electricity. Last year the boat
was probably run in larger waves for comparison. Both engines have a 150 amp
alternator and sea water pump.
Any way you look at it the Sabb drive system is much more fuel efficient than
the conventional system. I realize that a two blade larger diameter prop is
more efficient than a smaller three blade propeller whether it is controllable
or not and the Perkins was a larger cubic inch displacement. My calculations
work out to 38% better mileage. At the very outside a controllable pitch
propeller probably delivers 20% to 30% better fuel economy.
