World Cat 325 DC with Twin Yamaha 300 HP – 105% Faster at 3000 RPM
In September 2019, BoatTEST evaluated a radical new propeller from Sharrow Marine. Its unique loop-blade design was revolutionary and we were intrigued. We compared an aluminum version to two stainless-steel propellers on a 20’ (6.1 m) bowrider that weighed 3,453 lbs. (1,566.25 kg) and was powered by a 150-hp Mercury four-stroke outboard. (See the report below for full details.)
In short, we discovered that the Sharrow was faster at all rpm settings, planed with less rpm, had more reverse thrust, gripped the water better in turns, and had better mpg readings at nearly every speed, particularly in the midrange.
Some wondered if we just found the sweet spot for that prop in that outboard-powered bowrider.
Round Two
To answer those questions, Sharrow commissioned BoatTEST to run a second evaluation of its propeller, this time on a 32’2” (9.8 m) World Cat 325 DC catamaran powered by twin 300-hp Yamaha outboards. With three people, fuel full, and test gear aboard, our test model had a weight of 13,694 lbs. (6,211.49 kg).
We put the boat through the same test procedure we use for every performance test we conduct, taking speed, fuel consumption, and decibel readings in opposite directions at 500-rpm intervals. First, we ran the boat with the propellers recommended for the application by the boat and engine manufacturers, Yamaha’s Saltwater Series II stainless-steel 15 3/4” x 15” (40.01 cm x 38.1 cm) three-blade propellers turning in the standard rotation.
Real-World Testing
Because the average boater spends about 60% of his/her time running in the mid RPM range, we’re starting by focusing on best cruise, which we define as planing speed with the greatest range. For our test boat, we found the best cruise at 4000 rpm where she ran 23.8 mph and burned 21.2 gph. This translated to 1.1 mpg and a range of 282 statute miles while holding 10% of the 32 DC’s 279-gallon (1,056.13-liter) fuel capacity in reserve.
With all the data acquired with the stock propellers, we hauled the boat and put on 15.5” x 15.4” (39.37 cm x 39.12 cm) three-bladed Sharrow stainless-steel wheels, topped off the fuel and headed back out on the water with the same test crew. Conditions remained consistent for our second test.
With the Sharrow props, which were designed specifically for our test boat, we found the 325 DC’s best range at 3000 rpm where she ran 21.7 mph, burned 14.8 gph, and wrung 1.5 miles out of a gallon of gas. This gave her a range of 368 statute miles with the same 10% of the boat’s fuel capacity held in reserve.
Noteworthy Differences
Looking at the results, the Sharrows’ most economical rpm was 1000 revs lower than the stock propellers and the boat ran 2.1 mph slower. The biggest difference was the fuel consumption. With the conventional wheels, the boat burned 21.1 gph, but with the Sharrows, that number dropped to 14.8 gph. That translated to 1.5 mpg for the Sharrows compared to 1.1 mpg with the stock props, a 36% advantage.
Our test boat's range also increased to 368 statute miles, which is 86 miles farther than the stock setup. For anglers heading out to the canyons, that’s worth a closer look.
Taking a look at some other numbers, at idle, the Sharrow props were 24% more fuel-efficient. The international maritime agency ICOMIA estimates that a boat spends 40% of its duty cycle running at idle, so this could be important over time.
All-Important Fuel Efficiency
Working our way up the power curve, at 10 mph, the efficiency of the stock propellers drops to .8 mpg because the boat is trying to break over its bow waves and get on plane, but can’t do it at 2500 rpm. At the same rpm, however, the Sharrows planed the boat at 16 mph and burned was getting 1.4 mpg of fuel, which is nearly at peak efficiency and 75% better than the stock wheels.
At 20 to 25 mph, the Sharrows maintained an advantage of 36% in miles per gallon and at 35 mph, the efficiency for both sets of propellers evened off. At WOT with the Yamaha propellers, we hit a top speed of 41.6 mph at 5900 rpm where we recorded 52.4 gph. With the Sharrows, we hit 42 mph at 5500 rpm and burned 53.9 gph. Both of these sets of figures were calculated to .8 mpg and nearly identical range.
Which Props are Quicker?
Because time to plane can be a highly subjective test number, we stayed with tracking acceleration through specific mph settings. From zero to 20 mph, the Sharrows were 2.2 seconds quicker. They maintained their advantage through 30 mph (1.8 seconds) and 40 mph (2.6 seconds).
In summary, the Sharrow propellers planed solidly at 3000 rpm and were faster at all rpm. Capt. Steve felt they had more thrust in reverse, which improves low-speed maneuverability for a tall boat like the 325 DC. They also maintained their grip in tight turns and we felt less vibration across the power curve.