Pursuit S328: Faster and More Fuel Efficient with Sharrow Props
The Pursuit S328 center console is a man-size boat at 12,160 lb. (5,527 kg.), including the engines. That’s a lot of weight to lift up on plane, so it is little wonder that during tests conducted by Sharrows techs, the boat burned less fuel at all RPM. Because Sharrow props lift the stern, and don’t dig a hole in the water, they are faster to plane. When you look at the design of the two props side by side you can see the reason why.
Simply by looking at the two props above the differences are obvious: the standard, old-technology pro at left has three blades that spin through the water. The Sharrow prop effectively has 6 blades turning through water. Further, Sharrows do not have straight blades, rather they have a single blade that extends out then loops back to attach to the hub, thus effectively creating two blades, not one. Altogether there are effectively six blades on the Sharrow props tested.
Which prop do you think will have more “grip” on the water?
Thrashing the Water
It is that “grip” that everyone who operates a boat powered by a Sharrow prop feels. They feel it when turning at high speed, when backing, or when docking slowly. Because they are looped blades, the six Sharrow blades don’t “cut” through the water. Rather, they “thrash” the water, with the leading loop grabbing the fluid and sending back to the second loop, which kicks it back on its way.
That two-step action is one of the things that allow the Sharrow prop to “advance” farther with each 360-degree revolution than the conventional wheel which just cuts through the water.
Sharrow says it has “True Advance” because its props come far closer to the theoretical advance rate than conventional designs. The chart above you can see that at 3500 RPM the props (and the vessel) are advancing 15.65 inches for each complete prop revolution – not 18 inches. That means the Sharrow prop is not 100% efficient; rather it is 86.9% efficient at that RPM.
On the other hand, the conventional design at 3500 RPM only moves 9.42” forward. The Sharrow prop advances 66% more with every revolution of the prop. This is one of the main reasons that the Sharrow prop is more fuel efficient.
Propeller “slip” is one thing that outboard engine companies don’t talk much about as they beat their chests about their great horsepower or top-end speed. The reason is that conventional props are all inefficient to one degree or another, so why talk about it? To do so would just confuse the customer!
In the chart above, at 3500 RPM the conventional props (red line), is slipping 48% -- that is it is 48% inefficient -- and the Sharrow prop (blue line) is slipping 13%, or that much inefficient.
The above chart shows the practical outcome of the Sharrow prop’s superior advance rate. At 3500 RPM the boat with the Sharrows is traveling about 29 mph and getting 1.40 mpg. The old props are pushing the boat about 27 mph and getting 1.19 mpg. At that point the Sharrow’s are 18% more fuel efficient.
Range is The Name of the Game
Fishermen going out the canyons need range to get 100 miles offshore or more. Since the amount on fuel in the tank can’t be increased, fuel efficiency – more miles per gallon – is what will increase range. Depending on what the sea conditions are like, most anglers would like to travel at 30 or 40 mph, so the Sharrows will get from 25 to 54 miles more range for the boat.
If the sea is lumpy, the skipper may choose to pull the boat back to 23 mph or so, where the boat gets 76 more miles to the tank.
Everyone wants to know how fast the boat will go, but the Sharrow props were not designed for speed. But in the case of the Pursuit S238 and the SWS II props, the Sharrows were faster at all RPM. This is unusual, as often the Sharrows get beaten at the top end.
Even more important than WOT speed is speed in the mid RPM range where the boat is run most of the time. Note that at 3500 RPM, which is probably the best place to run this boat, the boat goes 11.8 mph faster with Sharrow props than with the conventional props which are still struggling to get this boat on plane.
Observations
This one is a no brainer. The Sharrow props are superior on all counts in terms of performance. What these numbers don’t show are actually more important than performance to a lot of people. What most people comment on right away when riding on a boat powered by Sharrow props, is how quiet the boat is. That’s because of the nature of the prop wash conventional props create – but that is a story for another time.