Sharrow Props Make the Regal 33 SAV 103% Faster at 3500 RPM
Sharrow Marine conducted comparative speed runs on a Regal 33 SAV that gets a lot of usage, more than most boats from the sound of it, in speaking with the owner. It got so much use, in fact, that he ordered a set of Sharrow props to see if they could lower his fuel bill.
The first thing that he noticed was that the Sharrow props lifted the stern which dropped the bow. Because the design grips the water, rather than just spinning in it, Sharrow props create thrust right from the start, and the stern lifts and bow falls.
Conventional props don’t grip the water well and drive the stern down not up.
Because so much weight is in the stern - the engines, batteries, generator and Seakeeper gyro, if that option is elected -- when the hammer is slammed down, the conventional props spin, push the stern down which makes the bow go up. When the bow comes up, forward vision can become obstructed on any boat.
The Problem of Visibility Getting on Plane
Getting on plane for many boats can be difficult. Because most 4-stroke engines have low torque at low RPM, it is hard for them to get lots of power to the water. These engines when taking off lower the stern and raise the boat. Boat designers know this and in the case of Regal did careful calculations to make sure the skipper has good visibility until the boat gets on plan and flattens out.
Because Sharrow props grip the water much better than standard 3 or 4-blade props, they are able to transfer what power is available to the water more effectively. Throughout the low and mid RPM range they are able to produce greater thrust than most conventional props in most applications.
That’s why Regal’s naval architects designed the droop into the 33 SAV’s bow. Of course, Regal isn’t the only builder that must design their boats this way, many builders, depending on the type of boat, do.
But most of the designers of center console boats do not design-in bow droop. One reason is that their owners often take the boats 100 miles offshore to fish, and there the higher the bow’s freeboard, the better. Another reason is that many fishermen use the bow platform or seating surfaces for casting. A drooping bow could create a safety hazard if an angler lost their balance.
Boats should get on plane without having to use trim tabs. But many boaters use them to get their bow down quicker so they can see forward, and to get on plane. But putting the tabs down only creates more drag, making it even harder for the engines to get over the hump.
Once on plane the tabs should be up, and then only used to balance the boat. Now is when the engine trim can be used to lower the bow. Too much trim will make the boat porpoise, as can still having the flaps down. Because Sharrow props grip the water, lift the stern, generally tabs are not needed.
Higher Speed Sooner
As can be seen in the chart above, the dramatic different in speed takes place at 3000 RPM when the boat with Sharrow props breaks away going 30% faster than the 33 SAV with the props that come with the boat. At about 3300 the boat is solidly on plane going 20 MPH, something that boat can’t achieve with standard props until 4000 RPM – 700 RPM higher.
At 3500 RPM the Sharrow props propelled the boat at 27.5 mph, 14 mph or 103% faster than the props that Regal delivered with the Yamaha engines.
The big speed differences continue as the boat is throttled up, right up to the top RPM. This is actually something that the Sharrow props don’t always do, but in the case of the Regal 33 SAV, the Sharrow props are faster from the idle to WOT speeds.
More Fuel Efficient Across the Board
Because of the chop that exists on Tampa Bay and into the Gulf of Mexico, the owner of this particular boat generally runs his boat around 26-28 MPH. His wife likes riding in the bow, and going faster can be uncomfortable depending on the conditions.
As can be seen in the chart above, that is precisely the sweet spot for Sharrow props when it comes to maximizing fuel efficiency. Being 35% more fuel efficient at 27-28 MPH was precisely what the boat owner was looking for, but being even 14% more efficient at 32 MPH is remarkable.
Of course, the corollary of fuel efficiency is greater range, and the Regal 33 SAV has about 35% greater range just where this owner happens to run his boat. We’re told that the longest weekend trips that this owner makes are about 150 miles, so running short of fuel with either make of prop was never a concern.
A Welcome Bonus
But what the owner of this boat never thought about, because he didn’t know it was possible, was how much more quiet the boat was with Sharrow props. Ironically, for years boaters thought the ear-piercing “engine” noise was coming from the outboard engine, but that turns out not to be so.
As demonstrated by Mercury marine in their state-of-the-art acoustical test room where they measure the effect that different tweaks have on the actual engines, most of what we think of engine noise is actually coming from the water the wake, rooster tail and from the tip vortices off conventional propeller blades, according the company president Chris Drees.
We’re told by Sharrow Marine customer satisfaction reps, that most of their customers rave about the big reduction in noise, and that alone is worth the price of admission.
While Sharrow props improve the performance of most boats we have tested in the mid RPM range, for the Regal 33 SAV, these props improved the performance idle to WOT in terms of speed, fuel economy and range – a winning trifecta for the lucky owner.