Imagine you’re the foreman of a busy shipyard. You get a call from the captain of a yacht that has just struck a submerged object and needs a propeller replaced. You have to get the boat into the yard and find time to haul it or put it in dry dock to swap the wheel.
What if you could just tell the captain to limp the boat into your facility, have him tie up along your staging dock and send a diver down to replace the damaged blade? He’d be in and out in an hour.
It sounds far-fetched, but Teignbridge Propellers International Ltd., which is based in the United Kingdom, has a modular propeller called the Clamp on Blade. It’s designed for merchant, commercial, military and yachting applications. Instead of having to carry spare props, the vessel can carry a couple of extra blades for each propeller. All the blades are CNC machined and interchangeable for a given propeller.
“It’s a great option for anyone who’s operating where there is debris or shifting sand,” says Mark Phare, sales and marketing director for Teignbridge. “The great advantage is that although the Camp on Blade price is one and a half times the cost of a conventional propeller, you only need to purchase a few extra blades instead of a whole spare.”
Phare says that the only other company offering a modular propeller is Rolls-Royce, and it’s a more complicated piece. With the Teignbridge Clamp on Blade, each blade is separate and fits into a slot in a hub. A patented clamp goes over the end, securing the blades in place.
“It’s much smaller and simpler than any similar design,” Phare says.
While the Clamp on Blade might be smaller and simpler than other designs, most propellers now being designed for recreational boating are anything but. As recently as five years ago, the only dimensions that mattered were diameter and pitch. Now, customers in every segment are learning about blade area, rake angle and other specifications as the new generation of propellers aims at more individualized applications — and manufacturers are responding by offering more types of propellers than ever.
As the supplier to Azimut, Sunseeker, the Ferretti Group and others, Teignbridge sees owners of those vessels changing their priorities.
“In the past, it was all about who was the top gun in the harbor and could he get a half-knot more,” Phare says. “Their main focus now is quietness and being free from vibration. They want to make sure there are no ripples in their gin and tonic and that they eat and sleep in quiet.”
Teignbridge is adjusting its propeller design to meet those demands. It is “skewing” blade tips — meaning they are thinned and bent over at a 90-degree angle at the outer ends, to route water away from the hull bottom — and increasing the number of blades on the new designs.
“With standard designs, you get more vortex noise coming off the tip, so the water hits the hull,” Phare says, adding that trying to get the optimum blade area sometimes involves going from four to six blades. “Once you get to six and even seven blades, you’re pretty well maxed out,” he says.
Teignbridge also is looking at alternative materials such as composites for struts and rudders, but Phare says that for propellers, the company is sticking with the three-part alloy known as Nibral, which is short for nickel-bronze-aluminum. Stainless steel has been tried; because the blades are thinner, they get better speed, but customers don’t want to pay the extra price.
On the sportfishing side, Hatteras Yachts and Viking Yachts both use Veem Propellers from Australia. Hatteras also uses Michigan Wheel as a primary supplier. Scott Sorenson, director of supply chain for Hatteras, says top speed is still a priority on the sportfishing tournament scene.
“We get a lot of extra pressure to hit that 40-knot number,” Sorenson says. “A lot of sportfishing is about bragging rights, getting there first and coming home with the biggest fish.”
Hatteras has always been known for using deep gear ratios, and that means big, heavy propellers for maximum efficiency. All Hatteras props are custom designed for each model and horsepower. On the company’s largest motoryachts such as the Hatteras M75 Panacera and M90 Panacera, Sorenson says, eight-bladed Michigan propellers are common. Through the years, the company has tried other propeller manufacturers, which provide a little more flexibility in sourcing smaller wheels for smaller boats.
“Michigan and Veem have the capability to make larger, highly customized propellers for our specific requirements,” Sorenson says. “Hatteras has an in-house prop-tuning shop to further customize every set for each boat for maximum speed and smoothest ride.”
Bigger and better?
Remember when a ski boat was a direct-drive inboard about 19 feet long and the goal was to make as little wake as possible? So does Eric Johnson, president and CEO of Johnson Propeller Co. in Loudon, Tenn., who shakes his head when he sees the new breed of 25-foot wakesports boats making waves taller than a single-story home.
“You still have to have that relationship between the propeller and the engine and the boat, and you need to have it make sense, but these boats are getting so much bigger and heavier,” he says. “We’re building 18-inch diameter props now, which five years ago was laughable.”
There’s more to it — much more — than just making a bigger propeller to get more bite for a bigger boat. If there were only space underneath a boat for a 15-inch prop, then the required 18-inch model wouldn’t fit in the same space at the same angle without the tips hitting the bottom of the boat.
In most cases, says Johnson, changing the rake angle of the blades won’t deliver the clearance needed. The larger diameter now requires a new shaft angle, usually about 20 degrees, which then puts the propeller at a different angle.
“That’s like tucking an outboard way under,” Johnson says. The propeller, engine-mounting system and shaft log all need to be adjusted to get the propeller back to the proper position under the boat.
Johnson saw the change coming because it started with gear ratios. Tournament ski boats had 1:1 ratios. When boats got bigger and heavier for wakeboarding and wakesurfing, they went to 1.5:1. It didn’t take long for 1.5:1 to be less than ideal, and Johnson told boatbuilders: “If you really want to push this weight, we need to change the gear ratios.” Johnson expects 2:1 to be the number for the foreseeable future because many smaller builders haven’t even gone to that yet (the expense is too high to change hull molds to match the new prop shaft angles). As with yacht propellers, Nibral remains the material of choice for the company.
Johnson has done some five-blade designs in the past, but most of the wheels he’s doing for the 2:1 and 1.76:1 ratios are four-blades. “I think we can refine the five-blades even more,” he says.
While Johnson Propeller Co. is focused on making props for bigger towboats, Mercury Marine and its Mercury Racing division are concentrating on props for bigger engines. When Scott Reichow, propellers manager for Mercury Racing, learned that the company’s high-performance division was preparing to unveil its 400-hp Verado 400R in 2015, he started working on the Max 5, an outboard version of the Maximus five-blade prop developed for Mercury Racing sterndrives.
“As we come out with new engines, we come out with new propellers,” Reichow says. “Props are a big part of maximizing the performance of our engines. We marry the product to the application.”
Reichow wouldn’t say how long it takes to create a new propeller, explaining that engineering design, modeling, prototype manufacturing and testing on various boats all tie into the process. However, the company has come up with propellers on short notice. This year, the elite division of offshore powerboat racing, the Unlimited Class, voted to race with Mercury Racing’s 1,100-hp engines. Most of the boats in the class that is now called Class 1 USA run BPM surface-piercing drives instead of Mercury’s M8 or Six drive. CNC cleaver props for the Mercury drives have a rake angle of 15 or 18 degrees, and Reichow said the company had been “twisting” its 15-degree designs down to 13 degrees to accommodate boats with BPM or Arneson drives. This year, the company will introduce 12-degree rake angle cleavers specifically for that application.
In the early 2000s, Hering Propellers in Marysville, Washington, first unveiled CNC cleaver propellers. The props have that name because they have a sharp leading edge and a tip with a flat trailing edge, similar to a butcher’s cleaver.
Around 2005, Mercury Racing started making its own CNC-designed cleavers. Early versions had a 15-degree rake angle, and then customer feedback told the company that 18 degrees worked better in most catamarans and in some V-bottoms. In 2010, the company introduced 21 degrees of rake angle.
Mercury’s racing products include different blade thicknesses for 600 hp, 900 hp, 1,350 hp and 1,800 hp. “We have a thickness curve based on the horsepower, and the hub will grow based on the horsepower,” Reichow says. Before offering these new propellers, the company was putting 1,200-hp props on more powerful engines and breaking off blades. He said cup and rake angle are the same. The only change is in the thickness where the blade comes off the hub.
All new Mercury propellers are designed with CNC and computer-aided design because engineers can assess the propeller in given environments without actually putting it on a boat. Before a wheel goes into production, all prototypes are water tested.
Mercury Racing’s most popular propeller is the Bravo One. Reichow says there are many variations of that model. At Mercury Racing alone, there are 16 families of propellers, while the mainstream Mercury facilities offer another 24 series of stainless-steel and aluminum propellers.
Two series of Mercury propellers, the Enertia and Enertia Eco, are made from the company’s X7 that Reichow says is “stronger, tougher and more expensive to make than our traditional stainless steel.” Mercury has worked with other materials over the years, and Reichow recalls one titanium prop from the 1980s. “The titanium is half the weight, which is cool when you pick it up, but not so cool for strength,” Reichow says. “You would have to double the thickness to match the durability of the stainless-steel version.”
Regardless of the application or segment, propellers continue to evolve like other boat components. They’re going to become more specialized for the application, especially based on customer requests.
“Many of my ideas come from those guys,” Reichow says. “It’s to solve a need. You’re helping the end user.”
This article originally appeared in the October 2019 issue.