Rolling underway? Ugh! It’s the bane of power boating. It turns some folks green.
Over the years, various methods of dampening this sickening side-to-side motion have been developed —paravanes, stabilizer fins and gyro stabilization. Now comes the new, new thing: rotor stabilization.
We were recently given the opportunity to sea trial the very first American installation of one of these systems. As life-long delivery skippers who’ve run hundreds of passage-making motor vessels, sometimes by necessity in heavy seas, we were very curious to check out this rotor stabilization system.
According to their Dutch maker Dynamic Marine Systems, rotor stabilization is an all-electric method suited for low-speed displacement and semi-displacement motor yachts of up to 30 meters LOA. Called the MagnusMaster, it relies on the “Magnus Effect,” first discovered by Heinrich Gustav Magnus in the mid-nineteenth century.
Magnus wanted to find out why spinning artillery shells had a trajectory deviation. By definition the effect works this way: “If you pass a rapidly rotating smooth object through a fluid medium, a resulting force is created on the object causing its path to be deflected.”
In other words the rotor acts like an airplane wing, causing lift. On a boat, it’s the movement through the water that produces flow over the spinning rotors, which in turn produces either an upward or downward force — depending on the direction the rotors spin.
These first Magnus rotors in the US were installed in April, 2022, in San Diego on a Cape Horn 58 trawler Lahaina Sailor, owned by Dave Abrams. He’d purchased the boat at the Seattle Boats Afloat show in 2016, but she was built in 2000 in eastern Canada. Lahaina Sailor has an ice-rated steel double hull with bilge keels. Carrying 4,300 gallons of fuel Lahaina Sailor has a range of 5,000 miles at 8 knots. Turned out, that’s well within the 12-knot maximum speed allowable for the Magnus to work.
“She will take us anywhere in safety,” Abrams said of Lahaina Sailor, “and can handle a lot more than the crew can. But her only short coming was she was not stabilized. She has a rather flat stern section and would roll like a pig in quartering seas.”
After making trips up into British Columbia, then down to Mexico’s Sea of Cortez and then back to her home base in San Diego, Abrams realized that his beloved Lahaina Sailor’s one negative characteristic was almost enough to put her up for sale and look for a boat that didn’t roll so badly.
At the same time, he started to investigate stabilization. He determined that gyros wouldn’t work because of her 86-ton displacement; the necessary multiple systems would take up too much space. Fins wouldn’t work either, because of her double hull with fuel in between and bilge keels.
Abrams also investigated DMS Magnus Master and eventually decided to go with it. Seeing that a retrofit stabilization would work for Lahaina Sailor, he decided to stick with the boat.
He said he determined DMS was the best fit for several reasons. Their system could be installed in his engine room and give easy access to the actuator motors. Also having it back aft was best placement for access and had ample space. A big plus was that this aft placement would counter Lahaina Sailor’s roll where it was occurring, in the aft section of the vessel where the hull was getting lifted in following and quartering seas.
He liked the idea of an all-electric systems; he could run it off either his generator or his inverters and would not have to install additional hydraulic components as fin stabilization would have required. He liked being able to put the rotors in a park position whenever stabilization was not needed, thus eliminating any speed reduction penalty from when they were in use. And for safety, internal shear bolts prevent hull damage in case of impact to the external rotors.
Due to Lahaina Sailor’s double-hulled steel hull, Abrams’ two main considerations were 1) where to place the actuators and 2) how to mount them to maintain structural integrity. DMS came up with a unique mounting-box system and also sent him a technician from Holland to help with the installation during Lahaina Sailor’s haul out in San Diego.
Hooking up the actuators was pretty straightforward because the electrical control box is right near them, and he just had to run wiring to the actuators and up to the control head in the pilot house.
Poking around on board
When we came on board Lahaina Sailor at her slip at a Shelter Island marina, Dave and Amanda Abrams gave us the tour of the boat, and we studied lots of photos and videos taken before and during their recent haul out when the DMS was installed.
Next was seeing the DMS installation in the engine room, all the way aft. We could see that, although this is a double hulled boat, the floor of the engine room is not. If it had been doubled, then the installation would have been considerably more complicated.
We remarked about the ample open space. Abrams showed us where, in order to open more room around where the port and starboard DMS motors and thru-hulls were planned to go, they decided to first remove an old wing engine that had been installed closer to the center line by the previous owner. Visible there now was a large flat welded steel patch covering the 12-inch round hole where that wing-engine shaft had previously passed through the hull.
All the DMS stuff is installed pretty compactly right where the engine-room floor meets the hull walls, on both the port and starboard sides. What you see is the top of the steel mounting boxes that Abrams had designed and approved by DMS specifically for Lahaina Sailor’s specs. The mounting boxes were welded securely between the boat’s steel frames and stringers, beefing up the area. But the mounting boxes mainly provide new stable platforms about inches above the actual floor where the DMS actuator motors and thru-hulls were installed.
Atop each mounting box is the DMS actuator motor. Mounted on a bulkhead nearby is that motor’s electrical control box, and from it four color coded wires lead forward, to the electronic operational panel up on the bridge.
What you can’t see is the actuator’s five-inch diameter steel shaft that houses the minimal wiring bundle as it goes straight down through the mounting box and through the vessel’s single 5/8-inch steel hull. If we were diving today, we’d see that just below the hull on each side, the actuator motor shaft goes into a stubby 90 degree elbow from which protrudes the actual DMS cylindrical rotors. The cylindrical rotors are smooth, black carbon fiber, no blades or fins.
With Lahaina Sailor parked in her slip, the rotors are pivoted aft in “park mode.” But when underway and deployed the rotor cylinders swing forward until they’re perpendicular to the center line of the hull.
Abrams installed a new nine-kilowatt Northern Lights generator to provide power solely to the DMS motors. Lahaina Sailor also has six-kw worth of inverter power, and each rotor requires only 1.5 kilowatts to operate at max load.
Sea trials off San Diego
Up in the pilot house. Abrams lit off this new generator and the main engine (John Deere 6068 turbo), and he flipped a breaker to energize the DMS electronic control panel. Then we headed out to sea.
Still in the harbor making a steady 7.6 knots, Dave demonstrated how to operate DMS’s touch-screen control panel, which he had mounted conveniently at about four o’clock from the wheel. At first, the rotors were locked in “park” position, indicated on the touch-screen panel like two stubby wings swept aft. So to deploy the stabilization, we first unlock them (red light touched off) and then touch deploy.
The panel’s graphic display showed the rotors gradually swinging outboard or 90° from their swept aft in park position. It took exactly 12.5 seconds for the DMS rotors to swing outboard and begin stabilizing the boat.
Did we feel it? Yes, as the rotors worked (rotating up to 1,000 RPM), we could immediately feel the boat’s slight rolling motion steady up. We were still in San Diego’s harbor channel and making less than eight knots.
Abrams demonstrated how, by moving the main engine control lever into neutral, the DMS rotors automatically swung back into their park position. This could be considered a safety feature, so the pilot can’t forget and accidentally damage the rotors while coming alongside a dock or into a slip.
It also demonstrates why DMS stabilization is not available when you’re having to pop the main propulsion in and out of gear, such as during close maneuvering. More significantly, it shows why it’s not available while the boat is at anchor.
Again, we deployed the rotors as we began to feel long ocean swells at the seaward end of Zuniga Jetty. This time we watched two different inclinometers. Lahaina Sailor went from 1.5 degrees of roll down to zero as the rotors swung into action.
Before we reached open ocean conditions, Abrams instructed us to grab on to something, because he was going to demonstrate “forced roll” mode. We complied, and when he activated it, the rotors spun in the opposite directions from their normal stabilization mode. It was astonishing how quickly this 85-ton vessel doing just a little less than eight knots heeled over to 10 degrees by the inclinometers. It became obvious what a significant amount of torque the Magnus effect exerts on a vessel.
A mile outside the shelter of Point Loma, we had six- to eight-knot WNW wind with initially only about a one- to two-foot swell right on the beam. Without the stabilizers engaged we had a five-degree max roll. With the MagnusMaster units engaged that roll was reduced by about 80%, based on the inclinometers.
Discouraged by such light seas, we decided to induce our own roll, so we performed several helm-hard-over maneuvers in different directions relative to the swell, which was finally building. Without the DMS stabilizers engaged we noted a 12-degree roll on both the inclinometers, and on the same maneuver with the DMS rotors engaged we got a six degree roll. In this case, a roughly 50 percent reduction during hard maneuvers of the kind that you rarely need to perform.
Out past the San Diego sea buoy, we finally had white caps and bigger swell. We continued testing the stabilizers’ effect by turning down swell with the swell over our quarter, a couple times over both port and starboard quarters.
Quartering: this was the exact situation where Lahaina Sailor had always rolled her worst. This was her only negative characteristic, but it was the one that almost got her sold off.
During our tests, while quartering she consistently experienced six-degree rolls without stabilizers, yet amazingly registered less than one degree of roll in nearly identical down-swell runs with the DMS stabilizers engaged. We think she passed her exam.
On the way back into San Diego Bay, we checked our speed with and without stabilizers engaged. We calculated that the stabilization had cost Lahaina Sailor 0.4 knots of speed. Not bad.
Admittedly our number of data points was quite low, but even in light seas we could see that the Magnus effect is a real thing.
Lahaina Sailor’s owners loved her enough, despite her roll tendency, to invest in a rotor stabilization retrofit. n
Pat and John Rains are both licensed masters, power voyaging delivery captains and authors based in San Diego.