Two speed propeller Page 2 - Sail Magazine

Two speed propeller Page 2

Black clouds bearing cold rain showers are racing across the sky. The VHF radio is broadcasting gale warnings. This is not the day to be testing propellers, but nevertheless we are headed out of a marina near Aarhus, in Denmark, on a Bavaria 42 equipped with a Gori three-bladed folding propeller.The three- and four-bladed Goris are unique in the propeller world. They look much like any
Author:
Publish date:
gori_3_blade

The Denmark Test

The point of our testing in Denmark was to see how some of these things played out in practice. We first ran the Bavaria 42 with a Gori propeller in both normal and overdrive modes, then hauled the boat, changed the Gori for a conventional fixed three-bladed propeller, and ran the same tests again. We did crash stops to see how quickly the propellers could stop the boat from full speed ahead. We also brought a second, nearly identical Bavaria 42 into the picture. After putting the Gori prop on one boat and the fixed prop on the other, we sailed the two side by side to compare their performance.

With the wind gusting over 35 knots, objective testing was difficult. We ran parallel courses back and forth with the wind on the beam, measuring boat speed against engine speed at different engine speeds, and averaged the results to negate any current effects. At any given engine speed, the boat with the Gori prop clearly moved faster in overdrive mode. Gori has performed similar tests in more favorable conditions aboard a Beneteau 40, a Bavaria 44, and a Hallberg-Rassy 37. All showed speed increases of up to 20 percent. Perhaps what is more significant is the reduction in noise and vibration achieved at any given boat speed by reducing engine rpms, typically by about 400, at normal cruising speeds.

Under sail the boat with the Gori propeller was consistently faster than the boat with the fixed propeller, which is exactly what we expected. During crash stops, the Gori did significantly better than the fixed propeller.

Learning Curve

To use a Gori propeller, a boat operator must learn some new tricks. If the boat is stationary when put into forward, the Gori goes into normal mode. To engage overdrive the boat must be put into reverse, which opens the blades in the other direction, and moved astern until minimal speed is built up. The gear lever is then shifted into forward with the boat still moving backwards. The reverse flow of the water over the blades holds them open in the overdrive position, where they remain once the prop starts turning in the other direction. To switch back to normal mode the engine must be put into neutral, which allows the blades to fold under the pressure of the water moving past the boat, and then forward gear is re-engaged.

When maneuvering in harbor, this means the propeller goes into overdrive if the boat is backed down and then put into forward gear. If you want to avoid this, you must briefly put the transmission in neutral once the boat has forward motion and then go into forward gear again to shift the blades back to normal. At sea, if the wind drops and you decide to motorsail into overdrive mode, you have to put the engine in reverse and go backwards a bit before shifting into forward gear. You must also take care not to put the propeller in overdrive at full speed, as this will overload the engine. If such an overload is sustained for any length of time, engine damage could occur.

The Gori propeller’s unique overdrive feature sets it apart from other folding props and should make it attractive to sailors who want increased efficiency under sail, but who also spend significant amounts of time motoring at cruising speed. The Gori, however, is also relatively expensive, so sailors on a budget may want to carefully weigh the advantages of having a two-speed propeller.

Related

TOTW_PromoSite

SAIL's Tip of the Week

Presented by Vetus-Maxwell.Got a tip? Send it to sailmail@sailmagazine.comDitch the stress Owners of high-freeboard yachts best boarded via the stern sugar-scoop like to back them into a slip, but the process can be fraught on a windy day or when there’s a current running, ...read more

Sun-Odyssey-490-Bertrand_DUQUENNE-aft

Boat Review: Jeanneau Sun Odyssey 490

True innovation in monohull sailboat design can be a bit elusive these days. That’s not to say that there are no more new ideas, but it does seem that many new tweaks and introductions are a bit incremental: let’s say evolutionary rather than revolutionary. Just when it seems ...read more

X3M-family

Gear: X3M Flight blocks

Block PartyThe elegance of these new X3M Flight blocks from Ubi Maior conceals the fact that they can handle loads of up to 15 tons. Designed to be used with a variety of textile loops, as fixed or snatch blocks, the X3M blocks have resin frames to carry the loops and anodized ...read more

03-BAVARIA-C34_Interior-2k_2

Ask Sail: The Right Cabin Sole Finish

Q: I am working on refinishing my cabin floorboards. I have brought them home and sanded the old finish off and would appreciate comments on using varnish or polyurethane for the sole.— Danny Love, Grand Rivers, KYDON CASEY REPLIES Polyurethane is the better choice for a cabin ...read more

shutterstock_peterisland

The Caribbean Charter Trade Rides Again

“The BVI is now a bit like it was 20 years ago,” Josie Tucci, vice president of sales and marketing for sister companies Sunsail and The Moorings, told me last December. “Instead of full bars, it may be a guy on the beach with a cooler and a barbeque, but the spirit of the place ...read more

Dragging01

Waterlines: Fear of Dragging

If you have a paranoid personality, anchoring out can be a validating experience. On the one hand, it seems rather simple. You amble up to the bow of your boat, drop a lump of metal overboard, let out some rode and secure it somehow. Then you stroll back to your cockpit and ...read more