Re: torque shift props
Hey here is a full read I found:<br /><br />Reprint of article published in TRAILER BOATS MAGAZINE.<br />"In our tests, the low-end pitch settings resulted in sterling acceleration when set to 13 1/2 inches, awesome acceleration at 11 1/2 inches and brutal acceleration at 91/2 inches."<br />REVOLUTIONARY NEW PROP<br /><br />Land & Sea Torque-Shift meets your needs automatically, with surprising results<br /><br /> BY JIM BARRON<br /><br />The subject of props always seems to come up in boating discussions, but few props have developed as much interest as the Land & Sea Torque-Shift. Adjustable-pitch props and variable-pitch props are not new. Ocean liners have used variable-pitch props for years and, in some cases, the pitch can be reversed to allow backing without the need of a separate transmission. This type of prop requires a considerable amount of mechanical or hydraulic linkage and isn't too practical for outboards and stern drives.<br /><br />Some composite props are designed to allow blades to flex, with the claim that they automatically adjust their pitch to match the load. The Land & Sea prop is not a true variable-pitch. Rather, it is a shifting prop that goes from one predetermined pitch to another. The design is clever. The shift point is controlled by the operator, and our initial experiences with this prop indicate that it works well, is efficient and is capable of solving a lot of boating problems.<br /><br />As we stated earlier, this is a prop that is capable of shifting from one pitch to another. The stainless-steel blades actually pivot in the hub, and different blade sets are available to match the top-speed capabilities of your boat. The maximum pitch currently available is 32 inches, and that blade set is adjustable so that the pitch my be held to 24 inches maximum. The minimum pitch available with this blade set is 12 inches, and with the use of shims, the minimum pitch can be held to approximately 16 inches.<br /><br />The blade set for our test boat, a 20-foot Sanger Barefoot Skier with a 200-hp Evinrude, had an upper pitch range of 26 to 19 inches and a lower range of 9 1/2 inches to approximately 13 1/2 inches. The upper and lower pitch ranges are user-adjustable to match the requirements of the boat.<br /><br />On our test boat, we could accelerate to a plane with a 9 1/2-inch-pitch prop, let the prop shift, then cruise with a 26-inch - pitch prop. We found that limiting the top end pitch to approximately 24 inches gave us the best speed. Limiting the bottom-end pitch to 11 1/2 inches provided the smoothest shifting and excellent low-end acceleration.<br /><br />Using the extremes of the pitch range provided a real wallop in low-end acceleration, but the engine wasn't happy with the 26-inch-pitch on top end and bogged down just after shifting. Using the 9 1/2 inch, low-end pitch with the 24-inch top-end pitch preserved the initial low-end wallop with the best top end, but the shift point was just past planing speed and engine rpm was climbing rapidly into the red zone. The 11 1/2-inch, low-end setting had us planing comfortably and resulted in shifts that kept engine rpm high enough to continue to pull strongly.<br /><br />In our tests, the low-end pitch settings resulted in sterling acceleration when set to 13 1/2 inches, awesome acceleration at 11 1/2 inches and brutal acceleration at 91/2 inches. The various low-end pitches translate into a top speed of approximately 38, 33 and 26 mph, respectively, at 6000 rpm. These speeds were taken with the engine trimmed down to prevent the prop from shifting, a control feature we will discuss later.<br /><br />The shifting mechanism of the Torque-Shift prop is ingenious and controlled by several factors, which include a set of springs that return the prop to the lowpitch position at idle, a cam profile on the shank of the blades, centrifugal forces of the spinning blades and trim angle that control the center of pressure on the face of the blade. All of these forces work together to control blade shifting.<br /><br />When no force is acting on the blades, the springs hold the prop in the low-pitch position. When accelerating, two things happen. With the bow trimmed down, first the center of pressure (the force of the water acting on the blade) is concentrated toward the trailing edge of the blade. This is behind the pivot point of the blade, and the resulting forces tend to hold the blade in the low-pitch position. Second, as propeller rpm increases, centrifugal forces try to push the blades away from the hub and the diameter of the prop actually increases from 14 to 14 5/8 inches as the prop shifts from low to high pitch. The cam profile on the blade shank forces the blade to twist to its high-pitch setting as the blades move away from the hub. As long as the center of pressure is on the trailing edge of the blades and is greater than the centrifugal forces acting on the hub, the prop will stay in the low-pitch position.<br /><br />When we trim the drive unit out, the center of pressure on the blade moves toward the leading edge. The water forces are now concentrated ahead of the pivot point of the blades. When these forces, combined with the centrifugal forces of the blades trying to move away from the hub, overcome spring tension, the prop shifts to its high-pitch position. The operator controls the shift point of the prop by trimming in or out and the throttle setting.<br /><br />The shift points under a given set of conditions are determined by blade weight, and shift cam profile. When properly set up, the operator can force an earlier upshift by trimming out further or sooner, or can force a downshift by trimming down and lightly backing off the throttle momentarily. Once shifted, the prop will stay where it is. This allows the low-pitch setting to be used at reasonably high speeds (limited by engine rpm) for heavy-duty ski towing or the high-pitch setting can be used at moderate cruising speeds for maximum economy while sight-seeing. The shifts are solid, not mushy, and are similar to a car's automatic transmission. Downshifts also are very apparent as the boat slows and the engine speeds up, again not unlike downshifting an automotive transmission.<br /><br />Adjustable components include the blade-pitch range, blade cam profiles, spring tension, three-or four-blade hubs, cleaver and round-eared blades. In short, there is a wide range of parts to play with and Land & Sea has computerized effects of various components and engines to determine which parts work best in a given application. Once in the user's hands, there are still a lot of adjustments available and this is half the fun of using the prop. The high-pitch limit is set with a setscrew on each blade, easily adjusted with the prop on the boat. The low-pitch settings are controlled by placing shims between the hub and the diffuser ring. This requires disassembly of the prop. A single turn of the setscrew equals approximately a two-inch change in pitch on the top end, and each shim under the diffuser ring equals about two inches in pitch at the lower end.<br /><br />We ran some comparisons with the Sanger. Our baseline was the boat with the engine mounted on a transom jack that was set at its lowest position of 22 1/2 inches and set back 6 1/2 inches. The boat was fitted with a stock 23-inch-pitch OMC aluminum prop. Top speed was an indicated 62 mph at 5800 rpm. Acceleration from 0 to 30 was 6.7 seconds.<br /><br />The Torque-Shift prop, adjusted to a maximum pitch of approximately 24 inches, produced a top speed of 64 mph at 5600 rpm and accelerated from 0 to 30 in 4.8 seconds, with the lower limit set at approximately 11-1/2-inch-pitch. We recorded a top speed of 66 mph with the engine three inches higher on the transom. With the engine jacked that high, acceleration was approximately one second slower. There was more speed available with even higher engine settings, because the prop was still biting strongly and not ventilating. However, even though top speeds were increasing, our crew felt they were doing something wrong because 0 to 30 times were also increasing.<br /><br />There are many boat owners out there who constantly complain about not enough power to pull skiers. In short, if this prop will fit your unit, it will solve 99 percent of the problems. The prop is designed to fit V-6 and V-8 outboards and most Cobra, Yamaha and MerCruiser stern drives. Not announced, but reportedly under consideration, is a smaller prop for the bigger four-cylinder outboards and smaller Cobra stern drives. At approximately $500 a copy, it's not inexpensive, but we can't think of any product at twice the price that will make such a difference in performance. The unit is well made, simple and fun to adjust, re-buildable and works as advertised.<br /><br />As centrifugal force pulls the blades from the hub, a cam action on the blade shank causes the prop blade to shift to a higher pitch.
<br /><br />The Viberation everybody complains about is from a lack of care in the set-up.......<br />All three Blades Must be Tuned, Exactly the Same....<br />
