Quantitative Data on the Evolution Marine Shaft System
Based on a study by the University of Maine Department of Engineering and Ultra-Sonic Acoustics Inc., of the EMSS installed on a 42-foot Grand Banks powered by a 3116 Caterpillar:
- 83% decrease in hull vibration
- 40% decrease in horizontal vibration
- 16% reduction in engine vibration
- 17 dBA noise reduction at the helm and in aft cabin
Based on a study by Gibbon Associates Consulting Services of the EMSS installed in a 30-foot Black Watch powered by twin 350 Crusaders:
- "[At] 3200 engine rpm: Measurements indicate approximately 3 to 16 dB lower vibratory acceleration levels for the 'after' series, depending on specific octave band; which would then represent approximately 30% to 60% lower vibratory acceleration..."
The Evolution Marine Shaft System (EMSS) is a complete shaft system from engine to propeller. It's comprised of two major components: 1) the "oil-lubricated section" containing a '22' alloy stainless steel shaft enclosed in a 316L stainless steel shaft log tube with aft bearing housing and forward thrust bearing housing, and 2) the internal connecting shaft with a splined slip joint and flexible joints at each end.
Other system components include the engine adapter, mounting flanges, and monitor tank with its fittings and hoses.
The oil-lubricated section penetrates the hull. Essentially, it's the shaft enclosed in a non-turning shaft log tube. Generally, this tube is 316L stainless steel with an approximate wall thickness of 3/8 inch. It is extremely strong approaching the tensile and yield strengths of the shaft itself.
At the aft end, near the propeller, this shaft log tube mechanically mates with an aft bronze bearing housing consisting of a bearing cap that bolts directly to a mating bronze flange. This mating flange can be of various designs depending on whether the installation involves a sternpost/keel or strut configuration. For sternpost/keel configurations, the flange can have two or four bolts. This flange might only be a three-piece collar machined to accept the bearing cap and machined to bolt directly to fiberglass stern tubes or the aft face of the strut barrels.
Within the aft bearing cap are two double lip seals plus a needle bearing. These operate on their own hardened races. At the aft end of the shaft log tube, there is a plain, "free-floating"bearing. Additional needle and plain bearings are utilized based on the application and length of the shaft log tube.
As the shaft and shaft log tube enter the hull, they mate mechanically with a larger diameter steel thrust bearing assembly. This thrust bearing assembly consists of a three-piece housing covering two tapered thrust bearings mechanically affixed to the shaft and operating within their own hardened race cones, a front double-lip seal with its own hardened race, and two double-lip seals -- one in front of the shaft log tube and an abutting seal in the aft cover of the thrust bearing housing. The shaft protrudes through the front of this thrust bearing housing and is keyed to accept a split collar shaft flange. The forward face of this split collar flange is machined to accept the bolt pattern of the internal connecting shaft.
The internal shaft connecting the oil-lubricated section to the adapter/transmission of the engine is of universal/constant-velocity joints/rubber flex joints by themselves or combined and may accommodate various angles between the engine and the shaft. Whenever space allows, a splined slip yoke is utilized to facilitate installation and to further accommodate the "free-floating motion" of a soft-mounted engine.
The Evolution Marine Shaft System is engineered to be as fail-safe as possible, with an extremely strong, non-turning shaft log tube containing the shaft, two oil chambers, various bearings and five double-lip seals.
Once the oil-lubricated section is attached to the hull with water-tight integrity, either at the sternpost/keel or the internal bulkhead for a strut configuration; the propeller thrust is transferred from the engine/reduction gear to the hull. Because there is no propeller thrust on the engine/reduction gear, the engine may be isolated from the hull with truly soft motor mounts. This alone will significantly reduce engine vibration to the hull and sound levels throughout the vessel. As much as 83 percent less hull vibration with a resulting reduction in sound of 17 decibels has been recorded.
Without propeller thrust on the internal connecting shaft, this shaft with its flexible joints and splined slip joint may accommodate various engine shaft angles based on torque and revolutions of the shaft.
The shaft being held with half-thousandths clearance at each end, with mechanical bearings in an oil bath, typical propeller slippage is significantly reduced. The EMSS makes the propeller much more efficient, which fosters increased speed and fuel economy. With the shaft and mechanical bearings turning in an oil bath, shaft drag is at a minimum. Additionally, the EMSS with its non-turning shaft log tubes in a strut configuration, eliminates the detrimental turbulence of water in front of a propeller caused by a turning shaft. This, too, increases the propeller efficiency.
While greatly improving the environment aboard a vessel, the EMSS significantly improves propulsion. The Evolution Marine Shaft System is a long-running, low-maintenance, oil-lubricated shaft system that truly complements the entire vessel.