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Toronto Area Sea Ray Dealers Where Land Ends Life Begins
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Propellers

Your Sea Ray has been equipped with propellers that our tests have shown to be the best suited for general use under normal conditions and load. In some situations, you may wish to change propellers to give your boat slightly different performance characteristics.

In general, changing to a lower-pitch propeller will increase acceleration and load-pulling ability, but with a slight decrease in top speed. Conversely, moving to a higher-pitch propeller will attain higher top speed with a light load, but will sacrifice acceleration and power.

Your particular requirements should be discussed with your Sea Ray dealer. UNDER NO CIRCUMSTANCES USE A PROPELLER THAT ALLOWS THE ENGINE TO OPERATE AT HIGHER THAN RECOMMENDED RPM OR AN RPM THAT IS LOWER THAN THE RECOMMENDED WIDE OPEN THROTTLE (WOT) RPM RANGE GIVEN BY THE ENGINE MANUFACTURER.

Basic Characteristics

Propellers have two basic characteristics: diameter and pitch. Diameter is the distance in inches measured across the propeller hub line from the outer edge of the 360 that is made by the propeller's blades during rotation. Pitch is the distance in inches that a propeller will travel if rotated one revolution without any slippage. For example, a propeller with a 12-inch pitch, when rotated 360, would theoretically, advance 12 inches through the water. No 12-inch pitch blade will, in a single rotation, advance a boat 12 inches. This variance is referred to as slippage. When describing a propeller, both the diameter and pitch are given. The diameter is referenced first and the pitch is second. Therefore, a 14" x 19" propeller would have a 14-inch diameter and a 19-inch blade pitch.

Torque and Its Correction

Some of the more powerful motors create a considerable torque effect - that is, a twisting motion causing the boat to ride with one sheer lower than the other. This twisting reaction is caused by the direction of propeller rotation lifting one side of the boat. This causes uneven drag, so that the boat's bow may tend to fall off in one direction or the other from the intended course given by the wheel. Torque action may occur when maximum or close-to-maximum rated horsepower is applied. Any slight torque may be offset by shifting passenger or gear weight to the high side of the boat.

Damage

Propellers should be free of nicks, excessive pitting and any distortions that alter propellers from their original design. A badly damaged propeller should be replaced, but those that are chipped, bent or merely knocked out of shape can be reconditioned by your marine dealer. When doing extensive cruising, it is advisable to carry an extra propeller aboard. Operating your boat with a damaged propeller will reduce its top speed, may introduce undesirable handling characteristics and will definitely increase fuel consumption. A damaged propeller may also create unpleasant vibrations leading to an increased sound level. These excessive vibrations will hasten wear to rotating and reciprocating engine components and may cause costly damage.

Ventilation, Its Causes and Corrections

While often called "cavitation," ventilation is really a different effect. At times when a boat enters or leaves a sharp turn, the propeller seems to slip and lose thrust and the engine may over-speed. This problem is normally caused by air or aerated water entering the propeller. (A damaged propeller can also cause ventilation.) Ventilation can usually be corrected by one or more of the following: Replace the damaged or incorrect propeller with the recommended one. Set the outdrive at a lesser trim angle (trim the unit downward).

Cavitation, Its Causes and Corrections

Cavitation is a phenomenon that occurs in all propeller-driven craft under certain conditions. The surface of propeller blades are not perfectly flat, and as water is drawn through the blades to be discharged aft into the propeller's slipstream, the water flowing over the curved surface of the blade encounters areas of greater and less pressure. In those areas of reduced pressure, air bubbles are formed. When they move out of the low pressure area, these bubbles collapse. If these bubbles collapse while in contact with an object, such as part of the propeller blade or a trim plane, the bubbles create highly localized forces that can erode the surface of the object. In the case of the propeller, such damage is sometimes called a "burn." It may be caused by an irregularity in the propeller's leading edge, and should be corrected by reconditioning the propeller or by replacement. Cavitation is a normal occurrence in modern boats, and prop inspection should be part of routine maintenance.


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