Chapter 2: Installation 492.8 Mechanical Drive SystemsRotary Drive UnitThe rotary drive is coupled to the steering by a chain drive. Most steeringgear manufacturer's supply special autopilot drive attachments (manyinclude this as standard). The Edson Company is a good source.MountingHaving selected the position for attachment of the autopilot drive chain, itis necessary to determine the chain reduction ratio.Count the number of turns of the steering gear shaft (driven sprocket)when the rudder is driven from hardover to hardover. Determine thesprocket sizes required from the following table.17192515131715131715131517Driven SprocketDriver Sprocket767657575738383825252525251 2 3 4 5 61234567Number of Driven SprocketTurns Hardover HardoverChain Reduction RatioRotary Drive Chain Reduction RatiosType 1Type 2D757-1These ratios provide good steering performance for most vessels. If thevessel is thought to have unusual steering characteristics, contact ourProduct Support Department, or an authorised representative, for advice.A standard 3/8in. or 1/2in. pitch chain is recommended for the chain driveand, ideally, the drive sprocket should not have less than 15 teeth. Boreand keyway dimensions for the drive unit sprocket are detailed in thefollowing illustration. It is essential that these bore and keyway dimensionsare strictly adhered to. All sprockets must be keyed, set screwed to theirshaft and finally secured with loctite.
