It should be borne in mind that the reduction
ratios are for the average case and that vessels
broadly classified by length and hull type can vary
significantly in steering characteristics. Selection
of the correct chain reduction ratio is not over
cri,tical however, and any mismatch can be
corrected during sea trials by an adjustment to
the gain control switch on the course computer.
Standard
W’
or
W’
pitch chain is recommended
for the chain drive and the drive sprocket ideally
should not have less than 15 teeth. Bore and
ke!/way dimensions for the drive unit sprocket are
detailed in Fig. 19. It is essential that these bore
and
keyway
dimensions are strictly adhered to.
All sprockets must be keyed and grub screwed
to their shaft and finallv secured with ‘Loctite’.
The drive unit is mounted by bolting to a
substantial frame member (Fig20)The mounting
foot is secured to the drive unit by four equally
sp,aced caphead screws and may be rotated
through 90” to provide a more convenient
mounting position if required (Fig. 21). In some
TYPE 2: ROTARY DRIVE CHAIN
REDUCTION RATIOS
6.0
Displacement Craft
Fig. 17
I.
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x”.
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