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Steering
issues.
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Wheel
steering |
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Bob
Kupps installed his wheel steering with the steering drum on the right,
and mentions it's 110mm id and gives 6 turns lock to lock.
The generally
recognised number of turns from lock to lock is three (and for some
autopilots this needs to be adhered to +/- 1/2 turn).
Also generally
accepted is to have rudder stops at 33 deg. Steering effect is lessened
considerably over this angle, the rudders tend to act as brakes, and the
forces involved when going astern increase dramatically.
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Lets
look at Bobs gear
as an example.
Three turns round his drum is 110 * 22/7 * 3 = 1035mm.
The point along the tiller at which we can measure 1035mm of travel lock
to lock (being 33deg off centre line) is around 925mm from the turning point (line through the pintles).
If I was setting
the steering up for this boat I'd tie the steering rope around the tiller
at this point and then assess what affect this would have on
ramps/sheets/dinghies/engines etc. If it worked, then I'd found where the
attachment point should be. SB
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Starting
from scratch
you might chose the fixing point first and then determine the
size of drum... Since tiller pilots specify 18inches (450mm)from the pivot
this has always seemed to me a sensible point to attach the steering
(although I'd accept it's odd logic ;-)).
All that then needs
doing is to cut off the tillers say 150mm beyond this to fashion for an
emergency tiller to be connected, perhaps aluminium tube with nice shaped
wooden plug sized for a comfortable hand grip?
Don't forget to
introduce Ackerman angle into the equation when fitting the tiller bar to
your new, short tillers. When Steve T & I looked at this some years
ago we came up with about 15deg for the beamy Tiki's, perhaps down to
10deg on the classics...
Not to be ignored, on Bobs set-up, if we installed the tiller-bar at the
steering line attachment point we just calculated, we're talking 225mm (9
inch) offset! Most people think this looks excessive so end up
compromising, and that will be better than not installing any.
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Tiller
steering |
click on
image for larger version |
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Jeff
Fullmer asks about altering his tiller set-up as it interferes with his
engine.
I've a photo of his
Tanenui so we can see the set-up, the Ackerman angle is built into the
curve of the tillers, and the tillers are angled so, when straight,
they're almost parallel with the decks. When the helm goes over, because
of the angle of the pintles, the tillers drop down, and of course the tiller
bar.
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The
tillers slide into a metal fixture bolted to the rudder on this particular
boat so new ones need to be made, allowing the tiller to "peak up a
bit". Half way between parallel with the deck & 90deg to the
forward edge of the rudder looks OK with short tillers with wheel
steering, with the long tillers you just need
to raise them enough to clear, anymore will place them awkwardly high for
the helmsman. |
The
tiller-bar doesn't need to be so near the end of the tiller which may help
to clear the engine - but a stand-off bracket will need to be fitted to
retain the same Ackerman angle...
New tillers could
be made straight, if required, but a long stand-off bracket would then have
to be fitted, which the tiller-bar connects to (see also the wheel
steering text). SB |
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This page was last updated on 23-Apr-2001. |
