Michal wrote:
Dear All,

I'm involved in building a 40 ft cat called Format1200, see:

http://www.format-system.de/designs.html

The cat if fairly light (6 tons) and fast. It
s main propulsion is the mainsail.

We now have to choose the steering system. There will be a wheel in the
cocpit ,an autopilot is also required, (ontop on GPS, radar etc).

There are obviously two rudders. The boat will be used for blue water
cruising.

Do you have a suggestion for a combined hydraulic/autopilot system which
would work well on this boat?

Any pro/contra vs. mechanical steering other than the "feedback" feel?

Thanks M




Hydraulic is the most popular for reliability & maintenance. Most auto
pilot systems can come with "occy" hydraulic pumps for the system &
they're usually more efficient (use less battery) that the mechanical
auto pilot drives.

On the separate rudder steering subject may I mention??? I'm sure
you're already well aware of this, but it's very important if you want
the best performance from a wide cat; when setting up the system make
sure the relationship(s) between the two rudders comply with (or as much
as possible) the ackerman principles. (lines extended through the pivot
points, pintles & tiller end, need to intersect at the boat's centreline
at it's point of rotation, usually around 1/3 the WL length)

i.e.
(i) When on extreme rudder angles, say throwing a tack on a very quiet
day, the inside rudder needs to have a much greater angle on it that the
outside hull's rudder (the inside hull actually scribes a tighter turn
arc than the outside hull)

(ii) Were both rudders to turn at the same angles they act as very
effective brakes working against each other & on those very light days,
with a very light boat (not much momentum) can end you in irons.

(iii) The variations can be arranged/managed quite easily by the
positioning/length of the effective tillers relative to the rudder
pintles or even via the hydraulics on some systems.

Just so long as you're aware of the issue, it is always of interest to
see sometimes hugely expensive so called high performance cats with no
attention paid to this, indeed you even see them with the system setup
so it operates in reverse!!! Be aware keep silent!! some of these multi
hullers are a bit sensitive to questions or inquiries as to why they
need rudder brakes??? how do you disengage the when you want to keep
moving in a turn?? etc:-), it's even worse, if you're older, much worse
if you're not a bloke & much much much worse if you're both!!:-)

After you've won the club championship in your first year out,
trouncing the exact same boats & they bail you up in the corner on the
hows & why fores (don't be hurt they take this club racing stuff
seriously, why?? who knows??!!!), you'll inevitably get blank looks when
you raise this with other multihullers, don't whatever you do try to
debate it with them, for you are doomed from the beginning:-) Best to
just take them outside the yacht club & have them watch the front wheels
on their own car as you turn the steering wheel from lock to lock; then
run!!!!!:-) After all this costs nothing to properly setup & can give
you a performance boost way above their endless cheque book, latest gadgets.


K