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

"Michal" wrote in message
...
Dear All,

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

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

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?

Any big cat that I have steered has almost no "feel". So hydraulic works as
well as any other type and does make fitting an autopilot simpler and
cheaper. It's first cost is likely to be higher.

If you go hydraulic, then try to fit a steering cylinder to just one rudder
stock and put a tie bar to connect to the other rudder stock tiller - it is
much simpler than dual cylinders which get out of alignment over time and
have to have the rudders re-aligned.

The design or designer should have some figures for expected rudder torque
so that you can choose the correct size system.

Our catamaran (Woods 40' Meander) has a rope drum attached to the steering
wheel. Steering ropes lead under the bridgedeck to tillers on top of the
tilt up rudders. Very simple, easy to fix system, but I still don't know
how I'm going to fit an autopilot to it (other than the cockpit wheel type
which I don't trust for long passages).


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

"Michal" wrote in message
...

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


My suggestion is that the two rudders should be connected together via a
mechanical system and then use one hydraulic ram to operate both rudders,
rather than trying to use two hydraulic rams to operate each rudder. I have
used the two ram approach and have found that they are never in alignment.
It is easy to realign them, but I had to do it far more often than I liked.

Rod

Rod McInnis wrote:
My suggestion is that the two rudders should be connected together via a
mechanical system and then use one hydraulic ram to operate both rudders,
rather than trying to use two hydraulic rams to operate each rudder. I have
used the two ram approach and have found that they are never in alignment.
It is easy to realign them, but I had to do it far more often than I liked.

This is good advice. Two seperate actuators ('rams') will not stay
synchronized with each other over any lengthy period of time or number
of cycles. It's a fluid system, not a locked train. That's why you also
need a rudder angle indicator on a hydraulic system rather than marking
a 'king spoke' on the wheel... the king spoke at center will be a
different spoke every time you go sailing!

Fresh Breezes- Doug King

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

"K. Smith" wrote in message
...
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 really agree with this. Our new 40' cat has this setup (when the rudders
are pointed straight ahead, the individual tillers are pointed inward).
Tacks very easily compared to other cruising cats I've sailed. The
daggerboards probably help too but the rudders seem to make the difference.


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

Evan Gatehouse wrote:
"K. Smith" wrote in message
...

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 really agree with this. Our new 40' cat has this setup (when the rudders
are pointed straight ahead, the individual tillers are pointed inward).
Tacks very easily compared to other cruising cats I've sailed. The
daggerboards probably help too but the rudders seem to make the difference.


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)



Yes Evan; when set straight ahead, if you were to extend notional
straight lines from the pintles through the tiller hinge points, you'd
(hopefully:-)) find they intersect in the centre of the boat at the
point of rotation, with daggerboards it'd be the centre of those.

Thanks.

K