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Old 21-01-2007, 04:05   #16
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a different aproach

Hi there
This might be a little off a main steering system. But it might not. I plan to steer my etec center mount motor with an ezy-glide inc steering system, ezy-stik 111 steering. It won't be a bow thruster but it will help.
Mike
S/v wampum
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Old 21-01-2007, 14:42   #17
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Originally Posted by Talbot
Thanks for the data on the hydraulic systems. I have not had one in a boat, and have certainly learnt a lot from this. The one thing that is missing in your diagrams is how you include a hydraulic control from the autopilot?

It looks like I lost this question in the paperwork a while back.

It just T's in up stream from the PRD/bypass valve. The hand wheel pump has flow locks (no feed back) and the auto pilot pump can only flow towards the cylinder. If one opens the bypass everything goes in a circle.
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Old 24-04-2007, 06:04   #18
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Hi Talbot,
If there was a solid bar joining the rudders how do you achieve differential rudder angles ? I would appreciate a diagram as I am constructing something similar .
Cheers , Jezza

Just thought about your comment on Ackerman steering . With a car turning left , the inside wheel turns more degrees than the outer wheel .
Comments please !
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Old 24-04-2007, 12:29   #19
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Quote:
Originally Posted by jezza
If there was a solid bar joining the rudders how do you achieve differential rudder angles ? I would appreciate a diagram as I am constructing something similar .
Cheers , Jezza
You would need to install an idler system between the rudders.

http://members.cox.net/bdfelice/Ackerman/ackerman.htm
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Old 24-04-2007, 15:11   #20
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Quote:
Originally Posted by jezza
Hi Talbot,
If there was a solid bar joining the rudders how do you achieve differential rudder angles ? I would appreciate a diagram as I am constructing something similar .
Cheers , Jezza

Just thought about your comment on Ackerman steering . With a car turning left , the inside wheel turns more degrees than the outer wheel .
Comments please !
Ackerman is essential on a car, because the tyres cant slip against the road without suffering rapid wear. Rudders slip to some extent almost all the time, so ackerman isn't really an essential for a cat.

However you can acheive it with a solid bar connecting the tillers - if the tillers dont meet the bar at 90' - ie if the tillers were offset away from the centreline of the cat you would actually have differential rudder, with the "inside" rudder turning more than the "outside" one.

How you calculate the amount of differential required to match the turning circle of the boat is another question........
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Old 24-04-2007, 16:38   #21
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Correction - the tillers need to be offset TOWARD the centreline of the boat.
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Old 24-04-2007, 22:25   #22
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On a car the steering arms are arranged so that if lines are drawn from the pivots and through the tie rod ends they will meet at the rearward point about which the car will rotate, ie: the centre of the rear axle.
A sailing cat having a substantial amount of rocker would rotate around the centre of lateral resistance. this is probably about the deepest part of the hull but it depends on the underwater cross sectional shape, a v shaped forefoot with very rounded aft sections would move the CLR foreward.
Setting up an Ackerman arrangement is thus easy. Draw a line from the CLR to each rudder shaft. The steering arms are installed to this angle.

Mike
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Old 25-04-2007, 04:45   #23
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ACKERMAN Cont.

Hi All ,
Perhaps a few too many expressos and Doms last night ,
however , Mike , I do agree with your comments .
My situation is that I have reduced the length of the mini keels by 2/3's so not quite sure ( read - No Idea ! ) where the CLR is .
Also in the midst of constructing a hard top out of PP honeycomb , interesting pics to follow !
44' Cruisingcat , check the attachment re formulae .
Just need to be able to turn this thing a little better than a tram !
Cheers , and Happy Days to all

"Exhilaration is that feeling you get just after a great idea hits you, and just before you realize what's wrong with it."
- Rex Harrison

GO LUNA ROSSO

Australia for some reason can't afford to send a team to the AC !!!


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Old 27-04-2007, 19:34   #24
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Jezza, I know how to work out the Ackerman angles for a car, but for a boat...... in your diagram you would only be estimating what value L is, (and L could even be variable in different conditions) and you would almost be guessing at what R will be. (and R could also vary)
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Old 27-04-2007, 19:36   #25
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Quote:
Originally Posted by Whimsical
Setting up an Ackerman arrangement is thus easy. Draw a line from the CLR to each rudder shaft. The steering arms are installed to this angle.

Mike
Wouldn't a line from the CLR to the rudder shaft just run down the centreline of the boat?
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Old 28-04-2007, 03:06   #26
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44cruisingcat - Shift the CLR point to the centreline of the boat. The rudder shafts are in the hulls so the steering arms are not parralell to the longitudinal axis. Thus the steering points are closer together than the rudder shafts.
Note there should be a tie rod between the two arms and the steering drives this or another steering arm that can be at any angle to suit the install.

Jezza = I doubt it would be highly critical. I would just pick a point slightly in front of the deepest section of the hull.
That diag just solves for the angle of the wheels for a given turning radius it doesn't solve the offset to achieve the diferential movement.

If all this don't make sense I will have to try and get a drawing package to illustrate it.

Mike
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Old 28-04-2007, 07:51   #27
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Quote:
Originally Posted by northerncat
thinking of all the ways that i could set up my steering for my cat and i was just wondering whether any one has used that morse? cable steering that they use for runabout steering? this would seem to ba a relatively cheap easy way to your helm connected to your rudders
sean
Hi ....

For push-pull cable systems .... the FP Tobago uses a good system. It works very well ..... AND you can connect an autopilot directly to the tiller arm and it works fine. One thing though: with these systems ... if they start getting stiff or rough .... it's probably time to change the cable.

As for hydraulic systems ... They kill the feed back you get from the rudder. Personally I like to know I've got weatherhelm without relying on the rudder angle repeater .... that might just be lying. Also there are a lot of hydraulic systems in the Caribbean that are leaking or have valve problems. Probably okay for the experienced .... but perhaps not a job for the average sailor.

Cheers
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Old 28-04-2007, 17:40   #28
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When considering Ackerman angles, does the length of the tiller arm make a difference?

Mike
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Old 28-04-2007, 18:05   #29
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The length of the tiller arm only determines the length of movement required to obtain a given angle and the amount of force, at the rod end, required to shift it.
EG If you use a hydralic ram with 12 inces of movement the arm length must be set so the lateral movement is less than this for the required rudder angles.
Mike
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Old 29-04-2007, 04:45   #30
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Thanks All ,
I didn't mean to create such a big topic . Good food for thought anyway .
Whimsical -- sounds like the best and simplest approach . Has to be better than having the rudders parellel at all angles of steering .
Cheers
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