I was unwise to attempt to help on the basis of too little
information. I hope that Glenn can visualize this
arrangement better.
But better yet would be a diagram to put in front of a person
familar with hydraulic steering layouts, I'd think.

Brian W

On Tue, 16 Dec 2003 14:31:19 -0000, "garry crothers"
wrote:


Perhaps I am missing something in my calculation, taken from Vetus calalogue
I had contemplated using approx 20cm brackets set back from the pintels by
same 20cm distance.
(using Vetus MTC72 ram with a stroke of 225mmm I would need 196mm lever to
give me 2 x 35 degree rotation of rudder)

Area of rudder 0.69 m2
Max Speed 16 Kmh
Force on rudder = 23.3 X 0.69 x (16 x 16)
approx 4000N

Torque = Force on Rudder x Lever.
4000 x 0.2
800Nm


This figure is just outside of the rated capacity of the MTC72, thats why I
was asking if I used two Rams , one on each side of the rudder, can I divide
the torque required by 2.
///
garry

At this point I am kind of lost myself. Steering rams are rated for
operating more or less perpindicular to a tiller arm off the pivot
point. Alternately they are mounted off the transom at an angle as with
an outdrive.

What I think Garry is talking about is mounting the rams off the stern
parallel to the 7.5 sq.ft. rudder to brackets extending about 8" off
either side of the rudder. To me that seems to be a very odd
configuration that can't be calculated using the normal vendor supplied
formulas.

Brian Whatcott wrote:
I was unwise to attempt to help on the basis of too little
information. I hope that Glenn can visualize this
arrangement better.
But better yet would be a diagram to put in front of a person
familar with hydraulic steering layouts, I'd think.

Brian W

On Tue, 16 Dec 2003 14:31:19 -0000, "garry crothers"
wrote:



Perhaps I am missing something in my calculation, taken from Vetus calalogue
I had contemplated using approx 20cm brackets set back from the pintels by
same 20cm distance.
(using Vetus MTC72 ram with a stroke of 225mmm I would need 196mm lever to
give me 2 x 35 degree rotation of rudder)

Area of rudder 0.69 m2
Max Speed 16 Kmh
Force on rudder = 23.3 X 0.69 x (16 x 16)
approx 4000N

Torque = Force on Rudder x Lever.
4000 x 0.2
800Nm


This figure is just outside of the rated capacity of the MTC72, thats why I
was asking if I used two Rams , one on each side of the rudder, can I divide
the torque required by 2.

///

garry




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Glenn Ashmore" wrote in message
news:ufQDb.5545$JD6.4631@lakeread04...
At this point I am kind of lost myself. Steering rams are rated for
operating more or less perpindicular to a tiller arm off the pivot
point. Alternately they are mounted off the transom at an angle as with
an outdrive.

What I think Garry is talking about is mounting the rams off the stern
parallel to the 7.5 sq.ft. rudder to brackets extending about 8" off
either side of the rudder. To me that seems to be a very odd
configuration that can't be calculated using the normal vendor supplied
formulas.

Say you have a bracket extending 8" off either side, and this extension is
mounted, say 8" off from the pivot point of the rudder. Then the mounting
point of the ram om this bracket is at the same point as if you would have
two tillers of 11.3" (pythagoras), each at an angle of 45 degrees from the
rudder. If you mount the each ram perpendicular to this 'virtual' tiller,
wouldn't that create the same setup as one tiller and two rams parallel to
the 'transom' (which he doesn't have)?

Meindert

Meindert Sprang wrote:
"Glenn Ashmore" wrote in message
news:ufQDb.5545$JD6.4631@lakeread04...

At this point I am kind of lost myself. Steering rams are rated for
operating more or less perpindicular to a tiller arm off the pivot
point. Alternately they are mounted off the transom at an angle as with
an outdrive.

What I think Garry is talking about is mounting the rams off the stern
parallel to the 7.5 sq.ft. rudder to brackets extending about 8" off
either side of the rudder. To me that seems to be a very odd
configuration that can't be calculated using the normal vendor supplied
formulas.


Say you have a bracket extending 8" off either side, and this extension is
mounted, say 8" off from the pivot point of the rudder. Then the mounting
point of the ram om this bracket is at the same point as if you would have
two tillers of 11.3" (pythagoras), each at an angle of 45 degrees from the
rudder. If you mount the each ram perpendicular to this 'virtual' tiller,
wouldn't that create the same setup as one tiller and two rams parallel to
the 'transom' (which he doesn't have)?

Meindert



That makes sense but he wants to mount the rams parallel to the rudder
which, if the setup is roughly 200mm square will set them at about 45º
to the "virtual tiller" in the center position. That arangement will
reduce the effective ram force by about 1/3. To complicate matters, the
Vetus MTC72 is 487mm long in the center position so the ram pivot has to
be mounted 287mm forward of the pintle. The geometry becomes a trapezoid
rather than a parallelogram and puts the action out of balance. A quick
Autocad sketch indicates 99 mm out and 140 mm in. He would have to use
two rams or the rudder would turn one way faster than the other.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Glenn Ashmore" wrote in message
news:isYDb.5581$JD6.2101@lakeread04...
That makes sense but he wants to mount the rams parallel to the rudder
which, if the setup is roughly 200mm square will set them at about 45º
to the "virtual tiller" in the center position. That arangement will
reduce the effective ram force by about 1/3. To complicate matters, the
Vetus MTC72 is 487mm long in the center position so the ram pivot has to
be mounted 287mm forward of the pintle. The geometry becomes a trapezoid
rather than a parallelogram and puts the action out of balance. A quick
Autocad sketch indicates 99 mm out and 140 mm in. He would have to use
two rams or the rudder would turn one way faster than the other.

Indeed!

Meindert