I am do the sums to calculate the required size of hydraulic ram need to
drive a transom hung rudder.

I read somewhere that it is preferable to use two rams (one on each side )
to minimise the amount of twisting forces on a rudder.

If I decide to go for this method, is it acceptable to divide the torque
requirement by two.

I.E
If I need a 90KgM torque to drive the rudder, can I size the rams for 2 x
45, or should I use 2 x 90 ?

garry

"Glenn Ashmore" wrote in message
news:rJiDb.4799$JD6.1854@lakeread04...
If the cylinders are single action each needs to take the full load. If
double acting it gets more complicated both in calculation and
installing. The pulling force is reduced by the area of the rod.


Excuse my ignorance, but how can I tell if the cylinder is double action or
single. I've just looked at the Vetus catalogue and cant see any reference
to single or double?


For
example a 2" cylinder with a 1" rod will have a pull force about 75% of
the push so you can't quite divide by 2.

I kinda thought that it would just be as simple as divide by 2...



thanks again
garry

If the cylinders are single action each needs to take the full load. If
double acting it gets more complicated both in calculation and
installing. The pulling force is reduced by the area of the rod. For
example a 2" cylinder with a 1" rod will have a pull force about 75% of
the push so you can't quite divide by 2.

garry crothers wrote:

I am do the sums to calculate the required size of hydraulic ram need to
drive a transom hung rudder.

I read somewhere that it is preferable to use two rams (one on each side )
to minimise the amount of twisting forces on a rudder.

If I decide to go for this method, is it acceptable to divide the torque
requirement by two.

I.E
If I need a 90KgM torque to drive the rudder, can I size the rams for 2 x
45, or should I use 2 x 90 ?

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

The Vettus system is a double acting "balanced" cylinder. Balanced
cylinders have the rod going all the way through so the pressure is the
same in both directions. In that case you can divide by 2.

Keep in mind though that if you use two cylinders you need to double the
capacity of the pump to get the same number of hard over turns.

garry crothers wrote:

"Glenn Ashmore" wrote in message
news:rJiDb.4799$JD6.1854@lakeread04...

If the cylinders are single action each needs to take the full load. If
double acting it gets more complicated both in calculation and
installing. The pulling force is reduced by the area of the rod.



Excuse my ignorance, but how can I tell if the cylinder is double action or
single. I've just looked at the Vetus catalogue and cant see any reference
to single or double?


For

example a 2" cylinder with a 1" rod will have a pull force about 75% of
the push so you can't quite divide by 2.


I kinda thought that it would just be as simple as divide by 2...



thanks again
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:rJiDb.4799$JD6.1854@lakeread04...
If the cylinders are single action each needs to take the full load. If
double acting it gets more complicated both in calculation and
installing. The pulling force is reduced by the area of the rod. For
example a 2" cylinder with a 1" rod will have a pull force about 75% of
the push so you can't quite divide by 2.

Unless the rod comes out at both ends.....

Meindert

"garry crothers" wrote in message
...
Excuse my ignorance, but how can I tell if the cylinder is double action
or
single. I've just looked at the Vetus catalogue and cant see any
reference
to single or double?

I think all Vetus cylinders are double action. If you see one hose nipple on
each end of the cylinder, they definately are.

Besides, I fail to see how two rams can prevent any twist anywhere in the
rudder system.

Meindert

"Meindert Sprang" wrote in message
...
"garry crothers" wrote in message
...
Excuse my ignorance, but how can I tell if the cylinder is double action
or
single. I've just looked at the Vetus catalogue and cant see any
reference
to single or double?

I think all Vetus cylinders are double action. If you see one hose nipple
on
each end of the cylinder, they definately are.

Besides, I fail to see how two rams can prevent any twist anywhere in the
rudder system.

Meindert

I believe that the advantage with two rams is that, because one cylinder
pushes aft, while the other pulls forward with the same force, the only
force on the rudder stock is the desired twisting, and no side loading is
imposed, as the case would be with the use of a single cylinder.

But then again I am no expert,

garry

Doing a really rough vector analysis it appears that with the rudder
within 15º of midships there is very little difference in the turning
force between a single and a double cylinder setup but because one
cylinder is pushing out while the other is pulling in, the pressure on
the pintle is somewhat less. Not sure it is enough to justify a second
cylinder with the extra cost, hose and fittings though.

Not much to be gained in redundancy either. The most likely point of
failure is not the cylinders but the pump, hose and fittings.

garry crothers wrote:

"Meindert Sprang" wrote in message
...

"garry crothers" wrote in message
...

Excuse my ignorance, but how can I tell if the cylinder is double action

or

single. I've just looked at the Vetus catalogue and cant see any

reference

to single or double?

I think all Vetus cylinders are double action. If you see one hose nipple

on

each end of the cylinder, they definately are.

Besides, I fail to see how two rams can prevent any twist anywhere in the
rudder system.

Meindert


I believe that the advantage with two rams is that, because one cylinder
pushes aft, while the other pulls forward with the same force, the only
force on the rudder stock is the desired twisting, and no side loading is
imposed, as the case would be with the use of a single cylinder.

But then again I am no expert,

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:QgkDb.4899$JD6.4249@lakeread04...
Doing a really rough vector analysis it appears that with the rudder
within 15º of midships there is very little difference in the turning
force between a single and a double cylinder setup but because one
cylinder is pushing out while the other is pulling in, the pressure on
the pintle is somewhat less. Not sure it is enough to justify a second
cylinder with the extra cost, hose and fittings though.

Not much to be gained in redundancy either. The most likely point of
failure is not the cylinders but the pump, hose and fittings.



Well, it would certainly make life a lot simpler if you reckon I could get
away with it.
I dont know much about hydraulics, hence the question, I will speak to
some of the suppliers for further opinions.

thanks again for your input

garry

On Mon, 15 Dec 2003 12:54:24 -0000, "garry crothers"
wrote:

I am do the sums to calculate the required size of hydraulic ram need to
drive a transom hung rudder.

I read somewhere that it is preferable to use two rams (one on each side )
to minimise the amount of twisting forces on a rudder.

If I decide to go for this method, is it acceptable to divide the torque
requirement by two.

I.E
If I need a 90KgM torque to drive the rudder, can I size the rams for 2 x
45, or should I use 2 x 90 ?

garry

If you are visualizing what I am visualizing, then two single acting
rams can substiture for one double acting ram.
Each s.a. ram needs to develop the full torque: one to starboard, the
other to port. There is no difference on the torque experienced by
the rudder post, as far as I can see.

Brian W