"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 14:24:24 -0000, "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

Quite! :-) (no offence)

Brian W

"garry crothers" wrote in message
...

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.

Ok, you're right. But my gut feeling tells me that this side load is
relatively small, especially compared to the side load induced by the water
pressure against the rudder.

Meindert