"Glenn Ashmore" wrote in message
news:Uu%Db.5870$JD6.4178@lakeread04...


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.


Took me a little while to figure this out. Being over 50 I have trouble
working with all these newfangled French measurements. I work in feet
knots and pounds. To me KmH is that other dial on the speedometer and a
Newton is a cookie with figs in the middle. :-)

Other than the physical arangement of the rams I see a problem with your
figures.

To get the torque at the pintle you have to divide the total force on
the rudder by the distance from the pivot point to the center of force
on the rudder, not the length of the tiller arm.



AAhhh!!!
I new I was missing something in that calculation

snip

OTOH, you might wonder where the other 40% of the force went. It is
pulling against your pintle so you might better give the whole idea a
bit more thought.
--
Glenn Ashmore



o.k
I'm convinced, I'll lose the 2nd ram idea, and go back to the drawing
board and redo the figures.

Thanks for all your help Glenn

garry