Outboard/hydraulic steering geometry

[engscot]

I have just finished servicing the hydraulic steering on my outboard and was struck by the geometry. The travel of the hydraulic ram is linear, +/-3 1/2 inches from the dead ahead position (7" total travel). The tiller bar on the outboard, which is bolted to the hydraulic ram, when free, wants to travel in an arc of 8 1/2 inches radius. If we take the dead ahead position as being the 'neutral' position, then at 3 1/2 inches (linear) away, the tiller bar wants to be 3/4 inch distant, perpendicular to the ram. I am puzzled how these two different movements can work together?

I will be grateful for any enlightenment.

Engscot

 

[jfm]

I have just finished servicing the hydraulic steering on my outboard and was struck by the geometry. The travel of the hydraulic ram is linear, +/-3 1/2 inches from the dead ahead position (7" total travel). The tiller bar on the outboard, which is bolted to the hydraulic ram, when free, wants to travel in an arc of 8 1/2 inches radius. If we take the dead ahead position as being the 'neutral' position, then at 3 1/2 inches (linear) away, the tiller bar wants to be 3/4 inch distant, perpendicular to the ram. I am puzzled how these two different movements can work together?

I will be grateful for any enlightenment.

Engscot

There are lots of different detialed designs so would need a pic to comment on yours specifically but there are two basic answers commonly used. Some systems have a single link bar, about a foot long, that connects the tiller to the end of the hydraulic ram, and this link bar swivels at each end so it can rotate in the horizontal plane to allow for the 3/4inch perpendicular movement you refer to. Usually called "side mount". I doubt this is what you have, as the geometry is so obvious you wouldn't be asking the question

The other type - which i suspect you have- has the hydraulics back to front in that the hydraulic cylinder moves while the ram stays still, and is kept still by being connected by arms to the tilt tube of the outboard. Usually called "front mount". The 3/4 inch travel you mention is usually dealt with by having a slot in the attachment to the tiller so the connecting bolt can slide, though I recall seeing some designs (that I didn't rate, and they are rarer) with a rose joint instead.

Sea-Star is the big brand (ex teleflex) and if you look at page 1 (using the printed page numbers, or page 6/80 of the pdf file) of this manual you'll see both the link arm and the slot solution for side-mount and front-mount versions. Page 21 shows the slot in more detial.

http://ww2.seastarsteering.com/PDFs/296221-E.pdf

 

[scottie]

when fitting push pull cables to levers they are not set up 90deg to the end of the lever but 90deg to the mid point of the arc the lever goes through to equal out movement the cable end swivels through ie 90deg to a bit in from the end
much easier to draw than explane
it would be the same principle with a swivelling hydraulic ram or an engine set up to take a cable