Hydraulic ram placement for steering.

Gerr's book has this passage:

"...sometimes find it’s installed at right angles to the tiller when the rudder is amidships. This is not good. It puts the cylinder off angle at either end of its stroke. Instead, the cylinder must be installed so that it’s at right angles to the amidships tiller location when the rudder is turned 35 degrees either way..."

I just can't make out what he's trying to say here. I can't imagine any other way than to mount the ram at right-angles to the tiller arm when the rudder is amidships. If mounted at right-angles when the rudder is 35 degrees one way or the other, then there's surely an asymmetric angle to the tiller when it's at the other rotation?! Confused to say the least.

Gerr, Dave (2008-12-22). BOAT MECHANICAL SYST HB EB (Kindle Locations 5745-5747). McGraw-Hill.

 

Basically, it is bad English. Unless there are some drawings to explain what it means, perpendicular to the center location is the correct installation.

 

555hhh

 

At sea my internet connection does not allow me to read bandwidth intense blogs. I cant read Sven comment.

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I think Gerr is correct on this one if you are talking about a balanced cylinder. In Gerr's way, there will be the same stroke excursion and same torque factor applied from center to either side. If perpendicular when centered, neither will be true, so you have a different number of turns center to lock. If using an unbalanced cylinder, you can solve for a location that is least annoying to you.

In a worst case installation with the cylinder pivot offset only about twice the steering arm length, there is about a 3% difference in the throw from center to in vs from center to out at 35 degrees when the ram is perpendicular to the steering arm with the arm centered. However, torque would differ by about 13% between in and out. More relevantly, the torque at the in position at 35 deg of steering would be about 8% less than if the cylinder was positioned per Gerr. The greater the offset to arm length ratio, the less the effect.

 

Another piggy back question:

Anyone familiar with the best way to put hydraulic ram steering on a catamaran with kick up rudder cassettes?

 

Kick up rudder steering

 

Actually he is worried about torque and throw as Phil alluded to. See the sketch below, the lower arrangement is the perfered one.

 

I think this is what he intends - see attachement. Same as above