OK to Mount Hydraulic Steering Rams on Deck?

[GRIT]

Most folks would have to angle the rudders for a mock Ackerman effect. I'm not sure how you'd rig that so that they're both straight, and the inboard one moves more than the outboard one. How exactly is that done on a boat, and does anyone actually have a boat that is set up like this?

I'm still not convinced, not even close.

Cheers.
Paul.

[GRIT]

Originally Posted by Chotu

Extending this post’s logic, wouldn’t the hull need to bend into a C shape to the same arc as the turn too? With each hull bending different amounts?

Also, wouldn’t the hull be the real brake here since it doesn’t do that?

Ackerman works well on point contacts like wheels, but we have lines of contact, which make things way, way more complex.

As an example, how do you Ackerman an old-fashioned wood and metal sled on metal runners?

I didn't even think of the hulls!

Good point!

Cheers.
Paul.

[rslifkin]

Originally Posted by GRIT

Most folks would have to angle the rudders for a mock Ackerman effect. I'm not sure how you'd rig that so that they're both straight, and the inboard one moves more than the outboard one. How exactly is that done on a boat, and does anyone actually have a boat that is set up like this?

I'm still not convinced, not even close.

Cheers.
Paul.

For hydraulic steering, rotating the steering arms on the rudder shafts and then adjusting the rudders to the desired position should do the trick if I'm not losing my mind. That would give you a setup where for a given amount of cylinder movement off center, each rudder would turn further in one direction vs the other.

[GRIT]

Originally Posted by rslifkin

For hydraulic steering, rotating the steering arms on the rudder shafts and then adjusting the rudders to the desired position should do the trick if I'm not losing my mind. That would give you a setup where for a given amount of cylinder movement off center, each rudder would turn further in one direction vs the other.

That can't give much, can it? Maybe a degree?

Good thought though. I was imagining lopsided quadrants..

I know when I was researching my system, it was recommended to avoid attaching the rods at the 90 degree point. Though I believe it had to do with the dead spot at 90, but I won't swear by it.

Cheers.
Paul.

[Chotu]

I was picturing quadrants that are not a section of a circle, but a section of an oval.

[GRIT]

Originally Posted by Chotu

I was picturing quadrants that are not a section of a circle, but a section of an oval.

Yes, that seems more likely.

Paul.

[rslifkin]

Oval quadrants would do the trick too. I've got no idea how much Ackerman you'd want if it were determined to be beneficial. I'd expect my idea of moving the steering arms would only get a couple of degrees at most.

[Dave_S]

When driving a rudder shaft with linear motion you get the least degrees of rotation for a given linear movement when the line through the the centreline of the rudder shaft to the attachment point is at right angles to the rams movement and maximum rotation when the two lines approach collinear. The rate of rotation increase is not linear when shown on a graph with the rate of increase accelerating the further from 90° you get.

To apply Ackerman, set both the rudders at 0° attach one ram to the rudder at say 30° CW. The other at 30° ACW. One ram pushes the other pulls with equal linear travel. In this scenario one rudder is pushing towards 90° (decreasing rotation) and the other is pulling away from 90° (increasing rotation) so the rate of rotation is different for each.

If you want more Ackerman effect change the 30° to a greater angle or less for less. You can also change the mount point for the other end of the ram for a similar effect.

Easy and effective, working out what you want is hard. If I was doing it I think I'd make it adjustable. Start with a best guess and experiment.

[Dave_S]

Originally Posted by GRIT

Most folks would have to angle the rudders for a mock Ackerman effect. I'm not sure how you'd rig that so that they're both straight, and the inboard one moves more than the outboard one. How exactly is that done on a boat, and does anyone actually have a boat that is set up like this?

I'm still not convinced, not even close.

Cheers.
Paul.

My boat is set up as above.

[GRIT]

Originally Posted by Dave_S

When driving a rudder shaft with linear motion you get the least degrees of rotation for a given linear movement when the line through the the centreline of the rudder shaft to the attachment point is at right angles to the rams movement and maximum rotation when the two lines approach collinear. The rate of rotation increase is not linear when shown on a graph with the rate of increase accelerating the further from 90° you get.

To apply Ackerman, set both the rudders at 0° attach one ram to the rudder at say 30° CW. The other at 30° ACW. One ram pushes the other pulls with equal linear travel. In this scenario one rudder is pushing towards 90° (decreasing rotation) and the other is pulling away from 90° (increasing rotation) so the rate of rotation is different for each.

If you want more Ackerman effect change the 30° to a greater angle or less for less. You can also change the mount point for the other end of the ram for a similar effect.

Easy and effective, working out what you want is hard. If I was doing it I think I'd make it adjustable. Start with a best guess and experiment.

Interesting. And a great explanation of how to do it. Thanks Dave.

Any idea what the maximum angle difference is at max turn?

Cheers.
Paul.

[Dieseldude]

Originally Posted by Chotu

Do those with kickup rudders have their hydraulic steering rams mounted outside on deck?

No corrosion worries?

Planning my install.

If you want to pay the cost of stainless steel hydraulic rams and components, deck mounted rams should be fine. Note that chrome plated ram rods tend to pit with constant sea water exposure. If such rods are closely examined on older commercial vessels, many will be found pitted. A well chosen stainless alloy is much more resilient. But even stainless that is subject to sea water will need occasional cleaning and polishing, as even stainless can corrode.

[garyfdl]

Originally Posted by Dieseldude

If you want to pay the cost of stainless steel hydraulic rams ... But even stainless that is subject to sea water will need occasional cleaning and polishing, as even stainless can corrode.

I've been out of the hydraulics industry for a bit. But I did work on and designed systems for marine applications through the 90's and none of the components were stainless.

As to cylinder rods in particular, my understanding is they are chromed because chrome is very hard and will take a much higher polish than stainless.

[Dave_S]

Originally Posted by GRIT

Interesting. And a great explanation of how to do it. Thanks Dave.

Any idea what the maximum angle difference is at max turn?

Cheers.
Paul.

Any amount you want.

Way beyond what you would need on a catamaran.

You are only really limited by mechanical disadvantage. You could keep going with it until the loads become unacceptable. I'm tempted to say infinite theoretically.

[Dieseldude]

Originally Posted by garyfdl

I've been out of the hydraulics industry for a bit. But I did work on and designed systems for marine applications through the 90's and none of the components were stainless.

As to cylinder rods in particular, my understanding is they are chromed because chrome is very hard and will take a much higher polish than stainless.

Yes, you are right about the properties of chrome. But I have seen a lot of pitted chrome on such things as deck crane rams. In some cases it is due to abuse. But chrome exposed to sea water can flake and pit. A well chromed ram rod can last a long time outdoors in sea spray. But pitting can happen too. A pitted ram will eventually damage the seal.

[Chotu]

Originally Posted by Dieseldude

Yes, you are right about the properties of chrome. But I have seen a lot of pitted chrome on such things as deck crane rams. In some cases it is due to abuse. But chrome exposed to sea water can flake and pit. A well chromed ram rod can last a long time outdoors in sea spray. But pitting can happen too. A pitted ram will eventually damage the seal.

So the moral of the story is probably to leave the rudders hard over when not in use to put the chrome inside the ram?