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Old 04-03-2012, 07:31   #16
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Re: Hydraulic Hose - Copper Tube versus Hose

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Originally Posted by colemj View Post
Ah, so I think I am understanding your system better. Is this correct - you will have a solid bar connecting the two rudders? If so, then you will not have creep AND you will be able to set an Ackerman angle.

The Ackerman angle is an offset between the two tiller arms so that the rudders are both centered going straight, but when you turn the rudders, the inside rudder turns more than the outside, which allows the hulls to turn in different radius's. This is used in automobiles, but the same principle is useful in catamarans. You will need to calculate the correct angle for your hull length and then simply mount the tiller arms so that each one carries half that angle. When you look down at the tiller arms when the rudders are centered, the tiller arms will look toed inward. The bar connecting the tiller arms controls the turn angles.

I agree that rerouting the cable system would be tricky and I would go with hydraulic also.

Are you using two cylinders with the return from one connected to the input of the other or just a single cylinder?

You are an unusual Catana owner - all the rest of them rave about the advantages of the outside helms and say they would never own a boat without them.

Mark
Thanks for the info on the ackerman stuff. Do not have physical tie-bar between rudders. the hydraulic guy is here:
Alignment Valve For "Hydraulic Tie Bar - Teleflex Marine HA5471-2 - iboats
Seems it allows for realignment not prevention:
"The SeaStar cylinder alignment valve will allow for the periodic required realignment of two outboard motors or rudders that are linked together with a hydraulic tie bar as opposed to a solid link or a mechanical tie bar."

By creeping out of alignment - I hope it is not hourly? - perhaps yearly , or every 5000 - 10000 miles?

I have 2 cylinders.

Not a fan of the helms - and will be great to be done with them.

thx
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Old 04-03-2012, 07:39   #17
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Re: Hydraulic Hose - Copper Tube versus Hose

I have a friend with a Catana with hydraulic steering like you are installing. He needs to realign his rudders periodically - perhaps 3x per year? I will ask him how often he needs to do it. He is cruising full time, so the boat is used a lot. It's not a big problem, just mark inside the boat where the rudder centerlines are and move them back when they get out of alignment.

Mark
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Old 04-03-2012, 08:47   #18
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Re: Hydraulic Hose - Copper Tube versus Hose

Have a hydraulic system on my boat that is similar to what OP is considering. Capilano helm pump, copper tubing, flexible hyro hose to connect copper tubing to the twin rams, Raymarine hydraulic autohelm system (no separate drive -- just a hydro pump -- very energy efficient).

Rudders are interconnected with large Teleflex push/pull cable. Occasionally things get out of sync and the helm gets stiff...just a couple of short turns of the wheel back and forth clears it up.

The steering rams have bleeder valves on them which are interconnected with clear tubing. This is handy when bleeding the system because you can let the air and fluid bleed back and forth between the chambers of the ram until you have the system bled (air ultimately finds it way back to the fluid reservoir), no hydro fluid all over the place, then just close the bleeder valves.

I have BA-125 rams which are a bit of a pain to rebuild because some of the seals are difficult to access. Looks like newer versions of these have a better design. You will need to periodically replace the seals on your steering rams so take a look at the service manual for the ram you want to use to make sure it is easy to service. The only specialized tool I need to service mine is a pin-wrench. Other than the inconveniently located seals, it is an easy job.

I carry a spare steering ram so that if one starts to leak I can just swap it out and rebuild when I have the time.

Over a 10 year period I've only had a few issues: ram seal wear (normal maintenance), shaft seal wore out on autohelm pump resulting in a hyrdo leak and degraded steering (I carry a spare pump head and motor now). Carry lots of extra hyrdo fluid in case you spring a leak -- when the autohelm shaft seal failed we were returning from offshore and went through about a gallon of fluid getting back in, but kept the steering working.

One singificant difference between hydraulic and mechanical steering to be aware of is that with hyrdo you have absolutely no feedback at the helm. If you feel pressure at the helm then something is wrong.
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Old 04-03-2012, 09:03   #19
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Lightbulb Re: Hydraulic Hose - Copper Tube versus Hose

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Originally Posted by colemj View Post
The Ackerman angle is an offset between the two tiller arms so that the rudders are both centered going straight, but when you turn the rudders, the inside rudder turns more than the outside, which allows the hulls to turn in different radius's. This is used in automobiles...
Mark
This is one of the things I like about sailing...there is always something new to learn.

I've run a lot of different cats and never even heard of the "Akerman Effect", but I will be crawling around below decks looking for the related fittings in the future!
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Old 04-03-2012, 10:31   #20
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Re: Hydraulic Hose - Copper Tube versus Hose

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Originally Posted by belizesailor View Post
Have a hydraulic system on my boat that is similar to what OP is considering. Capilano helm pump, copper tubing, flexible hyro hose to connect copper tubing to the twin rams, Raymarine hydraulic autohelm system (no separate drive -- just a hydro pump -- very energy efficient).

Rudders are interconnected with large Teleflex push/pull cable. Occasionally things get out of sync and the helm gets stiff...just a couple of short turns of the wheel back and forth clears it up.

The steering rams have bleeder valves on them which are interconnected with clear tubing. This is handy when bleeding the system because you can let the air and fluid bleed back and forth between the chambers of the ram until you have the system bled (air ultimately finds it way back to the fluid reservoir), no hydro fluid all over the place, then just close the bleeder valves.

I have BA-125 rams which are a bit of a pain to rebuild because some of the seals are difficult to access. Looks like newer versions of these have a better design. You will need to periodically replace the seals on your steering rams so take a look at the service manual for the ram you want to use to make sure it is easy to service. The only specialized tool I need to service mine is a pin-wrench. Other than the inconveniently located seals, it is an easy job.

I carry a spare steering ram so that if one starts to leak I can just swap it out and rebuild when I have the time.

Over a 10 year period I've only had a few issues: ram seal wear (normal maintenance), shaft seal wore out on autohelm pump resulting in a hyrdo leak and degraded steering (I carry a spare pump head and motor now). Carry lots of extra hyrdo fluid in case you spring a leak -- when the autohelm shaft seal failed we were returning from offshore and went through about a gallon of fluid getting back in, but kept the steering working.

One singificant difference between hydraulic and mechanical steering to be aware of is that with hyrdo you have absolutely no feedback at the helm. If you feel pressure at the helm then something is wrong.
thanks
do you have any pics?
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Old 04-03-2012, 10:38   #21
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Re: Hydraulic Hose - Copper Tube versus Hose

Im vacillating between doing it all, just the lines, or letting the pros do it all.
I reckon at least do the lines: cut the holes, find the routing, bend and pull it thru. Will save a bundle of labor charges, as nobody knows the routes thru the hulls like I do.
And take it from there.

Also.
There is the cable system still tying the 2 rudders together.
Would it be useful to leave it? or no point?
thx
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Old 04-03-2012, 11:57   #22
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Re: Hydraulic Hose - Copper Tube versus Hose

I don't know about the cost differential, but hydraulic hose will likely be much stronger than copper tubing and a lot easier to install. My system is a bit smaller than yours but IIRC the 3/8" copper tube option had a burst strength of 800psi whereas the hydraulic tubing the manufacturer recommended has a burst pressure of 2200psi at a fraction of the cost. Installation was dead-easy due to not having to make bends.
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Old 04-03-2012, 12:12   #23
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Re: Hydraulic Hose - Copper Tube versus Hose

Ackermans angle,,,think of a cars left and right wheel as it turns the corner,,,the outside wheel always has the longest distance to cover,,and the inner the shortest.
If both wheels where turned at approximately the same rate from center, then the wheel which was on the outside of the turn would be dragged through it's radius because it was trying to travel through a wider arc.
Ackermans angle is used to compute the amount of offset in the steering mechanism to adjust for this action. thereby decreasing the amount of slewing the outer wheel would be doing,,,,the same theory applies to twin boat hulls,,,,,draw it out on paper,,you will see the action.
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Old 04-03-2012, 19:07   #24
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Re: Hydraulic Hose - Copper Tube versus Hose

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thanks
do you have any pics?
Sure, will post some soon.
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Old 04-03-2012, 19:16   #25
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Re: Hydraulic Hose - Copper Tube versus Hose

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Ackermans angle,,,think of a cars left and right wheel as it turns the corner,,,the outside wheel always has the longest distance to cover,,and the inner the shortest...
All makes good sense. Familiar with the concept from cars, but not the specific terminology (Akerman) and details of implementation.

On a car of course, you have a more positive friction connection to the ground so something has to give somewhere. On a boat, seems like side slip through water etc would compensate for the different arcs of the hulls. My steering system for example has nothing I recognize as implementing an Akerman angle, but she turns just fine.

How much of a difference does this make in boat turning performance? Any examples of boats that have Ackerman angle set-ups?
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Old 05-03-2012, 07:38   #26
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Re: Hydraulic Hose - Copper Tube versus Hose

To effect an Ackerman compensation, the rudders must have a solid connection to each other via a bar and tiller arms. The tiller arms are offset at the appropriate angles from one another and the bar keeps them in proportion to each other.

While this setup does help in turning radius, the largest advantage is in maintaining speed through a turn because the parasitic drag from the outer hull is reduced in the turn. So faster tacks, and more speed through the tack. Cruising boats manufacturers are not often concerned with this and most people owning these boats never notice. Unless you are racing and tacking often, there isn't much advantage.

Mark
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Old 05-03-2012, 07:59   #27
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That's a relief i usually travel in straight lines.
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Old 05-03-2012, 08:30   #28
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Re: Hydraulic Hose - Copper Tube versus Hose

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thanks
do you have any pics?
Pics attached showing helm pump, auto helm pump, port side steering ram, and attachment points for steering ram and tie bar (teleflex cable) to rudder post.

Note this is the original installation, bending and routing of copper tubing clearly done by someone who knew what they were doing.

I agree with the strategy you were considering earlier, do a lot of the grunt work yourself and get a pro to do the pipe-fitting. I've done a number of projects this way with good results...either myself of my guys doing the grunt work and someone with more specialized skills doing the critical stuff.
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Old 05-03-2012, 08:34   #29
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Re: Hydraulic Hose - Copper Tube versus Hose

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Originally Posted by colemj View Post
To effect an Ackerman compensation, the rudders must have a solid connection to each other via a bar and tiller arms. The tiller arms are offset at the appropriate angles from one another and the bar keeps them in proportion to each other.

While this setup does help in turning radius, the largest advantage is in maintaining speed through a turn because the parasitic drag from the outer hull is reduced in the turn. So faster tacks, and more speed through the tack. Cruising boats manufacturers are not often concerned with this and most people owning these boats never notice. Unless you are racing and tacking often, there isn't much advantage.

Mark
Thanks for the info...think I will leave this project off my list.

I've sailed a few Mantas, but never worked on their steering system: do they have an Ackerman compensation installation?
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Old 05-03-2012, 09:32   #30
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Re: Hydraulic Hose - Copper Tube versus Hose

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Pics attached showing helm pump, auto helm pump, port side steering ram, and attachment points for steering ram and tie bar (teleflex cable) to rudder post.

Note this is the original installation, bending and routing of copper tubing clearly done by someone who knew what they were doing.

I agree with the strategy you were considering earlier, do a lot of the grunt work yourself and get a pro to do the pipe-fitting. I've done a number of projects this way with good results...either myself of my guys doing the grunt work and someone with more specialized skills doing the critical stuff.
thanks for those pics.
Gives me the inspiration to get to it.
Researched fittings etc last night - price is getting high if I order all from teleflex -and still plenty of other stuff. Will decide if I can wing it all with copper and flare nuts. Seems most of the gear has 3/8" FPT fittings, some with 1/2" flare fittings.
So will have to convert to 5/8".
thanks
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