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Old 30-06-2008, 05:05   #106
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Quote:
Originally Posted by Nordic cat View Post
I have been working with Jefa to find a steering system with feedback that willlet me have 3 helm stations.

The solution they have come up with uses gearboxes and torque tubes, see the simple sketch enclosed.

By dismounting one or more of the wheels, we can save on the power required when cruising long distances.

Anyone with comments on pros and cons?

Regards

Alan

Alan,

It looks like a very elegant solution. I think torque tubes are more robust than cables, and more reliable than hydraulic. When you say "dismounting", do you mean removing the wheel altogether or just de-clutching it? If you were able to disengage each wheel at its gearbox, that would be most efficient imo.

Kevin
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Old 30-06-2008, 16:28   #107
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Akermann

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Originally Posted by beiland
Definitely use Akermann effect....just like toe-in for front wheels of automobiles. Cats need to be 'turn......ed' thru the tack, and while doing so you want the least drag.
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Originally Posted by BigCat View Post
It isn't normally done on cruising cats. Perhaps it is because it is less necessary than on ultralight cats because the extra displacement helps them around?
Cruising cats can get in irons to. It's not difficult to do.
Attached Files
File Type: pdf Ackermann Steering Geometry.pdf (71.8 KB, 130 views)
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Old 30-06-2008, 16:48   #108
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Ackerman, no tiller bar

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Cruising cats can get in irons to. It's not difficult to do.
Yes, but on the average cruising cat you have no tiller bar, because of, for example, stern steps, a stern platform, engines, and engine support systems.
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Old 30-06-2008, 16:57   #109
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I would think you could still use Ackerman angles even with dual hydraulic rams simply by mounting the rams on the same side of the hull in each hull and toeing in the tiller arms.

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Old 30-06-2008, 18:25   #110
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The last cat built without ackerman geometry was the Alphacat 12! My experience is limited to cats under 50', but I think most of them had tiller bars, albeit some were hidden.
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Old 30-06-2008, 19:44   #111
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Originally Posted by sandy daugherty View Post
The last cat built without ackerman geometry was the Alphacat 12! My experience is limited to cats under 50', but I think most of them had tiller bars, albeit some were hidden.
I beg to differ. In fact I don't know of any cruising cats WITH Ackermann steering geometry, although no doubt there are some. Certainly none of the hydraulically steered cats I've seen have it.

TBH I've made provision to have Ackermann geometry in my boat, the tillers can be set at an angle greater or less than 90' to the rudder, and the hydraulic rams fitted in line with the longditudinal axis, which will give Ackermann effect. (I WAS a believer, untill I looked into it more deeply)

But I really don't think there would be any noticable benefit. Rudders don't work like wheels, they dont "grip" the water. They actually work by "slipping" , generating lift by having an angle of attack. In a very tight turn one rudder may be generating slightly more lift than the other, due to it having a slightly greater angle of attack, but both would still be generating lift in the same direction. They wouldn't be working against each other like car wheels would.

So even working out how much Ackermann is required would be complex in the extreme - you'd need to be able to work out what rudder angle will produce what radius of turn - they don't steer like a car, where you can say "X angle of steering lock will result in Y radius of turn, based on Z wheelbase."

In fact in a boat the turning radius for a given rudder angle would almost certainly vary with speed, would definitely vary with sail balance and probably even how the boat was loaded.
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Old 02-07-2008, 14:45   #112
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Originally Posted by BigCat View Post
Are you saying you are unimpressed with the feedback available with a sailing valve, or are you talking about the stock installation which normally has an anti-feedback valve installed inside the pump? In my experience, there is a modest feedback with a sailing valve. It isn't powerful, but it will spin the wheel from pressure on the rudder.
If you are going to have multiple helm stations, or a hydraulic autopilot, then you need to have the anti-feedback valves installed. Other wise turning one wheel (or the A/P pump) to the left could simply result the other wheel turning to the right, instead of turning the rudder.

Either that or you would need to lock any unused help pump, or have isolation valves for them, which could also be viable options.
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Old 06-07-2008, 13:58   #113
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Differ away, Big Cat! YEMV. (I've been waiting to say that!)

Did I understand you to say in a different string you are now building?
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Old 06-07-2008, 15:07   #114
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Hi Sandy,

Not in build yet, I expect to get the ball rolling within a month or two- Just got the first quote in yesterday, so I need to work through it then start asking the questions.

What does YEMV stand for????

Any comments? I like your insight and appreciate your views, so just give it to me straight. Things are easier to change on paper.

Regards

Alan
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Old 07-07-2008, 04:20   #115
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Old 07-07-2008, 14:59   #116
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Quote:
Originally Posted by 44'cruisingcat View Post
If you are going to have multiple helm stations, or a hydraulic autopilot, then you need to have the anti-feedback valves installed. Other wise turning one wheel (or the A/P pump) to the left could simply result the other wheel turning to the right, instead of turning the rudder.

Either that or you would need to lock any unused help pump, or have isolation valves for them, which could also be viable options.
Automatic lock valves like Hydrive makes are also an option and work great
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Old 07-07-2008, 15:07   #117
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Still fiddling with details on the Jefa torque tube system, but it is proving difficult to get the level of acess I want to all components as well as the redundancy I want.

I might end up with an hydraulic system, and Hydrive is high on the list.

Also balancing the numbers, the torque tube system costs around 3 times the hydraulics

Regards

Alan
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Old 07-07-2008, 15:14   #118
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Quote:
Originally Posted by Nordic cat View Post
Still fiddling with details on the Jefa torque tube system, but it is proving difficult to get the level of acess I want to all components as well as the redundancy I want.

I might end up with an hydraulic system, and Hydrive is high on the list.

Also balancing the numbers, the torque tube system costs around 3 times the hydraulics

Regards

Alan
We are very happy with the HYdrive system in comnbination with the Jefa rudder stocks in 6082 aluminium anodized and combined with carbon fiber balance rudder blades.
We actually get a feel of the rudders although it is not really necessary since most of the actual sailing time is on the autopilot.
If you get alu rudder stock makle sure they are anodized with 25 Mu in order to prevent any corrosion and make sure the rudder stock is not in contact with any other metal part
Greetings and good luck with the planning

Gideon
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Old 07-07-2008, 15:36   #119
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I've had a Hydrive system on a previous boat, and was completely happy with it.

Will almost certainly be using them on the new boat.

One note though, Hydrive have a form you can fill out with your boat specs and rudder design, from which they will advise on which system to use. But they recommend systems that are way beyond what is required, at least for a multi. I guess they are just covering themselves, but the system they were advising me to use could generate over 300kg/m of torque!! I wonder if my home made rudders could cope with that! And frankly, on rudders of only around 1/2 a square metre area I can't see why they would see that as being neccessary.

For rudder shafts and tubes, I've gone with composites. From Exel composites: www.exel.net - Exel Group

They also make very good tapered fibreglass staunchions, and I've used their solid fibreglass rod and tube to make composite mooring cleats too.
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Old 07-07-2008, 20:11   #120
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Quote:
Originally Posted by 44'cruisingcat View Post

One note though, Hydrive have a form you can fill out with your boat specs and rudder design, from which they will advise on which system to use. But they recommend systems that are way beyond what is required, at least for a multi. I guess they are just covering themselves, but the system they were advising me to use could generate over 300kg/m of torque!! I wonder if my home made rudders could cope with that! And frankly, on rudders of only around 1/2 a square metre area I can't see why they would see that as being neccessary.

For rudder shafts and tubes, I've gone with composites. From Exel composites: www.exel.net - Exel Group
That's huge.
For mine I went with what they recommended for a sistership which was 110 kg/m and I thought that seemed excessive. The helm pump is 10kg alone.
I was thinking of the same but I need to taper them to fit the rudder section, must ask them about that. How much is a pair of tubes and shafts.

Mike
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