New Bi-Rig Performance Cruiser

[Maren]

Originally Posted by BigCat

The hydraulic steering systems used on small to medium sized yachts don't use power.

BigCat and 44'crusingcat: I am familiar with hydraulics however, the first page I went to (feedback options for sailboats) mentioned 12 and 24 volt options. The second page (catamarans) I went to after I had posted my response. That page notes a totally manual setup.

The wheel turns a manual pump that pumps the fluid, and the fluid pushes against rams attached to tillers.

Right, similar to your car. Nothing new there.

It isn't a lot of feedback, but it's definitely there

Now that's interesting. More feedback under certain types of conditions or are you familiar?

[Nordic cat]

The Hydrive system is what I have been looking at for the hydraulic option with a "feedback valve" at each helm station.

Good idea of working on selecting the right diameter of piston to improve feedback, -thanks.

I'm also looking at using a Jefa torque tube system, where the 3 helms connect to a central torque tube via geaboxes. The central torque tube ends up in a bevel gearbox that is mounted between the 2 rudders. The link arm between the rudders is then in 2 pieces that are joined at the bevel gearbox.

So the rotation of the torque tube is converted to an horisontal sideways movement in the bevel gearbox, that moves the crosslink tube and the rudders.

See here: Jefa Steering Systems

Look at the transmission steering section for the bevel reduction gearboxes.
I'm considering running the main torque tube under the bridgedeck, but all options are still open.

Another option is to use a system that is split with 2 helms connecting to one side of the rudder link tube, and one to the other side, but I'm being told to stay away from wire/rope systems due to problems in adjusting the slack between firm steering and poor feedback or more slack and good fedback.

Any of you have experience with these systems for multiple helms? Any feedback (excuse the pun) would be interesting.


Regards

Alan

[beiland]

Originally Posted by BigCat

When I read the first post about the Radical Bay's steering problems, I sent an e-mail to his company, suggesting that they read it and respond to this forum. They didn't respond. The usual responses to steering problems like this are bigger rudders and moving the rig aft, or raking the masts aft. Moving the daggerboard forward would be another solution. I don't think the biplane rig is responsible here, as this problem hasn't been reported with other biplane rigged boats, but it has been encountered with boats having rigs on the centerline. The issue is almost certainly either one of too much lead-the CE being too far forward of the CLR, or the rudders just aren't big enough. I have links to other sites about biplane boats at the bottom of my web page, under a heading that gathers them together as a category.

Originally Posted by multihullsailor6

1) The wisdom says "release the windward sheet and sail head to wind on the lee sail, then dumping that and sail off with the leeward sail? Could also try doing the same with the centerboards. Lift the leeward one pre tack, sail away with the ww one up, lw one down".

Here is a comment from the owner/skipper of this cat: "We have tried the sail configuration as explained above, but had still best results sailing up to the point rudder not to tight, releasing lee sail to reduce drag of lee-hull until new lee sail tacks and hauling close new windward sail."

Originally Posted by multihullsailor6

What I can now tell you about tacking this boat is

1) In wind under 20kts-ish just before commencing the tack release the windward sheet totally and tack on the leeward sail. Wait for the (new) windward sail to fill and push the bows around, then slowly sheet in the leeward sail and off you go. Only in really flat conditions would we play around with the daggerboards to assist the tacking effort.
Results 10/10

2) In wind in the 20-25-ish kts we have a problem! Depending on wave action we cannot tack and have to gybe.
Results 4/10

3) In winds of approx. 30kts and more we cannot tack nor gybe!!
When tacking the boat would stall 10 degrees from the turn, even sailing backwards did not work to push the bows through the wind.
Attempting a gybe, the pressure on the rudders was incredible, could run down-wind but not turn further to the leeward side. Ended up anchoring in 40kts of wind on a lee shore! (Can really recommend the Fortress anchor!). And managed to break the mast / gooseneck boom connection due to a gybe which went wrong.

This weekend's experience has put a big damper on my otherwise positive aspects of this rig design!

There appears to be some real problems with tacking this bi-rig. I might suggest it is a factor of having two distinct turning forces on either side of the vessel as a result of the bi-rig, AND two distinct turning pivot points via the two boards, keels, whatever on either side as well. I've not had time to fully analyze the force diagrams, but I believe it could have a lot to do with the problem. It's not as though you can resolve the two forces on either side into one central force on centerline as is often mistakenly done on multihulls

So what I might suggest is at least eliminating the two 'pivot points' and centralizing them into a central mounted CB affair similar to that I suggest here:

Asymmetrical CB's, nacelle mounted
http://www.cruisersforum.com/forums/...5&postcount=12

You've done a lot of nice work on your design Alan, and this might be a solution to the easing the tacking problem...pivot around one central point.

[Nordic cat]

Originally Posted by beiland

There appears to be some real problems with tacking this bi-rig. I might suggest it is a factor of having two distinct turning forces on either side of the vessel as a result of the bi-rig, AND two distinct turning pivot points via the two boards, keels, whatever on either side as well. I've not had time to fully analyze the force diagrams, but I believe it could have a lot to do with the problem. It's not as though you can resolve the two forces on either side into one central force on centerline as is often mistakenly done on multihulls

So what I might suggest is at least eliminating the two 'pivot points' and centralizing them into a central mounted CB affair similar to that I suggest here:

Asymmetrical CB's, nacelle mounted
http://www.cruisersforum.com/forums/...5&postcount=12

You've done a lot of nice work on your design Alan, and this might be a solution to the easing the tacking problem...pivot around one central point.

Thanks Brian, the project is moving along slowly but steadily, as it is done in my spare time, my work still takes up too much of my day!!

Regarding the tacking issue, I think part of the problem with the Radical Bay is the low weight, that gives low inertia to drive you through the tack. Also having the daggerboards correctly positioned in relation to the sail centre should help.

The 2 larger bi-rigs down in NZ do not have any tacking problems according to Derek Kelsall.

I had a long look at centreboards, but they are very inefficient compared to daggerboards when they are surface piercing. The AR is low to begin with and they don't have any "mirror effect" with nu hull to seal them on top. Also the forces involved become difficult to handle under adverse conditions.

I am thinking of using an "Akermann" rudder configuration to ease tacking, anyone have experience with this?

Regards

Alan

[BigCat]

Oddly enough, Kanter, in the Cruising Catamaran Communique, says you can get this problem if your CE is too far aft on a catamaran. This is contrary to the reasoning given regarding rig design in monohulls, but there you have his views. He says the excessive weather helm in that situation won't let the boat pay off onto the other tack.

[Nordic cat]

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

[BigCat]

Originally Posted by Nordic cat

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

Cool! Does the system allow you to easily detach not only the wheel, but the gearing and tubes that attach to it? Your phrasing could be interpreted as meaning either that only the wheel or also its attached gearing could be (easily?) detached. How does all of this attach to the rudders, given that there are usually engines, engine support systems, and stern stairs in the way? Just curious -

[beiland]

Originally Posted by Nordic cat

...I am thinking of using an "Akermann" rudder configuration to ease tacking, anyone have experience with this?

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.

[BigCat]

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.

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?

[CarlF]

With three wheels and two rudders it sure would be nice if you didn't have a single point of failure in that one fore-aft torque tube. If it breaks or jams you have a very bad day. OF course, they're not supposed to break or jamb...

I'm not sure about the Jeffa system, but could they configure it so that you had a starboard steering system consisting of the starboard rudder and the aft most wheel and a port system consisting of the forward two wheels and the port rudder? You would have two torque tubes going back to the rudders.

The two systems would connect together in the stern with a tie rod between the two gear boxes so it would steer as one. That way, if you lose a torque tube you can disconnect the tie rod and steer with the good system.

With this solution, you would save one bevelhead box but add one gearbox. Cost or friction might make it not worth the bother.

Carl

[44'cruisingcat]

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.

In cars Akermann angle actually generates increasing toe out with increasing steering angle. Cars HAVE to have it, or they will wear their tyres out very quickly.

Boats don't wear their rudders out.

Rudders work by generating thrust from having an angle of attack relative to the water flow. They don't track like car tyres. Not having any Akermann will mean the rudders will possibly generate slightly different amounts of side-thrust, but I doubt if there would be a measurable increase in drag.

[44'cruisingcat]

Originally Posted by Nordic cat

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

Depends on where you want your helms. In some places installation could still be very difficult/impossible.

With multiple helm stations hydraulic is hard to beat for ease of installation.

For instance, initially I will have two helm stations, at the rear of the cockpit on either side. But later I might decide to have a third, inside. With hydraulics this will be an easy retro-fit, in fact you could have additional helm pumps virtually wherever you want.

Autopilots are also an easy install. Just a matter of plumbing in an electric pump.

There are downsides, like the lack of feedback though.

[Therapy]

Originally Posted by 44'cruisingcat

There are downsides, like the lack of feedback though.

My impression with near zero hands-on experience is that cats don't give much feedback anyway compared to monos.

[fastcat435]

Originally Posted by Therapy

My impression with near zero hands-on experience is that cats don't give much feedback anyway compared to monos.

Having much feedback is not very important since 99 % of the sailnig is done with the autopilot working harbour manuvering is done without but also with no real reason for a feedback.
We Use the new Hydrive hydraulic system with rudder feedback , and it works well but even so I do not find it necessary.
Greetings

[BigCat]

Originally Posted by 44'cruisingcat

There are downsides, like the lack of feedback though.

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.