-CBTF and VARA-

An anono(30man) on the Sailing Anarchy site came up with a very interesting idea: combine VARA and CBTF. (see:
http://www.socasailboats.com/VARA_System/body_vara_system.html
Vara is a rudder/foil system that allows "variable aspect ratio rudders" as well as rudders that retract similarly to a daggerboard. The patented system allows for rudder rake as well as athwartship pivot of the rudder blade.
CBTF has been criticised for the vulnerabiliy
of the forward foil in open sea racing and designing a small trailerable CBTF boat with fixed(non retractable) rotating foils has seemed impractical. This idea seems like it could change all that since it would allow CBTF boats to carry a spare forward foil for about the same or less weight than the twin asymetrical boards+trunks used on boats like Open 60's and the Volvo 70-if the VARA system was equivalently as strong . Trailering
would be a piece of cake with the VARA+ CBTF system -the foils would be easy to retract along with the canting keel.
A NA friend has mentioned to me that a system similar to the VARA system has been used for some time and another anono on the other forum has mentioned that International Canoes may have originated a system like this.
At any rate, the VARA system is used on the Melges 32 and by Hunter, Henderson and others.
Seems like the combination of the two systems in one boat could aleviate some of the concerns about CBTF as well as providing designers with the ability to design smaller trailerable boats using the two together.

 

Intresting!
However, it's use on a small boat...
First you'd have a large canting system that needs to be retractable. I have yet to see one so I'm not sure what that would look like, but that would surely use up a lot of space down below. And with two VARA trunks one forward and one aft, they'd also use up quite a bit of space.
Where would you have space to store and handle sails?

Or do you thinkit could be done small enough? Maybe it could...

Combining VARA w twin foil /canting keel seems like it could be a good idea.
I wish CTBF never did patent the damn system. Patenting incremental innovations is to me a bad thing as it inhibits paralell design and development.

 

Having just fitted a wheel-steered (twin wheels, too) system with a similar type of rudder to a 56-footer, I can state quite happily that I would not recommend this system for larger boats
On the smaller boats, tiller-steered as in the ad, it looks good, but the area of the boat where the rudder exits had better be _completely_ flat.
Steve

 

Precisely. I think some people don't think well in 3D, or try to understand the mechanics of various systems.

If you have a chord of 12" or so on a VARA-type rudder you'll need a flat of at least that dimension, plus wall thickness of the carrier, plus bearing thickness. So maybe 14" of athwartships "keel flat" (as we used to call it back in the old days of IOR) up in the forward third of the hull. That would be a very strange hull shape, and not very good for wetted area.

Now consider rocker. Hulls are not flat on the bottom fore/aft. Even if the hull is generally flat enough in the area of the forward rudder you will have a change in the leading edge angle when the rudder is turned if the bottom is not parallel to the DWL. This might present some problems.

Maybe the resident canting/foiling guru will provide a 2D drawing or 3D model (with calculations) to show how this will work, but I sure won't be holding my breath waiting.

 

Is VARA patented too?

 

Vara System - Variable aspect rudder assembly - US Patent #5791277

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=5791277.WKU.&OS=PN/5791277&RS=PN/5791277

 

All too tru guys, I wrote my reply before thinking...
A big nugh flat in front of the keel... Er no way
Sheez I'm daft at times...

Instad of VARA, to be retractable it seems a simpler thing to engineer a slotbased rudder instead, no needs for flats but still retractable albeit only fully and only when aligned.

 

That would be a solution, but first blush seems that the quadrant would have to be above the slot, above the deck, and would have to be disconnected from whatever steering cables are used before raising it.

 

Well I use that for a tiller rudder on my new design, no wires no quadrant no problems

With a wheel it would be a a ******* to engineer. Not impossible though.
Above the main slot yes, but not necessarily above deck. With a "cog" driven system you could seperate the quadrant from the rudder axle and then have an protective upper plate above at deck level.

Anyone knows how the forward foil control looks on Maximus ? Secret perhaps...

 

I think that the poor fellow sitting on the foredeck with the tiller for the forward rudder might be a bit wet at the end of the day. It might also be difficult to get both helmsmen to work together properly. Even with tiller steering I think you will have to have a linkage/quadrant to steer the canard.

Maybe not impossible to do. Maybe hydraulic drive?

On a mythical 30 foot trailerable boat the freeboard at the canard will probably be no more than 3 feet. I think you'll want more than 3 feet of canard, but let's say say 3 feet, so the top of the canard will protrude just above deck when raised. Above the top of the canard you will need the sliding housing that holds the lower bearing (maybe 1 foot tall), and above that you'll have 2 feet of shaft to reach the upper bearing at deck level.

When you raise up the canard you would have about a foot of lower bearing housing, then 2 feet of shaft, then the upper bearing/linkage assembly sitting up more than 3 feet in the air in the middle of your foredeck.

That could pose a few problems with sails, sheets, etc.

I'm sure the resident expert in canting/foiling knows, since he has stated that it infringes on a known patent. I wonder if he will post a sketch of it?

 

fs 24

Here's a damn good looking 24 footer. The question is: is it CBTF or RIPOFF?
Don't know the answer but it looks like it could use a retractable foil system for trailering-can't tell if it has one or not-can't read the fine print on the specs.
Certainly appears to be the smallest CBTF boat yet....
http://www.fast-sail.com/datos/data/caractin.htm

 

Clarification...

Slotbased rudder inmy post i refferred to a standard retractable rudder. Was not thinking of using it in a CTBF context... My Bad

I'm still very interested in finding out how it's done on ctbf and maximus though.

Edit:
Re the fast zero. Wether it's a rip of or not I don't think they see it as an export to the US so they dont care about us patents...

 

Sorry, I was thinking twin foils.

I do think the VARA standard rudder is an interesting idea. It would be nice to get a feel for the weight differences between a nice carbon shaft standard bearing set up and the VARA drum/blade/bearings. Cost as well (disregarding any patent fees). However, I don't think you would end up with a flat area large enough on most designs.

I would also like to see this. With a board & flap it also seems they would need to have some sort of linkage above the deck.

Again Oh Lordy doesn't provide any technical input into the discussion. He obviously doesn't have the ability to actually design the details for these "great" ideas he comes up with. Then he chimes in with something off topic, something he doesn't even have the facts about, and insinuates the people involved are doing something wrong. What a piece of work.

 

"Is it CBTF or RIPOFF"

Doug, what's with the "ripoff" tag? People are allowed to use ideas that are not patented in their country, without being slandered and defamed by you. If CBTF Co decided not to patent in Spain, Spanish boatbuilders are free to use CBTF and you have no right to insult and denigrate them.

If you're talking of some sort of moral right, what about the fact that YOU use assymetric spinnakers, a "trademarked" copy of an old Moth idea, foils, sliding ballast.....all ideas created by OTHERS (or so it seems - in the case of the Wing Tip rig you claim it's your creation but provide no details how it varies from gaffs or Moth rigs).

Are you ripping anyone off by using these features, developed by others? If it's OK for you to use ideas developed by others, why can't the creators of this 24 footer?

 

a french boat cannot be "ripping off" a US patent. CBTFco's patent only covers the US, because the US patent office is the only one in the entire world stupid enough to grant it. I believe the trim tab controls on Maximus and Nicorette are hydraulic rams, while Skandia has a quadrant and wire system.