CBTF(Canting Ballast Twin Foil)

[D'ARTOIS]

Go to the site and in the lower part of the colofon you'll find breakthru hulls,
I even got a reply - suggesting to use two canting keels instead of one.

[nico]

I think Genuine Risk paid the full amount for CBTF, see http://www.torresen.com/sailing/cont...ves/001019.php

Found the article-definitly CBTF

[rob denney]

G'day,
There appears to be no doubt that CBTF and buckets of cash have made monos faster. But that is nothing to get excited about considering how slow monos are.

So how about the next steps? Start with some of the the things that make CBTF slow.
1) the strut and the ballast move through the water, which must be slower than moving through air.
2) the ballast is in the water, which makes it effectively lighter than if it was in the air.
3) it requires a large amount of machinery to move it from side to side, which is dead weight.
4) the ballast strut is short for draft reasons so the ballast has to be heavier than otherwise.
5) The ballast and strut have to be dragged downwind, when it is not all needed.
6) the boat still heels, making the sails and steering foils less efficient.

So, an improvement would be to have the ballast strut above the water, with a lot less ballast, on a longer (telescoping) strut, running on rebated tracks from gunwhale to gunwhale under the boat. The tracks are covered when not in use. Could have two struts to keep everything in line.

Attached sketch shows an Open 60 monohull. 2m high, 6m wide, 18m long. It has a hollow bulb 4m long x 1m dia, on the ends of 14m telescoping struts. This can be half filled with about 1.5 tonnes of water. RM is 21,000kgm, the same as a 5 tonne bulb on a 4m strut.

The rm is rthe same if the boat is tacked, but the strut/ballast is not. Alternatively, it could be filled with 3 tonnes of water for double the righting moment.

Telescoping, pumping and location around the hull would be altered as the boat heeled. Not a whole lot more work than the current CBTF/water ballast boats require.

Removes about a third (3-3.5 tonnes),of the boat's weight (8+ tonnes??) which in a class where they spend hundred's of thousands of dollars to save a few kgs, is a pretty big saving. In light air, empty the bulb and the weight saving is 5 tonnes. Plus, the drag of the strut and bulb is reduced enormously, as they are in air, not water. It easily fulfills the 10 degree heel rule and self rights from upside down. All sorts of variations are possible, but this example used easy numbers and scenarios, plus some assumptions about the Open 60's.

For all you bar room lawyers, what is there in the rules that allows canting keels, multiple off centre foils in the water, water ballast and full time engine running to power it all forbids this?

Of course, get away from money, rules and outmoded boat types and there is a much cheaper, better and faster solution.

Assume the above as a starting point. Then
1) Make the hull and the ballast pod double ended.
2) Make the rudders rotate through 360 degrees.
3) Design the rig so it can rotate through 180 degrees. This removes the need to tack the boat or the ballast. Instead, you learn to shunt, which is far less effort.
4) Make the ballast pod just large enough for the crew to live in it along with all the stuff from the big hull, which can now be made much lower, lighter and narrower. Having the crew and gear on the end of the struts means the ballast can be dispensed with.
5) Throw away the tracks, telescoping, pumping and strut moving stuff , plus all the expensive, heavy machinery required to do this.
6) Call it a harryproa http://www.harryproa.com/

Regards,

Rob

Well,not quite the same but sounds like two good ideas, but wheres the sketch?

[rob denney]

Doug,

Said it was attached. Try this.


regards,

tob

Thanks, Rob. Here is a link to a couple of pictures and a sketch of a system I experimented with on rc models:
http://www.microsail.com/pbs.html

[gybeset]

with a day or three to go Hellimoto has "lost all pressure" in the cant system and has LASHED it in a central posi.
Canting is obviously old tech in this class of racer but needs contingency , default central positioning on a demonstratable emergency method.

I agree with back up and or some sort of emergency method to center the keel.
Just as a clarification Hellimoto and none of the Vendee boats are CBTF-just canters with twin asy boards and a fixed keel or two...

[gybeset]

Originally Posted by usa2

skandia originally didnt have that daggerboard, or the bowsprit. They were added after the boat was first trialed and the daggerboard reduces the leeway suffered while reaching. The bowsprit was added after they realized the boat went so fast that symmetrical spinnakers were slower in nearly all wind conditions. I wonder why Skandia was first conceived without the daggerboard?

Under Syd Hob cat rules cant is limited to 10%, so was designed w/o canard as they possibly didn't need it, she won and beat KM,in other races the larger cant allowable and the fact that KM was being optimized and triggered a parallel program on Skandia, canard plus sprit.
btw even before the sprit Skandia had no normal spin poles and set assys from the stem.

Given the above it is doubtful that a canard is necessary for reaching; only upwind, this is the same if you lift centrboards on dinghys a proportional amount. What Skandia really lacked ( and most boats it seems) is a contingency to fix wobbly keel in a central position, as race-finishing and lifesaving backup.

[gybeset]

[quote=Lorsail]Brian, there is no right or wrong thread as far as I'm concerned;

LOL !!! So long as yr spruiking CantBabble !!! now if the reverse was true and ppl insisted on talking other than Cant/K/cbtf that may draw a 'wrong thread' response !!

On a differnt note I don't think you need seperate threads Cant and CBTF, flavours of the same theme.

There may be sense in dividing a discussion on cantRC and cantFullSize, after all there are lives at stake outside the model world. Of course RC can be referred to as a demonstration of new ideas, to use these ideas as 'evidence' in full-size scenario is not always valid re scalability

then we could have to be 'very sad' when a picture of an upside down canter is full-size or a whimsical "back to the drawing board Q' if is a model.
I guess in theory yr model may be 'lost at sea' with all the age-old emotion (the Norse lit a candle for each hand of a ship that never came home). but is more likely in a duck pond!

In one particular fellas case in may not be 'back to the drawing board', rather back to the designer/builder. and cancel that patent/licence.

re Skandia 'great boat' , dunno she having trouble beating KM, we might only know when dhe comes up against another 30 mtr canter.

I vote for transparency in model/full-size opinion !!!!!!!

[usa2]

pressure on the boats sails while reaching is greater than going upwind, becuase skandia would be flying a asymmetrical and a staysail forward, which means you get a lot of lee helm.The dagger board would help there the most. It also does help upwind obviously, but it has the most effect on cancelling leeway while close and beam reaching. If skandia had CBTF, the foils would help a lot going upwind, as you can angle them to produce enormous amounts of lift. But she didnt.

[doesitfloat]

I have raced against Genuine Risk and Alchemey the year before. Genuine Risk took the maximum swing keel twin foil and Alchemy was water balasted retractable keel. I don't have the dimentions of the two in front of me just going from memory. Risk was narrower than alchemey. Both were first to finish in the Mackinaw races so they are faster than convential designs. I thought Risk reached it's hull speed faster than Alchemey. In other words light air the swing keel kept the boat moving: I think the narrow beam aided in that too, But it lost it's advantage aroung 8 kts. I say this because they couldn't gain distance on us when we kept the boat speed up. Risk was not fast on a reach. At one point we were going 22 they were at 16 on a reach. On a similar reach against Alchemey we were going 21-23 and they were doing 17-18.
To sum up my position I think a swing keel will win more races due to it's light wind performance, and all the records will go to the water balasted because they can go faster in the right conditions.

Interesting perspective. In the last(If I remember correctly) Bermuda race a good test between water ballast and canting keels also took place. The two z86's with CBTF trounced the only waterballast z86 ever built.
The concensus of many of the articles I've read that have analyzed the two concepts is that the canting keel would be faster in most conditions with less of an advantage in the highest wind and roughest conditions....
In the last Sydney Hobart Konica Minolta was ahead of Skandia at the time they both were disabled. KM has a fixed keel with waterballast and Skandia ,though not CBTF, did have a canting keel with a forward daggerboard.

[usa2]

doesitfloat-
What boat were you on, just out of curiousity?