CBTF(Canting Ballast Twin Foil)

[gybeset]

Originally Posted by usa2

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

That the point I believe, he was ON a boat, you two (or one actually) are wriggling Radio Control joysticks at 'em

Knobs (twirlers)

in the full scale world you are dreamers/theorists

[doesitfloat]

I was on Earthvoyager. A formula 60 Tri.

[usa2]

actually, i sail on full size boats more often than i sail RC ones.

I love rc sailing and using rc boats to test prototypes but I have almost 50 years of sailing and racing experience with most of it on full size boats from an 80' schooner to my 16 foot hydrofoil...

[gybeset]

I will keep my my S anarchist type remarks to a minimum on this forum , as RC has validity to boat design and is obviously a quick, cost effective method of comparing , esp in a two boat testing sense, as well as fun. Re scalability it cannot always crossover tho

p.s the WB z86 was considered first generation in the B race.

[usa2]

as most people involved with yacht design know, scaling up/down doesnt work, as there are too many variables to change. I believe the purpose of this forum was to discuss CBTF on fullsize boats such as Z-86s and the like. And Windquest(previously Zephyrus V) was considered first generation. I dont think the hulls on the CBTF Z-86s are exactly like Windquest's, so therefore the comparism isnt entirely fair. Granted, the CBTF's did kill her, but thats sort of like comparing a first generation AC class with say SUI-64 or NZL-82.

What designers understand is that some boats/technologies can be scaled up or down AND that some things will change.
Graham Bantock one of the foremost model yacht designers did an F100 One Meter model yacht design for me. He has a vpp specific to model yachts and he ran the F100 CBTF model against an F100 fixed keel design of his as well as against and International One Meter design of his. He ran the boats in multiple "races" on many different courses and wind conditions. The bottom line was that the CBTF model was without question the fastest and the fixed keel F100 second.(the F100 is a wanabe "unlimited" development class with very small numbers worldwide)
He proved with that analysis that a well designed CBTF model SHOULD be able to beat a well designed fixed keel F100 or an IOM.At the time he did this study his vpp was not set up for "collective" evaluation so the probable outcome using collective upwind would be even better according to Graham.
Some of the major differences between full size CBTF and the model include the fact that the model was faster with much lower aspect ratio(3/1) foils than a full size CBTF boat. Another major difference was that in models a foil with a t/c ratio of 6-7% is far superior to a thicker one and so the fin has more wetted surface than a comparable full size CBTF boat.
Contrary to a popular myth the rc CBTF boat can be set up very precisely to utilize "collective" effectively but programmable radio control is needed.
So if you know what you're doing some technologies can be scaled down and function simalarly to their larger sisters.Unfortunately, in rc sailing and unbelievably in this new century NONE of the recognized RC development classes whether in the AMYA or in the "International" classes allow movable ballast. So whats happening is limited to a few experimenters here and there....(including me).

[usa2]

that is true that concepts can be scaled up/down, but if you made a scale model of say Morning Glory, you would either need a deeper keel, more ballast, or less sail area, because on a scale model the thing would just capsize because there wouldnt be enough righting moment counteracting the force on the sails. going to the model boat world, the soling 1 meters there have keels that are about 1/3 of the hulls overall length. On a real soling, if you didnt change this ratio, that would mean the keel would be a little over 8 feet deep. that wouldnt be accurate, would it?

[Skippy]

Has anyone ever made a dinghy-size CBTF for testing? The pilot might be required to remain on the centerline for a fair comparison, and the ballast can probably be controlled manually.

Theres an expert designer/builder in New Zealand that sometimes posts here that is considering CBTF for a 16' single hander-sort of like the mini 12's that you sit down in. He's already done preliminary design work...

[usa2]

but that wouldnt be for testing would it? And if you raced it against a boat like a mini 12, it would get slaughtered....

Just out of curiosity what would lead you to believe that a heavy displacement 12 footer could beat a light displacement 16 footer with a canting keel?
By the way, he is considering an electrically moved keel....

[usa2]

Mini 12s doesnt refer to their length, it refers to what they look like. They are actually 14 feet long. And as it has been seen, in small boats CBTF only makes a marginal difference. Off the wind the CBTF boat would most likely have the advantage, but then it wouldnt be like a mini 12, as they are 2.4 metre boats that are optimized for upwind work. If he gave it an electrically moved keel, that would greatly aid the CBTF boat, but if one was match racing against a mini 12, the 12 should just engage in a tacking duel and wear down the batteries on the other boat.. I suppose a really fair test of this concept would be to get 2 identical boats, and put the CBTF system on one, and leave the other one conventional. CBTF in most conditions is just faster outright, but there are tactics involved with racing these things. If you are match racing a conventional boat against a CBTF, obviously the two skippers are going to try to feed off the other boats weaknesses-in this case it would be the fixed keel being able to tack a bit faster than the CBTF boat and without needing stored energy to do so.

[yipster]

some cbtf info at http://www.cbtfco.com/wrapper.php?pa...echdetail.html (could be the link is posted before)

[CT 249]

Also, in very light airs the non-CBTF boat would have an enormous advantage in that the skipper/crew would be allowed to paddle the boat; pump the sails; roll tack as much as they want; or use other ways of utilizing the stored power of the crew.

After all, surely if the CBTF boat can break the normal rules by using stored power, it's only fair to allow the other boat to break the normal rules too??