canting keels and all that

[tspeer]

You weren't kidding when you said it was a model of a 12 metre!

I guess you'll just have to take the lines off her, work out the hydrostatics, and see how the stability works out for the rig you plan to use.

A retracting bulb keel might be a good option. Perhaps it could come up just behind the mast so there's not too much interruption to the interior volume.

[Tohbi]

i've been thinking of a daggerboard type keel but this boat is only 4' wide and any kind of intrusion into the cabin will be very invasive. moreover, i've been wanting to avoid a compression post altogether and just beef up the scantlings across the frames to support the mast.

what about shortening the existing keel [it is several inches thick beamwise] and welding a facsimile of the existing wing to a shank that will fit inside the keel in a kind of "T" shape? the keel could, then, be filled with weighted material: epoxy-saturated lead or fortified concrete, for instance. hopefully, the shank encapsuled within this mixture will be strong.

you mentioned that the boat is probably designed to sit on the wing so, maybe, it can be made strong enough to take the weight through this process.

i'm thinking that some surface area that is lost through shortening can be regained by adding a bit of blade behind the shortened keel. do these mods sound unradical enough to work without compromising handling too much?

[Tohbi]

some of the keel dimensions may be affected by the change in sailplan. as you know, ac yachts have very tall masts but i'm shortening this to fit the trailersailer application.

i've designed a standing mast pulpit that will allow the mast to be hinged and, simply, folded back. this reduces the mast to 15', necessitating a gaff mains'l. with a furling staysail, the total sail area should be around 170' with approx -2% lead.

the '87 ac boat that is the progeny [i think] of this hull is aprox 66' long with a 45' lwl. so this 21' model should have corresponding dimensions.

so i'm changing the rig, as well as the keel, and trying to get them to balance.

[tspeer]

Why not go with a gunter rig? Short mast, and taller rig when sailing.

[Tohbi]

tom, i've never seen a gunter rig except on paper, much less sailed one. they look kind of fragile and inefficient, but i know looks can be deceiving.

what's the advantage over the gaff rig?

[tspeer]

I've not sailed one, either, but mechanically it's like a gaff rig with the peak halyard all the way in. Aerodynamically, it's like a jib-headed rig, so the center of effort's in the same place and it's taller for better efficiency. It just seemed like a better fit to the hull you have, while still meeting your need for short spars.

Without a doubt the best systen so far for canting keels is CBTF. Upwind with the collective feature you can dial out leeway by turning the rudders both the same direction; manouvering is done by turning both rudders opposite directions.
I've just received a completed design for a One Meter model from Graham Bantck for a F100 CBTF. He used a proprietary VPP in doing the design and "raced" the F100CBTF against a fixed keel F100: no contest: the delta's ranged from 100-to 500 seconds per mile!
We were concerned that the wetted surface penalty in a model(greater than fullsize) would cause design problems that might not allow CBTF to work at this scale: wrong! Now to the building....

[tspeer]

Just for comparison, it would be really interesting to see how the CBTF compares to a 1 meter multihull of the same sail area!

I'm curious as to how the VPP handled trimming of the foils for zero leeway and what effect that was assumed to have. Or did the VPP not take the heading of the hull and yawing moments into account?

The current VPP was not able to model the foils for zero leeway; So the results are correct not just for a CBTF model but for a model using a fixed daggerboard as well; another model sailor and designer, Craig Smith is working on a VPP for canting keels. Bantock consulted with the Wolfson Unit on modelling this boat correctly.Contact me by e-mail and I can give you his e-mail if you have any technical questions-nice guy and one of the best model sailors and designers in the world!
So what that means probably is that the CBTF boat using collective steering upwind will have a better VMG upwind than a fixed daggerboard version though downwind the daggerboard model could pull up the board.But CBTF offers one further advantage: reduction in wavemaking drag with the proper positioning of the twin rudders... So I'm going to build two 100% identical models with the same SA : one with cbtf; one with a retractable gybing daggerboard and race them.As a related note: the Formula 100 class ,originally started in France, and just getting started here is the ONLY one meter monohull class to allow movable ballast!! Except, I guess ,for the new just getting started maxZ86 model(yep-86" LOA with canting keel and spinnaker legal) just given the go ahead by Bill Lee.....
There is a new model class called the multiONE(www.rcmultihulls.com) which is a one meter multihull class; max SA 1100sq.inches(The F100=1300 sq.inches). The problem with small multihulls that have high beam to length ratio hulls is that they pitchpole in the blink of an eye--so they need to be sailed with hydrofoils in my veiw. I'm doing a Formula 48 class(LOA 48" ) multihull using instantly retractable main foils and have already built a 56" model that is beyond fast. Foils on small multihulls add a great deal of speed but their biggest contribution is to control.Using a version of Dr. Bradfields altitude control sysem the boats develop their own righting moment and are extremely stable in pitch and roll. They foil in as little as 5mph of wind and the bigger model(F3) has been reported by a couple of owners to tack ON the foils. Never happened in testing(very, very close) but they swear it happens on a regular basis...
So a one meter multihull to sail in more than 5mph of wind MUST use foils in my opinion... In the old days there was even a recognized multihull class in the AMYA(www.amya.org) but they faded away because of the problems I mentioned plus being poor designs. The new models tack on a dime and are incredibly fast around any course.

[colin.goldrick]

Changing the subject a bit, I have been trying to track down some info on the bearings or whatever that are used to support the keel/

Are there any off the shelf items that are suitable? The keel I am designing is only in the order or 3-400 kg (6-800 lbs).

Any ideas?

[ClarkT]

Colin, if you are designing for extremely high bearing loads, I've found HyComp (www.hycompinc.com) materials to be very tough. This stuff is a real pain to machine, but can handle some really high loads.

Crossflow Reduces Speed In The Tangential Direction Intended Especially At Speed Directed To Lifting Craft Through Vertical (upward Pressures). Any Thoughts How To;
1. Maintain Maximum Speed In An Upward Motion (vertical Direction) While Reducing Crossflow And Lifting Stern To Prevent Deaccelaration

[Tactic]

Doug ,
Have you built and delivered any of the Bantock designed F100 boats yet?
Are there any pics on the web?

Cheers
Brett

No F100's yet but three smaller prototypes test ing a new canting keel trunk and on deck Power Ballast System. The trunk works ok(no hump) and the PBS allows the battery to move to windward when the keel does-it is a small curved carbon rack on which the battery module slides-"solid state" instead of the carbon tube racks shown on other boats on the microsail site. One proto is 22" and two are 30" with identical weight and main only rigs but one is set up with CBTF and the other the kFOIL...All three proto's move the keel from center to 55 degrees in just over one second.
The CBTF setup of the one 30 was worked out with the approval/help of Bill Burns of CBTFco as an experiment and has the aft foil transom hung with a removable hydrofoil on the tip.
These boats aren't products so I don't see the value of posting pictures probably until the F100 is ready. But I could change my mind -they're pretty neat looking little boats..
....The model business has been extremely low priority this year and that won't change for a few weeks longer..

[yago]

Lots of canting keels in the current Vendee Globe race, check out pics and videos on http://www.vendeeglobe.org/, more videos on http://vendee-globe.vendee.fr/
On some of the videos it looks as if the keels are cranked up almost to the side of the hull ;-)
But then, almost all the boats now have big and deep lateral daggerboards in addition to the thin keels that are mopre and more reduced to a balllast-holders only.