The new Bantock designed F100 will have a canting keel. The experimental microMOTH has a sliding on deck rack system called a Trapeze Power Ballast System because it moves weight in a similar fashion to a crew on a trapeze dinghy.
The D4Z catamaran in the Formula 48 class also uses a Trapeze Power Ballast System.
I’m looking into the advantages that could be gained in the F100 class by the combination of these systems. A boat would have both canting keel and sliding rack.
One of the facts of a rule like the Formula 100 is that boats could easily be built to the light weather or heavy weather performance end of the rule. In fact in a class without movable ballast that might be required to be competitive.
Since the F100 is the only development class to allow movable ballast things are a lot different in this class-design wise.
If a hull could be designed to have a fairly wide displacement range say 6lb’s to 8 lb’s a hybrid system might make sense. The key princible would be to get as much weight on the boat to act as righting moment instead of dead weight. On a canting keel only boat the battery and keel winch are dead weight just adding drag. On a hybrid system the battery AND the winch could be placed in the sliding cart and the winch would operate both the keel and rack. Additionally, one of the advantages of the rack is that it is easy to add weight or remove weight but the keel bulb could be relatively simply changed as well. This system would allow a 6lb boat-maybe even 5.5lbs to have the Righting moment of a much heavier IOM and to also be “re-configured” as the wind picks up to a heavier displacement with 100% of the additional weight going into righting moment.Both configurations would allow the full A rig of around 1200 square inches to be carried and the heaviest configuration would allow that rig to be carried somewhat above the max wind for an IOM “A” rig. The hybrid system would also allow the weight in the rack to be moved aft downwind automatically as the sheet is let out or not at all. Based on what I’ve learned so far this seems like a far better solution on a model than moving the weight of a canting keel back using a winch since the rack would be under far less load.
Testing this system in the F100 class should be very interesting…
This system would allow a 6lb boat-maybe even 5.5lbs to have the Righting moment of a much heavier IOM and to also be “re-configured” as the wind picks up to a heavier displacement with 100% of the additional weight going into righting moment.Both configurations would allow the full A rig of around 1200 square inches to be carried and the heaviest configuration would allow that rig to be carried somewhat above the max wind for an IOM “A” rig.
Doug Lord microsail.com monofoiler.com
High Technology Sailing/Racing
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Once the hull is at hull speed excess sail area will do little for you unless the hull can get on a plane. Since you’ve mentioned polar plots. What is the hull speed for this craft and what’s the sail area needed to get there for 3, 5, and 10 mph winds? Pick your wind angle.
(2nd reply; first disappeared during posting;see problems section)
No polars exist for any form of hybrid design-yet. The only polar I have so far is for the original CBTF -first incarnation. It showed a 200 second a mile upwind superiority over a fixed keel F100(which itself demonstrated a 200 sec per mile superiority over an IOM) of the CBTF boat in 6 true and above. Below 6 the margin dropped until even an IOM could beat the F100 CBTF in 2 true.
With that data and other data it was shown that for a CBTF design to meet the design brief:the fastest one meter monohull-it would have to have a retracting forward rudder. Failing that a retractabe daggerboard would have to be used --installed AFT of the canting keel.
The final design is some time from being completed ; when it is I will publish some infor- mation in a fourth report under the Articles section of this site(click on Home and it will be on the right)
I was asking you to address the efficiency of the hull and rig combination in comparison to hull speed.
Again, it seems to me there’s diminishing return as the wind speed builds as the hull is closer to it’s top speed regardless of power unless it can plane. In a class such as the F100 it seems this is critical to placing the right amount of sail area for the wind/sea state to optimize performance.
The traditionally defined theoretical hull speed for a boat this length is 2.42knots but a narrow beam low wetted surface hull can exceed this significantly without planing in the strictest definition; the speed increase is similar in character to a cat hull which can easily exceed its hull speed with a combination,first of high beam to length ratio(12/1 thru 22/1 for both models and full size cats) and second high power to carry sail. These boats do not plain ,generally, at these higher speeds (up to speed length ratio’s of 4/1 or so).
The new F100 will exceed traditionally accepted theoretical hull speed limits ;the original incarnation was clocked on the computer at above 3.5knots already.
One of the possible great advantages of the Wing Tip Rig(peaked up square top) is that it can be effectively depowered upwind much more effectively than a triangular planform then powered up off the wind where the xtr area can do some good. The righting moment comparison between the fixed keel F100 and canting keel F100 at 8 pounds of displacement shows that at 20 degrees angle of heel the canting keel boat can develop almost twice the RM of the fixed keel boat.These are preliminary results from a non optimized design and will only get better in the final design.