Large scale RC boat design and build project - with questions

I currently own and race an IOM RC sailboat, and I also designed and built my own custom wing-sailed Class 2 radio controlled ice yacht. I have extensive keelboat racing experience and I'm a decent sailor, but certainly no designer.

My IOM with B rig in 25 knots of wind


My Class 2 RC Ice Boat


I'm planning to build a large radio controlled sailboat. The goal is to enter and win the 2015 Great RC Ocean Race - a distance race for RC sailboats on the West coast of Canada. I will be entering the unlimited class - must be radio controlled and must be wind powered. The race has been won by a 1.5m wing-sailed cat called Fang. A quick youtube search will give you an idea of what it looks like. That's my primary competition.

To beat the cat, I want to go as big as I can. With the rear seats down in my car, I can fit up to 9 feet in length. That limitation applies to the both the hull length and the rig, unless either can be designed to break down into shorter lengths. I don't want to put anything on the roof, and I don't want to get a bigger car.

I took a long look at the 2M AC One Design boat built by John Fries. It's a really sexy boat and probably very fast. Is it fast enough to beat the Fang? Not sure. Upwind in chop, probably yes. Downwind, probably not as long as the Fang stays upright. For a short while I considered just buying a 2M AC and using that. But that's not as much fun as building it yourself, and I want to be sure it's faster than the competition.

So the goal is to create the biggest RC monohull that will fit in my car, and hopefully the fastest RC monohull there is.

 

Questions about boat design:

1) Is there an accepted ratio between sail area and foil area? I have some potential foils already, so based on that can I work out how much sail area I can have? Is it that simple, or are there more complex factors involved?

2) How important is freeboard? On a full size boat the occupants probably want to stay dry. On an RC boat, as long as it's reasonably sealed, how much does it matter if it sits really low in the water? Obviously less buoyancy requires less material and consequently weighs less. Is there a law of diminishing return here? Do I get to a point of increasing wetted surface area by having less boat out of the water than in it?

 

CF,
Calgary, my home town.
I am familiar with both types of sailing but not with the competition or the rules.
First off: if this is the goal, why be limited by the size of your car?
Put it on the roof!
Or in a trailer!

 

Because I need to drive it to the coast from Calgary. A trailer is not practical. And on the roof it will get damaged.

Nine feet is bigger than any RC boat I've heard of, so I'm thinking that should be big enough.

 

Sounds like a neat race and cool project. Are multihulls ruled out?

 

Nonsense.
Build a case or a covered wrack.
Don't let this be a restriction.

 

Nine feet is large as RC boats go but not so large it will win IMHO. Keel boats are still limited to around hull speed ~4knots for a 9 footer. Multihulls and ballast shifters are not so limited. Consider the DOG Americas Cup race in the 70s where a 200+ft winged mono got beat by a 60ft cat.

There is a robotic ballasted (self righting) trimaran running around the oceans going for a record. I would base my design on it but with wider beam and bruce foils for dynamic stability.

http://saildrone.com/

Size is not such a big problem. Folding 17ft kayaks fit in 3 ft bags and the saildrone wing does not require much energy for wing control.

 

CF,
Are you available to Skype tonight at 10 pm your time?
If so, send me your coordinates by Personal Message (left click on my name).
I need more details but may be able to help you considerably.

 

For some reason I can't find the PM option. It might be because I've only just joined the forum. I did find the email option, but your profile seems to be set to not accept emails from members.

 

The PM system will automatically activate for your account after a short delay once you make one more post here CrunchyFrog. (The reason it's not on immediately for brand new users is to help keep spammers/bots from signing up to send PM spam.) Sorry for the inconvenience, and welcome to the forum.

 

Here's one more post!

 

Good contact.
Thanks all.

 

Multis are not ruled out. See reference to Fang catamaran above.

My plan is for canting keel that cants the ballast right out of the water. This effectively achieves the same benefits of a multi but with less structure. See Speed Dream for reference. I also plan a furling or tube-snuffed asym kite.

The foils will be twin cannard, one front and one rear, both rotate for steering. See Schock 40 for reference.

So, my original 2 questions still stand. Any pro or amateur designers have any thoughts?

 

Canting keels raise performance past hull speed while retaining some stability by keeping the dense ballast low. Canting the ballast clear of the water adds a little more righting (volume of the ballast times density of water times distance to float center) but it puts you at negative reserve righting. I don't think you have the control to keep that upright so you will end up canting less or sailing with heel far greater than optimal. The mass of your boat will be greater than a multihull and you can not reduce it when you don't need righting downwind. If you want to shift weight above the waterline you don't need the complication of doing it from below -Doug has an RC ballast shift rig and some experience operating it. I prefer pumping water to shift ballast because it goes neutral at the waterline and you can dump it when you don't need it downwind and in light wind.

In 'no holds bared' competition multihull beats monohull. The difference in your competition is limited control and capsize. Limited control also favors multihull so capsize is THE trick. With a floating wing you can eliminate a big part of the stability curve and with very small ballast on deep keels make the boat self righting. You might even be able to make it self righting by just using the wing to fly it back upright.

CCTF makes a fast keel boat but it doesn't hold a candle to what multihulls can do. To beat a smart multihull like fang you would need at least an order of magnitude (10X not 1.5X) greater size and cost.

 

Thanks ,CF. I wanted you to know about this project: a 7' cat with a 12' wing rig being done by a very experienced modeler with help from the top brain of the Canadian Little Americas Cup Team:
http://www.rcgroups.com/forums/showthread.php?t=1887900
Your plan sounds very good-a monohull with foils and movable ballast can certainly beat any multihull as the Moth has proven. I have resevations about the Speed Dream project because the keel pivots from the center of the boat making it 100% certain that the fin will be immersed to some degree causing much drag. The system on "Q" seems better in that it can get the fin and bulb way clear of the water. And there is another boat that is silar to "Q" whose name I can't remember. Should be in the "Flying Canting Keel" thread-I'll post a link if I can find it.
About 15 years ago I built several production models with spinnakers and/or hydrofoils. I took one of the spinnaker models and a model scow and added a "Trapeze Power Ballast System" that could move weight very quickly side to side and fore and aft. I then built several prototypes using a low weight fixed keel for self righting and simplicity with the same system. My take ,after all that , was that a system with a deep but low weight fixed keel and movable ballast was the ideal configuration for monohull movable ballast. I'm afraid that the 180 degree+ canting keel will be problemaic on an rc boat. I put the system on a cat and on the 36" microMoth as well. I have schematics of both a twin pole symmetric spinnaker system(simplest) and an asymmetric system(complicated). At one time I was the "official" model builder for CBTF toward the end of my model making business. The production CBTF model was never introduced ,but I learned a lot. I'd be glad to discuss any questions you may have.
I wish you good luck!
--- http://www.boatdesign.net/forums/sailboats/flying-canting-keel-extraordinary-innovation-30806.html
---My 15' "dinghy" design with a Trapeze Movable Ballast System: http://www.boatdesign.net/forums/sailboats/crossbow-fl-43615.html

Pictures,L to R : 1) & 2) "Q" , 3) Melges 24RC with asy spin and Trapeze Movable Ballast System,4) microMOTH with TMPS, 5) Melges with TMPS, 6) two production rc spinnaker boats, 7,--9) My MPX Test Model-nearly finished 5' LOA, nearly 7' wide(see thread in "Multihulls" http://www.boatdesign.net/forums/mu...lf-righting-trimaran-test-model-36058-82.html ) :