Footy Class Catamaran possible within the rules? - Page 11 - RC Groups
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Apr 17, 2017, 11:07 AM
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Dick L.'s Avatar
Jim,
Understood and why I didn't go down that road. Even my Force 2 60 cat is barely sailable, but improved somewhat when I added a bit of weight in each hull. A little slower getting going but enough weight to get it through lulls. Got to buy some small screws. Had it apart to waterproof beams and hulls, and my youngest grandson knocked the tray onto floor. Been finding a few in carpet, but it will be faster and easier to hit the hardware store and pick up a handfull of them. LOL

He started sailing my DF65 and is doing pretty good for a 6 yr. old, but likes his electric train best.

The Force cat is ok and marginal, but still hard to sail. Will have to get my 1 meter repaired after getting it back from a guy who trashed it and then wanted his money back after three years of use. I finally convinced him to send it back on his dime. Most major was he broke rearcross beam from port ama. Rest is mostly cosmetic.
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Apr 18, 2017, 02:55 PM
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My suggestion of using Ackerman steering on catamarans is somewhat illustrated by mijj's videos. If your idea of sailing a multihull is reaching back and forth then I guess how tacking onto the other tack is not very important. Speed of tacking is important in racing.

Backing up to turn your boat or jybing by heading down until the sails flop over on the new tack is a painfully method and loses ground which in a race is taboo. I see a lot of these videos from various proponents of their boats, of cats reaching back and forth. It makes them look fast but that is not sailing. They need to show performance pointing and going down wing (even if it means reaching to get to a down wind location) in all wind conditions. I would like to see how these boats handle on a triangular course. Particularly if they are sold as a new one design class.

There are some videos of racing multihulls to class standards from Great Briton. These boats tack like monohulls, granted with some backing up here and there. But that are development class boats with competition, that generally solves design goofs and produces a better boat.
Apr 18, 2017, 07:42 PM
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Dick L.'s Avatar
Been saying/thinking the same thing.

Would be more impressed to see them on all points of sail to see windward and leeward course performance - or even triangular performance. Most everyone can sail while reaching. How about some "REAL" course racing performance? Too much to ask?
Apr 18, 2017, 08:52 PM
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Neil,

From my experience, making a multihull sail up-wind and tack nicely on a large scale relatively easy (1m and larger). On a small-scale it is another matter entirely.

Jim.
Apr 19, 2017, 08:43 AM
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I was talking about how to make cats tack better by not dragging one of the two rudders in a turn. Tris turn like a monohull in that one rudder turns the boat and if you are not going to foil your trimaran then it should be designed so that the outer hull should raise in a turn and the other inner hull should sink slightly to be a pivot of sorts.

My Proa has one rudder. I can sail it on all points and tack like a monohull. It is only 11 3/4" long and 11 3/4" wide with hulls that are slightly angled inwards. So I think tacking multihulls is very possible no matter how long the hulls are.

The only drawback to Ackerman steering is it is complicated and to get it right and needs some experiment. I think most builders want simple. Ackerman steering requires a bit more attention to build, and may not be as light weight as simply connecting both rudders in parallel. Like everything on our boats weight is the main consideration, but done well Ackerman steering should not tip the scales. My main observation is that a hell of a lot attention is focused on sail winches and rudders are almost an afterthought. I think that Ackerman steering could be the next mini breakthrough in racing catamarans in a regatta. But right now it seems that cat owners seem content with just reaching back and forth.
Apr 19, 2017, 10:03 AM
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Ackerman is a pretty commonly considered design concept for full size catamarans. I can't think of a reason it should be ignored for smaller variants. All that is needed is an offset of the tiller from the rudder. See picture. If anyone knows how to include ascii art inline with posts, please educate me.

Getting the angle correct is a compromise in that it is a little tricky to predicts the boats turning radius for a given rudder angle.

For a multi-hull to be a good tacker, the aero drag should be minimized, perhaps a wing sail as MJJ has experimented with. The downsides of scaling down a multi-hull all tend to hurt tacking though, lighter-weight, short hull length and proportionately high L/B ratios.

Good luck and I'm sure we will enjoy following along with your experiments.
Last edited by lhurt; Apr 19, 2017 at 10:17 AM. Reason: spaces smashed in drawing
Apr 21, 2017, 06:31 AM
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akerman sterring or twin rudder ?


I agree Ackerman steering takes a bit to set up plus the fact that the smaller you get in the boat size the less weight there is to help you drift through the tack does not help If you do not use the Ackerman type steering you will get excess drag from the rudder that is not matching its position in the turning
circle usually the inner rudder, this adds to the original cats are notorious for tacking problems. This brings me to the Proas using the fore and aft rudders
with no fixed fin. These are easy to set up from one servo and are always in balance if set up right in the design, also the boat can reverse direction with no problems. As for the catamaran In 1950 I sailed a 12 foot catamaran made out of 5gallon oil drums, it had fore and aft rudders in order to make it tack, later
we added centre foil to act as a pivot on which they could act to improve tacking. I wonder weather the twin rudder ie fore and aft could work better on
a normal cat using the rocker shape of the hulls to form a vague pivot point ? As I have a spare 65m catamaran hull I think I will have to give it a try. I will see if I can dig out a photo of that old catamaran !!! Regards to all Tricat
Apr 21, 2017, 06:35 AM
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Akerman steering or twin rudder ?


I agree Ackerman steering takes a bit to set up plus the fact that the smaller you get in the boat size the less weight there is to help you drift through the tack does not help If you do not use the Ackerman type steering you will get excess drag from the rudder that is not matching its position in the turning
circle usually the inner rudder, this adds to the original cats are notorious for tacking problems. This brings me to the Proas using the fore and aft rudders
with no fixed fin. These are easy to set up from one servo and are always in balance if set up right in the design, also the boat can reverse direction with no problems. As for the catamaran In 1950 I sailed a 12 foot catamaran made out of 5gallon oil drums, it had fore and aft rudders in order to make it tack, later
we added centre foil to act as a pivot on which they could act to improve tacking. I wonder weather the twin rudder ie fore and aft could work better on
a normal cat using the rocker shape of the hulls to form a vague pivot point ? As I have a spare 65m catamaran hull I think I will have to give it a try. I will see if I can dig out a photo of that old catamaran !!! Regards to all Tricat
Apr 21, 2017, 12:28 PM
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Tricat,

What I was trying to suggest was a way of steering a cat with a rudder on each hull so that it would reliably tack in racing conditions. Proas, which have fore and aft rudders on the main hull don't tack, they shunt. To shunt one has to bear off, move the sail around to the new tack, pull up what was the stern rudder because that end of the boat is now the bow, drop the rudder into the water on what was formally the bow, slowly haul in the sail as you go up through the reaches to the desired point of sail. On big boats shunting can be done rather swiftly because the crew on board can move quickly. In model boats the skipper is on shore and can't shunt very fast and won't be on board to fix any mess ups. Also, to shunt on a model you need more servos to make the move act smoothly = more weight.

In a race, doing a shunt would require that no one was to lee, and being the windward boat when you start your shunt you do not have right of way over leeward boats. Shunting also sacrifices a lot of hard gained ground to pull off. That is why setting up your catamaran with Ackerman steering is probably the best solution to make tacking the racing cat more reliable. If that is too hard to consider, build a trimaran!
Apr 23, 2017, 04:17 PM
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Ackerman steering !


Hi Guys, Neil I take your point. A fleet of say 20 RG65 plus a shunting RG65 at the start, a wind shift requires the fleet to tack ???????I pity the OOD !?
I built a 65M with Ackerman steering, once you know the turning circle you require you run a line at 90deg. around about the main foil which the hull spins around when tacking etc., Imagine the hull pivoting on this line, measure the turning circle at the centre line of the hull to where you want it to be.
From this point run a line through each of the rudders pivot point. At this point the rudder blades should be at a tangent to the turning circle at each rudder point. IE the inner rudder will have more of an angle than the outer one. I tried a single bar to tie the rudder arms, and the used a single arm from a servo to a Micro Magic rudder arm pivot without its locking screw. It was not very good idea too much slop. So it seems the best is to link the two rudder arms to their respective angles then pick one of the rudders to have the servo linked to it, I have seen this used and seems to work well, only on a footy
May I step away ? the mind boggles. Regards to all Tricat
Apr 26, 2017, 10:04 AM
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Well, I am sure this discussion of Ackerman steering is helpful for bigger cat builders but we have been straying from this thread's original focus,
how to get a multihull boat to fit into the Footy rules. I have come up with one working solution, lets hear some other ideas. Bear in mind that the whole point of multihulls is to replace ballast with buoyancy. That concept makes for a very light boat, not possible in the monohull Footy. A big plus is no lead to effect your health and poison the lake you sail in.

So some of the Footy catamarans I have seen here have a central keel fin and a lead bulb. Not the brightest of ideas and is just a compromise between a monohull and a cat. They also sport a central rudder, I consider this to be a a source of drag, as soon as the boat gets up to speed this type of rudder configuration induces cavitation (tiny bubbles that travel along the rudder and break flow over the foil of the rudder). It is pretty universal that rudders on r/c model boats are under the rear of the hull, creating an end plate to flow. The slot in the Footy measurement box for an overhanging rudder was probably a means of including older foot long designs into the class. The slot is generally no longer used, just as the slot at the other end of the box was for bowsprits (I consider bowsprits to be dangerous in model racing).

So lets start thinking about how to use the Footy rules to our advantage. I don't think it is impossible, and I don't think it should mean we need to create a whole new special box configuration to make it too easy to make a basic multihull. I think the idea I would like to see is multis and monos going head to head on the race course. Multis are not banned from the Footy rules so lets go show the settled concept of monohull Footies on its head.
Apr 27, 2017, 06:14 PM
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Curious...where are footys currently being raced in the US? I mostly read about fun footy activities and events here....
Apr 29, 2017, 06:18 PM
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Some Footy racing takes place in New England bot most active in Florida. Southern California has some action but Dick has a good feel for both Footys and multihulls in the US.
Apr 30, 2017, 11:04 AM
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footycat


Hi Niel, You have got me on board ,I have just spent time sending a reply on the footy cat Just be fore sending I was checking it when it vanished never to be seen again.
It had a lot of info in it. To cut it short I am going to build a Depron cat to footy rules including Ackerman steering .The basic block shape will be as follows
12" x 1.25" x 1" L x B x D. the total hull depth will be 3.5" to start with until I get to setting up the radio gear area. I read somewhere that Footies are around 16 oz. in weight , roughly 27.7 cubic inches. My calculations allowing for a rough foil shape and rocker should give around 20 cubic inches which is fine seeing there will be no lead/weight involved. I will build one hull to see what it looks like shape wise, then proceed to build up structure wise. One thought I had is of using helicopter rear rotor blades for rudders and looking at small helicopter rotor blades for main foils. I have two of each from a previous venture that went wrong and scrapped the hulls which were bigger than a footy. Will post any progress that should be of interest Regards to All Tricat
May 01, 2017, 01:36 AM
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Hi Tricat
Please keep posting to show progress on this project. As you can see, I've been using Depron for Footy Monohulls and am really interested to see how your cat works-out.
I have been introducing more and more curves into my hulls and can imagine that a box section cat hull would look pretty good, even with a flat bottom, and come in at 10g per hull.
Phil


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