Has anyone tried to build twin keel footy. I am experimenting with that idea just as an possibilitiy. It is stil in project phase. So I would like to here your opinions.
I’ve never heard of it with a Footy, but in the 1960s John Lewis designed two extremely successful 10-raters called Herald and Moonstone. If you trade in your supply of dragon’s teeth for a copy of Prieast & Lewis’s bookm on Model Racing Yachts, you will find full details including linesplans and the design arguments.
This is what i made so far. It is made in MaxSurf, but i am transferring it to freeShip because i plan to make it of balsa.
Currently I am testing hydrostatic using Hydromax.
Interesting, but you can’t have two rudders
Bob
I fear I’m going to be a little sh@#.
Is the 2 rudder ruling really official? If so, is there somewhere rule interpretation can be viewed because, otherwise we’re all going to travel the same roads twice.
As for the two keel concept … does the somewhat slightly improved righting moment justify the additional drag? What are the thoughts behind it … ?
Herald and Moonstone ‘flew’ the windward keel. The (not very legible) drawings of Alex Austin’s Chris Dicks Award entry might repay study.
Since Bill Hagerup scrapped a half built twin-rudder boat half-way through the gestation of the rule (see Wesite Photo Gallery) , I think we can be pretty certain that the intention was that twin rudders should be illegal.
Given the recent distress caused by allegations that the technical committee “manipulated” rules to secure an advantage for their own designs, I would have thought that much more care would be taken over rule interpretations than before.
There are a couple of areas where the rules are unclear and, since “anything not specifically restricted or prohibited is permitted”, you would think that restrictive interpretations would be rare.
Nowhere in the rules are multiple rudders explicitly restricted or forbidden - therefore (by the spirit AND the wording of the class rules) they should be legal.
The rules say you are restricted to four AA size batteries. The AMYA spin on this is that you must have precisely 4 AA batteries. Now there are upper restrictions, and there are lower restrictions, but a restriction is not a prescription. If you say there is a speed restriction of 40 mph on a section of road, you do not interpret this as meaning that you must travel at precisely 40 mph or you are committing an offence. It means you cannot travel faster than 40mph. That is an upper restriction. Some sections of road have lower restrictions. On those sections, you cannot travel at less than the restriction. So, when “batteries are restricted to 4 no. AA size batteries placed within the hull”, this means you can have either 4 or fewer than 4, or 4 or more than 4. It does not mean you must have precisely 4. This unjustified insistence on “precisely 4” CAN be interpreted as the older guys with toy boats restricting the class so that their tubby boats are not slaughtered by the kids’ skiffs.
Oh goody (not) here we go again…
Keelgate?
:devil:
Sorry Angus - couldn’t resist.
Please do me a favour. Having discovered the hard way that not everyone is quite as benign in their objectives as me (I hope), I worded that very carefully: I said ‘intended’.
I am perfectly aware that the rule is not drafted with legalistic perfection. Before I was press ganged into the job of MYA class seretary and thereby (more or less by default) onto the Technical Committee, I made myself less than entirely popular by pointing this out in this forum.
However, it must be remembered that the rule was intended to be SIMPLE, like the boats. I have no doubt that workable interpretations can be found. Inevitably they will not satisfy everyone, but they will be made fairly and as interpretations of the rule as it exists. It is, of course, possible to change the rule. In the meantime, it is my firm view - and I believe that of my colleagues on the technical committee - that the prime rule of interpretation is that ‘anything not specifically restricted or prohibited is allowed’.
I think it is very important that we put the recent fiasco behind us and adopt the attitude that rule interpretatations should not be a source of back-biting and acrimony but should represent attempts by men of good will (on the part of the requestor, the committee and the audience around the arena) to define in detail exactly what constitutes a Footy as the class develops.
I think that it is also important that we get out of the attitude that anything coming close to the rule is in some way underhand or ‘cheating’. The Footy is a development class. It is the job of anyone designing one for competition purposes to produce a boat that is faster than any before it. Inevitably this will sometimes involve probing the limits set by the rule. We do not play chess with 7 pawns because going to the limit of 8 would be ‘cheating’.
I didn’t mean to cause such a debate. My question was of Hydrodinamic nature.
Also since Footy is not recognized as a class in Croatia, and also where I live there is no modelling clubs, I wasn’t paying too much attention on the rules. Main concern was that main dimensions comply with box rule.
My opinion is that two smaller fins produce less drag than one deeper, also i think that smaller fins will produce much less yaw motion tan deep fins.
Twin keel sailboat is my graduation project on Faculty of Naval architecture, and footy is perfect platform to test some things.
If something works on such chubby boat like footy, than it should work on sleek huls also. And also you can build footy hull from scrap balsa left from some other build or you can build whole hull from single block of styrofoam.
Crashimir!
I think you are almost certainly right about the yawing moment. As to the drag, I have my doubts. Shallower draft will (presumably) give lower aspect ratio and hence higher induced drag when going to windward. On the other hand, I have carried out some experiments from which I have done some calculations. These suggest (very tentatively) that in extreme pitch conditions the lower part of maximum draft keel of any sensible section will stall: in really extreme conditions, the flow velocity becomes negative for part of the pitch cycle.
I do not put these forward as definitive results. The experimental method was crude and some of the mathematical assumptions are untested, to put it mildly. However, they are suggestive.
If you really get into these little boats, look at the Official Footy Website for details of open events in the United Kingdom this summer. I know that prices in Croatia are not those of Western Europe and that students the world over are poor - but … There are quite cheap flights from Ljubljana to Britain and the train fare from (say) Zagreb to Ljubljana is not dear. Alternatively, there are cheap flights from Venice. I am sure that you would be very well looked after here were you to come and your stay could be made very cheap. I am not sure whether I Croatian citizen needs a visa to enter UK, but it would be quite posdsible to provide visa support at this end.
On the subject of the rudder rule, I don’t think we’ve had an official interpretation yet. We’ve discussed it some, here and on the FootyUSA yahoo group, but if that could be considered a ruling I’d like to see a summary posted on the technical section of the website. I, for one, am curious even though I don’t think I’d use 2 rudders.
If someone submitted a plan for twin rudders that they think is legal, the tech committee will make a ruling. The last ruling seemed fair. We just had some communication issues. I’m trying to decide if completely open communication is best or having the committee go off alone and report back. I personally trust the other Footy builders enough to have a civil discussion regarding a proposal, even with our recent history. Realizing that communications may stall, some of us have lives outside of this hobby, and that people will have differing opinions should not deter us from seeking interpretations. We can do this.
…
My intention with this thread was to get some feedback from fellow modellers about something I build. So debates about registering of classes don’t interest me much here.
If you want to discuss that why you don’t start a thread about it.
Angus, thanks for your thoughts on twin keels. That is the reason for this thread, to collect as much experience from other modellers.
Footy I buld is not intended for some great speeds, because a yacht I design is also a leisure family boat, not a regatta machine. Shallow draught and ease of sailing are my main concern.
Also thanks for invitation. I plan to visit UK this summer, my cousin works in London, but it could be a problem because of the firm I work in. It is small inland shipyard and curently I am only naval architect (to be) there. So it is hard to get a week or two of leave.
I’m going to try to shed some light on the question of multiple rudders.
Though it might be argued that the rule does not expressly forbid multiple rudders, the intent of the team that developed the Footy rule was that there should be only one rudder. It’s pretty difficult to word a rule so beautifully that everyone will interpret it in exactly the same way. Reviewing the wording of the rule, though, note that any reference to rudder is singular, reflecting the team’s intent. That, too, is why there is only one slot in the box, centered to allow a single rudder to extend beyond the stern.
The Committee hasn’t published a ruling on this, because we never received a request to do so.
Hope that’s helpful…Bill H
RIGHT crashimir - we’ll unhighjack your thread. Non-techies, please go away.
If you are not aware of the Arthur Robb designed Bluebird of Thorne, you should be. See
http://www.boatbuilding.com/article.php/advantagesoftwinkeels/print
If you look on the web you will find out quite a lot more about her.
Point 3. in the attached link is interesting. Reading between the lines of an article by Van Oosanen in Seahorse in 1988, it appears likely that the basic reason why Stars & Stripes 87 outclassed Kiwi Magic and Kookaburra was that the pressure wave from her forward raked fin tended to flatten the wave train. Trying out this principle on a short series of narrow, lightweight bulb-keeled racing yachts suggested that there may well have been something in this.
Hope this helps!
Yes I read the article you mantion. As the matter of fact it was one of reasons I decided to try something like twin keel. And hull form of my project (monohul at bow and changing to somewhat twin hull in the stern) is inspired with another jewel of ship design. The Alcyone, of Cousteau society. It was designed to minimise the need for propulsing power.
Since twin rudder is definitely not an option, out go two rudders and in goes one.
I am not familiar with underwater hull of Stars and Stripes '87. I thought that it is very familiar with Australia 3 from '83.
I apologise for my mistake. Winner of AC in 1983 was Aus 2, not Aus 3.
Distribution of volume in both keel and canoe body was radically different. S&S 87 had a much higher prismatic coeffiient both forward and aft of the mid-body and the keel ws a ‘Roman nose’ with positive curvature in the leading edge. Combined this probably filled in the wave train under the quarters at medium to high reaching speeds, conditions in which S&S 87 excelled.