Footy Design, What Has Been Resolved?

Footy Class General Discussion (Footy)
1

Over the last three years I’ve been following this discussion, vigorous forum debate has kept lurkers and contributors enthused and engaged. I wonder if it’s time to summarize the discussions and see if consensus has been reached or if the subjects have just been talked to death. Remember, none-of-this has anything at all to do with rules.

Design Issues

Length:
It is widely accepted that the boat is no longer limited to 12 inches.
Has it thus been determined that the longer boats are faster?
Has it thus been determined that be dint of its 8% longer LWL the longer boats are easier handling?

Weight:
Lighter is better was the claim, primarily because of reduced whetted surface and because “lighter is better everywhere else”
Heavier, it was also argued, meant better handling due to added momentum.

Width:
Argued to death in the Transat 6.5’s as Footy thread.
Thinner is probably better balanced, can be designed to with less whetted surface, but … who is winning races?

Immersed Transom:
It was argued that an immersed transom did not affect Footy’s as one would normally expect. Then it was intimated otherwise.

Foils:
Given the relatively low speeds of a Footy, has a general width been accepted … Reynolds numbers might suggest greater than 10% but but but … ?

Bouancy in the Ends:
Experiments were made. Drawings were drawn.
By pushing volumes aft and forward do we end up with a slippier boat? A better handling boat? A boat less inclined to dive? Or do we end up with a hobby horse?

Out of interest sake, I’d suggest that maybe just maybe the designers taking Riptide (the classic M with the “perfect” metacentric shelf … if that’s in fact how it was referred to) as inspiration, either consciously or serendipitously, were the designers having come closest to the ideal.

It would be interesting to hear those who have opinions, and which of you don’t, to first state the opinion before arguing the why, and then see what kind of consensus may or may not have developed.

I’ll start: if I were to build a boat tomorrow

Length: 13 inches
Width: 4 inches
Displacement: 400 grams
Foils: 10%
Shape: Narrow Transom
Transom: Out of Water
Balanced: Yes, as perfectly as possible

Regards, Trevor

2

Hi Trevor,

My Tanto design comes close to fitting the bill. The difference is that she draws 500-520 grams with a narrow stern above the water. She was inspired by the vane Marbleheads that I used to sail as a boy. Tanto is well balanced, well behaved and I think pretty fast. She is easy to sail so I can concentrate on where I want to be on the course instead of watching the boat. She is also simple to build with only four hull panels.

So, perhaps Tanto is revolutionary in her conservative nod to vane boat design.

3

Trevor,
It seems that with every regatta, we hope the Footy design issues that you mentioned will have been resolved, but it seems that all that happens is more questions are raised.

Niel’s diagonal boats are very fast (and well sailed) and my favorite boat right now is a 13" X 3 1/2" “Cobra” design, but until they get beaten, my short, fat, American Footy and Micron2 hulls are the ones to beat in the northeast. The Nationals next month should be very interesting as they go up against the super skinny boats from the south. Maybe then we can say that some of the issues have been settled.
Regards,
Scott

4

IMO, Footy design has slowed much. There are many designes which are so good that nobody seems to want to do one better, like the Kittywake or the 507. I hope that we can get some statistics from the NCR as to how many of each design are there.

Every once in a while, somebody like Niel gets an inspiration, and another new model design pops up.

5

Tomo, I disagree a bit…there’s lots of Footy innovation going on. New hull designs from several of us tinkerers (the one Scott mentioned is my latest, and I intend to publish it after Orlando) as well as some interesting things in rigs being explored (per the swing rig thread.)

Clearly, though, the answers are not yet understood. My own work suggests that narrow Footys are good, that wide Footys are good, that 400g Footys are good, that 500g Footys are good, and (I think) that 700g Footys are good. My boats have definitely shown that transoms clear of the water perform well…and that immersed transoms perform well. Same with bows. McRigs work well…swing rigs work well…sloop rigs work well. I’m pretty happy with volumes that are similar in bow and stern…that seems to work well. I like full-depth fins…they seem to work well. Skinny fins work well…as do wide fins. I do vote with Niel for well-balanced hulls…meaning narrower sterns rather than arrow shapes, so that the hull stays level when heeled. But that may just be personal preference…I, like Niel, have studied the vane-sailed Marbleheads and respect that heritage…maybe because I like sailing VMs at Redd’s Pond…all those wonderful boats that sailed there for so many years…vane sailing is so elegant.

But isn’t that kind of the neat thing about Footys? Some of us have been doing Footys for more than 5 years, and we still don’t have the answers. If we did, wouldn’t that be boring? Might as well sail a Soling 1m…fun sailing, but not much opportunity to explore the possiblilities.

So I think everyone should build a fat/skinny, light/heavy, long/short, deep/shallow, McRigged/sloop-rigged Footy and get out there and have some fun finding out what it will do!

All the best…Bill H

6

Yep!

When I first met Flavio, we discovered that we had quite different approaches to design - because we were trying to do two quite different things. He took that attitude thay you started from a known point - say a Razor - and moved conservatively in whatever you thought was the right direction. This means that you are unlikely to make any dramatic gains, but you are unlikely to end up with a total disaster either.

I tend to work on the basis of going as far as you dare in a particular direction. If it seems to work, push it furher, If it doesn’t withdraw a bit. This is useful for exploring the limits of the rule envelope.

So far, I think the only thing that we can pretty definitely say is WRONG is simple flat plate fins. I think this is pretty much proven by the catastrophic performance of a 507 straight out of the box. Modified to come rather closer to what the designer (me) intended, 507s are reasonably cmpetitive. The changes made to bring this about a pretty varied, but the one thing that seems to be essential is to replace the fin with some sort of aerofoil section.

There are also quite a lot of things that we can say are NOT WRONG. By this I mean things that 2 or 3 years ago might be thought of as the kiss of death, but which have proved to be at least compatible with a competitive boat.
[ol]
[li]Una rigs
[/li][li]Narrow beam
[/li][li]Immersed transoms
[/li][li]Bullet stems
[/li][li]Light displacement
[/li][li]very light construction
[/li][li]Thick foils
[/li][li]Narrow sterns
[/li][li]Vastly reduced rocker
[/li][li]Very high prismatic coefficients indeed
[/li][/ol]

Whether any of them (except possibly for Very Light Construction) is actually positively RIGHT remains to be seen!

:graduate::zbeer::zbeer::zbeer:

7

Our Tanglewood design team has been playing with keel length on our “Jim-Bobs”. Being an engineer, I simply think in terms of righting moment and like em long. Brent Carter seems also to like em long and wins most events. His 10 oz balast on a narrow 15 oz total boat & swing rig is hard to beat.

Feedback on long vs short keels and keel side profiles would be appreciated.

Then there is the Skipper factor and how he sets his sails and whether he pinches or foots and general sailing skills. This is a big factor that can make “Good look Bad” or “Bad look Good”.

For funs sake. let’s hope the experimenting continues.

8

This particular thread has drawn me out of the lair of my studies for the sole reason that I was one of those who made so much noise about design, and so, I figured I might as well chime in again. grins

It seems to me that the design of the “Footy-type” while far from being complete, has, to a large degree been steered by the type of racing that footydom tends to participate in. This design concept we speak of mainly concerns itself with racing Footys – meaning simply that the less competitive set of Footy owners will probably not change their design brief all that much due the outcome of this thread. This racing seems to very often end up being quite a bit of upwind/downwind work, with a very broad reach or two tossed in for good measure. (This type of racing indicates rather long, slender triangle courses, or even more slender windward/leeward courses, both of which seem to be standards for footy racing around the world.) This fact cannot be overlooked as we look at the things we know about footy design. Hulls with very narrow entries and slender forms go faster upwind when compared to a wider boat, and given that to date, Footys do not exhibit the capability to plane off the wind (or on any other point of sail for that matter :rolleyes: ) there is valid argument that a narrow boat also goes downwind in displacement mode faster than a blunt, leaf-like shape.

Given this aspect of the design brief I second many of the notes made by previous posters, a “long-hull” Footy is mathmatically more directionally stable, and has a greater waterline length on most (if not all) points of sail when compared to a design of broader girth and shorter length. I say mathmatically because the Footy is a boat that is so tender to sail to its performance limit, that the likelihood of the average sailor reaching that limit seems rather slim. Footys are hard to see at a distance, are very sensitive to changes in wind, wave, and control input, are quick to accelerate, and equally quick to stop. A skipper may have the most advanced Footy out there, but he will still be served up a steaming dish of humble pie by the oldest boat in the fleet if he cannot capitalize on his boat’s performance.

The hobby-horsing issue is one that, to my knowledge, continues to plague the design… Changes in battery rules and more wide-spread adoption of the long-hull Footy may help with some of this, but the problem remains, if a Footy hits a patch of short, steep chop, it is going to stop.

Downwind submarining was of old another foible of the Footy. While I have heard less and less about it as of late, I must assume that it is still an issue after a fashion, (although perhaps less of one than I imagine.) Obvious solutions have been to add buoyancy in the bow, and lower the aspect ratio of the rigs footys carry.

A final issue with the Footy has, in my experience, been the boat’s desire to lift its rudder from the water as it heels. While this has certainly been partially due to the width of several of the boats exiting the SMM ways of old, between submarining, hobby-horsing, heeling, stopping dead in the water, and the other myriad little things that our footy’s do, rudder effectiveness is not always what we would like it to be. Moving the rudder around the vessel has not been much examined due in part to the perceived benefits gained by having a large space between the keel and the aft-mounted rudder. Therefore, to combat ineffectiveness, footy rudders have become almost comically large affairs.

On these points, I believe, lie much of what the Footy is, as previously mentioned, current thinking seems to be pointed towards a slender, longer-than-12-inches boat, of medium rocker, with a narrow bow entry, a necessarily pinched tail (do to constraints of fitting into a box diagonally) carrying a mid-aspect rig (probably no taller than 16-18 inches… the first Bearfoot carried a 21" tall rig.) Freeboard is relatively high given the length of the boat, and the appendages are oversized and spade-like. Bulbs do not seem to have found a stable point as of yet, nor will they, I suspect, as many are cast at home in somewhat slap-together molds.

In all honesty, I do not believe that the “Footy-arch-type” has been found. Nor, do I believe that it will be in the terribly near future. The concept of a 12" long box is simply too wide-open to allow a type to form rapidly.

Alright… the troll has woken… and now must be put back to sleep in lieu of a calculus exam, an macro-economics class, and the torrent of other courses that steal time from more amusing endeavors. Until we meet again, farewell!:graduate::devil3::devil3:

9

Nice to have you emerge, Barrett, albeit briefly. A nice summary of design points, I think.

Bill H

10

To Niel

Those are large foils on Tanto … I’m certain they contribute to the ease of handling you report from the design … apart from that, they move the LCR and LCB aft (though not certain how substantively) … they contribute to a higher displacement and marginally increased drag. None of which is good or bad, they’re just observations.

That said, I’m midway through drawing a new design and am fiddling with foils and their placement … I’m curious why you chose the foils you did, particularly the large rudder …

11

Hi Trevor and all that are perusing! With large foils, like all things Footy, the way things are supposed to be by existing theory and math don’t always, and often seldom, hold true it seems.

I have always been partial to big rudders as anyone familiar with my M boats or 36/600s knows. The caveat is that big rudders make inputs more extreme so a lighter touch on the transmitter stick is required. The larger rudder acts like a more moderate sized one if you don’t use all the throw. I only use full rudder for major maneuvers, tacking in strong winds, avoiding another boat’s unexpected change of course, power mark roundings and the like. I also use cable steering in these larger classes which gives me more even input/control over the range of the rudder servo’s throw.

On a Footy a large rudder with a wide swing in the linkage will do more harm than good in inexperienced hands. It is very easy to over-steer and end up with some pretty wild handling when the wind is really blowing. Such situations are not for the faint of heart. Once a sailor has gained some experience though a large rudder can be a real godsend in those conditions. Not just as Barrett suggests, by keeping the rudder in the water, but because there is more potential to control the boat where a smaller foil would stall and not be able to stabilize the boat’s course.

One way to break in a larger rudder is to adjust the linkage to reduce the angle of the rudder in relation to the angle of the servo’s maximum throw. This provides less rudder turning for the transmitter input. As the sailor becomes more attuned to using a bigger rudder the linkage can be incrementally adjusted to a one-to-one ratio.

12

Some other thoughts; when the craft is scaled down it is not operating in a scaled down environment. Anyone familiar with model aircraft is aware that the airfoils need to be larger than scale for the pilot to have control over the plane.

In model yachts there is not as much at stake if the skipper finds his boat overpowered and not responding to rudder input. It likely that the gust will let up at some point and he will again be able to sail. Not the same as crashing a plane.

The issue of how big to make the foils on a Footy boils down to the perception of drag versus lift. The tendency is to favor reducing drag by reducing area (and saving weight). This can also be attributed to the conservative impulse to mimic what works in the larger, hi-tech racing classes. But is this a sound direction for Footies? Well, there are a few guys (myself included) that think with narrow keel fins there is a point at which they become too area starved to attach flow over their surface to create lift. These fins operate on the edge of stalling and with the natural gyrations that a Footy goes through when underway it is amazing that they go forward at all. Narrow keel fins also don’t do much to counteract sideslipping, one of the Footy’s Achilles Heels.

Now I find it interesting that such a broad range of designs perform fairly equally on the race course. Many of the posts on this forum make this observation. This can be interpreted to mean that any changes one makes on a competitive boat are probably not going to be perceptible. So does a larger area keel fin add to drag? Not that I notice. Does the larger area keel fin provide more lift on Tanto? I couldn’t say for sure because I haven’t tried a narrower one. But I do think that she points pretty high and I have noticed that she doesn’t sideslip as much as some of the boats I’ve sailed with. Oh, I also think Tanto is pretty fast so my current thinking is that increased drag (even if its significant) is not an issue performance-wise with these boats.

13

Hi Niel,

Are there any photos posted of Tanto here or on the Yahoo Footy group? After looking at the pictures of your Brujo in the AMYA Footy issue, I’m curious as to your final verdict on the steeply angled foredeck. Did it help prevent nosediving, or at least make control of the boat easier if a nosedive occurred? Were there other benefits/disadvantages of this type of deck?

Regards,
Bill Nielsen
Oakland Park, FL USA
AMYA #0835

14

Neil I think it fair to add that newer transmitters also allow you have Dual Rate so you can limit the throw at the flick of a switch ~ I find it great

15

Andy - I had dual rate throw on my M boat back in the early '90’s. I thought the concept was great until I had the reduced throw in place unintentionally at a mark rounding in traffic. Before the next heat I reset the switch to the normal position, Ca glued it in place, and snipped off the toggle lever. Since then I have only used mechanical methods for rudder control. It may just be me but I can’t cope with more than two controls in the midst of a competitive fleet.

Bill N. - There are some photos of Tanto earlier in this thread. Tanto is to be my contribution to homebuilders out there. I have the hull panels on CADD but I’m still working on some builder’s notes to go with them. When all this comes together I will transfer it to .pdf file format for distribution.

As for Brujo the cutwater deck works like a charm. The diagonal + angled placement increases the waterline length a bit but more to the point the boat’s bow overhangs the waterline. This, in effect, provides a great deal more reserve bouyancy up front where it counts. This deck treatment is the only part of the boat that I’m satisfied with.

I made an error somewhere in my execution of the boat and the first Brujo has some stalling issues. Keel placement is the probable culprit. I will report more about her when I’ve gotten the bugs worked out.

The one caveat to Brujo’s orientation in the measurement box is that to gain the added length and forward bow overhang the keel depth ends up a bit shorter than if her placement were more conventional. The bulb is also a less sleek than I’d like due to the angled orientation. There is some merit to the shorter keel, it theoretically reduces a boat’s hobby-horsing. I don’t think that Brujo is more tender that most Footies so the shorter keel depth my not be too great a factor in upwind performance.

One other thing about Brujo’s unusual placement is that the rig is mounted on the crest of the cutwater deck. The cutwater deck’s ridge line runs parallel to the lip of the box. This rig location is necessary so as to raise the rig up to a point that it will clear the top edge of the box as the sail is rotated to confirm its legality. Thus, the sail rig is carried a couple of inches higher than on other boats so that rig heights had to be adjusted accordingly.

16

Thanks Niel,

Dealing with a Footy’s tendency to bury it’s bow is one of the biggest challenges to sailing them. Anything that can be done at the design stage to eliminate or mitigate that tendency is a big step forward. I think the Footy’s tendency to bury it’s bow (because when it happens it is so visibly obvious to onlookers), is one reason people who are already involved in R/C sailing don’t take the class as seriously as they should.

Thanks for posting the pictures of Tanto under sail, it’s good to see pictures of a boat both in and out of the water, it makes it easier to see how it really looks.

Regards,
Bill Nielsen
Oakland Park (Ft, Lauderdale), FL USA
AMYA #0835

17

You are welcome Bill -

In the photo of Tanto sailing the bow is more depressed than usual. In this shot there is quite a large wave that she’s just passed over and her stern is lifting. In lighter conditions she sits with about three inches of bow above the water. Her high freeboard helps to keep the deck edge out of the water (drag producer).

I have not found that this design is prone to hobby-horsing and in upstate NY where I vacation this would be considered pretty calm conditions. There are always some waves but not always a lot of wind. But when the wind blows things can get interesting. I’ve been sailing my Footies in conditions that I wouldn’t put my M boat through.