Jumbo footies

The 1.5 kg Footy (see recent post in Cauldron Stir of the Week) is - to my great surprise - not as daft as it sounds.

For the result of 5 minutes doodling over a cup of coffee, see http://s111.photobucket.com/albums/n138/angusrichardson/jumbo/

Note that this involves a very heavily immersed transom - see the !2 Metre US 25 Mariner thread.


Doesn’t surprise me too much. I may be a poor sailor (probably, since I only have 10 hours experience) but increased mass would help me change tacks. My footy often stalls before it can swing over to the other tack. Especially hard with some chop or wake from bigger boats. Increased momentum would not be a bad thing in my opinion. I’m getting tired of making 270 degree gybes instead of 90 degree tacks to get upwind, 8-10 mph winds.

That’s just what worries me about jumbos. Scaling down from a bigger boat the frontal area goes down slower than the displacement (=mass). This means that wave pentration gets worse compared with a bigger boat, hence the tendency not to go about. The problem is that if you make the bow pointier to overcome this, you get submarining problems. Add some more mass and you may possibly get more submarining problems (see below) but you almost certainly make the bow blunter - so it hits oncoming waves like a brick wall.

The Armadillo design (see Footy Plans) is an attempt to deal with this problem. The ‘duck’s ass’ run moves the centres of bouyancy and flotation (and hence the CG and fin) way aft which increases the moment to drim 1 mm by the bow substantially. We’ll see if it works.

The sketch attached to this thread is literally no more than 5 min over a cup of coffee just to see what would happen if you attempted to put that much displacement into the length of a Footy. The immersed transom is intended to serve the same purpose as the ‘duck’s ass’ - only more so. It might conceivably work, but it might well not.

One difficulty with the jumbo is that the bulb will be huge - and presumably at maximum draft. This will lower the centre of resistance, increasing the tripping (submarining) couple. The attendant big rig will raise the centre of effort with the same effect. In other words, the forces tending to induce submarining will be much higher. God knows whether this will be more than countered by the greater trimming moment of the wider, fuller-ended hull. Without doing any sums my first guess is that submarining will be a serious problem and that the brute will be unable to use its huge transverse stability upwind because of a lack of fore-and-aft stability downwind.


not only that, but have you ever seen an full size optimist sailboat plowing downwind? just as you were saying, i can see this thing acting like an oil tanker down wind…

On the other hand, the rules don’t say it has to float! For flat, concrete bottomed ponds, just add wheels. No wave drag. Use model car components. ‘Hull’ volume quite small. Rig could be made tow work. Whee’s that section on ice yachts?

Would someone get Angus his medication please… :scared:

And I thought I’d made submarining a virtue.

A 3.25 lb. Footy? Thats a new definition of jumbo. My Bantam used to be the jumbo boat in that its beam predated the box rule. She weighs in at what used to be the heavy benchmark at 630 gms.
I don’t see the point of using really massive displacement to try to overcome the tender shortcomings of the Footy upwind or the apparent difficulty a lot of skippers seem to have tacking the boat in wind and chop. My boat stands up to wind and chop well, I have no problem tacking in rough conditions, and while she does sail nose down off wind in these conditions she has never nose-dived (I carry a lot of reserve bouyancy above the waterline in the bow. Hint: in gusty conditions sailing on a series of broad reaches is faster and avoids most nose-diving incidents).
So, improving the sea handling ability of the Footy is not achievable with increased displacement without compromising downwind speed or light air acceleration. The limitations of the box rule beam-wise were set in place to maintain the look of the “ideal boat”. Perhaps the Footy isn’t an “ideal boat” after all and needs us to take another tack to improve its performance while maintaining its primary limitation, the 12 inch hull length.
The solution I proposed a while ago was to lower the long sides of the box to six inches. This would allow designers to experiment with spreading the beam for upwind stability while keeping the overall displacement within common tolerances. This idea has the added bonus of making a diagonally placed design impractical because there are no upper corners to the box. I still think that this is a good idea. We may find that the “ideal Footy” should be broader than the rule currently allows. We may find that increasing the beam may not help at all and the six inch beam will still be the norm, in which case nothing is gained and nothing is lost. But as things stand we don’t know the answer to this question and one byproduct of the current beam restriction is that our fleet will continue to struggle in the broad range of sailing conditions.