ponderings on hulls

i had my boat out today in 5-10 knts, and as i was watching how the boat handled the chop, and the breeze, etc, i started thinking about all the talk about multi footys…
here is what i came up with.

  • because of the size of these boats, they will have an inherent issue with seaworthyness. primarily for and aft pitching. this, it seems to me would be aggravated by the nessicary narrowness of the hulls of a multi.
  • also because of the need for reserve bouyancy forward to counter the effects of the pitching problem, the hulls would need to be shaped like spoons, [draft/beam forward] or it would have to be a wave peircing design [think team Phillips]
  • all of that said, it seems to me that there would be and insumountable problem with a multi that was 12" long and any width. it is going to pitchpole, or, be so incredibly broad hulled that it might as well be a mono…

perhaps i am just saying things that have been said too amny times before… please, add your thoughts!

My opinion on a Footy multi ( a cat) is that it won’t have enough beem to be stable. It would still need a center hull or a keel. The radio gear of course will help, but how much? Maybe somebody has already done some experimentation with that? I’m putting down notes to work on over the winter. My current idea is a cat that looks like a tri with a third, boxy hull, to house the radio & the 5-8 ounces lead, but does not touch the water.

On the side, would you require a Footy multi to fit into the box, or could it use a scissoring frame to collapse, and hence fit bigger hulls in the same area/volume? We should decide on this first, because any subsequent designs would be contingent on that.

That sounds like it would fall to the ‘in sailing trim’ requirement of the rules Tomo.

I am pretty sure your thoughts are right 420sailor. Have you watched the wavelets on your local pond to discern the peak to peak distance in a reasonable breeze… I have estimated 5" to 7" on our small lake. I think that is worth taking note of… but I could be wrong.

Graham
USA10

Very interesting analysis 420. You wanted comments so …

  • because of the size of these boats, they will have an inherent issue with seaworthyness. primarily for and aft pitching. this, it seems to me would be aggravated by the nessicary narrowness of the hulls of a multi.

I think it is indisputably correct that the moment to change trim by n mm is inevitably greatly reduced.

  • also because of the need for reserve bouyancy forward to counter the effects of the pitching problem, the hulls would need to be shaped like spoons, [draft/beam forward] or it would have to be a wave peircing design [think team Phillips]

You could use a delta hull with LCB and LCF well aft so that the 'bow’is very long. (that’s the reason for my interest in Mariner). Freebord forwad would probably be a bit higher. In a multi, since there are no restrictions on hollows/chines/flare, you could combine this with some sort of widely flaring bow (see McA;pine Downey Hellcat, Iroquois, etc)

  • all of that said, it seems to me that there would be and insumountable problem with a multi that was 12" long and any width. it is going to pitchpole, or, be so incredibly broad hulled that it might as well be a mono…

On the other hand, the sail are needed is less and a wider boat possibly gives the opportunity to lower the centre of effort )rig on each hull).

I think that practically you are probably right, but that may just be my middle-aged conserevatism and lack of imagination

YOU could always consider using a twin mast rig, like the Tri-foiler.

waterline extends to 16+ inches … bouancy has to move way back … a reverse spoon if you wish … anybody done it? … may be worth banging together by somebody not involved in a damn fool foiling project …

Untitled-1.jpg

This one I can’t resist. A Super-Armadillo!

‘Oh dear’ he said… shaking his head slightly and heading for the door. :pirate:

OK. Overall length of 400 mm. Thumbnail lines at http://s111.photobucket.com/albums/n138/angusrichardson/wolfhound/.

I’m not sure if the hull will go in the box as is, but I’m virtually certain tha a small axe job on out-of-water bits that do not affect performance will do the trick.

We end up with quite a wholesome hull with medium light displacement and a moderate beam to length ratioo. As far as can be predicted statially, hull balance is near perfect up to approx. 35 degrees of heel. Righting moment is higher than any over our other Footy designs - more than enough to offset the higher wetted area. This means that we can reduce draft, thereby cutting the trippng couple and preventing submarining. Moment to trim 1 cm is much higher despite relatively forward position of LCB, LCF and elimination of Mariner-type stern. What is most important is that the displacement-length ratio has fallen from a portly 394 with Red Fox to a far more sylph-like 233 - which is not in the planing regime but certainly something that can be expected to surf - and that the resistance curve starts to become steep at a speed about 20% higher.

Now we have to produce a workable set of foils and a rig that will also go in the box. This may not be easy!

I see the advantages of longer LOA in this stretch of the box rule (which is fine), but wouldn’t there be some trade off by not being able to have a jib? Might not point as high? What is the possibility of making it a bit shorter and having a jib fit thru the slot in the box? Or would it be legal to put the boat the other direction in the box and take advantage of the deeper slot of the other end?
Bob

All good questions Bob: all I said was that I had a nice xaboe bidy: now I have to fit foils and rig within the rule. Not easy.

hmmm … haven’t seen a xaboe bidy for some time … kids threw mine in with the kindling … what time is it over there, btw ?

in responce to your question about wave length graham, i was sailing in a salt-water lagoon that is not my usual venue, but the wavelets seemed to be short and steep, 5-6" apart, and about 4" high… i don’t think a footy would have as much of a problem in longer waves, even if they were taller, simply because it would be able to move with the swell… it seems to me it is just steep chop these and any boat has problems with…

420 - PLEASE.

Try drawing some waves 5-6" apart and 4" high. I’m sure it was a nasty short schop, but that short and steep it’s breaking - and how!

May I suggest reading this thread at this juncture…
http://www.rcsailing.net/forum1/showthread.php?t=3302&highlight=bigfoot

Has our position of the spirit of the Footy rule chanced so much that the suggestion of a 16" footy brings little response? Maybe so.

The diagonal Bigfoot discussion seemed to end because the narrow beam would most likely have been a major down side, so in the end it was probably not a major threat. In this instance though things are different. I have just spent no more than an hour and drawn a quite reasonable 15 inch long (14.6" waterline) yacht based on my new 12" design ‘Banshee’ with NO beam compromise. It has a jib, albeit fairly small and mainsail, all of the rig rises above the box, only the rudder utilises the rear slot as per the rules. In fact it does not even push the rules never mind over extend them.

But I am concerned about the spirit of the footy rule. This is not a fault of tmark but it could be the first major fault of the rule. We have a good following building now, and I have always felt that alot of that is because the footy is only a foot long and has an appeal all of it’s own because of that. When I say to an interested bystander that my boat is a foot long… the reaction is immediate because ‘only a foot’ means something, somehow and catches the imagination.

Such a large jump in length as this idea offers may be almost like starting a new class to those of us who are here for the reason stated. Quite likely many will not want to follow the new trend.

I manufacture Footy kits as most will know, however my design process can have this 15" boat on the water in two weeks quite easily if I had to and I feel confident that I could make it work. So I hope that demonstrates that my thoughts expressed here are not driven by a commercial need to hold the rule. I have more concern for my past customers who would potentially have uncompetitive boats rather quickly.

Graham

Graham, I agree that your customers are a quite legitimate problem.

Since I have just ordered 11 kits off you (the order stands) and construction of a custom boat (the order also stands) I think I can reasonably be said to have a certain interest!

I very much want the Footy to succeed. I agree that ‘Footy’ is a nice gimmick word and that 12" was a nice gimmick length. However, it must be admitted that many of the less desirable characteristis of the class are due to a lack of longitudnal stability.

As to existing customers, the ‘hard core’ of Footy enthusiasts as typified by this Forum are home builders. The ethos is one of development and hence of design obsolescence. New customers who do not have that level of curioisity are obviously a problem. It is possible to tighten up the rule tremendously to preserve the original vision: to do so is to eliminate much of the attraction for the more enterprising designer and to lock the classes’ worst features in permanently.

I hate to try to do this again - I’ve been pouring it like soothing goop over every recent piece of pressure on the rule - but once again the idea of a Beta division comes to mind - a place where boats that have been outclasssed by rule developments can play happily. This need not be a matter for the central rule makers. ISORA’s Class C was locally defined and survived independently of the malverstations of the RORC and IOR rule makers for about 25 years. I believe that some model yacht classes such as Marbleheads do much the same thing. The important thing about Class C was that it was based on the physical characteristics of the boat, not date of build. This meant that a brand new ‘old-fashioned’ design could go straight into Class C.

I did not say ‘gimmick’ I said…
“When I say to an interested bystander that my boat is a foot long… the reaction is immediate because ‘only a foot’ means something, somehow and catches the imagination.”

So far I have understood the challenge of the small boat to be the reason for all of this interest… not that it is just some gimmick! Was the Footy name not chosen because it conveys a certain charm intrinsic in the idea of a 12" boat?

We need to look at the realities of footys before we criticise them I think… not the imagined problems. I sail my Footys almost every week and deliberately in all conditions. I have to say that I do not see great evidence of quote “the less desirable characteristis of the class are due to a lack of longitudnal stability.” Yes of course submarining is still a problem, as it is with much longer yachts too. I am learning to control the situation and choose to tack downwind or partially haul in to control the dive. That is a challenge and fun to try to master plus of course I (like others) am responding to the design challenge to minimise the effect. When I sail in chop and a good blow I see the bow cutting cleanly through… carefully watching the masthead for pitching I have seen little with my latest rigs. Reasonable platforming is my goal and I am seeing good results.

Quote… “It is possible to tighten up the rule tremendously to preserve the original vision: to do so is to eliminate much of the attraction for the more enterprising designer and to lock the classes’ worst features in permanently.”

Before we use such damning language for the 12" boat I believe that we should get out there and sail them more, have fun and learn how to use them. Practical sailing experience does mean something… it is not the poor relation of theoretical debate. As I am not apparently ‘an enterprising designer’ from your inference I shall just have to continue to apply my unenterprising design skills to the apparently greater challenge of the short boat.

Having said that I know the long boat is an interesting challenge too, but my concern is with not splitting this small world we are creating here. Presumably you know the phrase ‘falling between two stools’?

Graham :slight_smile: and yes I can still smile because they are only footys after all.

Well, I certainly agree with Graham that we will definetely lose the charm of our class with longer boats. The questions from innocent bystanders will require a explanation of rules. And, the, a further explanation of how to bend the rules.
I am no boat designer, but I already see some problems associated to this latest interpretation. Yes, you can fit a longer hull into the box by this method, but I believe there is going to be a big problem in placing the rig in it’s proper position. Without a jib, or even a small one, you are placing the Ce far aft of a normal rig. There is no ability to move it forward as it would not fit in the box. My understanding of a cat rig is that it needs to be well forward of the CLR to get any sort of sail area. I guess that it is going to just come down to somebody building one.
Bob

… they have been built … heard via PM from a guy who has done so … the fox IS in the chicken coop … (why did it take so long, btw) …

as for the cat rig, is there something in the rules not obvious to me? … turn the boat around, trim the boom to leeward … tada … seems to me she’d be more submarine than boat, though …

I mentioned turning the boat around, but I would suppose that would be a call for the rules makers. It is, afterall, a rudder slot. My gaff rigged catboat does not submarine anymore than any other boat.
Bob