Thinner Footy?

Footy Class General Discussion (Footy)
41

There has been a lot of discussion (and even some testing) on the topic of fat vs thin, but much of the really useful information is obscured by other differences in the boats, such as weight, transom, and shape. I have a basic question for the naval architects out there:

Consider two hulls of identical weight , water line length, and general shape. Hull #1 has twice the water line beam of hull #2, but the draft is less, to get the same displacement. Which hull will inherently have less drag? Is it a significant difference?

This is probably something that is in a basic textbook somewhere.

42

Just a place-holder before Flavio gets back!

There are textbook explanation, but like textbooks in most complex subjects they fudge.

In principle a narrow hull has substantially less drag than a wide one - hence (for example) naval destroyers which can have beam:length ratios as extreme as 10:1. In a sailing boat the (quite considerable) reducion in drag is offset to a geater or lesser extent by the reduction in stability (=horsepower) with the narrower hull,

Over to Flavio

Incidentally, I am not entirely certain that my imersed transom designs result in less form drag. What I am almost certain of is that the immersed transom dsign moves the centre of flotation aft. This should mean (by basic Archimedes on levers) that the ‘anti-submarining momemt’ is greater.

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While moving the weight aft should help the submarining issue somewhat, there are other things to consider as well. Moving the center of effort as far aft as possible, would increase the amount of hull forward of that CoE and reduce the tendency to bury the bow. Of course, moving the keel aft would be needed to maintain the proper balance between the sails and the underwater appendages, but that would reduce the steering moment of the rudder, UNLESS the rudder were mounted in the bow (canard). In the seventies, there was a version of the Marblehead class design called Epic that I believe was originally designed as a canard, but was later reconfigured into a more conventional keel/rudder layout and became quite successful for it’s day. I don’t know if the design was changed due to problems with the canard arrangement, or if it was simply a result of the resistance to something new. Supposedly, the canard allows use of a smaller rudder as well as allowing the boat to point higher, but it also might be overly sensitive and subject to more stalling problems, resulting in less control. I would think it might also be more likely to ‘stub its toe’ on a run, but since I haven’t tried it yet, I can’t be sure. One of the advantages of the Footy is that boats can be built cheaply and quickly, so it would be easy to build two versions of the same boat, one with a canard layout and the other conventional, to get a reasonable comparison of any advantages and/or disadvantages between the two. Too bad Burt Rutan isn’t into Footys!

Regards,
Bill Nielsen
Oakland Park, FL USA

44

Bill,

My BC2 was designed started life with a forward rudder. The reason I abandoned it early on was the fact that the forward rudder although smaller than the aft rudder I typically use moved the CLR of the hull very far forward. The resultant need to move the CE forward meant:

  1. I now had less leverage in the pitch axis to hold the bow up.
  2. The jib was frequently in the water.

As I thought about the boat heeling and moving through the water on a beat I also didn’t like the idea of the rudder pulling the nose down and to leeward to compensate for the desired slight weather helm.

I’m not saying it can’t work but the keel needs to be way back to get the CLR aft.

If you do try two versions of the same hull I would make sure the canard version had the keel located well aft of the conventional setup. a little geometry should give you a good starting point.

Perhaps I’ll put BC2 back in the pool to locate the static CLR. Then I can draw up a canard version with the correct appendage locations to give the same CLR. The boat sails very well in a conventional configuration. I’ll be curious to see just how far back the keel would have to move to achieve the same balance.

Take care,

Brent

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Hi Brent,
For the canard Footy, I was thinking of placing the keel all the way aft, even farther back than on your super slim Footy (BC4? - The boat I said at Vero didn’t look like a boat…). I had thought about incorporating the rudder on the trailing edge of the keel (like a vertical strip aileron), but I think it might not be very effective there, so I considered the canard with the rudder up front, but not all the way forward since the hull gets so narrow, there wouldn’t be room for the steering linkage. That linkage would need to be fully enclosed within the hull to help keep water out, although a deck mounted servo might work too. Did you get as far as testing a canard rudder on your boat, or did you change your mind before then? I may not get to the point of building anything, but the hull form I’ve been thinking about for the two boats is a sharpie, not unlike BC2, but with hard chines. If you build it first, it will save me the trouble! :slight_smile:

Regards,
Bill

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I thionk this was my first Footy design. I eventiually decided it was too radical a first step and shelved it. Ot might be interresting to resurrect it.

If anyone wants a go, I can supply a full-size lines plan.

:zbeer::zbeer:

47

I’ve made a few modifications to the 2"/50mm beam BC3. The keel has been moved forward slightly so there is a 2.875"/73mm gap from the keel trailing edge to the rudder leading edge. It is sporting its third rudder design and the bulb has been moved farther aft. The static waterline now has 2.375"/60mm of the 3.5"/89mm deep stern submerged. The entire stem sits just out of the water. As soon as the sail fills this changes considerably but it has enough reserve bouyancy to hold up the bow as well as or better than BC1 or BC2.

The other key item to getting the boat to tack reliably seems to have been a tendency on my part to sail my boats with too much weather helm. In the last two weeks I’ve found that by setting a more balanced helm on all three boats they tack better. Live and learn.

Yesterday after the Titusville Footy regatta I put BC3 on the water. It was blowing pretty good by then so for fun I stuck the 12"/305mm B fathead swing rig on BC3. We had a great time sailing it all over the pond. For the first time ever with a Footy I enjoyed downwind runs in high wind. With the short rig in high winds the boat was going very well. I now find myself looking forward to sailing in those conditions with a skinny boat. I’ll be going forward with an even narrower hull. I want to see what is too thin.

I know of at least 5 skinny hulls currently being developed/built in Florida and look forward to seeing the boats at future regattas. Before long my 4"/100mm BC1 will seem like a fat boat.

Take care,

Brent

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I HAVE SEEN THE LIGHT !
I had the pleasure of racing Brent’s BC 2 in sunday’s Titusville (Florida) event after my new, very rough, ‘wide’ (90mm beam) double ender had terminal servo-itis during the ‘practice race’. The 70mm beam BC 2 was a joy to sail with big rig in an estimated 12kts gusting to 16 +. There were white horses (caps) on the Indian River and wavelets on the pond. A delight to windward, pointing, tracking and tacking like a 30 sq metre. Downwind submarining ? - yes, but only in-attention broaches, the little sweetie ploughed on straight downwind and still steered despite a bow down angle at times reminiscent of a ‘Das Boot’ crash dive. BC 2 sails like a traditional keelboat not like a broachy, bobbing Footy ! BC 1, sailed very well by Brent, won the event of course, but only by by a hair. ( 1 point on the discards) A testament to the abilities of the narrower BC 2, great boat speed and controlability despite being sailed by a moron. I’m now so enthused about the narrow semi-heavies with tall swing rigs that I have become yet another disciple of the Florida guru, my new wider (72mm) beam, BC 2 inspired (shameless copy), will soon go from drawing board to foam. Thanks Brent for the opportunity to sail your boats and for converting me to the cause. Paul

49

In experimenting with boats of different shapes, it seems that 2 of the most important issues in tuning are the fore-and-aft position of keelfin and sail/mast ( along with keel bulb weight, overall weight, battery position, and sail configuration). I strive in my model work to develop modular systems to allow a platform for adjustment that is sturdy but light weight. How are you setting up your sailboats to change these sail/fin relationships - if glued in, the system would be the lightest but would require dremelling out and rebuilding to make any changes. It seems to me that if parameters are established for the most useful range of position of these elements can be determined, that a mastbox of appropriate dimensions could be constructed that could easily be duplicated and put in any design hull to allow easy changes - especially in a prototype.

Thoughts?

Nate

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Alain Jousse got this pick of my boat at the R1 regatta Saturday…before my receiver failed in race 1!

The boat is essentially a skinny version of Cobra, and fits diagonally and a bit stern down in the box. I think it has promise, but I don’t think I’ve quite found the sweet spot yet for rig balance…maybe about 1/4" forward…haven’t had enough pond time to get it sorted out…working far too much this summer (why couldn’t they want me in the winter?) so other than my Saturday club Soling racing, I haven’t had much chance to play with boats since Birkenhead.

The R1 regatta gave me a unique chance to watch others sail…and we had some of the best in the country there. Between Niel, Scott, Cliff, and Herb there would be enough regional and national trophies to sink a J boat! What I saw was confirmation of feelings that Scott, Angus and I have had for a while. That is, that a good hull is needed to be competitive…but that it’s unlikely that any hull will be such a standout performer as to beat all comers.

IMHO the breakthrough opportunity is to build on Brett’s innovations in rigs. There’s much to learn and much to be gained…the Footy performance challenge will keep us all busy for some time to come.

The good news is that Footys have come a long way in the last couple years, and proven themselves to be capable, though tricky, in the toughest conditions. I’m sure we’ll learn lots more in the next couple years, too.

That Footys attracted topnotch skippers like we had this weekend gives me the warm fuzzies…even though it means I’ll never win!!

Best to all…Bill H

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Nate,

I’m doing all my building now from blue or pink insulation foam which makes changing the position of mast or keel relatively simple. I cut the mast tube hole with a piece of the same diameter tubing that is sharpened on one end. I can spin this into the hull by hand to cut a nice clean hole for the mast tube. I don’t bother to glue the tube in until I’m satisfied with the location. If I need to change it I pull the tube out stick a plug of foam back in and drill another hole.

Similarly the keel slot is formed with a heated piece of coat hanger and the keel glued in only externally with low temp hot glue. If it needs changed I can cut the hot glue fillet off and remove the keel. Fill the old slot with foam and cut a new one.

You could easily build modular adjustable or multi-position mast steps and keel boxes that you could insert/remove from foam hulls to your heart’s content.

If you haven’t tried the foam yet I can’t recommend it highly enough. Once you develop a hull you love then you can do a fibreglass or carbon version of it, knowing the design will work well and that you won’t have to live with it just because you’ve invested too much effort in an unproven design.

The ease of construction will get you to try things you wouldn’t using other methods. Now that the 2" beam BC3 is sailing well the 1.5" beam hull is moving forward. I’m approaching a 9:1 beam to length ratio. Skinny indeed…

Take care,

Brent

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Excellent! I had stayed away from foam for primary construction because someone had said it was too heavy. Do you cover it with a layer of something for sailing? Do you carve out the interior for components to place them low or place them in shallow holes near the deck? I like the concept you use.

On my end, I have completed 2 examples of mast/keel boxes. This one weighs 12 grams.

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What is the best way to shape the foam hulls? I made a free sailing trimaran for my daughter out of pink foam, but the foam tended to tear when I tried to shape it with sandpaper.

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Finer sandpaper.

Or you could hot-wire cut it, and then sand it, but in my experience, sandpaper is the best way to smoothly and quickly get foam to the shape you want…

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Nate, Greg Bill et al,

Bill, I liked hearing about a skinny version of the Cobra. How skinny? :slight_smile:

Nate, I’m sorry to hear someone told you foam was too heavy. Most of my hulls are under 25grams. Keep in mind you don’t have to add internal support for mast, keel, servos, rudder etc. Unless others have really improved their technique this is an acceptable weight by any standard. I don’t even bother to hollow out the unused foam from the foredeck at these weights. If the extra 4 grams or so is an issue you certainly could though. Are other hulls with supporting structure being built in this weight range? If so could they be done by an average guy with average tools?

See the pictures in post #1 and #34 of this thread regarding the placement of servos on my boats. I use a piece of heated bent coat hanger and a small jig to cut cut press fit holes for the Hitec HS55 (rudder) and HS82MG (sail servo) I use.

Post #4 describes the finishing of the boats. I do sail them bare until I’m reasonably happy with the design. Be sure to use only water based polyurethane. Thin epoxy is even better for providing a hard shell.

Greg, I rough shape the hulls with a Stanley Surform tool, sort of cheese grater for wood or bondo. You can get them at hardware stores. Next step is to sand with 80 grit on a sanding block, then 150 grit, 240 grit and 400 just before coating. The foam does seem to like to be sanded in a certain direction sometimes so I often only sand in one direction, not back and forth. Also keep your paper clean to reduce tear outs.

The guys around here who are trying foam hulls are having a lot of fun and producing better boats every time out. It is really addictive.

Take care,

Brent

56

A friend builds 19’ Lightning sailboats and often uses foam for making shapes. He likes to build models before building full size.

I believe he uses a special type of foam and recently gave me some pcs for trying new Footy huls. The foam is green.

I could ask exactly what type he buys, but I suspect someone here knows. Maybe same as used for building surfboards?

Da NewberryYooper Frank, eh

57

what were the dimensions angus?

the picce looks pretty neat too…

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Please bare with me as this is some group think out-loud. Hope to get some help from you-all figuring out the right set of ratios and fudge factors for the “Perfect NDC”

Here is the initial thought. Angus thinks metric. I think inches. Many different boat designs. Some boats fat, Some boats skinny. How to compare apples to oranges?

Now for the reference boat. Visualize a normalized circle of unit radus (1).

Top - At the top,represents sail area. There a TBD fudge factor that when mulltiplied times area = 1.

Bottom - This factor is the righting moment. Simply balast weight times distance from water line to C/L of balast times fudge factor to = 1…

Left - This is the waterline length divided by max waterline beam width times a fudge factor to = 1.

Right - Total weight divided by balast weight times FF to = 1.

I need someone to select a boat to represent the perfect boat/perfect circle so that T:B:L:R (Points of Circle) are 1:1:1:1. Other boat designs can be compaed to this boat.

Based on this reference boat, we can publish the following Fudge Factors.

…TFF

.LFF…RFF

…BFF

Thus, instead of a whole list of parameters, we could simply visualize an out of shape circle or four factors.

As the wind conditions change, it will be interesting to see what shape the circle takes for the winning boats?

The four points suggested are just to be considered a starting point. Suggested changes are encouraged and hopefully a useful model for boat performance can be developed.

If this should be a separate thread, that is fine w/me.

FastFrank/No Relation to Fudge Factor

59

I took my testbed v-12 to the oven this weekend

rather than cut sections out and make her skinny, I cut the transom out and then squeezed the gunwales together. with tape then put it under light heat to “re learn” the new shape.

I will take pics. later… I have narrowed up the deck to about 4" the deck flares out about 1/3" of an inch on either side of the deck, boat can only fit in the box diagonal, but not pitched fore or aft any transom is about 2/3 of the it normal width but its twice as tall.

boat would have to be healed over grater than 45* for the deck to be under water. it has a profile mulch that of an offshore power boat, in that as you move forward past the mast, the deck begins to slope back towards the water. which gives me a lot less buoyancy up front…

from the front it looks like its been "over inflated below the deck as it bulges out below the deck.

I still have lots of space, inside enough that a short arm with a double purchase should give me enough sheeting action for a swing rig.

I plan to carry an 8oz bulb, with a rudder shaped like that of a Victoria but just a bit smaller.

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For years now, I’ve been concentrating on hard-chine designs…so that people would have a few easy-to-build designs available, like Razor and Cobra. I’ve had a round hull on the drawing board for a while, though, and Brent’s experience with foam inspired me to try it.

The design is for a skinny…90mm beam, 330 or so LOA…For those who remember way back to Halfpint, this is kind of a stretched version.

I printed my sections and spray-glued them to one inch foam scraps I had around…then cut them out on my bandsaw, glued them together, and sanded the whole thing by hand to fair it out. It worked very easily…no chipping problems or anything…took one afternoon to get to this point.

The hull without any cutouts for electronics weighs 45 grams prior to painting…not too bad.

Have fun with Footys…Bill H

Here’s a few pics: