E.L.F. Extra Light Footy (concept)

Footy Class General Discussion (Footy)
1

Since my big boat sailing season has come to an end, and I’ve had a little more free time, I decided to aggressively explore a corner of the box, specifically weight. My goal was a displacement of sub 200g. In reality I was attempting to explore numbers that work for larger classes at a footy scale.

My final numbers for this quick and dirty design into light footing are:

LOA = 341.25 mm
LWL = 338.1 mm
B (on deck) = 56.7mm
B wl = 56.51
Displacement = 182 g

This produces a DLR of 136.37, which by big boat terms is potentially pretty quick.

To achieve these numbers I constructed the boat out of 2mm depron with minimal internal reinforcement. I’ve used a Carbon Fiber helicopter blade for the keel fin, which in retrospect is much too heavy at 18g, but the weight is in an acceptable place so I’ve decided to keep it. I have used my standard battery arrangement, which is a 1200mah lithium ion digital camera battery with vac formed holder (14g), a 6 gram rudder servo and a stronger sail servo that tips the scales at 12.6g. I rounded out the whole with an 80 gram keel bulb for a ballast ratio of ~ 44%

The boat is a slight double diagonal, with the transom angled down in the box. The hull is chined with a 4 piece hull construction, with the transom set slightly forward of the extreme end of the boat so it has a quasi sugar scoop. With everything bonded together I was astonished at how stiff the panels are. Actually much stiffer than my vac formed Red TYDES, which to me means the boat is over built. :slight_smile: However, from conception to sailing, total time was less than 12 hours.

As is usual with something like this, I started out thinking this would be an excellent light(er) air boat, however the calm winds that have prevailed recently gave way to stronger breezes of 10-15kts. It was a true trial by fire. As expected the boat was a bit difficult to tack, however with some careful planning and set up, you over sheet the sail as you ease the rudder over and I had about a 90% success rate in today’s wavy/choppy conditions. I will say when sailing close to shore with a bit of rebounding breeze E.L.F. was incredibly responsive. The jury will be out until I can line up against at the very least a RED TYDE, until then I’m not giving up on it.

If anyone wants the hull panel developments and further build notes please let me know I am happy to share.

-Nathan

2

Hi Nathan
A very impressive concept and build. My narrowest hull do date is, compared to yours, a whopping 80mm and my lightest boat weighed in at a something more like 250 g!
Please would you explain what is a DLR number and how you arrive at one?
I for one would be very interested to see ‘hull panel developments and further build notes’.
Cheers
Phil

3

Hi Phil,

Thank you for the kind words.

DLR = Displacement Length Ratio

It’s a generic measure of a boats mass relative to it’s waterline length. Generally the higher the number the “piggier” the boat. As with so many nautical based formula it’s calculated with imperial units (feet and pounds). The Formula is:

displacement(lb)/2240 / (.01 * Lwl (ft))^3

So for this boat that equates to:

displacement = 182g = .401248 lbs, Lwl = 333.81mm = 1.09517 ft, .401248/2240 / (.01 * 1.09517)^3 = 136.37

With respect to build notes + drawings I’ve attached them here, in both US paper sizes and ISO paper sizes.

The only items not described are the keel and rudder, as well as their placements. However for the keel I used a standard 340mm CF helicopter blade, trimmed where necessary.
http://hobbyking.com/hobbyking/store/__18077__325mm_Carbon_Fiber_Main_Blades.html

and the rudder is just a piece of balsa carved into approximate shape with shaft epoxied into place.

The mast tube (for a McRig) is glued to the forward side of the forward bulkhead, and the keel leading edge is to be glued to the aft side of the aft bulkhead.
The rudder tube is glued on the aft side of the transom bulkhead. While not exactly light weight I used low temp hot melt glue for speed and ease to mount both the keel in the boat and the mast and rudder tubes.
The servos are on as small a cartridge assembly as possible. I use a generic lithium battery that goes fits one of the digital cameras in the house. The model is EN-EL 10. As described before bulkheads, hull and deck are from 2mm Depron.

-Nathan

4

An update.

I had the opportunity over the weekend to do some side by side with the E.L.F and a Red TYDE. The conclusions were pretty simple to see. It should be noted that the boats were not sailing with the exact same rigs. Red TYDE had my standard “B” rig, and the E.L.F. was using a generic McRig with about 40% less area. The wind was puffy from about 10-18kts.

The Red TYDE (Tipping the scales at 335g and 65% ballast ratio) is, as expected, an upwind machine. The comparison uphill was akin to Oracle VS. ETNZ in the later races upwind. RT was higher and faster, lower and faster, and same height and faster.
The ELF was twitchy, hard to control and in general difficult to get into the groove which attributed to a good deal of the differences.

Downwind the story was different. With less volume and significantly less weight ELF was a bit faster. Some of the drastic differences were it’s acceleration and ability to keep the bow clear going down wind. As it should ELF was pushing less water, and that made the biggest difference.

However in a typical race Red TYDE would be significantly faster around the track.

What to fix:

I’m considering adding fillets to the keel blade fore and aft to extend the root of the keel. This should help steady the general tracking of the boat, I’m resisting the urge to add more bulb weight.

-Nathan

5

Well done, Nathan…you are setting the bar for Footy innovation in the USA.

I hope you will bring the boat up to New Hampshire next spring…I’d like to sail it, regardless of whether you think it is competitive. Exploring the boundaries of design in an Open Class is always fun.

I had trouble tacking reliably with boats 300g or less. They didn’t seem to have enough momentum to get through the wind reliably. A missed tack can be too costly in a race, so I went back up to 350g or more. I’m sure part of the problem is my sailing skills, but maybe there’s a design characteristic that I didn’t figure out that could solve that problem.

My light boats didn’t have as impressive a ballast ratio as yours, though they were not bad. They couldn’t carry as much sail as heavier designs, so they were typically down one rig size from the fleet. That didn’t seem to matter, because the smaller rig still got them up to boat speed as fast as the heavier boats.

Keep an eye on the area around the joint between the hull and fin. I abandoned Depron because two boats developed cracks in that area, and I thought that reinforcements would add weight that would defeat the concept.

Stay in touch, and let me know if you are planning to be up my way…I’d be glad to have you visit.

Bill

6

Hi Nathan
Thanks for keeping us all updated with your progress.
Since you set out to design a light boat, I completely understand your reluctance to add any extra weight to ELF. However, it may be more revealing to test the two boats if they had the same ballast ratio? Take some lead off Red Tyde or add some to ELF?! For what it’s worth, the latter seems a better idea to me.
Reading about the problems you encountered, particularly in tacking in choppy conditions, made me wonder ‘how light is too light’? My only experience of ‘light boat’ performance was seeing how well Scott Wallace’s Depron, Bill Hagerup designed, Ranger performed, up wind and down wind, at last year’s Footy Gold Cup. I can’t remember the ‘all up weight’ but I feel it must be getting close to as light as you can get a fast Footy to be…or is it ?!
Cheers
Phil

7

First, I can get used to this flat panel hull building. Hydrodynamically I still cringe, but oh well, the price to pay for being able to design, build and sail a boat in one weekend.

I did/do have some trouble tacking ELF in the breezier conditions, I typically set up my boats so that with the trim adjustment maxed in I can get the sail to as near as center line as possible, but spend most of the time sailing with sail trim adjustment most of the way down/out. I found that going into a tack if I slid the adjuster up (after having sufficient speed) and then easing the rudder over slowly the boat would make it through the eye of the wind. With the sail still over trimmed the leading edge was catching the bow and setting it down a quick ease and the boat was back on it’s way. Admittedly it requires nimble fingers and a bit of luck, but it works most of the time, even with a few waves.

Regarding the integrity of the Depron hull I think I am lucking out due to the decreased loads of the light boat. With a keel bulb of 80g there just isn’t enough force to make significant problems, however the boat is still “new” so wear and tear haven’t taken their toll yet. One thing the construction has is; the leading edge of the fin is glued to the bulkhead structure, the deck, and the bottom, with Hot melt Glue (low temp). I attempted to make the structure as redundant as possible. Could it be lighter? Probably. But I still want the boat to make it back to shore, not just complete the race.

I will definitely add the boat to my stable and bring it with me to future regattas. I also plan on two more developments. The first and easiest is to remove about 80g of lead from a Red Tyde Bulb and do some side by side testing with that. This would still leave Red TYDE at 56% Ballast ratio, but it puts me in the ballpark of my next displacement figure of 250g. I’m at the point where I think a RED Tyde is too stable going upwind, and is too draggy downwind to handle a larger cloud of sail area, Going lighter makes a slightly more difficult boat to sail, but hopefully a faster boat overall.

I have an almost complete design for a flat panel 250g boat to sail against. I’ve given up on the double diagonal boat. I think it’s sacrificing too much draft at these lighter displacements and lower ballast ratios. Pushing the ballast as far from the waterline as possible is absolutely essential to go upwind. Regardless I have a feeling that 250g could be a sweet spot. If testing proves my theory, a vacuum formed hull could be in the future.

Bill, I’m a glutton for cold, so I’m still planning on sailing so long as the water is not hard. If you’re interested in meeting somewhere in-between in the next couple of weekends I am more than willing. Has anyone done, or is it possible to sail a footy at the Minuteman Man Yacht Club 4hr Enduro?

I’ll keep you posted on my travels.

-Nathan

8

After fully playing with a RED Tyde Vs the ELF I decided it was time to go back to the drawing board and come up with development #2

//youtu.be/sO5zSsV1n_8

This video shows just how much slower upwind the ELF (1) was comparatively.

Dev #2 is a progression of #1 but with significantly more weight, although still very light by Footy standards.

Weight/Displacement = 240g
LWL = 324mm
LOD= 325 mm
B = 59.66mm
Bwl = 59.66mm
150g Ballast.

Construction is the same as ELF1 with 2mm depron. The keel fin is a custom laminate of balsa core, and carbon fiber unidirectional strands, then filled and fared with West System light fairing filler. Rudder is carved/sanded from 1/4" balsa (no I don’t use the full thickness) with a carbon shaft.

As you can see the Rudder is “different” I’ve carved Tubercles into the leading edge. The concept is pretty neat, they are an idea stolen from nature. The basics are that by creating leading edge protrusions you can delay the onset of stall at higher angles of attack at a minimal drag penalty. I decided to trial this idea, with the thought that by delaying stall I can use larger rudder angles to force the boat to tack more quickly and alleviate some of the difficulties in tacking boats without momentum. So far it seems to be working. More to come, I’ll be sailing against a few other Red TYDES on Thursday, it should be an interesting showing.

-Nathan

9

Great video, Nathan. Our water is a bit hard for sailing now, or I’d try the rudder mod, too. Shortly before he died, Scott Spacie sent me an article about the concept.

I think your systematic approach to finding the weight limit is a good one. I’m very interested to see if you come to the same conclusion that I have…through less systematic development.

Keep up the good work…Bill

10

Precision building is the secret sauce to the lightweight footy. The heavier ones have more tolerance to building error and mistakes when sailing.

11

Hi Phil, Nathan
Sorry, been absent from Footy’s for a while as i took a year out to work, and travel round the USA/Canada.

Back in for this years regatta’s and just preping the very boat Phil was talking about. (well a new version, as the old one had picked up leaks…)
It weighed 310g all up, with 215g ballast, so a pretty respectable 60+%.
I’ve been tuning my rigs, and honing my skills in my absence, so i hope to show the light end, can throw a heavy punch :slight_smile:

Phil, i am particularly ken on your new carbon Suiss 1 footy. Nice wide shoulders, and quite a full bow (remins me of a slimmed down moonshadow/Razor 3, to a little extent (and i don’t think that is a bad thing!)
It’ll be very interesting to see it sail :slight_smile:

Nathan, I like your boat, and admire your building skills.
I had been looking at a ULF (ultra light footy) around the same weight, but aiming for 50% or greater ballast… i can see it’s going to be a challenge.
I was looking for a Ldr, similar to a IOM, or better…

I’d also been tinkering with ideas of unballasted( ok, maybe the min ballast to allow self righting) catamerans, or Scows…

A couple of pics attached.

Nathan, how went no 2?

Regards
Scott

12

A quazi update.

I’ve been hard at work with another hobby, although one that will eventually give back to the footy so my apologies for the absent updates. (I’ll update on that when I’m a bit further along)

#2 of the ELF was much quicker than the #1, however I ran into some watertight integrity issues. Obtaining UHU-Por in the U.S. is not the easiest of tasks so I had been using Beacon Foam-Tac. ELF 1 used up my first bottle so ordered up some more, but apparently they have changed the formula, and butt joining the seams is no longer waterproof… frustrating.

I’ve started another production of the second design using 1/64" balsa but the holidays and other commitments have gotten in the way.

However at the end of November I held a very informal footy event on Thanksgiving day. To date I’ve built quite a few Red TYDE’s for my family and close friends, and used the holiday as an excuse to put them all in the water for a couple of brief but VERY cold and extremely windy races. Since I did not want to be the winner of the event, (since I’ve built everybody else’s boat) I decided to sail the leaky ELF 2 design. In 20-25 kts the boats were all over powered regardless of total weight. But going upwind in these extreme conditions the ELF 2 held its own against the Red Tyde and even went on to win one of the races. Unfortunately the water got to the electronics before the end of the series so my plan held true and I did not win the day.

Hopefully the balsa version will be as light as the depron ones, and I can explore this a bit further, if everything pans out I will be campaigning a 250g boat come springtime.

-Nathan

13

Cheeers for the update Nathan :slight_smile:
Glad to hear number 2 was faster…
I’m also quite impressed by your red tyde designs. :slight_smile:

I’ve not quite managed to keep balsa as light as Depron. A single skin glass hulll can be (if yur good enough)

I look forward to hearing yur results for this year,

14

I said I would update about what I have going on in my “design” house.

For Christmas I was given the parts to a 3D Printer and have spent the first few months this year assembling and calibrating it. While I think I will never be fully done with the calibration I have it close enough for now, that I can start using it for things Footy.

After some deliberation I have decided to re-visit my ELF concept/project. There were a couple of things about the ELF that bothered me while sailing and I think with a slightly more concentrated approach, more reasonable results can be taken from the idea. The original ELF was conceived in one afternoon, (Thursday) drawn in the computer the next morning, and the hull was assembled while I was on a conference call that afternoon (Friday). I hacked apart a rotor blade from a helicopter for the keel and stole a rudder from an early Red TYDE and was sailing on Sunday afternoon. Needless to say the Boat was rushed to the water.

As a result of this hastiness I always had the impression the keel was “tripping” the boat with excessive drag. I suspect this is due to the relatively “fat” sections that Helicopter blades use to delay the onset of stall. This with a narrow chord on the keel, the potential was never fully reached. ( the boat would go sideways until it got enough speed to develop lift.)

When considering what I would do differently I’m initially brought back to the design numbers. Due to the expedited nature of the design process, I didn’t fully realize my target numbers for LCB and Prismatic Coefficient. I think that the misplacement of these two factors caused the boat to excessively lift the transom while going forward effectively shortening the waterline. I also felt like I was giving up too much righting moment by going double diagonal in the box with such a light boat. As a result of this and my new printer I’ve started back down the path of a new light boats series.

All the boats will utilize the same keel shape in both plan and section. The boats will also feature the same rudder design including tubercles to aid in heavy air/wind turning. My plan is to print a mold for the keel blade in two halves and then laminate two layers of 10g/m Eglass with 1 layer of unidirectional carbon fiber per side. I will then bond the two halves together. My expectation is for a stiff keel blade of less than 15g. For the rudder I plan on printing the blade in halves in ABS plastic using the rudder post as the alignment for bonding. My weight estimate for the rudder blade is 8g.

For the Hulls I plan on using Vacuum formed Polystyrene. I have had very good success with this method at creating light reasonably robust boats. I plan to print the mold for vac forming. I don’t think I will get the same longevity as my wooden mold for the Red TYDE. but I am not looking into making this a production boat. The better part about printing a mold is my time spent physically carving/shaping is most likely reduced to about an hour. Due to the volume capacity of my print bed I will have to print the molds in two halves (bow and stern) and then join them and do final smoothing with sand paper.

I’ll keep you posted as my work progresses. For now here’s the profile shot of the first design in the series.

15

Hi Nathan
Thanks for the latest update.
I’m rather curious about ‘tubercles’ as I’m afraid I’ve never heard of this term before. Please could you explain what they are and how they work?
Anything which can ‘aid in heavy air/wind turning’ sound like it could be a good idea.
Thanks in advance
Phil

16

Phil,

Tubercles are an idea stolen from nature, specifically humpback whales. The basic principal is that they channel flow across a foil reducing it’s tendency to stall. When applied to a rudder it allows the rudder to use larger turning angles (angles of attack) without stalling, meaning you can jam the stick over and get the boat to whip through a tack or gybe. One would think there is a high drag penalty for having a bumpy leading edge, but you can make the rudder smaller in section and chord for equal control.

Here is an article i found that gives some detail about tubercles http://www.asknature.org/strategy/3f2fb504a0cd000eae85d5dcc4915dd4#.Uyb9hfZsjyc

On the 3D printed rudder side. I made one this weekend for a total weight of 4.4g it worked very well on a Red TYDE in 5-12kts of wind. I’ll have pictures soon.

-Nathan

17

Hello Nathan,

Just to explain the concept…Of course, I think you knew this thesis.

https://dspace.mit.edu/bitstream/handle/1721.1/42917/245535660.pdf?sequence=1

Apparently it works on Rambler!!! But, it is also true with a Reynolds number about 20 000/25 000 (see p 52 fig 3-12)…

Jean-François Bessière
French registrar

18

Jean-Francois,

Thanks for the link! From what I understand (after talking with Rambler’s sail maker) they will have the first test of the rudders tomorrow. I know they work on a footy… it will be interesting to see if these stay on R88.

-Nathan Titcomb

19

Hi Nathan,

Looking at this photo, , two questions : Why tubercules only at the extremity of the rudder? and why not on the fin keel?
Have you got some informations about the first test of the R88’ rudder?

See you soon

Jean-François Bessière

20

Hello Jean-Francois,

I can’t attest to the full reasons here, I am just a boat designer, not a hydrodynamics expert! From what I understand, the reason not to have Tubercles on the keel or dagger boards is due to the fact that they almost never operate in the conditions where Tubercles become beneficial. Tubercles work best where there is a very large angle of attack relative to the flow of the fluid. Dagger boards and Keels most often operate in the 2-10* angle. Only when the boat has really messed up would they be useful, otherwise you do pay a slight drag penalty.

For the location of the Tubercles on R88, I suspect that currently Juan-K and his team might be the only people who know the answer. For my Footy Rudder and the other examples I have seen from Paul Bieker on his Rip Tide series of boats, the tubercles have been on the upper portions of the blades. In my mind this placement at the top is more likely to help prevent ventilation (suction of air down the leading edge) of the foil.

Perhaps Juan is thinking that the tubercles at the bottom of the blades will help establish flow sooner as the rudder re-enters the water coming off a heel. Therefore the boat will have more control going into a tack/gybe. But with much of what Juan does, we really don’t know what he’s up to. Other than to be always different.

Happy holidays!

-Nathan