Construction techniques/ballast ratio

The thing that got me thinking about Angus and Moonshadow the other day was that I was building a new hull which seemed pretty light and I was wondering how it compared to Moonshadow.

Brett’s careful construction of Moonshadow resulted in a lightweight hull with a ballast ratio around 65%. That’s not all that challenging if building a 500-600 gram boat…but it is a significant challenge when building to 350 grams or less. Brett set a high bar for Footy building that I don’t think has been beaten since.

One of the reasons for not equaling Brett’s performance is the difficulty of construction, using such lightweight glass laminations, etc. Not many Footy builders have the experience, skill, and patience with layups to match it. The thing that struck me when building my latest boat, though, is that…while not consciously trying to match Moonshadow…I’ve refined my “kitchen table” building over the last couple of years to the point where my boats come reasonably close to Brett’s mark. And there’s nothing exotic or difficult involved. Of course, I have the advantage of using 3 AAA batteries, where Brett was restricted to 4 AA’s back then.

The last boat I made for the 2012 season was 350 grams ready-to-sail, with a 210 gram bulb. That’s a 60% ballast ratio. The boat I’m building now is looking a little better, and should come in at 62-63%.

Construction is 1/64 ply for the hull panels, 1/16 balsa for the deck, 1/8 basswood for the foils. The fin has a carbon strip down the center to add stiffness, the rudder shaft is 1/8 carbon tube, and the bulb is attached to the fin using 1/8 carbon tube. The hulls are made using my tape-and-glue technique that someone called an “air build.” There are no internal reinforcements. The result is a very strong boat with no worries about unexpected collisions :slight_smile:

Is anyone else out there building 350 gram boats with better ballast ratios? What techniques are you using? Please share with us.


Hi Bill,

…“building 350 gram boats with better ballast ratios?”…

Your question suggest me another one : “What for, any rationale behind ?”


Because they sail very well, Claudio.

While there is no evidence that a particular displacement will ever dominate the class, there is plenty of evidence that the light ones are competitive. Moonshadow won the 2009 Euro Grand Prix. I got to see it really well, since my boat was mostly 6 feet behind it! My 350g boat placed second in last year’s Northeast Region Championship in the USA. Scott Wallis has campaigned a depron Ranger very well in the UK for the last year.

It’s just a personal preference, but I also like the look of a lightweight. The light displacement permits a relatively skinny hull, allowing a design that looks more like a racing boat. When built with a ballast ratio comparable to larger classes, I think it handles more like one, too.

Some have suggested that the success of Roger’s ICE means the heavier boats are best. I think their success is more likely because there are several of them sailing in most UK regattas and they have been given to some very, very good skippers.

Many of us hoped that we’d see a meeting of Moonshadow, skippered by Graham Elliot, vs ICE, skippered by Roger Stollery. That would have been really interesting and might have told us a lot…but unfortunately it never happened.

In 2009, Angus and Brett felt the light boat was the future for the class, and Moonshadow showed that they were certainly on a viable track. When I last visited Angus before he passed, though, we were talking about doing a mega-footy together to test against the lightweights. That idea died with with him, though. Angus was thinking that a really heavy boat could carry incredible gobs of sail and, therefore beat everyone. While I think it would have been fun to try, my counter argument was that ultimately all Footys go the same hull speed…the difference is how they accelerate, decelerate, and handle. I suggested that a light boat with a smaller sail would get to hull speed as quickly as a heavy boat with a larger sail…and that’s why I think we won’t see a particular displacement dominate the class.


Those weights are easily achievable, and I am happy to say, without any effort at all!
My entry level kids’ Footy is no where near a race beater as that is not the design goal, but accidentally the construction materials do point to where a cheap and fast Footy could go.
My skinny, 90mm, all plastic, kid proof Bottle Footy weighs exactly that, 350gm with a 200 gm bulb and maximum length wooden heli blade foil. 66gm hull without appendages. That shows that a vacuum formed PET hull with far less freeboard and minimal internal structure and modern radio gear can be easily made and kitted cheaply. It is strong, yet compressible and needs no finishing. Thin wood is however, breakable hence over building for water loads.
Another key element in weight that you may have overlooked is the battery. 3 x AAA is too heavy for racing. All my recreational Footys run on a single (1s) LiIon battery weighing less than 20gms! These are a little safer than soft packed LiPo but for racing a sub 10gm battery is cheap and has plenty of power for a few races.
I wonder what a completed polystyrene vacuum formed hull Footy weighs? Brett’s solid polystyrene mass produceable hull should be similarly light? And much better than the instantly sinkable Caribbean I sailed recently advertized as a 10 inch "Footy’! (Call Joysway, Brett!).
Claudio, I hope you vacuum form a plastic hull over that beautiful Esteral wooden mold and make a sub 350gm version with a lighter balanced Unarig.

Very nice all that Bill,
but aside the thumbs, I did not recall mentioning the wind force that should play a large role with low and high displacement, without forgetting the CE height and hull shadow shapes and fin length as well the wave dept !
In general, a light displacement boat tend to accelerated more rapidly then an heavy one, but it will decelerate also more rapidly. This of course is due the the reciprocal inertia.
So light boats are good up the few knots of wind and cease to be performing when the wind start raising.
Not rare to see expert competitors to make two racing boats with them with different design parameters and decide which one to use as function of the expected winds/wave conditions.
Being not a specialist of Footy, I will be happy to hears more about to become more familiar with this kind of models !

Thanks for joining in, guys…we haven’t had a good design discussion here for a while.

Rusty, I should have been clearer…I’m using 3 AAA lithium non-rechargeable batteries in a plastic Radio Shack holder. Total is 30 grams and it lasts for multiple regattas…not just a few races. I’m pretty satisfied with that. Though I know there’s an opportunity to shave some weight there, I like the convenience. My total electronics package is 60 grams.

Claudio, of course I agree that light boats decelerate faster…which contributes to my point about why I don’t think any particular displacement will dominate the class…I think the acceleration advantage of the light boat is, as you suggest, offset by the deceleration advantage of the heavy boat. In other words, it’s a wash. If that is true, then we need to look to other handling characteristics to gain advantage.

I wonder though, why do you think light boats are at a disadvantage in heavy air? If you are talking about them being more tender, that is why I think the ballast ratio can be important…your heavier Estero with about a 50% ballast ratio may not stand up better than my lightweight with a 60% ratio. Even if it does, I can reduce rig size and probably perform just as well, because I only need enough sail to get up to hull speed.


Brett, if you are still keeping an eye on things Footy…what do you think you could achieve in construction these days, given the smaller, lighter electronics that are readily available?

Would you still go for the lightweight? 250 grams? 70% ballast ratio?

p.s. The water is awfully hard up here…your end looks better :slight_smile:


Hi Bill,
This sketch to explain my point :

My imagination with a too light boat :

1: the Footy size compared with waves is like to meet a big storm for a normal boat.
2 : I never measured the wind at 30cm from the water level, but I’m expecting a sort of irregular and “pulsating” force to cope with the wavelet forms.
3 : I do not expect problems with low winds, the light Footy may still presenting a contrasting body with the relative light bulb and the pressure still transmitted to the Fin to produce a moving acceleration.
4 : With strong winds >8kt , the wavelet get bigger and the “small mass” of a Footy may be an handicap , the boat may be drifted with the help of the waves slopes and probably putting the mast horizontal to the water plan since the bulb is sufficiently small to counteract.

In general the bulb ratio to be efficient should be higher then 50%, far better if 70% since a taller sail plan will be permitted to search for efficiency. Only my Class M go over 72%
My design average is around 63/65% and I take care about the CE height when drawing a Sail Plan. In parallel I try to avoid to much long fin to avoid wet area particularly disturbing when running.

For what I could understand about Footy = to Zero, I would personally stay around 500g and 260g in the bulb or more if possible.

Just a funny story, when I applied for the Guinness record in 2007 with my MiniFreccia 152mm long with 2RC ch. and 72g.
The first trial was in a pool and the wind that day was blowing strongly trough the trees and was very irregular with gusts over 15/18kt. Some time the Minifreccia was literally lifted up from water and displaced some 50/60cm further away !
May be this is the reason why I’m reluctant to make small boats too light…


BWB the halfpinttoo is 33 grams with some flashing and the deck is 13…

Nice drawing, Claudio…it amazes me how quickly you can put together such nice diagrams.

Still, I’m not sure I understand why a heavy boat has advantage over a light boat in this situation. It would seem to me that if the righting moment is the same for both boats, then they should react in basically the same way.

I would think that a 350g boat with a 65% ballast ratio would stand up better than a 500g boat with a 50% ballast ratio (a common Footy build) assuming they are both sensibly rigged for the conditions.

Can anyone help me with this…I feel like I must be missing something basic :frowning:


Hi Bill,
for me, unless I’m wrong, is the total mass and consequential low inertia that count, a light object can be “pushed away” more easily when floating in a fluid, under wind force.
I do not know if all that can be calculated with righting and heeling moments since the total mass is not part of the formula and probably the calculations errors can be rather high in percentage for this type of object.
I suppose that this model size is navigating most of the time under “gale force”, since wind and water cannot be scaled down. My sketch above was trying to suggest that ! It become more dramatic with size reduction.
Now, if what I try to express is wrong, then “mea culpa” and apologizes for .

No apologies needed, Claudio…you are expressing your good opinions and doing it well.

Still, I was hoping someone might have more real experience, rather than theory. I’ve sailed both heavy and light Footys in a variety of conditions, and haven’t seen anything definitive in actual results. Your discussion got me thinking back to the first time I went to the UK for the first Euro GP in 2008. I had a fairly heavy Footy…my original Cobra. The first day we had very strong, gusty wind…and I did rather poorly. I wasn’t used to that kind of conditions in my racing here in the US…though that’s changed since then. Sunday dawned to calm, light air, and I was in my element. My boat was dominant that day. The opposite of what you might expect.

I sometimes think that the conventional wisdom in model sailing is a lot of speculation handed down long enough to be accepted as truth :slight_smile: In the absence of better data, I’m inclined to think that the boats that win do so based on the skill of their skippers, rather than any particular design advantage…but that’s just an opinion, too.

Although I’ve been playing with Footys for some time, I often feel like what I don’t know could fill a book…if only I knew what to write!

Keep working in this class…new ideas are good ideas.


Hi Bill
another story that occurred in France and probably somewhere else in the years 90. At that time I was new to RC models and pushed by a friend after stopping my activity with real boat racing with a Dragon. Before I was cruising with an heavy cutter Rival 38’, a little bit slow with low wind but perfect above 20kt. Was designed and made in UK of course. Thank to that quality we managed to save our life when crossing the Channel with force 8 and tide going against the wind direction. Waves up to 5/6 meters, sorry but this is another story …
Back to what I was intending to says: Class M . At that time was a general rush to make a class M as light as possible since in the hand of a famous sailor was a winner most of the times. Of course !! peoples were saying, is very light, this is the real winner boat !!! someone managed to make a class M for 3.95Kg and winning a championship. The hull was almost untouchable with the fear to produce a damage.
At the end of the 90’ the “light fashion” begin to turn toward heavier Class M after the success of an heavier boat.
Today successful Class M are around 4.3/4.4kg and above. Although penalized with low winds they become very efficient above 8kt. This is why often the “rich” skippers have two boats, one light ~4.0Kg and a prismatic below 0.55 and shorter fin and one above 4.5kg with prismatic of 0.59/0.60 and longer fin. My Class M are of the type “all-round” with ~4.35kg and prismatic of 0.57/0.58 and 48cm long fin.

With the AC120 models the story is just at the opposite, since supposed to be derived from the real ones, the model weight should be about 3.50Kg, but the Rules call for a minimum of 4.5kg. Of course an AC120 with 4.0kg would be better performing, after all the real ones would be proportionally much heavier but is not the case. This to says that there is a possible comparison with real world.
Unfortunately with smaller models this comparison cease to exist among the fact that is still difficult to construct very light boat. New electronics and battery technology offer better choice while expensive too.
In real world light structural boats are made aiming to achieve ‘planning’ conditions. This is t(he case of VOR type that are excellent within a certain wind angle only.
Our small models will practically never reach planning conditions since they never reach twice their ‘critical speed’.
Sorry for this long blah blah, I will consult nevertheless, one of my friend architect asking to bring more arguments on the subject.

The best ballast ratio I’ve managed to achieve is in the region of 65%, with my 3mm Depron ‘air build’ Box III as sailed in Sestriere. The water was very flat throughout the regatta, even when the wind was blowing it’s strongest and I felt the boat performed well. However, when sailing elsewhere on only slightly rougher water I felt they the boat was being pitched around too much by the wavelets or wind blown chop. Since such a high proportion of the total weigh is positioned so far below the hull, I think the whole thing was pivoting around the lead, rather like the reverse of a pendulum. I’m speculating that if anyone managed to achieve a ballast ratio of significantly greater than 65%, then the boat would be inclined to pivot about the lead even more.
It seemed to me that a slightly heavier hull may be less lightly to get knocked about so much. So here’s the question - does anyone know if there is a ballast ratio, above which performance may be expected deteriorate in choppy conditions?

Very interesting guys…I’d like to hear the naval architect point of view, as well as others’ observations while sailing. Flavio? Others?


Hi Bill,
My friend Eric Spongberg confirm what already written : light boat for light weather.

This is one of the paragraphs of his answer concerning the actual argument :


So, you are right in that very light boats will work only in very light wind. As the wind goes up, the boat heels more and so loses power and increases drag. A boat that heels less, even though it may be heavier, will always sail faster than a boat that heels more.

Even though the boat is heavier, because it is standing up straighter to the wind, it will be faster.

Another way to look at it is this: Suppose you take the argument to the ‘extreme’ - suppose the boat is as light as a paper cup, and the wind is as strong as a hurricane, what is going to happen? A paper cup in a hurricane is going to blow away, but a heavy ceramic mug is not going to blow away quite so hard or so fast.


What else I can says ? So far the form of the hull is not yet considered, but of course, with the same displacement, a Wide hull will exhibit a complete different behavior compared with a Narrow one and particularly with wavelets, i.e. by analogy the fisher cork …
A wide hull will tend to head up to the wind much more then a narrow one.
Wet area at low speed will induce more frictional resistance.
Pointing toward light hull and bulb high ratio, as an achievable technical performance, will produce only a light weather boat.
I think at this point I have completed my remarks and nothing more to add.


Thanks, Claudio.

I certainly understand the point that the boat that heels less will have the advantage.

What I still don’t understand is the assumption that a heavy boat will stand up better than a light boat. I always thought that was a function of leverage, not displacement.

If both the boats had the same ballast ratio, and both boats had the same sail area and aspect ratio, then I would easily agree with the argument that has been made.

But what if the heavy boat has a lower ballast ratio and a bigger sail (both typical in Footys) than the light boat? I can’t understand how that would not make a difference. If the fin on your Footy were only 2 inches deep, it would not stand up in heavy air regardless of its 500g displacement unless you put a really small sail on it.

I do get the point about the cup in the hurricane…everything has practical limits. I guess I’ll just build a couple more light ones and see where I think those limits are.

We got a bit off topic here. Anyone else want to contribute ideas on lightweight construction?


Dear Bill,

I am very happy to see on this forum, once again, an interesting debate about footy design.
Your thread opening has been in a pure " Angus fashion ".

I am the only modeller in the world that has been able to take part to all footy international championships without winning a single race.
A very skilled loser :wink:

I have taken advantage of my lowest ranking position looking at your cobra stern and doing my best to understand and explain what I have witnessed.
Lat but not least I have used my own purpose made softwares to carry out extensive hydrodinamic and hydrostatic analysis.
In almost all cases I have been able to match theory and real world experience.

One of the best lesson I learned from my professor of ship’s hydrodinamic was : if predicted ship’s speed doesn’t agree with real measured performances please remember that, most probaly, your calculation are wrong and the ship is right - not the opposite -
Unfortunately in many case this very common sense approach has been forgotten.

More about light vs heavy, and other naval architecture black holes, on my next posts


ps : My own “almost reproduction” Folletto has been able to achieve a remarkable 65% ballast ratio too

Flavio, I’m glad this stirred you up :slight_smile:

That was a real teaser you posted! I can’t wait to hear more…particularly about your performance software and what it tells us about Footys.

And while I may have won a few races in the 2 Euro GPs I attended, I would give up the wins for the opportunity to attend them all.

All the best…Bill

Hi Bill,
while waiting Flavio additional info, I just adds the following that I forgot to write down in my previous post.

This is putting in relations two boats of different displacement and introducing the scale factor.

Two boats of the same length 300mm:

Boat A = Dspl 500g - bulb 260g - sail area 1000cm² Original Design

Scaled down to 350g we get the following issue:

Boat B = Dspl 350g - bulb 182g - sail area 490cm² Reduced Weight/Displacement

To be a valid comparison, of course, the fin length shall be proportioned too.

The question is : are the 490cm² of sail producing the same boat speed and performance against wind forces ?

This do not account for the fact that the boat A has 240g for the construction while for the boat B there are only 168g available and do not account for various drags coming in from various items as well from the lower CE height.