Footy design – Freeship

I will do a series of posts about Footy design using Freeship. The Footy is a very nice boat very cheap and I think that it is a good class to diffuse the RC sailboat.

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One of the problems to design a Footy is choose a total length because, as by rule, it has to fit inside a parallelepiped 301.5 x 153 x 301.5 mm in length, width and height respectively.

Pool Shark 3D in box for measuring – Photo by Chris Staiger

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The diagonal of the box is 457 mm and the horizontal surface  diagonal is 341 mm.

The difficulty is that we need accommodate the keel and rudder in the box.

We know that the longer the waterline length greater the speed of the boat. As a curiosity we check what is the maximum speed possible for two Footy , one with length 305 mm and one with 457 mm

Vmax = ((0.305 / 0.3048) ^ 1 / 2) * 1.34 = 1, 34 knot

Vmax = ((0.457 / 0.3048) ^ 1 / 2) * 1.34 = 1.64 knot

about 22% higher.

However the geometry of a footy with a length of waterline 0.457 m or 457 mm would be interesting, I would say almost impossible and I do not know if it would be very effective because it would have a bow and a stern extremely thin and the bow inclined to aft.

Another problem would be the space and position available for the rudder, see the figure above, to the length of the Pool Shark increase, the rudder would have reduced its height and its width increased or have to move forward, reducing its efficiency.

The keel would have the same problem, would be lower and wider, signifying lost of efficiency, while here, we had an aggravating factor, the bulb would be closer to the hull and the boat would lose the ability to carry a good sail area.

The height of the keel including the bulb from the bottom of the boat, in the Pool Shark, is 17 cm and the rudder has height 11 cm, the width of the keel is 4.2 cm and the width of the rudder is 3.1 cm.

Measurements of Pool Shark, AMYA champion 2010:

Loa = 385 mm (total length)

Lwl = 350 mm (length waterline)

Beam = 115 mm  (maximum)

Displacement = 600 g

Height of the bow above the waterline = 60 mm

The Pool Shark 3D has great maneuverability, is very stable and can withstand quite a strong wind.

When I started the Carcara, my first Footy design, I had take the data from internet  and displacement is a key project data, I would say is the most important data, I work with a displacement of 400 g. When I received the Pool Shark 3D saw that the weight was with 600g.

Being the size of  Carcara practically equal to the Pool Shark 3D I saw that I would have to increase the displacement and the mold was finish.

The solution was to increase the depth of the Carcara about 1 cm and I increased the freeboard by 1 cm (height of the hull above the waterline). For the stern would not get immersed I moved the CG (Center Gravity) of the boat forward.

The Carcara has measures:

Loa = 38o mm

Lwl = 360 mm

Beam = 90 mm

Displacement = 600 g

Height of the bow above the waterline = 40 mm

The Carcara have a performance similar to the Pool Shark 3D and in lighter winds I noticed a better performance of Carcara, principally in windward.

I am thinking that in Footy class the expertise of each sailor (since the boat is balanced) will determine the result of the race, regardless of the boat, because the littles differences in velocity between boats.

From my point of view, at least for now, the important thing is the choice of displacement and sail area capacity, this, according to the weight of the bulb.

As in RG 65 the weight of the bulb is critical, the Pool Shark 3D has a 300 g bulb.

The experience with the Pool Shark 3D and Carcara say me that the Footy weight must be around 600 g with a maximum sail area around 1000 cm2, and in lighter air a few more.

The Carcara weights spreadsheet :

Carcará spreadsheet weights
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About Fred Schmidt

Engenheiro Naval interessado em projeto de veleiros radio-controlados. Naval Architect interested in RC sailboats design
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4 Responses to Footy design – Freeship

  1. Heya i’m for the primary time here. I found this board
    and I to find It really useful & it helped me out a
    lot. I hope to provide something back and aid others like you helped me.

  2. Fred Schmidt says:

    Hi Wayne,
    great your blog , I will link it on my Portuguese blog.
    About the weights:
    The problem is as you say – sailing conditions. My region have winds some strong and, I am thinking in increase the sail servo but in light airs I think that we can have more light sail servo.
    Really we can have a more light batteries. This 100g batteries is a four NiMH AA, but if we use four AAA we can have a better weight.
    I do not have much experience with Footy or other RC sailboat, this is my second Footy design and I can not evaluate immediately the influence in stability diminishing 100g in the bulb though we can calculate. This is a good line to investigate.]
    Thanks by the comment and I invite others peoples to comment.
    Cheers
    Fred

  3. Wayne says:

    Your weights seem to be high especially given the directions Brett and Angus were pursuing…
    One consideration that is immediately implementable is the budget for radio gear.
    The servos weights are debatable but 5 gm for rudder and 12-15 for sail servo would be achievable depending on whether a balanced rig and sailing conditions.
    Receiver and batteries should not exceed 20gm and half that is now achievable.
    This has an effect on the bulb weight, dropping 100gms should have no adverse effect on stability.

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