Footy 'Smoothy'

The following is an introduction from Thomas Grimm, President of the IFCA.
“The small Footy Class boats are united in the IFCA (International Footy Class Association). Important international regattas, such as the Footy Gold Cup, have taken place. Many other RC sailing events were organized in the individual member countries. Unfortunately, the number of activities in the RC class has decreased due to Corona and the aging membership. There are currently larger footy events in France, Poland and the Czech Republic. Our contribution to a new, easy-to-print footy boat is intended to help create new activities for joint RC classes.

The Smoothy has undergone 14 years of development. In 2010 the boat was launched under the name Conrad in Salem Schlosssee/Germany. Sven-Hinrich Klatt made the first drawings. I then built the boat using the usual construction methods according to the IFCA rules. After being revised, it took part in international RC regatta events such as the Footy Gold Cup in Italy and Germany/Salem under the name Orca. Building the Orca was a very lengthy job, with the construction of a negative mold, the lamination of the hull with carbon fiber and the gluing of the individual boat parts. That's why I thought that with 3D printing, even beginners would have success in assembling a footy. In Neville Green I found a good designer who knew boat sailing and especially construction. An excellent collaboration has developed. The result is now available in the form of the STL files for printing the Smoothy V3."

The design was implemented and refined in Onshape and I suggest you either view or make a copy of the design (https://cad.onshape.com/documents/098e2a1634b8e18a8c2051c4/w/81a98fb05449d34ce5819cee/e/55b9feaaee7fbc54ce9089d3?renderMode=0&uiState=6616e21494a551415eeebf92). Use Ctrl+Right Mouse to pan and Alt+Right Mouse to rotate. The design starts in the left tab (Smoothy) and advances through each tab. ‘Smooth++’ adds the hatch, rudder, foil and bulb. Finally, the tab ‘To Print’ collects all the model parts for export as STL’s. Builders will find that details, in particular locations/dimensions will be useful for assembly and the servo’s, bearing types and other parts are identified in Onshape.

Significant effort has been made to ensure that the ‘center of buoyancy’ and ‘center of mass’ are vertically aligned and that the ‘center of effort’ of the sails is correctly aligned with the hull/foil/rudder but time will tell if this is correct.

To date the model has been printed, assembled and had first sail. No doubt there will be some modifications, but it is a good starting point for anyone who wants to build, and I will update as necessary based on sailing experience and feedback.

Vase mode printing is one option for rc sailboats, but it brings with it several build problems which this technique avoids. The STL’s provided for the hull have a hull thickness of approximately 0.48mm and incorporate all the major elements e.g. provision for rudder, foil, mast and hull joint. Good 3D printer settings are important - see my comment containing printing tips for single wall hull prints. Choose a light colour for the hull to avoid overheating and distortion in sunlight. (PLEASE PUT ANY SETTING TIPS THAT YOU HAVE IN COMMENTS)

The center line ribs assist with stiffening the hull but can also result in surface flaws. In this case the ribs are spaced 0.15mm away from the hull surface. This makes the slicer, in each layer, complete the hull in one loop before printing the ribs and the gap is small enough that the hull and ribs merge into one.

The 'Hull Back' is printed with the transom on the bed and the 'Hull Front' with the center join on the bed.

I have tried to avoid the need for supports however the 'MainSheet Brace' needs support and smaller items benefit from a brim and slower speeds.

There are options for orientation when printing the ‘Rudder’ and ‘Foil’. One way is to split the STL’s vertically and print with the split face on the bed.

I opted to print the 'Rudder' vertically. However, this is relatively unstable and to help a support leg has been included in the STL. This can be easily removed after printing. Or alternatively use 'Tree Supports'.

The foil was printed diagonally on the bed and with the sharp trailing edge on the bed. This required good bed adhesion and assistance from a substantial brim. This orientation will benefit greatly from 'Tree Supports' and I suggest 3 on either side. This orientation results in a particularly good surface finish.

The 'Hatch Jigs' are used to temporarily clamp the 'Hatch Frame' to the 'Hull Back' while the glue cures. The hatch should be a snap fit to the frame/hull, if necessary, file the lip on the hatch to achieve a good snap fit.

The mainsheet arrangement is shown in the Onshape tab ‘Main Servo’. The ‘Mainsheet Block Support’ and 'Mainsheet Start Block' are fixed together with 2 2mm screws and glue. The line starts at the 'Mainsheet Start Block'. It next goes around the servo block and then another block, mounted on a projection (‘Mainsheet Block Support’) from the keel housing, before exiting the hull next to the mast hole. Ensure that the ‘Mainsheet Block Support’/'Mainsheet Start Block' assembly is an easy fit to the 'Hull Front'. One word of caution – to prevent damage, the mainsheet servo movement should be limited to +/-30% and the servo arm removed before powering up. After the correct position for the servo arm is established the final range of movement can be set, +/- 55% is suggested.

The small (MR52) bearing at the base of the mast (deep inside the hull) is 2mm ID and somehow needs to attach to the 5mm OD/3mm ID carbon fiber mast. I opted to glue a small length of 2mm carbon rod into the mast, however a possibly better solution is to glue a small length of 3mm carbon rod into the mast and then grind it down to 2mm.

STL’s for a bulb which is suitable for lead shot are included. Every attempt has been made to make this the correct size/weight but that is something that only sailing time will confirm. More experienced builders may opt to cast a suitable lead bulb instead of using lead shot.

The sail dimensions can be extracted from the Onshape tab ‘Rig’ and STL’s for the battens and sail corner reinforcement are included. As far as I can ascertain the swept back luff spar allows a flat sheet (50 micron Mylar or similar) to give a reasonably good sail shape, and sail curve induced in the foot is all that is necessary. Luff and foot tension can be adjusted with M3 screws. Allow 50mm for the wrap around the luff spar and use double sided tape to secure. Glue the head and luff/foot patches to the sail and tie off. The foot dimension needs to be 5 to 10mm larger than expected to allow for the foot curve. Other sail sizes could be adopted for different wind conditions, but the presented size is a good starting point.

Everything else is more or less, straight forward. There have been many printing iterations to arrive at the STL’s provided and consequently assembly should be relatively easy. If you decide to build, good luck.

PS - for something bigger look at https://www.thingiverse.com/thing:6719866

19/4/24 Block changed to 3 part design (plus V623ZZ bearing) to make printing easier. 0.2mm first layer and 0.1mm thereafter. Lubricate V623ZZ bearing, add 2 'Block New' to either side and temporarily fix with M3 screw. Then superglue 'Block Ring' to assembly.

29/4/24 'Mainsheet Start Block' added. this attaches to the 'Mainsheet Block Support' with 2 2mm screws and glue. 'Mainsheet Block Support, 'Hull Front' and 'TPU Bow Cap' updated.

18/05/2024 Onshape Stand tab modified to allow for different 'Dowel' diameters and clearance. I used 9mm dia wooden dowels which can be sharpened to better grip the ground. Alternatively a 'Foot' is included in Onshape which allows for a 4mm diamater stake. To use these features export the STL's from Onshape.

20/05/2024 First sail today in approx. 6knt of wind. Pleased to report that she seems well balanced and sails upwind and downwind with very little rudder correction. Seemed fast but difficult to judge.

15/06/2025 Some builders are printing the hatch in TPU and that appears to be a good idea. It may be necessary to experiment with small changes in the X and Y scaling (+2% has been suggested) however I found the no scale change works quite well.

20/06/2025 Flattened sail stl added to the end of stl list

22/06/2025 For a first class assembly video look at https://www.youtube.com/watch?v=g_R2IQhyy18&t=3801s.
However note that the 'Positioner' is intended to be hand held in the rear hull while the servo mount is glued in place.
Also fleet race video - https://www.youtube.com/watch?v=DF96ShrthGA&t=427s

24/06/2025 Hatch 'Remover' stl added. This helps to lever off the hatch.

29/06/2025 Flattened sail stl rotated dwg and pdf options added. The 'Rig-flattened 5sheets.pdf' is a full size pdf ready for printing.