How to build a UnaRig

I should be very grateful to receive some guidance on how to go about building a UnaRig (hope that’s the correct term).
I have learned that small dia carbon tubes linked with a wire torsion bar forms the main frame and mast stub, but exactly what sizes are recommended and what method is used to fix all the parts together?
I’ve been building swing rigs for my RG65’s and was thinking the swing rig may be the way to go with my Footy (hull nearing completion). However, my recent visit to this forum and the Footy web site indicates UnaRigs seem to be most prevalent on racing Footys. Is this correct?
Thanks in advance for your advice

I’m interested in this, too. The boats with the UnaRig were way faster than the other rigs at the regatta at the WoodenBoat Show last summer. was a long thread dealing with one type of una rig, which is especially popular on footies.

This adress may suggest some new trends on sailing Rigs.

My Delta Rig discussed in the ‘new classes’ is one interpretation.


As Claudio’s reference above points out, the term ‘una rig’ covers a wide variety of sail plans - basically anything that has one mast and one sail. A better term might be ‘McCormack Rig’ (or ‘McRig’ for short) in honor of Brett McCormack who popularized it for use with Footys.

The difference is that on the McRigs, the mast is 30 or so percent of the boom length back from the tack. This makes the boats handle better downwind and takes some of the load off the sheet upwind so a smaller servo can be used. Contact me separately and I’ll bore you silly about the effects of ultra low Reynolds Numbers as they apply to Footys and why they are more efficient than swing rigs.

The best reference would be to contact the AMYA ( and get a copy of issue 152 (the Footy issue) of Model Yachting. In the meantime, check out “Huntington Footys” on the PHOTO section of the Yahoo Footy site for shots of the rigs that finished 1,2, and 3 at the Region 1 Regionals as well as 1 and 3 at the Nationals and did so well at the Wooden Boat Show at Mystic.

And while you’re there, download the 507 Una rig pdf - its the only published plan of how to make a McCormack, albeit an old-rules B rig.

To ScottS: Please present your exposition of the effects of low Reynolds numbers on Footy rigs in this Forum—I am sure that there are quite a number of us who are both interested and are always seeking further enlightenment. I have been doing some design work on non-diving Footy hulls, but would be more than pleased to see anything you can contribute to the rig portion of Footy design and practice.

We have been meaning to make a post on the Aspect Ratio thread for sometime but just haven’t had time. So this is just the quick details of our current medium rig not a discussion about the rationale behind its design. We hope that this helps making your rig. We’re not sure if it will scale to a RG65. The sail has 5% camber at the top a bottom and 8% in the middle. There is 25% twist. Cut out the panels and stick them together with double sided tape. We use a luff pocket but from the pics on the forum many of the top boats seem to just use loops on the luff to the mast.

Peter & Clare

It may be of any help ?


Thank you, all contributors to this thread for the very helpful advice provided and I now realise this thread should have been titled:

‘HOW TO BUILD A McRIG’, giving due credit to Brett

My McRig questions have been answered and I simply need to go and experiment. However, one of Brett’s comments is now making me ask a slightly ‘off thread’, but very much related question:


Thanks in advance, again !

Hi Phil,

in principle the Fin is positioned under the Center of Buoyancy CB .
Imagine a vertical line starting from the CB, the Geometrical Center of the Fin and the Center of Gravity of the Bulb are sitting on the same line.
In practice the CG of the bulb may assume a slightly different position dictated by the need to keep the LWL horrizontal to the water plan. Much depends on the construction and on the various RC elements, servos and battery location and Rig.
This variation can be in the order of 5 to 10mm.

Hope this sketch is making clear how to proceed :

Personally, I position the Fin as such that the maximum thickness correspond to the vertical line passing trough the CB, therefore is fixed few mm backward.


Thanks for the very clear explanation of placing the fin in relation to the CB
Sorry to keep asking questions but…
In the case of a boat with a designed waterline which is part way up the transom, do you think the fin should be positioned even further aft than the CB?

Phil I have not understood your question !

I have read that some (fast) footys are designed to sail with their transom dragging below the surface (your diagram in post number 11 shows a waterline just at the bottom of the transom and so the transom would not drag in the water). There is an example of this concept on the one page overview of Papaya III in the plans section of the Footy web site.
I assume that once a submerged transom hull is moving forward with sufficient speed the water flows straight from the underside of the hull, releasing before having a chance of ‘curling’ back up on to the transom.
My question was asking if the ‘submerged transom’ type hull simply requires the fin to be positioned further aft than the hulls CB? I’m guessing this must be the case.

Hi Phil
I’m sorry again since I have no answers to your question, really I do not know if the Fin should be recessed backward and why . Footy is not my cup of tea.


Within limits, and for a Footy at least, the important feature is to position the Centre of Effort ( CoE ) of the sail in the correct position relative to the Centre of Lateral Resistance ( CoLR ) of all the underwater components - that means the hull canoe body, the fin and the rudder.

Now the aero and hydrodynamic experts will tell you that these points can move about when your boat is underway, which is true, BUT as a rule of thumb, I have established that my Footys work reasonably well if I set the plain geometric CoE of the sail to be about 30 mm forward of the geometric CoLR of the underwater bits.

The sail can be assessed using a spreadsheet if you are clever or by cutting-out a sail shape from thin card and hanging it from its corners. The underwater bits can be done in a similar manner if you have reasonably accurate drawings. If not then just put the complete hull assembly in a tank of water and very carefully poke it sideways with something pointy - like a pencil - and establish the position at which the hull moves bodily sideways without any tendency to rotate. Take your time with this, and check and check again.

Flavio’s explanation about the position of the fin relative to the Centre of Buoyancy is correct - you really don’t want to be messing about with batteries to correct the waterline. Try dunking the whole assembly – batteries, servos and Rx included - in a water tank with the bulb weight taped in place to check things before finally gluing the bulb to the fin.

The best idea is to get as close as you can theoretically. You can give yourself the best chance of success by fitting 2 or 3 mast positions around 10 mm apart or even fitting a different size or position of rudder. The mast positions allow you to shift the sail CoE about. Likewise a bigger rudder will move the hull CoLR rearwards. If all else fails you will have to cut or enlarge the Leech of the sail to move the sail CoE.



Great! This is a very clear and practical explanation of what I need to do.
Pushing the hull sideways with a ‘pointy thing’ is the ‘way to go’.
Thanks for all the advice in this (and other) thread(s) everyone. My questions have been answered.