Barry Hayes of UK Sailmakers Ireland (in conjunction with Jenny Howells of the RORC Rating Office) explains the main difference between a flying Jib and an IRC flying headsail
The main difference between a flying Jib and an IRC flying headsail is the flying Jib is non-overlapping and measures in as a headsail (Headsail Area HSA). The flying headsail (flying sail area FSA) is a small, flat and overlapping code zero which is a new sail type in IRC.
The flying headsail is a code zero development and has very little to do with a headsail as it's measured as a spinnaker/genoa. As big boats and double handed boats developed their offshore sails over the past few years, particularly now that there are more foiling boats, a hybrid sail was developed with the code zero as the starting point. The new sail measures somewhere between a code zero and a genoa. This sail didn't fit in any rating rule and was rated as a headsail if under 75% mid girth so was heavily penalised. IRC now has moved to include it in their measurement rule. So boats can use the sail offshore and have it rated.
You can see from the above photo the size of the sail in basic area.
The flying headsail is flatter than a code zero, more or less the shape of an overlapping genoa 1. The sail has a positive roach and the luff also projects forward a little off the straight line, but the clew is below the boom level. When you're reaching, you can ease the boom down without it running into the flying headsail sheet. It's normally sheeted behind the keel, but not on the stern of the boat. Normally, the best spot is next to the genoa winch. It must be tacked forward of the forestay and it's always a top-down furling sail as you need to furl the roach away and get a tight furl. It's also normally left on the bowsprit furled up so it need a clew strop and Velcro clew patch to keep it furled.
The measurement rule for the sail is complex. This adds a lot of new measurements to the IRC rule. Below you can see the different measurements needed to calculate the area of the sail. You need to measure it both as a genoa to determine area and as a spinnaker to determine the mid girth ratio, under the rule so the measurements are clear to IRC and they will know how the sail is set. Notably, the sail is set forward of the forestay, it's overlapping the rig, and has between 62.5 and 74.9% mid girth.
Headsails and Flying Headsails
21.7.1 Headsail area (HSA & FSA) shall be calculated from:
- HSA = 0.0625*HLU*(4*HLP + 6*HHW + 3*HTW + 2*HUW + 0.09)
- FSA = 0.0625*FLU*(4*FLP + 6*FHW + 3*FTW + 2*FUW + 0.09)
The sail is mainly used between 65 and 125 degrees AWA, so it doesn't go upwind or downwind. It is mainly used for reaching. Moreover, it's excellent on foiling boats with reaching struts or whisker poles who can sheet the sail outboard away from the mainsail. This really opens the slot between the main and the flying headsail. As the boat speed increases, this sail just gets faster and faster as your AWA comes forward. Like a blast reaching genoa in old money.
For most IRC racing boats, this sail is a considerable rating hit and would not give you bang for your buck. The points increase would not be worth it. If you're foiling, sail in a lot of apparent wind or have reaching struts, however, then this sail is worth it as it overlaps the rig and is only slightly smaller than your code zero. So, for boats like Fast 40s and Open 40s, it's an excellent option because they can get their AWA forward quickly and build on that with this sail.
For most IRC boats the flying jib (non-overlapping) is still the best option as it's the same size as your headsail and can be flown off the bowsprit. It's still "free" on IRC and can give you an extra knot plus upwind or reaching. The flying jib is still the way to go for most IRC boats being flat, easy to furl and you can leave it on the bowsprit.
In this photo, you can see the shape difference in the three sails: flying jib, flying headsail, and code zero. You also can see how flat the flying headsail is compared to the code zero. This flat sail would not give most IRC cruiser racers the power needed working upwind in light air which the code zero totally does. Also, the same applies to the flying Jib. It's a lot flatter and doesn't overpower the boat upwind over 10 kts., allowing you to sail at high angles.
Flying headsail Shape shot
In conclusion, if you're racing ISORA or in the bay, stick with your IRC flying Jib and code zero. But if you're a fast or foiling boat, or perhaps doing a long offshore race including a lot of reaching, the flying headsail is probably worth the money!
IRC rules 2021 and related advice is here
