Submitted on August 4, 2003 by John Hector

Question: Could you please let me know the performance reduction of a jib positioned 6 inches behind a furled genoa?

Answer: Hi John, the first thing you need to consider is that the two headstays need to be positioned far enough away from each other so that the forward sail is not in contact with the inner stay. If your forward stay sags aft and the sail rubs on the inner stay, it will make furling the sail much more difficult. Six inches sounds pretty close. Most cruising boats rigs are not tight enough to keep the headstay sag under 6", and you need to consider that the thickness of the roller furled sail will take up some of that space.

Headstay sag has a big effect on your boat's efficiency when sailing to windward. Less headstay sag results in tighter tacking angles. You can reduce headstay sag for better performance by tightening your standing rigging and specifically by tightening the backstay. However, when you place two headstays very close to each other, the backstay tension is transferred partly to the lazy stay, which stretches less than the loaded stay. The loaded stay can not be brought up as tightly as it would be in the absence of the second stay, so the loaded stay sags more. Some ocean racing boats designed for shorthanded sailing have two stays very close together, with both stays terminating on adjustable hydraulic rams at the deck end. The ram on the stay in use is tightened, and more importantly, the ram on the lazy stay is eased so that the backstay or cap shroud tension is transferred to the stay in use.

The final consideration is that a roller furled sail is very bulky. It will definitely have a negative impact on air flow around a sail set very close behind it. The greater the separation, the less of an effect the disturbed air will have.

If you want to quantify the effects of a close second stay in terms of headstay tension and air flow disturbance you would need to hire a marine engineer or a very good sail designer to build a graphical model of your boat. Practically, the decision for locating a second stay will come down to the structure under your deck (the stay will need to be anchored to a structural bulkhead or hull frame member, either directly or through a tie rod) and the possibilities for locating a lug and halyard sheave in the mast.

Regards,
Dan Neri

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