Maintaining Forestay Tension
An inherent problem of a fractional rig is its inability to exert as much tension on the forestay as a similar masthead rig. The reason for this is because the attachment point of the forestay is not directly opposite to the backstay. Under certain conditions, the moment arm that results from these offset attachment points can be used to advantage, as this is an effective method of inducing bend in the mast, which in turn flattens the mainsail. If the distance between the attachment points is too great, a mast of average stiffness will be unable to apply optimum forestay tension, unless one of the following mast-stiffening design features is used:
- Jumper Stays—These additional stays and their associated jumper struts limit the amount that the upper portion of the mast can bend, and thereby enable tension to be effectively transferred from the backstay to the forestay. Jumper stays were common in the first part of the 20th century. Their biggest disadvantage is weight and windage aloft.
- Running Backstays—These are supplemental temporary backstays (one on each side) that attach opposite of the forestay. They are very effective at generating forestay tension, but make the boat more difficult to tack because one running backstay needs to be released and the other one applied each time the boat tacks.
- Swept back spreaders—Swept back spreaders (or rather their associated shrouds, which attach to the deck significantly aft of the mast) provide significant fore-and-aft support to the mast, and thereby increase tension in the forestay. The biggest disadvantage of this scheme is that it makes it difficult to deliberately slacken the forestay for the purpose of making the jib fuller in light winds.
Read more about this topic: Fractional Rig
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