Backstay

In Chapter 6 we discussed how a sail designer adds curve to the luff of the mainsail to match the curve of the mast. He anticipates the amount of bend and designs the sail accordingly. If you are able to bend the mast more than the anticipated amount, the luff of the sail is pulled forward and the fabric stretches to accommodate the bend. This pulls shape from the rest of the sail and effectively flattens the chord of the mainsail. Conversely, if the mast has less bend than anticipated, the excess luff curve is thrust into the body of the sail adding depth to the sail. The amount of bend in the mast is controlled by the amount of tension you apply to the backstay. As stated earlier, on small boats like dinghies, the mast can be bent simply by tightening the mainsheet. But on keelboats you should have an adjustable backstay since the spar sections are much beefier and beyond the capability of the mainsheet to control.

In the past you may have noticed short, vertical marks along the luffs of some racing mainsails and wondered what they were. In fact, these are used to estimate the amount of bend in the mast. By sighting from the gooseneck and looking up the sail, you will be able to see how much the mast has bent by noting where the marks lie relative to an imaginary line running between the tack and head of the sail. If you know the distance between marks, you will know how much bend there is in the mast and you can use this knowledge as a reference for trimming the main at some other time.

Today, most large boats have a hydraulic ram at the base of the backstay that can be used to shorten its length. Some cruising boats have a threaded mechanical backstay adjuster similar to a mechanical boom vang, while small and medium-sized racing boats rely on a block-and-tackle purchase. Whatever the case, shortening the backstay pulls the top of the mast aft, forcing it to bend. As the mast bends, the luff of the sail is pulled forward and shape is removed from the sail.

Manual Backstay Adjuster Manual
This mechanical vang works well for tensioning the backstay, but it's slow and cumbersome and best left to cruisers.
Backstay Adjuster
The hand-drawn gauge attached to this hydraulic backstay adjuster gives the sail trimmer quick and easy reference points.

Swept back spreaders on Brad Van Liew's Open 60 Tommy Hilfiger Freedom America add lots of stability to the mast, but restrict the amount it can be bent.

Swept back spreaders on Brad Van Liew's Open 60 Tommy Hilfiger Freedom America add lots of stability to the mast, but restrict the amount it can be bent.

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How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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Responses

  • aaron
    What is the backstay used for on a boat?
    6 months ago

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