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Hoops v StropsRichard Battey gets in a tangle with mainsheet systems - Autumn 2003 |
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There has been so much talk about mainsheet hoops and strops recently for one reason or another that I thought it might be worth looking at the topic of mainsheet systems as a whole. The first point to be made is that the selection of mainsheet system is partly dependant upon the selection of kicking strap system, whether the boat is fitted with lowers or a strut, and whether the mast is stiff or soft. Both kicker and mainsheet play a role in controlling the leach tension of the main, and in bending the mast, and it is the balance between the two that dictates to an extent the options available to you. Sounds complicated? Not really. Pulling on the kicker thrusts the boom forward while simultaneously tightening the leech of the mainsail. The more powerful the kicker, the more the boom thrusts forward, and as it does so, the more it bends the mast low down. The mainsheet controls the leech of the main much more directly, and because it acts more perpendicular to the boom, it can pull the leech down quite tightly without bending the mast low down, but will bend the top mast if pulled hard enough. If you have a soft mast and no lowers or strut, the bend induced by a powerful kicker will be excessive and unwanted. In this case, a less powerful kicker, with a more powerful mainsheet will be wanted, to help achieve leech tension (required for power and pointing) without producing excessive low down bend. Where you have a stiffer mast and or lowers/strut, the forward thrust of the boom from the kicker will either be less pronounced or more effectively countered, in which case, a more powerful kicker can be used, which in turn means a less powerful mainsheet is needed. The other consideration will be whether your Rocket ship has a raking rig, or an older style �Barn Door� rig. For a modern style raking rig, with very narrow sheeting angles, boom on the centreline upwind is king! With the older style of rig, with wider sheeting angles, this is less crucial, although still desirable. At least as important is to maintain control of the leech when the mainsheet is eased for a gust � the boom will instantly rise with the tension off, and the upper leech will open. It is vital to be able to pull it back down again quickly, requiring some power in the sheeting system.  Having justified the kicker/ mainsheet equation and decided whether it is the powerful kicker, or the powerful mainsheet that it required, we can look at the options available. These are:
 Arrows show the traveller cleat is nowhere near handle you pull! Firstly, the main advantages of the hoop are that it is extremely simple apart from the moving parts that have to be fiddled with after each tack � and by raising the lower mainsheet block closer to the boom, it enables the boom to be brought close to the centreline. It is the desire for a close sheeting angle that has led to the development of sheeting systems; the most recent being the track traveller on the square hoop, the disadvantages with this system are that it is fiddly having to manually pull the car to windward after each tack to get the boom on the centreline. You can get the leeward side to uncleat automatically, but , it is a lot of hardware meaning extra weight and potential for failures. For the hoop to be totally effective it has to be tall and must be matched to a powerful kicker and lowers/strut. If it is a low hoop it is impossible to get the boom close to the centreline, which defeats the object. Centre Strops � Fig 4. A lower tech option where the kicker is powerful enough is the using of a rope or wire strop, either side of the thwart or across the transom as shown in figure 1. On my Merlin I used to use a square top hoop but have now been persuaded to change to strops and found that the system had two important advantages � simplicity and cheapness. Also it is extremely light which may provide a route for some overweight boats to shed a few kg�s. Although the strop arrangement looks as though it doesn�t afford much purchase, in fact I have found no difficulty at all in handling the mainsheet. The important factor, similar to the hoop, is getting the mainsheets strops the right height. Too low, and all you are doing when you pull the main in is duplicating the kicker. Too high, and when the mainsheet is block-to-block, the boom is not over the centre line but off to leeward. It is also important to remember that when the mast rake is altered, the strops will also have to be altered, simple guide, the lower the pin on the shroud purchase the lower the strops have to be and vice versa. This is the same when talking about the kicker; no kicker (light winds) then the strops needs to be long, whereas lots of kicker (strong winds) the strops need to be shorter. I would say with my level of sailing that I have two rake settings at most only, so therefore I need only two strop setting�s. There are two common ways of threading the mainsheet through the blocks with a hoop and strop system. Figure 3A is the better method because on a reach the helmsman can work the sheet really effectively by grabbing the aft part off the boom, cutting out a lot of the purchase to give pull/leverage to pump and promote planing on gusts or waves. Split Sheet Aft to Centre - Fig 1. The very early Merlin�s, when kickers were a lot less powerful than they are today, used a stern mainsheet system with a brass horse across the transom which produced purchase directly to the leech. This was an idea common to many classes in the early 60�s but has long since gone out of fashion. The more modern alternative is to use adjustable length strops or split mainsheets. The split sheet aft to centre system is by far the simplest and provides the trimming ability of the traveller. The mainsheet splits for the last metre and a half to form the strops for an aft mainsheet, that is run along the boom to a centre take-off point. The strop length needs to be carefully set up initially, but provided that when the mast is at it�s most upright the two parts of the sheet enter the boom block it will still work as you rake. The key to it is that when the split part of the sheet/strop run into the boom, it must be centred � by necessity of being pulled under equal tension from the two corners of the boat. Any further tension on the sheet simply loads the leech up directly. If extra purchase is required, one could use a similar system to that of laser�s and laser II�s. This has the disadvantage of needing a very long mainsheet and in light airs downwind it might tend to drop into the water. This is shown in figure 2.By using the sheet and vang/kicking strap together you will achieve any trim that a traveller can, and still tack the boat without having to adjust anything. The system is also simple only requiring a standard centre jammer in the middle of the boat. The disadvantages are threefold, firstly in the amount of rope you need. This makes it difficult to trim in quickly when two-sail reaching, ducking another boat or rounding marks. Secondly, where used on a wide boat, there can be fun and games when getting the tiller extension through space between the transom and centre parts of the system. It can either encourage excessive use of the rudder when tacking, or encourage the use of a shorter tiller extension, which limits the ability to hike sufficiently when windy, or to get weight forward and down when light weather. The final problem is gybing as the slack mainsheet is inclined to trap itself under the gunwale at the transom, round the tiller, round the helmsman etc providing potential problems in a blow! When it comes to responding to gusts, particularly upwind, the primary difference between the traditional sheeting system and the modern ones is the extent to which mainsail leech tension can be maintained. With a low power kicker, as soon as mainsheet tension is eased, the top of the leech twists open, spilling drive out of the top of the sail, and requiring manual effort to pull the leech closed again. With a high power kicker system, and a high take off point (ie strop or hoop), easing the mainsheet just adjusts the angle of attack of the sail, while holding the leech tension hard on. Restoring the boom to the centreline after the gust has hit requires a less powerful mainsheet system, making it easier to carry out the manoeuvre quickly and efficiently. The secret to the whole control of the leech scenario is really down the vang/kicking strap system, which will be covered in the next edition. In summary if I were fitting out a new Merlin now I would definitely opt for the strop in lieu of the hoop purely for simplicity and ease of use, however if all else were even I think I would use a hoop just because it is such a useful thing to hang on to in times of crisis! |