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There are a few basic types of mainsheets used on sailing dinghies. In this article, I will be comparing three different types.
1. Blocks Mounted Amidships
The mainsheet system seen below is the most basic type. A system with a 3:1 or 4:1 mechanical advantage is fitted on the boom and cockpit near where the skipper would be sitting when sailing close hauled.
Advantages
The amidships system is simple to rig, and does not require any special hardware. It is also easy to maneuver around when tacking or gybing. The mainsheet is very unlikely to catch on the transom of the boat, or around the tiller.
Disadvantages
The amidships system is limited to a mechanical advantage of 4:1 with most ball-bearing blocks. Using any more blocks leads to excessive friction, which makes the mainsheet more difficult to control. The amidships system pulls more downward than inward when sheeted in tight, causing the system act as a boom vang which is undesirable.
2. Blocks Mounted Amidships with Raised Hoop
The mainsheet system seen below is the same as the basic system seen above. One set of blocks is placed on a raised hoop mounted over the centreboard trunk.
Advantages
This system shares all of the advantages of the previous amidships system. The raised hoop corrects the problem of the mainsheet acting as a boom vang when the boom is sheeted in most of the way to the boat's centreline. The hoop also acts as a good handle when the boat has capsized.
Disadvantages
The hoop itself adds weight, and it can be difficult to create a strong mounting point to the boat. The hoop is under a great deal of stress in high winds, which could cause it to tear out if not mounted properly. The system still cannot realistically have a mechanical advantage greater than 4:1.
3. Aft-Mounted Blocks with Bridle
The mainsheet system seen below has blocks mounted at the aft end of the boom. The lower block is attached to a bridle which connects to the buoyancy tanks or gunwales on each side of the hull. There is a single block mounted on the boom, near where the block system would be on amidships mainsheet systems. The sheet typically passes through a single block mounted on the centreboard trunk or floor. On some dinghies which have wings, the mainsheet may pass directly from the boom to the skipper's hand.
Advantages
Since the blocks are mounted at the aft end of the boom instead of halfway along its length, the overall mechanical advantage is doubled when compared to amidships systems that have the same number of blocks. For this reason, it is possible to rig a 3:1 (or even 2:1) mechanical advantage, which will have less friction than a 4:1 system. This means that an aft mainsheet will be the easiest to control as it has the least resistance.
Disadvantages
It is possible for the mainsheet to hook around the rudder or on the edges of the transom with this configuration. The likelihood of it fouling can be reduced by mounting the bridle one foot forward of the transom instead of at the very aft end of the boat, and by preventing it from becoming too slack while sailing.
In the event that the mainsheet fouls at the aft end of the boat, the tiller extension can be used to free it without having to move aft in the boat to do it by hand. The technique can be seen in the figure below.
The sheet must be very long in order to allow the mainsail to be eased out fully. When the sail is sheeted inboard, there can be a long length of extra line interfering with other controls in the cockpit, or the skipper's legs.
The horizontal section of the sheet which connects the blocks on the boom can dangle when the sheet is slack. During a sudden gybe in high winds or a slow tack in low winds, the dangling line can interfere with the skipper when he is passing under the boom. It is possible, (though unlikely) for the slack section to interfere with the skipper's neck.
Travellers
It is common to rig a traveller with the mainsheet. On an amidships mainsheet, they are used to adjust the angle that the sheet pulls on the sail.
If the traveller is moved toward the windward side of the boat, the main sail can be sheeted far inboard without sheeting the boom downward.
If the traveller is moved toward the leeward side of the boat, the boom will be pulled downward when the sheet is pulled. With the fitment of a good boom vang, this functionality is not needed.
Amidships travellers are often very difficult to move around. They are also made of metal in most cases, which makes them painful to bump into.
Aft travellers are used for the same purpose as amidships travellers, and work in the same manner. They are difficult to adjust as they are usually mounted along the upper edge of the transom, which also has the effect of making climbs over the transom painful when recovering from a capsize.
Ratcheting Blocks
A ratcheting block can significantly reduce the amount of work that the skipper has to do to keep the sail trimmed. On long sailing trips or regattas, this can be a considerable advantage.
Conclusion
It is the opinion of the author that the ideal mainsheet is the aft-mounted type with a ratcheting block and no traveller. The low friction allows for easy control, and the drawbacks from slack lines can be avoided with good sailing technique. Without a traveller, a good boom vang must be fitted which can bear the upward load of the boom on its own while still being adjustable.
