I thought others might find it interesting to know what off-line information this question generated.

One very accomplished sailor and boat designer gave the following:

Theoretically, because of their beam, which allows wide travellers, multihulls don't need booms.

Not having them saves weight and cost.

As I found racing a 30 foot catamaran in big winds and seas, reefing a boomless sail can be a b...itch. You have to go almost head to wind and then try to cling to a wildly flogging mainsail leach while you transfer the mainsheet blocks to the reef clew. If the boat is going up and down in big waves, it gets even more challenging.

In some catamaran designs we use the boom as a compression strut that allows us to hook an extra tackle to the 'dead' end of the mainsheet, increasing mainsheet power.

We use a standard 7:1 Harken mainsheet system. Instead of dead ending the mainsheet to a becket on the upper block, we run it through a cheek block on the side of the boom, near the back. Once the dead end is turned, we attach it to a 2:1 or 3:1 tackle that runs along side the boom. The control end of the smaller tackle is lead to a 'head knocker' cleat on the bottom of the boom, near the middle. This allows us to use the 7:1 in light air and at mark roundings; while using the additional purchase of the smaller tackle for heavy air and fine tuning. This ability to have a 14:1 mainsheet on one catamaran and a 21:1 purchase on a different catamaran are the only reasons that we kept the booms when we modified our boats. Actually, on boat, the other reason is to hold the mainsheet far enough aft to make room for a bimini top.

It makes also makes trimming the mainsail a hell of a lot easier to do!


Another source provided the following:


What has been discovered about sailing, with and without a boom, is not surprising to any of us: -
• Without the boom, the mainsail can be eased instantly and safely regardless of the angle of heel;
• Without the boom there is less clutter in the boat;
• Without the boom, sheeting tension is high (as is the case with a jib or staysail which is set boomless);
• Without a boom, the mainsail can be brailed-up, clearing the interior of the boat instantly, and providing a short-term furling arrangement;
• Without the boom, selection of the geometrically-correct sheeting point is critical and inflexible, but fine control of sail camber on-the-wind is simple and seamless.

On the other hand,
• With the boom, sheeting point is not critical, and sheeting loads are reduced;
• With the boom, short tacking can take place with the sheet cleated, much reducing workload when short-handed;
• With the boom it is far easier to maintain sail shape when the sheets are eased – particularly if a boom-vang, wishbone, or sprit-boom is fitted.

Now, having said all that, I have to admit that it is more convenient to use the rig with the boom attached, especially in benign conditions, and I recommend a boom for general use. But when in the big stuff, the boomless mainsail set-up is safer. It is great to have a rig which can be used with or without a boom, and the change over is almost instant.

Sail Twist

In his article, Michael Storer points out that one of the great advantages of using some sort of vanging device (boom-vang, sprit-boom, balanced lug with downhaul etc) is that it reduces sail twist. This is a very good point, but there are certain conditions under which 20 or 30 degrees of twist in the sail is beneficial to windward performance. This is normally in very light winds, which is also the time when it is most easy to keep things under control without resorting to expensive and highly-stressed rigging components!

In the case of the spritsail, we have been using a very simple and cheap piece of gear which has allowed us to keep sail twist under good control – even when using the rig in a boomless configuration. The device is a vang leading to the peak of the sprit, and it cost around fifty cents. The sprit vang is not highly loaded, and we made ours from a piece of 3mm (1/8in) Venetian blind cord. Normally we run it through a small fairlead on the rudder head and cleat it in a V-jamber on the tiller. It does not need to be handled from tack to tack.