Why do mainsails have booms

[valhalla360]

Originally Posted by Djarraluda

Different rigs are available, some without a boom, but the Bermuda. Rig was developed and is more efficient.
Alternatives do include those with a loose footed main, see the Drascombe range of small open boats, right up to the 100 foot plus of the Thames Barge, which has a Spritsail rig. Spritsails on the big boats fuel up to the Sprit, and a 120ft boat was sailed by one man,, a boy and a dog. I have also seen an old gaffer without a boom, but no ideas if that was the original design.
In modern boats, most adopt the Bermudian rig which typically includes a boom, simply for the simplicity and performance combined.
Roger

The modern Sloop Rig/Bermuda Rig is more efficient UP WIND.

Downwind or beam reach there are other more efficient sail options.

Bermuda Rigs became something of the standard on pleasure boats because a large percentage of pleasure sailboats were used for racing and about the same time period as pleasure sailboats became common, materials that could accommodate the high forces generated by a Sloop Rig became available.

In short round the cans type races, a boat that can go up wind faster will usually win out because off the wind, once you hit hull speed, there was little to gain from a more efficient sail plan during a race. Even if in light winds and not hitting hull speed, the non-up wind legs often involved no tacking, so they tend to be of shorter duration again resulting in the up wind leg being a primary driver of who wins. The downsides could often be addressed in racing by large crews and close attention while flying huge spinnakers.

Early cruisers simply used boats that were available and that was often a Sloop Rigged boat.

Retrofitting an existing boat can be challenging but if I were having a boat designed from the ground up for cruising, I would seriously look into alternative rigs. while you don't want to sacrifice all windward ability, there are other sail plans that can be better for a cruising application. The biggest issue being you will have to become knowledgeable about the chosen sail plan as you can't rely on riggers and sail-makers to understand the needs of unusual rigs.

[seamaiden]

Love that!

Can't count the numerous times we've had to shout at someone: Watch your head!"

Originally Posted by vpbarkley

Yes, but a more important question, where did the name boom come from.

The answer: it's actually BOOM, the sound when it smacks you in the head.

Sorry, somebody had to say it.

[PuttingDoctor]

My staysail ketch has a boom but a loose foot main. I am able to get better shape out of the main I believe with this setup.
The outhaul / clew slides on a track mounted car. Couple this with the vertical external furler and you have infinite adjustment of the main.

[WantTo]

In 2003, (before I knew her) my wife bought a John Marples cabin sib trimaran with a boomless main. She and a friend sailed it from Baltimore around Cape Hatteras to SW Florida, then later from Florida to Mexico and back. The boat did not seem to suffer due to a lack of boom. Reefing was accomplished with rows of ties above the foot of the sail that were tied off to shorten the sail (like they all used to be).

[Montanan]

Reference: Boomless Sailing - MySailing.com.au

Alan Lucas explains why he designed a boomless boat, and how to rig one.

Soleares is an unconventional ketch, her mizzen and mainsail being radical in their lack of booms.

As for a conventional mainsail, when squared away its boom holds it out to the wind, making it an easily set and vital downwind force. To wantonly eliminate it was a tough decision to make but our commitment to adding a dedicated downwind rig made it practicable to fill its space with a mizzen staysail and main trysail, neither of which need booms and both are easy and quick to drop in a rising wind. Because a main trysail’s windage is up high in less troubled air it is more powerful than a mainsail for a given area and in light airs it can be replaced by a four-sided sail known as a ‘Fisherman’.

The main trysail is free setting, its single sheet passing through a block at the mizzen top and cleating off on deck below.

There are twin dihedral-angled foresails with their clews angled about 20 degrees forward of the luffs forming a gull wing effect that provides which provide excellent downwind balance and natural self steering influences which mitigate broaching.

[valhalla360]

Originally Posted by PuttingDoctor

My staysail ketch has a boom but a loose foot main. I am able to get better shape out of the main I believe with this setup.
The outhaul / clew slides on a track mounted car. Couple this with the vertical external furler and you have infinite adjustment of the main.

That looks like a great cruising rig as it makes sail handling very easy.

I'm sure racing sailors though are cringing at the idea that it's an ideal sail plan for performance.

The difference:
- Racers are willing to put in almost unlimited effort into managing the sails, so they are willing to deal with less convenient in an effort to squeeze out a tiny bit of additional performance.
- Cruisers will often accept less than ideal if it will take a lot of effort to squeeze the last bit of performance. For a cruiser, an easy to manipulate sail plan can be a performance booster as those tweeks take less effort, so they will actually make them.

Example: we would often run under genny alone if conditions were marginal or we only saw a couple of miles before we would have to furl the sails (say crossing a small bay on the ICW between narrow channels). Why? It took 10-15 seconds to deploy or furl the genny and it was done from the cockpit by 1 person. The mainsail, took both of us, 1 at the helm and 1 going up top to get the cover off the mainsail, then hoisting it, all with a reverse process to take it down...often it just wasn't worth the hassle, so we wouldn't.

It looks like your mainsail is basically a roller furler mounted behind the mast, so I assume you can deploy and furl the mainsail similarly in a few seconds. If we had that, we would probably use the mainsail more often.

[john manning]

I was taught that having a boom helps you flatten the main when you want to sail upwind. I have never been able to get that to work well. Possibly due to the cut of my mainsail.

Not all yachts have mainsail booms. Some have foresail booms.

[DefinitelyMe]

This is the Spirit of Bermuda, our local tallship. The rig was developed from the 17th century and this particular vessel is based on a Royal Naval ship that was depicted in a painting from 1831. At the time these were probably the fastest vessels in the world as well as the most weatherly sailing vessels. HMS Pickle, almost identical to the Spirit of Bermuda, famously took the news of Nelson's victory at the Battle of Trafalgar back to Britain.

This rig, the Bermuda rig, is what the vast majority of modern yacht rigs are based upon. Note that the foresail and mainsail are both loose-footed. Only the mizzen has a boom, and the reason for that is that, as others have said, the sheeting of the mizzen would otherwise be impossible while still maintaining sail area (which is important for us here in the summers, when the Bermuda-Acores high dominates).

She is fast. Much faster than the schooners of the Eastern Seaboard of the US and Canada which generally all have boomed sails. However, whereas those schooners are all based on (or are actually) old trading schooners which were designed to carry as much cargo as possible with a minimum crew, the Spirit of Bermuda is based upon an RN sloop of war, so it's hard to say whether the performance is due to sail configuration, hull shape or something else entirely. I'd have loved to have seen a race between her and the old Bluenose.