Why do mainsails have booms

[JayBee74]

To further clarify the thought behind the question, I realize that headsails I assume generally don't have a boom because you wouldn't be able to tack/gybe it past the the mast, but if you can run a headsail without a boom then why have a boom on the main?

To whit, I'm new to this sailing stuff, trying to learn all I can. Any book recommendations on where I can learn about different types of rigging and how/when to employ them?

thanks

[Adelie]

Easier to control the shape.
Also a lot of early boats didn't have backstays and the boom overhung the stern resulting in significantly greater area. Might be a holdover from an earlier era.

[NPCampbell]

I'm not an experienced sailor but I'll take a stab at it. With a boom, you can maintain the lateral tension on the foot of the sail even if the sail is extended past the sides of the boat. Without a boom, you can only maintain the shape of the foot of the mainsail if your mainsheet extends aft at 45 degrees or so. This means your mainsail can't extend aft as far and can't be flown outside the hulls while still maintaining the shape of the foot.

[Cheechako]

Shape control without tracks and fairleads running into the cockpit, or on a structure over the cockpit all over. And a mainsail has the reefing aspect to the problem also. You would have to have a lot of fairlead block positions, fore, aft, sides etc for a boomless main.

[Sailor647]

Because they do.

Try not to over-think this stuff. There have been hundreds of thousands, if not millions of people who have come before you in the sailing life. Try to trust in their experience and invention and know that if there was a better way, it might have been thought of and executed by now.

But do keep in mind that amazing inventions and innovation are happening every day by people in the racing and yachting communities.

Keep leaning. You'll love this life!

[wingssail]

Originally Posted by JayBee74

To further clarify the thought behind the question, I realize that headsails I assume generally don't have a boom because you wouldn't be able to tack/gybe it past the the mast, but if you can run a headsail without a boom then why have a boom on the main?

To whit, I'm new to this sailing stuff, trying to learn all I can. Any book recommendations on where I can learn about different types of rigging and how/when to employ them?

thanks

To answer your question directly, no, you actually CANNOT, in certain common situations, run a headsail without a boom either. Upwind or reaching, yes, it works. And on those points of sail it could work for a boom-less mainsail too if the sheeting point was in the right position (high enough and far enough aft).

When going downwind however, without a boom, the clew a headsail will usually come in close the the side of the vessel rather than stay outstretched leaving very little projected area. This is the reason people use whisker poles or spinnaker poles to hold out genoas. Yes, there are times when one can get a headsail to hold an outstretched shape, in a wing on wing configuration, but it is a hard line to sail for most boats.

It would be worse for mainsails since there is really no place where a mainsail can be sheeted such that it could fly, going downwind, without a boom. It would just collapse.

This is why true downwind sailing, either with a genoa or a spinnaker, usually requires a pole of some sort and why mainsails require a boom.

Using a sail such as with a asymmetrical spinnaker or a genoa, without a pole, you usually must reach up and increase the flow of wind over the sail to keep it filled. Some people drop the mainsail to encourage more wind on the headsail and help keep it full but very little power is generated this way.

With a boom, either on the headsail or the mainsail, you have more control over the shape of the sail; you can pull the clew out or ease it to control the depth, you can move it up or down to control the twist, and you can pull it back or ease it forward to precisely control the angle of the sail to the wind, and you are able to keep it projected before the wind and developing power.

[Cheechako]

Originally Posted by JayBee74

To further clarify the thought behind the question, I realize that headsails I assume generally don't have a boom because you wouldn't be able to tack/gybe it past the the mast, but if you can run a headsail without a boom then why have a boom on the main?

To whit, I'm new to this sailing stuff, trying to learn all I can. Any book recommendations on where I can learn about different types of rigging and how/when to employ them?

thanks

Because of the layout. A headsail is positioned such that you can use it with limited array of fairlead positions. (track on deck)
If you have two masts on your boat, then you could have a mainsail that is more like a headsail and have no boom. "Staysail Schooner".

Come to think of it:
You could make a mainsail that is more like a storm trysail shape I suppose and get it to work, but you would loose a lot of drive, or have a lot of clutter in the cockpit. You need to be able to pull the mainsail up near midships beating. Maybe a big traveler across the cockpit and a reef design such that the fairled position always stays in the same location? There are old boat designs that have a loose footed sail, but they dont sail like modern boats. Down wind they are fine though. Gentlemen motor to weather anyway!

[Adelie]

Originally Posted by Sailor647

Because they do.

Try not to over-think this stuff. There have been hundreds of thousands, if not millions of people who have come before you in the sailing life. Try to trust in their experience and invention and know that if there was a better way, it might have been thought of and executed by now.

But do keep in mind that amazing inventions and innovation are happening every day by people in the racing and yachting communities.

Keep leaning. You'll love this life!

You tell the OP to keep learning but at the beginning of your post you tell them not to overthink it.

Many catamarans go without booms on the main but they have a lot more beam than a typical monohull and the ones that use boomless mains tend to be faster so the apparent wind doesn't tend to go as far forward on a deep reach that with the wide beams means it works fine.

[barnakiel]

Well.


Some jibs have booms.


AND


Some mains have no booms.


When a boom makes sense, we have one. When we are better off without one, we do not have one.


Typical triangular main sail in a typical narrow boat would be hard to contain sailing downwind, without a boom.


b.

[wholybee]

A boom is much better at controlling shape. Once the shape is correct, you trim with the traveler, and the shape of the main will stay the same. However, if you turn and need to trim or ease the jib for the new point of sail not only does the angle of the jib change, but the shape changes. If you are on a reach and want to ease the jib, but also keep it flat, that is very difficult to do. On the main, just drop the traveler.

[markpierce]

My motorboat has no booms for its sails.

[thomm225]

Originally Posted by JayBee74

To further clarify the thought behind the question, I realize that headsails I assume generally don't have a boom because you wouldn't be able to tack/gybe it past the the mast, but if you can run a headsail without a boom then why have a boom on the main?

To whit, I'm new to this sailing stuff, trying to learn all I can. Any book recommendations on where I can learn about different types of rigging and how/when to employ them?

thanks

Like has been said, you can control the shape of the mainsail much better with a boom.

I actually had a boomless Beach Cat that I raced. (bought new in 1996) I loved it going upwind but never could get the mainsail adjusted right for downwind

The boat was a beast though as far as beach cats go and sailed like it was on rails with the leeward hull maybe 2/3 - 3/4 submerged and the other hull flying

My boat's sail number was .....225

You can see the boomless main at the very start of this video. There is a bottom batten and then some adjustment where the block it attached.

The guy in the video is sitting too far back though like many beach cat sailors seem to do and there's very little wind so no trapping out

https://www.youtube.com/watch?v=1Ytm...7C9375&index=8

[Don C L]

To get the most power out of a sail you have to control its camber and angle of attack. A boom does this. A boom on a jib would help it too, but its too impractical for most. A boom the way 99% of boats have it is not perfect either though because you can only control the camber well on the lower portion of the sail. A wishbone boom is better at controlling camber of the entire sail.

[Nicholson58]

Originally Posted by NPCampbell

I'm not an experienced sailor but I'll take a stab at it. With a boom, you can maintain the lateral tension on the foot of the sail even if the sail is extended past the sides of the boat. Without a boom, you can only maintain the shape of the foot of the mainsail if your mainsheet extends aft at 45 degrees or so. This means your mainsail can't extend aft as far and can't be flown outside the hulls while still maintaining the shape of the foot.

Correct.

AND. The boom allows infinite positions for the clew.
The sail shape can be maintained well off the wind.

Remember also that we sometimes use a pole to control the Genoa clew.

[Tillsbury]

You might be thinking of this the wrong way around. You need a boom. To have a boom in a headsail (some have them) they need to be short enough to make the jib self tacking, and even then they are lethal when they're flying around the deck below head height.

So the answer is that headsails without booms are far safer and can be far larger than if they had them, and the resulting inefficiencies are more than compensated for by size and safety.