Why a boom?

[kpgraci]

Being new to sailing I ask the questions that may never occur to more experienced sailors. I think the technical name for these types of questions is 'dumb'. So here it goes:

Why is the mainsail attached to a boom?

The foresail is not, and it works just fine. I know there are loose footed sails, but these rigs still have a boom, the foot is not attached only the clew. So I'm wondering why is a boom needed at all? Is it because there is no effective way to extend the sail out on a reach? In that case, wouldn't a pole work as well, or a block located aft of the transom (on some kind of support).

I know too the Main sail, like the mizzen mast sails on a ketch or yawl provided helm balance (whatever that is) so is that the purpose?

Has any designer tried a sail plan without a boom and found it lacking?

The things I think about when I'm not sailing.

 

[Paul Brinkley]

Not sure I can give a complete answer, but I know the range of positions and directions that you must apply support to the mainsail is different from those of the jib. Without a boom, it would be difficult to position and shape the main correctly. Consider, if you will, where the mainsail is positioned and how you would get it there without a boom. And, by the way, some jibs do use a boom! -Paul

 

[dscribner]

Check out the Cockpit Rig. Invented by Rainer Wieland. His boat has a mast coming out of the cockpit with (for lack of knowing what I'm talking about) three jibs; two set before the mast and one aft. It's fast on some tacks but slower down wind. Handles remarkably well. You can probably find him out on the net someplace.

 

[dparilla]

It's in the foot baby!

Well sort of. As most things in sailing, there are partial answers. The boom holds the foot of the sail out and allows it to maintain the proper angle to the wind without the leech being over tensioned and "curling". It is mainly (no pun intended) important when sailing to windward. To sheet a main without a frame would cause curling of the foot and stalling the sail. You would have to have the sheet pulled from far aft and wide of the cockpit to get the same sheeting angle without it. Think how far aft the cars are for the jib, and hard on the wind, the jib is almost flat. In these cases the main is providing greater thrust than the jib can. On a reach to a run, you could possibly get rid of the boom, but I think you would still lose a lot of dimensional control of the rig. There are reason that many "pole out" the jib when on a straight run, and a number of new boats are adding jib booms to the rig options.

 

[cephius (Dave)]

kpgraci,
Think of the boom as a permanent whisker pole.

The function of the boom can be preformed by other hardware or rigs. Take a look at wishbone rigs. These have been around a long time and are not just the realm of sail boards.

Rigs with fore masts often use loose footed sails. That's because there is still plenty of boat left to hang rigging from to shape and tension the fore sail.

The boom is great at providing the sail shape without cluttering up the cockpit.

 

[kenn]

The boom tensions the mainsail longitudinally (aka horizontally). This tension pulls the mainsail into the 'wing' profile necessary to generate lift from broad reach through to close-hauled.

See Bernoulli's Principle.

 

[Joe]

You need to be able to control the draft depth in the lower third of the mainsail and to set twist on all angles of attack. If you can figure a way to do this without an outhaul or a vang.... you can ditch the boom. With the headsail, you only have a lead car to make these adjustments or change to a differents size sail. With a mainsail, reefing replaces sail change; vang, cunningham, outhaul, backstay, sheet, halyard etc. all provided a myriad of tweaks for a singular sail.

There are a number of beach cats than do not use a boom... but in their case the twist and draft are controlled by highly purchased cunninghams and a plethora of adjustable, full length battens. The outhaul function is replaced by a long plate at the clew end of the main with mutliple holes to allow position choices for attaching mainsheet tackle which in turn controls foot tension. These rig configurations cannot accommodate a reef, nor can the sail be stored without complete removal.

So the bottom line is that you can sail without a boom if you modify your sail and are willing to give up some common mainsail features..... to what purpose I have no idea.

 

[PaulK]

You are right that jibs seem to work fine without booms. Jibs can also work well with them. Mains also work with or without booms. As Joe suggests, booms make it easier to make sail adjustments and have them be the same on both tacks. Boomless jibs need a sheet for each side. You need two tracks, and each jib lead has to be adjusted separately. You need port and starboard barber-haulers, etc. With a boom, you can set the sheet and leave it when you tack. One boomvang, not two. One traveller. One sheet. For large mains, booms also serve as a safety feature, to dampen the flapping of the clew when you tack. Imagine a boomless mainsail clew and sheets flying around in the cockpit the way the genoa sheets do on the foredeck. You would not want to be there! That may be why most mainsails are boomed. The tendency to have jibs that overlap the mast may be why you don't see as many boomed jibs.