Boomless mainsail

[zoidberg]

Several years ago I sailed a season on the successful Farrier FX-9 tri 'Triohe'. That boat had no conventional boom, instead using a grp batten along the sail-foot and the multi-part mainsheet attaching directly to the sail's clew.

I know that wasn't the world's first example of a boomless mainsail, but what do the more experienced and contrarian among us consider to be the pros and cons of trying the same 'bottom batten' trick on a conventional fully-battened mainsail...?

 

[KevinV]

How do you separate outhaul and downhaul?

 

[dunedin]

Probably works better on a fast trimaran, as the faster you go the further forward the apparent wind and can have a very wide traveller on the rear beam to control the sail shape.

But in 99% of cases there is a reason why booms are fitted - they work, especially when easing the sail to go downwind.

 

[Chiara’s slave]

The only advantage is simplicity. You have less control over sail shape, reefing is more difficult, how was that managed on the F9? I has a Dart Sting 15, on that you moved the mainsheet to the new clew on reefing. Can’t see that being popular on a larger boat.

 

[Baggywrinkle]

My TopCat catamaran didn't have a boom, but there was a traveller on the clew of the mainsail which allowed adjustment of the sail shape by pulling a short rope to move the traveller backwards and forwards. Problem was if it got flapping, there was quite a lot of weight in the clew. This is what it looked like and was attached to the bottom of the main sail at the clew. The shape could be changed while sailing without detaching the main sheet. .... reefing however, not possible so you just had to roll away the foresails and hang on ....


.... and they are very nice boats to sail ....

 

[zoidberg]

Velly intellesting....

 

[B27]

There are several cats like the Dart 18 which have no boom.
As with the cat pictured, they need very powerful mainsheet tackles compared to a boomed rig of the same area.
That's partly because they have no kicker to provide leach tension.
It also means you mostly use the sheet for leach tension and the traveller for adjusting the angle of the sail relative to the centreline.
That's maybe OK on a wide raft like a cat, but on a narrow yacht, you'd have no kicker offwind, the top of the main would be on the shrouds.
Also a cat tends to sail fast, with the apparent wind forwards and is a little more resistant to rolling when the top of the main is too eased. Not the case in a heavy narrow yacht.

The cat in the pic looks like it would benefit from a quick ease of the main, bear off to fill the gennaker properly and sheet in as it accelerates, but that's going to be hard work on the 8:1 mainsheet.

The opposite approach is used on many performance dinghies, once off the centreline, all the leach tension comes from the kicker. The sheet just pulls the boom across the boat. Needs a strong boom.

 

[Daydream believer]

On fast tris & cats the mainsail is not normally let right out so the clew can be kept over the track. That is because with the apparent wind being forward the sail has to be sheeted in more. Down wind the normall course would not be dead running, but tacking down wind. Hence the sail would still not be let right out beyond the track.
The foot length of the sail is governed by the radius of the track. Any loss of sail area has to be compensated for by a higher mast & greater mainsheet control to get the correct sail shape at the top. This normally means a trade off between extra falls in the mainsheet & a good traveller in/out haul system. If either causes extra friction the system starts to fail.
With a boom the sail foot can extend beyond any traveller thus allowing greater sail area lower down. The boom still has to be controlled, but less falls in the mainsheet & less load on the track can help sail adjustment.

 

[Daydream believer]

My TopCat catamaran didn't have a boom, but there was a traveller on the clew of the mainsail which allowed adjustment of the sail shape by pulling a short rope to move the traveller backwards and forwards. Problem was if it got flapping, there was quite a lot of weight in the clew. This is what it looked like and was attached to the bottom of the main sail at the clew. The shape could be changed while sailing without detaching the main sheet. .... reefing however, not possible so you just had to roll away the foresails and hang on ....

View attachment 171295

I would not like that cleating arrangement. Would be a pig to release in a hurry. or adjust from the opposite tack.

 

[Chiara’s slave]

Tris and cats have those kind of mainsheets even if they have a boom. We have a boom, a wide traveller and no kicker. The mainsheet is a 2 speed, 8:1 and 32:1 getting the required tension in the leech is done on fine tune, with your thighs doing the work. Boomed or boomless makes little difference

 

[B27]

Tris and cats have those kind of mainsheets even if they have a boom. We have a boom, a wide traveller and no kicker. The mainsheet is a 2 speed, 8:1 and 32:1 getting the required tension in the leech is done on fine tune, with your thighs doing the work. Boomed or boomless makes little difference

If you've got no kicker, then you'll need a lot of sheet, boom or no boom.
A lot of yachts are reliant on sheet for leach tension close hauled, because you'd need a massive boom to just use the vang as you might in many dinghies.
The difference is how you work the main on a reach.

 

[Chiara’s slave]

If you've got no kicker, then you'll need a lot of sheet, boom or no boom.
A lot of yachts are reliant on sheet for leach tension close hauled, because you'd need a massive boom to just use the vang as you might in many dinghies.
The difference is how you work the main on a reach.

Reaching for us, you only ease the sheet very slightly. It’s all on the traveller. We have a number of telltales to assist with all that.

 

[oldbloke]

Going to the other extreme, it works OK on luggers

 

[Baggywrinkle]

I would not like that cleating arrangement. Would be a pig to release in a hurry. or adjust from the opposite tack.

Releasing it involves sticking a finger between the cleat and the block and pulling the rope .... it's never under much tension so is easy to do. Releasing it gives the sail more depth, so in practice I only ever found myself releasing it to get more speed, so it usually wasn't frantic, flattening the sail just means pulling the red ball under the clew which is fast and efficient.

 

[Chiara’s slave]

Releasing it involves sticking a finger between the cleat and the block and pulling the rope .... it's never under much tension so is easy to do. Releasing it gives the sail more depth, so in practice I only ever found myself releasing it to get more speed, so it usually wasn't frantic, flattening the sail just means pulling the red ball under the clew which is fast and efficient.

Haha, if you want more power out of that thing, the wind is going to be light.

 

[B27]

That clew arrangement on the top cat is an interesting variation on the 'my sail is too long for the boom' problem.

 

[Chiara’s slave]

That clew arrangement on the top cat is an interesting variation on the 'my sail is too long for the boom' problem.

There may be a very little boom, about a foot long. Known on a cat as a mast spanner.

 

[Birdseye]

dredging through the memory there was a successful racer back in the 80s? who used to sail with his saiol cover roughly horizontal with the boom forming and end plate to prevent wind spilling down. This is a well established trick in aerodynamics. The guy was a Knight ie Sir something.

A boomless sail seems to go against this sort of approach if anything and wouldnt add to drive.

 

[Chiara’s slave]

dredging through the memory there was a successful racer back in the 80s? who used to sail with his saiol cover roughly horizontal with the boom forming and end plate to prevent wind spilling down. This is a well established trick in aerodynamics. The guy was a Knight ie Sir something.

A boomless sail seems to go against this sort of approach if anything and wouldnt add to drive.

That was the J classes in the 20s I thought. That is the 1920s, just in case.

 

[B27]

There may be a very little boom, about a foot long. Known on a cat as a mast spanner.

Also on a few dinghies e.g. Tasar.
A spanner controls the rotation of the mast.
Not really much like a boom, in the sense that a boom is there to 'boom out the sail' i.e. hold its corner away from the mast.