Mainsail Trimming

[rhr1956]

I know what a boom is and I know what the top batten is. I also understand what parallel means. I'll be damned if I can make the top batten parallel with the boom when trimming the sail. When is a parallel trim good or not applicable? Upwind-downwind??? Your explanations are greatly anticipated. Thanks

[GordMay]

Leach tension is controlled by the mainsheet and traveller upwind, and by the boom vang off the wind. Increased leech tension straightens the leech and cups the sail. Decreased leech tension eases the leech and twists the sail.

TO TIGHTEN THE LEECH:
1. Trim mainsheet harder when sailing on the wind.
2. Tension boom vang when sailing off the wind.
3. Tighten leech line to control leech flutter.

TO EASE THE LEECH:
1. Ease tension on mainsheet and boom vang. When beating in light winds, you’ll need to pull the traveler above the center line in order to trim the mainsail close enough while keeping the upper leech open.
2. Ease the leech cord.
3. In very light air, reduce the effect of the weight of the boom by tightening the topping lift.

See ➥ http://www.haarsticksailmakers.com/d...lTrimGuide.pdf

[Charlie]

RHR:
I trimmed mainsail on a IOR boat in the late 80's and read everything I could on the subject. Meaning this info might be dated. I found it impossible to keep the top batten parallel to the boom except for short periods of time. This was while going upwind. I had a number of different controls to adjust the sail including the boom vang, traveller, main sheet gross tune and fine tune, running backstay, and what we called the tip stay (the permanent backstay on a fractional rig). I would spend the entire race concentrating on the main sail and would shape it differently according to the conditions. For cruising, when going upwind, I think that the best you can hope for is to have the top telltale occasionally behind the sail and occasionally streaming. The main controls for this are the boom vang main sheet and traveller. The lower telltales should be streaming back. I hope this helps.

[rhr1956]

My boat does not have a boom vang. I do have:
Fixed back stay
Traveler
Topping Lift
Downhaul
Outhaul
leech cord
I have played very little with the outhaul. It doesn't seem to have any effect. (Foot of mainsail attaches to boom via boltrope). When raising the main I generally pull the halyard pretty tight, then set the downhaul until the luff in tight and flat. You think I'm over-doing the luff tightness? Back to the leech cord...do I use it to fine tune after trimming mainsheet and traveler?

[Charlie]

The outhaul controls the curvature in the bottom part of the sail. The stronger the wind the more outhaul is required. Topping lift controls how much you can tighten the leach of the sail. Unless you have nice racing sails the leechline is usually a set and forget kind of thing. If it is cupping the sail loosen it if the sail is fluttering tighten it. The downhaul pulls the boom down and controls where the deepest part of the sail is. On a mainsail you want the deepest part of the sail to be 1/2 way back on the sail. It is very difficult to explain without pictures etc. I would look on the web for a video on mainsail trimming it can be simple or complex depending on what you want. The easiest thing to remember is that most people over tighten everything. When your boat has a case of the slows loosen everything and then tighten it again slowly.

[rhr1956]

Is a boom vang something I should add. This is my second boat without one so I don't have any experience using one. My understanding is the boom vang is generally for downwind to keep the boom from raising and spilling air. Is that correct?

[pete33458]

Originally Posted by rhr1956

Is a boom vang something I should add. This is my second boat without one so I don't have any experience using one. My understanding is the boom vang is generally for downwind to keep the boom from raising and spilling air. Is that correct?

Yes that is correct. It will also help to flatten the sail on any point, but is most useful as you describe, since the mainsheet does more of that job as you point progressively higher. pete

[rhr1956]

Got it...thanks for the explanations folks. It's a bit clearer now. I will add a boom vang and stop focusing on that top batten.

[Surfer Girl]

Correct sail trim for any given point of sail, wind velocity and sail boat design is definitely an art and can take a lot of practice to get good at. A good place to start in understanding correct mainsail trim is to think of a sail as a vertical wing, which it partially is - it creates lift (which is one of the reasons modern sail boats can sail to windward) and also creates drag.
So generally, if you understand that to get the most out of boat speed you want to maximise lift and minimise drag. This basically means that you need to flatten (de-power) the mainsail the higher the wind velocity to keep the boat sailing fast BUT in control, or create a fuller profile, billow, curve (power up) in the sail in lighter conditions. How you do this, as others have mentioned, is via the mainsheet, main halyard tension, outhaul, vang, cunningham (downhaul), traveller and leech lines. By tightening these controls you achieve a flatter mainsail; by easing them, a fuller mainsail.

Understanding this is a good place to start. Definitely get a vang fitted to your vessel and a traveller, if you don't have one. Then read some books and go sailing and practise in your boat. Start by sailing close hauled in smoothish (sheltered) conditions in about 12 knots of wind where small changes in sail trim are instantly converted to more or less boat speed. Feel the balance in the helm (feedback), try to find the 'sweet spot'. Watch your log when you make adjustments to see if boat speed increases (or decreases) - if it increases, take note of what you did. When you're happy with what you've achieved tacking to windward, crack off a bit and try it on a close reach, a beam reach and a broad reach.

Don't do this in strong wind (just yet) because you risk the boat being overpowered, creating weather helm and allowing the boat to heel too much, which just confuses things...

The 2 most common mistakes people make is to crank the main halyard too tight (someone already mentioned this) and to not reef early enough. Especially up wind, too much sail only slows the boat down and stresses the rig, creates weather helm, more leeway and makes the helmsman's job that much harder (not to mention the mainsheet hand).

Above all else, go out and have fun

Hope this helps...