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Sail Trim & Rig Tuning

This page is all about making PERSPECTIVE sail as fast as she can.  It is very much a learning odyssey for us, as the J/100 does not have well established tuning guides.  At the bottom of the page, I’ve listed some example tuning guides from related boats, which will give us some general guidelines, but the specific settings aren’t directly applicable.

And here’s a great video to watch on the topic — a bit dated but full of expert commentary: North Sails Trim for Speed

What makes a boat go fast?

It’s pretty simple really, just four things:

  • Sail where there is more wind
  • Choose the right sails
  • Get the shape of each sail just right and magnifying each other
  • Position the crew for weight balance

But optimizing sail shape is pretty complex!  There are a lot of factors.  Here they are in approximate order of importance.

For the Mainsail:

  • Main sheet and/or Boom Vang
  • Traveler
  • Mast bend (pre-bend and/or backstay tension)
  • Halyard tension
  • Cunningham tension

And for the Genoa:

  • Jib Sheet
  • Jib car control lead
  • Forestay sag (pre-bend and/or backstay tension)
  • Halyard tension

And many of them are all inter-related.  So we’ll study each sail at a time and then put it all together.  But first, here are the ten commandments: Ten Commandments of Boat Speed

Mainsail Trim

Here’s a great reference website:  OneSails Mainsail Trim

Mainsail Trim 1 Mainsail Trim 2

And here’s a very handy article on the appropriate use of mainsail twist in different wind conditions — perfect for the mainsail trimmer:

Sail Trim Article


Here’s a great reference website: OneSails Foresail Trim

Genoa Trim 1 Genoa Trim 2

Spinnaker Trim

Here’s some reading that can be a good starting place:

Some more specific guidance

This table is worth checking before the race starts as a kind of checklist.  But it doesn’t talk about the halyard tension for the mainsail or the genoa.

Mainsail Trim Light Air (<8 knots) Medium Air (8-15 knots) Heavy Air (>15 knots) When do we adjust this
Top Batten Slightly open (i.e. angled to leeward) unless you have flat water and the higher end of this wind range. More waves require more twist. Parallel to the boom, or somewhat closed (i.e. angled to windward) in ideal pointing conditions. Slightly open. More twist as you get more overpowered. Constantly, using mainsheet or boom vang
Top Leech Telltale Flowing most of the time, if possible. Stalled a lot of the timealmost all the time in ideal pointing conditions. Flowing all the time. Constantly by adjusting traveler/mainsheet to optimize mainsail twist
 Backstay  Minimal (just enough to remove slack, loose enough to keep headstay sag and full jib). Moderate-more in flat water as you become overpowered. Maximum (or until you have too many overbend wrinkles). Occasionally while racing
Traveler Well above centerline-often as far to windward as possiblemust be far enough so boom is on (or above) centerline when main is trimmed properly. Slightly above centerlinejust far enough to keep the boom centered. On or below centerlinefarther to leeward as you get overpowered. Constantly.  Principal control for gust management.
Cunningham Well eased to keep sail fullthere are usually obvious wrinkles along the luff. Tension enough to keep draft at around 45%-usually a hint of luff wrinkles unless the sail is old and needs more luff tension to move draft forward. Pull hard to keep draft forward as mast bends. No wrinkles visible (except perhaps a hint of overbend wrinkles) Optimize before the race, adjust occasionally when sailing upwind.  Ease completely for downwind sailing.
Outhaul Moderately eased. Slightly tighter in very light air or very flat water. Tight. A little looser if waves are bigger than the wind. Very tight-take it to max black band on boom to flatten lower third of sail and open lower leech. Optimize before the race, adjust occasionally when sailing upwind.  Ease for sailing downwind
Boom Vang No tension! (Pull just enough to remove slack so it’s easier for crew to move across the boat when tacking). Trim main for sailing upwind and then snug vang. Pull vang tighter if you have to easemain to depower. Very tight to maintain leech tension, mast bend and flat sail shape when easing mainsheet. Decide before the race if we will use it upwind, otherwise leave it loose.
Sail Shape Sail is quite full overall. Depth roughly 13-16%. Maximum fullness 50% aft. Sail is in middle of designed range with minimal twist. Depth roughly 11-13%. Maximum fullness 45% aft. Sail is ‘bladed out.’ Depth roughly 9-12%. Maximum fullness 45% aft. Constantly monitor during the race and adjust controls as needed.
 Prebend Maximum. Need to bend mast (to match sail’s designed shape) without the mainsheet and backstay. Moderate. Just enough so adjusting the backstay gives you perfect trim simultaneously for both the mainsail and headsail. Minimum. If you have too much prebend the mast will overbend early. At the dock before setting out.  We need to learn how to “tune” the rig, to get the right amount of tension for each wind range.
Weather helm Your goal is a slight pull on the helm (a few degrees of rudder angle) for feel, but you can’t always get this. Your goal is a slight pull on the helm (a few degrees of rudder angle) for feel, but you can’t always get this. You are usually trying to reduce helm and rudder angle so you don’t have to fight the wheel or tiller. This is something the helmsman monitors while sailing to sense if the mainsail is overpowering the boat.
 Mast Rake Maximum. Balance the boat and increase helm by angling the mast aft.  Middle range. Minimum. Balance the boat and decrease helm by not angling the mast so far. Likely not adjusting this during the season.

And even more specific guidance

This is a polar table that describes how fast we should be able to go when we optimize everything, and gives some specific optimal settings for different wind conditions. This table is the result of a theoretical model for a J/100 with a different configuration than we will be sailing with:  it describes a 150% genoa, and an 80 square meter asymmetric spinnaker. For comparison, we will be sailing with a 155% genoa (or a 100% jib) and a slightly oversized symmetrical spinnaker.  Even so this will serve as a good starting point.

J100 Polar 150

It’ll be our job to begin creating a table like this of our own by tracking our speed, course, wind speed and all the settings we use.  It will take time, and meticulous record keeping.  So, as we are sailing along this season, we’ll pull out a card like the one below several times a night and record our performance and settings.

Sail Trim Tear Sheet

More reading