stupid trim question CE

[Grande Mastere Dreade]

fractional rig,  backstay adjuster, vang, cunningham, traveler,  single spreader inline...   full keel

to reduce weather helm i'm supposed to move the center of effort forward towards CLR point.  I can move crew weight (me and trimmer) around a little or hike out more, but what can I to trim wise?   I can add more cunninham to move the draft forward but what else?   or am I missing something else

 

[guerdon]

The easiest direct way to 'balance' your boat is to mark the C.E. of the sails on the deck, and then mark the C.L.R. of the hull with tape.  Now have a line going across the slip, dock, waterway to the "balance " point, pull the hull sideways with the line.  Try heeling the hull to change the hull shape [and the C.L.R].  It will soon become apparent which variable will help change your steering.  It sounds complicated but it avoids all the math and is really quite accurate.  I have used this for many hull types  and rigs.  Good luck to you.

 

[Grande Mastere Dreade]

mark the C.E. of the sails on the deck,    mark the C.L.R. of the hull

how do you find those

 

[fucket]

Depower the main, CE goes forward. Depower the jib, CE goes aft.

 

[Marcjsmith]

for the sails, the simplest is to bisect  the angle of the clew and draw a straight line to the mid point of the luff, an then do the same for the tack but draw your line to the mid point of the leech.

this will give you a fairly good approximation of the Ce of each sail.  now draw a line between the CE of the jib and main  the sails are about the same size then the CE will be the mid point of the line.  if the main is 2x the size of the jib, then the CE will be 2/3rd of the way down that line closer to the mains CE.

CLR is easy enough.  in that you want to find the spot on the hull where when you push on the boat it moves sideways.  if you push on the hull and and bow moves away from you.  try again further aft..

youv'e just found the CE and CLR of the boat in a static position..  once you start sailing, heeling over, moving the sails,  shifting crew weight, everything starts moving around then

 

[3apc]

• Depower main
  
• Power-up headsail
  
• bring draft forward on main (cunningham, halyard)
  
• Sail the boat flatter
  
• Ease main / traveler down
  
• Reef
  
• Bigger headsail
  

Obviously all appropriate in different circumstances / boats / conditions

 

[TJSoCal]

This image shows the relationships and how to find the geometric center of pressure. However, "marking it on deck" seems useless to me. As noted, the actual center of effort of an individual sail is not the measured center, it depends on trim and heel. And what's impacting the boat is not the CE of an individual sail, it's the combined CE of the main and jib and how that relates to CLR. So I don't know what marks on the deck would buy you.

The key to reducing weather helm, I think, is managing the CE of the main. You generally want to do two things:

1. reduce the force of the effort by depowering the main (think outhaul, backstay). Reducing the magnitude of the main CE vector will bring the combined CE down & forward

2. bring the CE of the main down & forward. Some people do this by travelling down. On the boat I sail on it usually works better to keep the trav up and ease the mainsheet a bit. This twists the top of the main off, which reduces heel (brings main CE down). Reducing heel, in addition to moving CE, will reduce weather helm

Increasing cunningham would bring the draft forward, counteracting your effort to depower the main. You could also power up the jib to move combined CE forward, which would reduce helm as long as it didn't increase heel too much.

Once you understand the dynamics and what actions should do what to CE & helm, I think the main thing is to sail your boat, experiment and find out what works best for you.

 

[IPLore]

To reduce weather helm.

 Move the mast butt forward and shorten the headstay. If you cannot move mast butt, then at least make sure the mast is chocked forward in the partmers. Moving the rig even slightly forward or reducing rake has a big effect on the helm.

 

[2savage]

To come up with meaningful responses it would be best to start with why you think you need to do this.  Are you getting too much helm?  Are you slow?  Before deciding to depower the main, are you in general overpowered?  If not, consider getting more shape in the headsail first maybe?

It's all a balancing act with no formula like CLR here on this piece of tape and CE main and CE jib on these bits of tape.

 knew a guy who balanced his boat perfectly and started to lose to pretty much everyone.  He initially bragged about his neutral helm.  well consider this.  a good portion of lift comes from your rudder, which should NOT be neutral upwind. 

Let the conversation continue............

 

[SCARECROW]

View attachment 284241

Old school system that works okish for traditional boats and sail plans.  Find a drawing like this of your boat.

1. Print as large as you can and cut out everything (sail plan) above the deck.

2. Pin cutout to wall by at top of mast, let the whole thing rotate and draw a vertical line down from pin.

3. Move to end of boom and repeat.

4. Move pin to jib tack and repeat.

where the lines cross will be the CLE.

Doing the same with a cutout of everything below waterline will achieve the same for the CLR

 

[DickDastardly]

fractional rig,  backstay adjuster, vang, cunningham, traveler,  single spreader inline...   full keel

to reduce weather helm i'm supposed to move the center of effort forward towards CLR point.  I can move crew weight (me and trimmer) around a little or hike out more, but what can I to trim wise?   I can add more cunninham to move the draft forward but what else?   or am I missing something else

You're right about Cunningham.  it will depower the main, open the leech and move that sail's CoE forward.  

Without tilting the rig or otherways changing its geometry:

• Twist the main  more - less sheet tension allows main to twist, moves CoE downwards (less heel) and forwards.  
  
• Drop traveller to reduce the power from the main and move rig CoE forwards 
  
• Sail flatter.  If the CoE is to leeward of the CLR it creates a weather helm turning moment (visualise looking at the heeled boat from above).  Plus, most hulls develop weather helm when heeled through asymmetry.
  
• Ensure the jib isn't stalled through oversheeting.  Less power from a stalled jib can move overall rig CoE aft.
  
• Check that the main is still in reasonable shape.  A stretched sail can develop a hooky leech that moves the sail CoE aft of the design point.
  
• Trim to the sea state.  Often motion through waves impacts weather helm cyclically.  You've not qualified whether this is a flat water issue or happens in the bumps.
  

 

[CaptainAhab]

Move the pivot of the rudder forwards. Beach cat style is to rake it under the boat. Fancy boat way is make the transom hung rudder so it leading edge is forward of the gudgeon and pintle. 

Or you can pull on all those strings

 

[Ease the sheet.]

Sounds like an older boat.

Are we talking rudder angle or rudder weight?

 

[SCANAS]

Crank the backstay on. 

 

[ROADKILL666]

THIS IS WHY I AM THE PIT MONKEY.

 

[JEB]

Designer / sailmaker may have CE and/or CLR diagrams they can share.

Is there another boat you can compare notes with?  This may have been solved within the fleet specific to the boat.

My J/30 got most impact from backstay adjustment in terms of de-powering the main and reducing helm.

 

[Carrera]

Not sure the size of the boat but since you mentioned just you and the trimmer I'm going to assume it is small. With that, I would experiment with moving your collective crew weight forward as well.

 

[Raked Aft\\]

Weather helm is a function of HEEL angle!  not as much CE.

 Depower/reduce sails to reduce heel.  That will solve your helm issue.

  to prove this, go out on a big breeze day and just put a jib up,  if you let go of the helm while the boat is heeled hard over, she will round up!

 

[blunted]

Weather helm is a function of HEEL angle!  not as much CE.

 Depower/reduce sails to reduce heel.  That will solve your helm issue.

  to prove this, go out on a big breeze day and just put a jib up,  if you let go of the helm while the boat is heeled hard over, she will round up!

You're half right, CE moves outboard and slightly down as a function of heel.

You guys are mostly talking 2D, this is a 3D problem. When the boat heels, the CE moves to leeward and applies more moment in yaw making the boat want to round up. this is why you bake "lead" into the equation on boats that heel. Lead being the extent to which you need to actually put the CE about 10-15% of LWL in front of CLR to make the boat settle, the lead accounts for the dynamic of moving the CE outboard as you heel.

This is why when you look at boats that sail upright, like multihulls, they really don't need lead to be balanced.

Marchaj has a good explanation of the effect. Skene has a good set of tools for graphically solving the problem.