E28+ mainsail trim

We installed a new foresail furler and now we seem to have created a trim problem as we have to put in a reef at 10-12kns of wind to prevent excessive weather helm. We don't get the boat over 5knts at the best of times when beating even after a good bottom cleaning and painting.
Dave

In the process of doing the furler, did you change the overall length of the headstay (even through what seemed like a small adjustment) that now has the mast at a greater rake? Too much rake might be your culprit. If you do a search on "mast rake" in the forums here you'll get some good threads on tuning the rig. Just my first thought if this all came about with the new furler and nothing else changed.

You must have changed your sail if there is such a big difference? There is a lot of talk about the 28+ being light on its feet but this doesnt sound right. What are you flying a 150?

E28+

We re-cut the 150 so it is now around 135-137. I think our problem is the change in forestay length and therefore a change in rake.
Dave

When you recut the 150 that moved the draft forward on the sail if the cut was at the luff this would add to the change the reduced sail area made.

Mast rake and weather helm

I made a quick and dirty diagram of what is going on here.

Basically, imagine forces around the mast wanting to twist to windward (weather helm) and away from the wind (lee helm).

The length of the lever is the distance from the Center of Lateral Effort of each sail to the vertical pivot (which for this discussion we'll assume it's the mast - close enough).

Force multiplied by lever arm length is TORQUE. To tune the boat properly, balance the forces. Torque in one direction can be balanced with torque in the other direction (see diagram).

Mast rake is only one of the tweaks. On the Ericson 28+, the mainsail is a big powerhouse so you have to flatten it in heavier air. Do this before you go to a reef. Remember, full sails make horsepower but they also make for heeling moment. Flatter mainsails move the lift vector so that it aims more forward than athwartship. To flatten the main, increase the outhaul and the cunningham (or halyard tension if no cunningham). Remember to ease the topping lift and sheet that puppy in. She'll stand up.

The same should be done for the jib. Increase halyard tension, which moves the sail draft forward and the resulting lift vector will move forward too, thus reducing heeling moment.

I hope this helps. If it is more confusing, then rag on me and I'll seek to clarify. email me at nickhandres@comcast.net if you want.


SV Rascal
Ericson 28+ #25310

Mast Rake, weather helm and the re-cut jib

After thinking about this a bit more, when you re-cut a bigger sail to a smaller sail, you move the Center of Lateral effort forward. I added it to the diagram on the left side so you can compare in concept even though I am not using dimensions.

FYI, my rig is balanced to the point that in a reasonably steady breeze, I have put a little friction on the wheel using the brake let her steer herself for 15-20 minutes or so. Of course, you can help her steer if you move your weight forward or aft but that is a different discussion.

diagram

forgot this....

Sail Trim

Razz:

Excellent posting and diagrams. (How DO you create them?)

As I recall, the 28+ is fractionally rigged, as is my 30+, and I have had a very hard time finding advice on sail trim for fractional rigs, with the very large main, stepped closer to the bow.

Your advice as to how to avoid weather helm is exactly what I have done over the years.

I am curious, do you have a 150 genoa, or have you gone to a smaller one? I seem to recall reading years ago that the genoa provided very little drive for the Fractional Rig, and was primarily used to provide slot effect for the main. Agree?

Check fundamentals

This might seem like basic stuff but... on my 28+ I've found that flattening the main (depowering it) by cranking on the backstay and using the Cunningham to flatten the main helps relieve weather helm. Those adjustments, and perhaps letting the traveller down a bit usually keeps things right without having to let out the main sheet twisting off the main which generally reduces our speed pretty quickly.

I'd agree with using backstay tension to flatten the main before reefing (on a fractional rig).

Also, how much headstay sag do you have when close-hauled? Excessive sag will also destroy pointing ability and increase heeling. I'd guess you should have no more than 6 or 8 inches of sag on a boat that size.

Tightening the backstay will do both of these things, but you'll ideally you'll want to play that depending on wind condition (if you have a backstay adjuster, rather than a turnbuckle). When beating in heavy wind, put on a bunch of tension (2000 pounds or so) to flatten the main and tighten the forestay. Downwind, release that tension, to provide a full main and genoa. Upwind in light air, go somewhere in between to have fair pointing angles, but rounder sail shape.

backstay adjuster fractional rig

With a fractional rig, the entire system should be at higher rig tension, and there should be less headstay sag to begin with. Increasing the backstay force will bend the mast a great deal, and thereby flatten the main, but should not greatly reduce headstay sag.

Or so I am told.

Any of you sail trim wonks who are more knowledgeable, please chime in and correct me.

tilwinter said:

Razz:

Excellent posting and diagrams. (How DO you create them?)

As I recall, the 28+ is fractionally rigged, as is my 30+, and I have had a very hard time finding advice on sail trim for fractional rigs, with the very large main, stepped closer to the bow.

Your advice as to how to avoid weather helm is exactly what I have done over the years.

I am curious, do you have a 150 genoa, or have you gone to a smaller one? I seem to recall reading years ago that the genoa provided very little drive for the Fractional Rig, and was primarily used to provide slot effect for the main. Agree?

Click to expand...

Tilwinter,
Thanks. I actually used a simple drawing program in AppleWorks to create the line drawing and just saved it as a jpeg.

The 28+ is a 7/8 rig and it has a powerful mainsail. I have sailed a lot with a dacron/mylar 155% genoa and it is great around here in lighter air. It is best to have a 130% and a 110% to go with it. 155% to 110% is too big a jump unless a front is moving in. You are in Baltimore so you know that July and August sailing around here is called bobbing or sheer terror for the lightning.

The 30+ is only 1' 5" longer than the 28+ so the rigs are very similar. I don't know that the mast is stepped farther forward much because the keel has to factor into the design too (not just the rig) Perhaps it is just a matter of inches.

The slot is very important but this rig isn't like that of a Flying Dutchman or a Lightning. It is much more like a masthead rig so I would treat it that way even though the main isn't a little slender thing like on the high aspect rigs. Actually, I put a new mainsail on this year with 2 full battens aloft and I am very pleased with this new design.

Fractional Rigs

In the Docs & Specs section here, go to the E-33 section. There are two "Owner's Bulletins" on sail trim and rig setup and adjustment/tensioning for fractional rigs. These were written by Don Kohlman of Ericson in 1983. They are basic level, yet informative for any fractional rig owner, not just for the E-33 or E-36.

P.S. If anybody has any more of these "Owner's Bulletins," scan them so Sean can add them to the Docs section.

Backstay tension

tilwinter said:

With a fractional rig, the entire system should be at higher rig tension, and there should be less headstay sag to begin with. Increasing the backstay force will bend the mast a great deal, and thereby flatten the main, but should not greatly reduce headstay sag.

Or so I am told.

Any of you sail trim wonks who are more knowledgeable, please chime in and correct me.

Click to expand...

I agree with using backstay tension but... it bends the mast which flattens the main and puts a huge load on the rig.

I would recommend using jack stays (there are tangs in the 28+ and 30+ mast) for them and it would be kinder to the boat. What do I use? An 8:1 backstay adjuster. (yeah yeah, do as I say, not as I do...)

Sag in the forestay is problematic and the best way to get it out is with jackstays. Also keep that backstay adjuster handy for flattening the main.

I have the 28+ and noticed the significant head to wind as the wind speed increases and adjusted for this (not overly successfully) with vang, outhaul and Cunningham.. I don't have backstay tensioning and from a mechanical POV I don't see how bending the mast backwards tightens the sail. If I simulate this by bending the "luff" of a triangular piece of paper the paper goes slack as it is being "folded" at the point of bending. How does backstay tensioning work to flatten the sail?

Second Star said:

I have the 28+ and noticed the significant head to wind as the wind speed increases and adjusted for this (not overly successfully) with vang, outhaul and Cunningham.. I don't have backstay tensioning and from a mechanical POV I don't see how bending the mast backwards tightens the sail. If I simulate this by bending the "luff" of a triangular piece of paper the paper goes slack as it is being "folded" at the point of bending. How does backstay tensioning work to flatten the sail?

Click to expand...

The piece of the puzzle you are missing here is the luff curve cut into the sail. In the extremes, if the mast is straight up and down, the distance between the luff and the leech are at its closest. So the curve in the luff turns into belly in the sail. That is fully powered up.

When the backstay is tightened and the mast bends back in an arc (following the luff curve), the distance between the luff and the leech is farther (longer?) now which stretches the sail and flattens by removing the belly. This is a depowered sail.

How much luff curve was designed and cut into your main is information your sailmaker would have.

Chris

Works really well with your fractional rig.

But the effect is limited. Can you further describe the problem, which seems to be excessive weather helm as the wind comes up?

Second Star said:

I have the 28+ and noticed the significant head to wind as the wind speed increases and adjusted for this (not overly successfully) with vang, outhaul and Cunningham.. I don't have backstay tensioning and from a mechanical POV I don't see how bending the mast backwards tightens the sail. If I simulate this by bending the "luff" of a triangular piece of paper the paper goes slack as it is being "folded" at the point of bending. How does backstay tensioning work to flatten the sail?

Click to expand...

I took me a long time to understand this, too. But it is the core fundamental of what we are talking about here. It seems so counterintuitive. How can you "flatten" a sail by "bending" a mast?

Think of the mast as being like a bow (as with a bow & arrow). When the string is pulled back (as happens when the back stay adjuster is tensioned), the tips of the bow are pulled closer together. So when the tips are drawn closer, the center of the bow must curve and "bow" forward. It is this foreward bowing of the mast which flattens the belly of the sail. It is the portion of the sail where the curve has been sewn into it, so any flattening has a positive impact toward de-powering the sail. It flattens and moves the draft (maximum curve) which remains, forward.

Your paper and stick model didn't work because your paper is truly flat whereas the sail has quite a bit of curve to it. It is truly three dimensional.

Thanks for the great input. I rebuilt the paper sail with about 1% curve over the length of the luff and did the experiment again and voila the sail flattened! I guess my "mistake" was that I thought the shape of the sail was built into the body of the sail rather than simply curving the luff and applying it to a straight mast. The curve pulls the clew up and limits how much it can be pulled down (and flatten the sail) until the sail is put back into its original shape by bending the mast.