Jib to Main Off Wind

[michaele69]

In Carl's excellent tuning article, he calls for a 10% longer attachment point for the jib than the main. This is to open the slot angle as the sails are let out. I have checked this against Rick's site and the Class drawing, and have each of them is different. There is a slight amount of guesswork involved as attach points measurements of the main is not a dirrect measurement, but....
Build site: jib 14, main 16.
Drawing: jib 13.5 main 13.25 to 13.50 depending upon where you measure.

What are ya'll's thoughts on this? What numbers do you use?

Thanks,

Michael Edwards - EC-12 1969

[s vernon]

Michael,
I am surprised no one has yet responded to this question. Maybe other people do not find it as fascinating as I do.

One difference between build site and "the plan" is that Rick has 16 inches of sheet travel while the plan has 15. So that would shorten things up.

I have a couple of boats. One goes wing and wing like the sails are glued out there. On the other one the sails prefer to flop back and forth with any little wind shift or slight course change. I have been meaning to write down the fairlead positions and sheet travel of the ez boat, so I will post them later along with approximate boom angles.

Getting back to the plan versus the building site, that small difference in jib fairlead location and big difference for the main seems funny. One should be "more right" than the other, it would seem.

Scott

[Rick West]

Carl's article is excellent and has been on site for a while.

It should be remembered the state on the Building Site there are two different thoughts; the west and the east. The west comes from the two manuals from which all building came for the site. The drawing is a East Coast product of learning and the righting moments and ballast design was different.

It has not been said that one is better than the other for no proof of this has verified. Since the retirement of Kelly Martin (west) all top rated sailors are in the east.

I will say this...free movement of the jib in light air is a function of BS tension in combination with the pivot point. Yes, depending on the boat, it is a learning thing.

...94

[Carl]

Michael, Scott,
Actually Lester Gilbert has a big write up about this issue.
The jib starts 12 degrees off centerline and the main starts 5 degrees.
The theory is you want both booms at the same angle to the wind at a given point of down wind sailing.
To do this you either have to speed up the main or slow down the jib as they swing out.
On a drum winch you can change the attachment points to the booms (while installing a new deck you can also adjust the fair lead locations to compensate for a better lead to the new boom attachment points).
On a arm winch you just change the attachment point to the arms.
Jib balance also has a lot to do with the jib flopping back and forth down wind.
Kahle balances all his weighted jib booms (no sail etc.) to neutral at the attachment point on the jib boom to the jib shroud rack.

Carl

[s vernon]

Some strange numbers from my better boat. Sheet travel 16 1/8 inches. main fairlead 17 5/8 inches aft of 25.5. jib fairlead 15 1/4 inches aft of 7 3/8.

Like I said, it works for me.
It does not not sound like you are going to be flooded with numbers.

What I like to do is to set up a sort of mule boat like the build site shows to see where the fairleads might like to be.

I'll try to remember to see how many degrees out my booms go today at the lake.

The other boat just got a new RMG and a radial jib fitting so it is getting some changes made to it in the fairlead dept.

Scott

[michaele69]

Well, it looks like I'm not going to get the numbers that Carl suggests. I have already installed my fairleads per the drawing. that gives me 14 3/4 from mast step to main fairlead, and 13 7/8 from center of jib rack to jib fairlead. I see from the setup on the build site that there is an offset aft of the pivot point of the jib, so that dimension will shorten even more. Rats.

I understand that ideally the fairlead should be directly underneath where the sheets come off of the booms, but if we were trying to change the numbers of this main/jib ratio, how much can we offset the attachment point before we start getting adverse effects?

Michael Edwards - EC-12 1969

[Carl]

Michael,

All this discussion is fun but not the end of the world.
You have a jib rack with adjustment points, a mast step with a few points of adjustment.
The entire rig will be moved as you tune your boat.
You can always change the attachment points on the booms after the boat is tuned.
At that time you can follow up on the travel of the jib and main sheet.
Some people are also talking about a second winch for the jib.
With the new transmitters and all the mixing etc. the travel of the jib and main sheet could be different.

Getting the fair lead just under the attachment point to the boom really is only worth the effort on the main if you expect to sheet vang the main. Very few people do.
Some also extend the fair lead up from the deck on a tube .



A quick check on a boat in the shop shows:
Dimension from the bow Jib fair lead 22 inches, main fair lead 39.
The main fair lead at 39 just slightly effects a normal hatch cover.

The summer is almost over - finish the boat and lets go sailing.

Carl

[michaele69]

I'm coming Carl.... I'm almost done. I've missed coming to the lake for the past several weeks so I could spend time on the boat. Other stuff keeps getting the way. So close, so close....

Michael Edwards - EC-12 1969

[greerdr]

Doesn't a jib tweaker make this problem moot ?

R.C.Greer

[RMDJBD]

Doc

That is what I was thinking. I have 3in of throw and can put my jib any where I want. I also use a Futaba 9cs trans since I fly Helis and I can set up to 3 special conditions on how much jib trim is adjusted as the RMG travels. All travels are propotional to what you set the condition to 1,2, and three. On top of all this I still have independant adjustment of the jib trim. In all the 9cs has 7 setable conditions.

How this works is like this, as I add power to the rotors I have to add tail rotor trim to keep the Heli going straight, so I use a conditoion switch to interface the tail rotor servo with the throttle. The amount is preset in a custom condition page which is turned on or off by a condition switch, the switch has three positions for three different custom conditions.

In the sailing world, as you trim the main through the RMG and are using a condition the jib trim servo(tail rotor) will move what you have programed in, the three conditions can be set if you want to three levels of wind or up wind, down wind and or reaching.

I have not studied the new Futaba computor 6 channel but this trans should have at least 2 conditions that you can program.










Bob Dudinsky
R.M.D.MARINE

[Rick West]

To complicated for me, guys. I just let my left fore finger do the talking when my brain jerks. The Futaba 6EX will do this too but the complication is on the water and sometimes it is too hot. Reading the big boat books messes me up more with the 12 while I do understand it. What we need is more design into the rigs so we can play with this stuff and see if it works on an EC12.

I love to sail at Charleston with the nice long legs in open water. You can actually get down to real sailing, carving the turns at the marks and through tacks, the long broad reach at the south end, changing the drive in the seas upwind and praying you have it right downwind way out in the pond where you can't see.

I can't wait for three full days of racing and playing during Wednesday rules. I hope it blows like stink!

...94

[DBrawner]

I'm with Rick on this one. As long as the sails go in and out and the rudder turns right and left, I am a happy camper.

DB

[Carl]

Reed,

Jib tweaker does the same.
But to use the tweaker you have to be able to see what is going on.

Some of us are lucky to see our own boat.

Carl