Jumpers on A rigs?

[fvracer1]

In all the classes I sail in, I keep getting preached, "keep it as light as you can on top". U was wondering if we really need jumpers on an A rig? I have 2 A's (a very light set of 505's and my second set are Windjammin) What real purpose do they serve and are they worth the hassle and added weight?

"When the cannon fires, harden up, tack or get out of my way"

[Rick West]

The jumpers control mast bend above the spreaders. On the Goldspar mast any backstay tension above 1.5 pounds will pull the top of the mast aft. If your sails are cut with no luff curve to the main, you want the mast straight.

It is needed even more with the Groovey mast.

In another words, the jumper in most cases controls the shape of the upper main.

...94

[Chuck Luscomb]

Frank,

The EC12 has a "fractional rig" which means the headstay attaches to the mast well below the mast head. Jumpers are used to keep the upper section, above the headstay, stable and straight. As Rick indicates, they are also used to control the shape of the main in the upper panels.

BTW, were did you get your 505 A suit?

Thanks,

Chuck
#84

[greerdr]

OK.
Let's agree jumpers are needed ; I most certainly do.I have not yet been schooled into Jake Leos VERY high tech & sexy double spreader rig,so let's talk an "old school" rig. What height for the jumper ?
The "Master"(and I say that with great respect),Mike Zellanack, recommends the strut be 1/2 the distance from the spreaders to the top of the rig. Why not 2 times the distance from jib attachment to masthead? That would seem to be the area of the rig most responsive to adjustment for main's top shape. The difference is 13 inches for the jumpers bottom attachment point.
I tend to think the 1/2 masthead to jib attachment strut seems better for a fractional rig .What say you?

R.C.Greer

[s vernon]

Optimizing says half way, but Bob Wells corrected that in the Summer 1999 issue (#115) of Model Yachting. That was the first (?) EC12 issue. He wrote an article - Enhancing a Used EC-12 - that says half way will give you an S bend in the mast - jib stay pulling forward and low located jumpers pushing aft - so he said jumpers 3/8 inch below the forestay exit and upper shrouds attached 3/8 inch above the forestay. "Centralizes the load."

Scott

[Merv49]

I'm just getting started here and find several conflicting sources when it comes to placement of the jumper and other mast hardware. Are the measurements on the EC12 building site accurate/adequate and in like with todays thinking? What is the current best location for the shroud lines, jumper, spreader, bottom jumper eye? Could someone measure the placement of these items and post the results here?
Thanks

Merv

[Capt. Flak]

When I first got started in the 12s I asked why the jumpers were located about 4 inches below the point where the jib stay attached to the mast. The reason given was it was half way between the top of the mast and the spreaders. This would be the mid-point to control the bend.

Two things hit me on this idea. One was that the point where the jib stay attaches to the mast IS the point where all the pressure is. That should be the place to put the jumpers so you can counter that force. Second was that having the jumpers below that point means that you are always having your topping lift get snagged on the jumpers.

Reichard Kahle made a one-piece jumper/tang for the jib stay. This is the best way to do it in my opinion. All my rigs have the jumpers at the same point of the Jib Stay now.

Joe Walter #24

[s vernon]

Merv,

I don't think anyone will measure every fitting location on their own rig and claim that their rig is the class standard. I imagine everyone's rig varies by a large fraction of an inch on several fittings. It seems to me that whatever info you find will do the job as long as you put the jumpers within half an inch or so of the jib stay conection on the mast (Not at 52). So jumpers would be at or just below the jib stay and uppers probably would be just above the jib stay.

Scott

[Merv49]

Thanks for the input guys.

Mervin

[greerdr]

I agree with what you have read:Keep the mast bent to what your sailmaker recommends by the number at the top of the sail.
When the wind increases pull some tension on everything and trim YOUR boat to the conditions.Some of us move the jib foot forward a hole followed by the mast step forward and then as it continues to build wind speed, sail on the bottom of the main and jib.
Much depends on your boats "balance point".
As to the opening question:yes jumpers are O.K. and often useful.

R.C.Greer