J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment prebend

A posted a picture of the mast prebend. Let me know if it looks like to much
http://phatom364.blogspot.com/

That looks like a massive amount of prebend to me, assuming the backstay is slack. It could be the photo though.

No it's alot, I can't get rid of it. the forestay is to length, the side stay are tension to 40, no backstay to speak of. I'm going to remeasure the forestay, but I had it odd the boat when I measured and added I think 2' for the deck plate.

See if it straightens some if you slacken the uppers. Check the bend by holding the main halyard against the mast by the boom and look what kind of gap you see up the mast.

I would disconnect the backstay and then work on the rig. You would be suprised how much a "slack" backstay can bend the mast.

David
#397 - Mallorca

Check the position of the mast butt on the cabin sole. It HAS to be 1" back from the angle down in the floor. This has a huge impact on mast prebend/rig tune-every 1/2" back in mast butt position pushes the top of the untensioned rig forward about two feet-so when the rig is tightened, the headstay will have way too much sag, and the mast will have way too much prebend.

Also-check that your lowers are also at 40 (I'm sure they are, but just in case...)

That backstay thing worked great for me. I was re-tuning this summer several times and I took the back stay adjuster off first and the last time I took the backstay off all the way during the tuning process. I increased boatspeed and seemed to get much better shape out of my Harrstick main.

Velocity Girl
#278
HHSA

Steve,....what do you mean 1" back of the angle? I have an '86 model and I hace am oval sleeve that fits into the mast extrusion
I do not have a choice for the position on the sole deck

Taras
Hull #532
BreakAaway
_)

The oval you refer to that the mast fits into must be set so the front of the mast is 1 inch back from the forward edge of the molded step the mast sits on. If it is not, you need to move it. Some are mounted with screws so the plate can be loosened and moved. Others require you to redrill the mounting holes.

"The oval you refer to that the mast fits into must be set so the front of the mast is 1 inch back from the forward edge of the molded step the mast sits on. If it is not, you need to move it. Some are mounted with screws so the plate can be loosened and moved. Others require you to redrill the mounting holes."

Can someone please elaborate on this.I thought I saw pics on this topic on this board somewhere. I want to check mine, as I'm trying to re-tune her now that the deck rebuild is almost complete.