tuning prebend question

[Roger (Ninette Manitoba)]

In preping to tune my rig in a few weeks, I am doing some reading, and looking at pictures of my rig. (see pic) I have a masthead rig (forestay) with a set of uppers that go to the FORWARD chainplates, a single set of lowers that go to the AFT set of chainplates, and a single backstay. All have turnbuckles for adjustment. As I read various tuning guides I always come to the point about tuning in about an inch of mast prebend, but it would seem that with my set up, the uppers and lowers may have been reversed by the PO. The way I look at the angles created by my uppers and lowers, there does not appear to be any way to induce prebend. The uppers are inline transversly with the mast base, and the lowers are aft of the transverse position. If I tighten the lowers the mid mast would move back, to create reverse bend! I can't see how tightening the uppers would induce the top back, even with the lowers looser. Is it possible that they have been reversed on the chainplates? If any of you are near your boat, or have a picture of a similar sized and rig set up as my boat, check it and tell me if your lowers go to the forward or aft chainplates.

 

[Ray T]

Rig tuning

Roger, I think you should forget about prebend and concentrate on getting your mast in column and straight up and down. The upper shrouds should go to the attachment point that forms the straightest line from deck through the spreaders to the masthead. The upper shrouds should be pretty tight and the middle shrouds should be somewhat looser. A tension gauge would help you here. The fore and aft stays should be fairly tight. If you could see your way clear to install a backstay tensioner you could leave the stays somewhat looser and tighten the tensioner when you were on a beat. I hope this clears it up for you. Good luck Ray T

 

[Roger (Ninette Manitoba)]

Thanks Ray, I have a loos gauge and

getting the mast in column and perpendicular amidship has been accomplished. I also have a loos gauge and the recomended tensions on each stay, so that will not be a problem. It was trying to get an inch of prebend in that was confusing me when all the stays went to the masthead, except the lowers which were aft of transverse. Thanks for the info about keeping the shrouds in line with the spreaders. That not only makes sense but confirms that the current setup is correct. I have to drop the mast this spring to replace the forestay and install a spreader light, then will retune without worrying about tuning in mastbend, which with this rig does not seem possible.