Bent Spar, Cape Dory 36

[cd36]

I have a '79 Cape Dory 36 with the original keel-stepped, low-aspect, single-spreader Spartan spar. The mast has a bow to port about mid-way between the spreaders and the head. It is straight fore and aft, but is out of column port to starboard about where my intermediate stays attach. This is true whether the mast is under tension or not - we winter mast down, and the bow is still evident when the mast is on the sawhorses.

I have experimented with eliminating the bow through tuning, but doing so requires unequal - and increased - tension on some of the stays and shrouds. This didn't seem wise, so I have always kept the rig tensions equal and balanced and done my best to get the mast as straight as possible.

What options do I have? Replacing the spar isn't in the budget. Can/Should I eliminate the bow with tuning? Is the spar stout enough to allay any concerns?

Thanks for the advice.

David

[Brian Duff]

How much 'bow' does the spar have when there is NO tension on the rig at all. I mean loose, or on horses.
Tell us in inches or relative to the mast width.
Is this 'bow' concentrated to one area (as in Kink or Bend) or spread evenly throughout the length of the mast ?

You indicate the 'bow' is in between the spreaders and the masthead, but imply you can remove it with tuning ? How tight are your shoruds when you consider the rig 'tuned' ?

More info please

[cd36]

Thanks for your reply.

I'm giving you a rough estimate here, but I'd say the bow is perhaps between 1" and 1-1/2" off center at its maximum when sighting along the track. And it is a bow or curve, not a sharp kink or bend. There is no obvious damage to the mast.

Regarding rig tune, I have the boat set up as follows: cap shrouds, 15%; intermediates, 12%; lowers (fwd and aft), 10%; headstay, 20%; backstay, 20%; staysail stay, 12%. All tensions were set using a Loos gauge.

Tweaking tension MOSTLY removes the bow, but not entirely. Specifically, upping starboard intermediate tension to more like 20%, while leaving port at 12%, removes most of the curve.

Hopefully that gives you a better idea. Again, I appreciate the advice.

David

[Brion Toss]

Hello,
If it is not kinked, I think it is close enough to straight that you could re-bend it. Aluminum is fairly forgiving, so try bending it well past straight, in the other direction, tightening the concave-side intermediate and the convex-side uppers, and slacking the opposing stays. I think you'll find that it doesn't take as much tension to do this as just straightening with the intermediates.
Leaving it as it is is another option, but seems more likely to lead eventually to a failure. Finally, you could always just tune it straight, with unequal tension on the wires. Under way this will tend towards the first option, as the convex-side intermediate will allow the mast to move to leeward, and gradually alter the shape.
Fair leads,
Brion Toss

[cd36]

Brion and Brian,

I took a picture of the rig today. It's a whopper at 10 MB, so it may take a bit to load. You can view the picture here.

Hopefully, Brion, your assessment remains the same after you see the image; I like the idea of being able to tune it back into column.

Thanks again.

David