Warped Spars - Help

[Sea Monkey]

I am looking at 33' gaffed rigged ketch but notice that both the main and the mizzen masts are bend fore and aft respectively. By at least 6" in the top 1/3 of the spar. These are hollow, fabricated spars and look almost new. I am concerned that this is a defect. The current owner doesn't know. There is no signs of checks or damage. The rigging appears proper. Any ideas? This doesn't seem right but I am moving from a glass/aluminum world to wood. Thanks

[rbgarr]

Are these spars rigged and in the boat, or lying stored ashore?

[Sea Monkey]

They are rigged and the boat is in the water.

[HizzenanHern]

Spars on many modern racing and higher-perfomance cruising boats are bowed at the top to enable sails to be cut deeper higher up. Rigs with adjustable backstays (turnbuckle and hydraulic on single backstays, cars and tracks at the gunnels for double backstays) are set up so that the spar can be bowed more or straightened from the deck, instantly, depending on wind strength (straigh mast, flat sail for high wind, bowed mast, pocketed sail for light air). In many other boats with all-static rigging, masts are still shaped or "tuned" to have a backward bend above the lower spreaders.

Masts intended to be arrow-straight when rigged and tuned can be bowed somewhat by tuning errors. Using the simplist rig for an example, a Marconi (sloop) rig with single backstay and one set of side stays: If the forestay is set a bit short and the backstay a bit long, and the side stays are tensioned too much, the mast will bow backward. More complicated rigs and tuning problems are the subject of a library-full of thick books and are beyond my depth to understand and describe. That's why there are professional riggers.

In the masts of a 33' ketch, a 6" backward bow shouldn't be bad IF the rig is not designed and set up with straight spars.

Evaluation, step one: examine the masts from front, back, both sides, adn all four 45-degree angles with binoculars. You do not want to see any kind of irregularity in the skin of the mast -- no ripples, dents, creases (other than obvious manufacturing technique creases up and down). You do not want to see any angles, only smooth arcs. You do not want to see any reversing arcs (S-curves).

Step two: talk to a sailmaker about the exact make, model, rig. He will know if the masts are supposed to be straight or bowed, and he will know how much bow is acceptable in both a straight and manufactured-bowed mast.

Step three (and one you ought to make in evaluating the boat for purchase and after-purchase safety, anyway): send a rigger up the mast in a bos'un's chair to make a complete survay of the rigging aloft, looking for all the tiny tell-tale signs of impending failure, repair, and expense he knows how to look for. Insist on a written report for your use in negotiations, and as a means of impressing landlubber insurance underwriters.

[HizzenanHern]

Originally posted by HizzenanHern:
Spars on many modern racing and higher-perfomance cruising boats are bowed at the top to enable sails to be cut deeper higher up. Rigs with adjustable backstays (turnbuckle and hydraulic on single backstays, cars and tracks at the gunnels for double backstays) are set up so that the spar can be bowed more or straightened from the deck, instantly, depending on wind strength (straight mast, flat sail for high wind, bowed mast, pocketed sail for light air). In many other boats with all-static rigging, masts are still shaped or "tuned" to have a backward bend above the lower spreaders.

Masts intended to be arrow-straight when rigged and tuned can be bowed somewhat by tuning errors. Using the simplist rig for an example, a Marconi (sloop) rig with single backstay and one set of side stays: If the forestay is set a bit short and the backstay a bit long, and the side stays are tensioned too much, the mast will bow backward. More complicated rigs and tuning problems are the subject of a library-full of thick books and are beyond my depth to understand and describe. That's why there are professional riggers.

In the masts of a 33' ketch, a 6" backward bow shouldn't be bad IF the rig is not designed and set up with straight spars.

Evaluation, step one: examine the masts from front, back, both sides, and all four 45-degree angles with binoculars. You do not want to see any kind of irregularity in the skin of the mast -- no ripples, dents, creases (other than obvious manufacturing technique creases up and down). You do not want to see any angles, only smooth arcs. You do not want to see any reversing arcs (S-curves), though very slight ones can be produced by tuning problems and adjusted out.

Step two: talk to a sailmaker about the exact make, model, and rig. He will know if the masts are supposed to be straight or bowed, and he will know how much bow is acceptable in both a straight and bowed-by-manufacture mast. (Masts of a ketch are more likely to be intended to be straight than bowed.)

Step three (and one you ought to make in evaluating the boat for purchase and after-purchase safety, anyway): send a rigger up the mast in a bos'un's chair to make a complete survey of the rigging aloft, looking for all the tiny tell-tale signs of impending failure, repair, and expense he knows how to look for. Insist on a written report for your use in negotiations, and as a means of impressing landlubber insurance underwriters.

[Todd Bradshaw]

One correction:
Generally mast bend adjustments affect draft in the opposite way. Increasing backstay tension to bow the masthead back and middle forward flattens the mainsail as the bowed mast approaches the same shape as the sail's luff curve, which is what forms the draft in the first place. This also tightens the headstay and jib halyard, reducing jib luff sag and flattening the jib as well. Easing the backstay to straighten out the mast turns the mainsail luff curve back into a draft producing shape and makes the sail fuller while easing jib stay and halyard tension allowing the extra fabric in the jib's luff curve to move aft forming more draft in the jib as well.

[Todd Bradshaw]

In reference to this boat, wooden masts are often tapered by removing material from the forward side of the spar, leaving the aft side straight. This can make them appear more curved than they actually are. Some riggers/sailors also pre-bend masts to stiffen them but that would be somewhat unusual on a gaff-rigged boat. It's also possible that the tuning job just wasn't very good and that things aren't adjusted properly.

It would be very unusual, from a sailmaking standpoint to build gaff sails for a boat with curved or bowed masts. Most gaff masts are quite solid and straight and without much taper or bend from the partners up to the gaff jaws. If you aren't certain what is going on, find somebody who can look at the boat and help - surveyor, designer, professional rigger, etc. before opening up your checkbook.

[Sea Monkey]

Thanks for all the help!

[Ed Harrow]

Never say never, but I ain't never seen a gaff-rigged boat where the mast was other than straight. Might be raked, raked forward even, but straight.

SM - do I read that the mizzen is bent aft, and the main forward, or am I reading too much into your statement, LOL.

Surveyor, surveyor.

[Scott Rosen]

I'm with Ed. On a gaff rig, you control the shape of the mainsail's leading edge by positioning the gaff (i.e., changing the angle of the gaff to the mast), not bending the mast. I've only seen "bent" masts on a Marconi rig. Sounds to me as if the rig is not properly tuned and is way too tight. Those little turnbuckles can produce a lot of force with just a little twist. While it doesn't take a rocket scientist to tune a simple rig, you'd be surprised how many people (including people who work in boat yards) don't know the first thing about tuning a traditional rig, or any rig for that matter. Also, tuning a rig on a wooden boat is often much different from tuning it on a glass boat. Glass boats are sometimes designed to have the shrouds tensioned very tight. In fact, in some glass boats, the hull is designed to have its proper shape ONLY when the shrouds are highly tensioned. Most, if not all, plank on frame wooden boats are not. I would start by checking the tension on all shrouds and stays. Loosen them to the point where they are just tighter than slack. Then examine the shape of the masts. They should be straight. If they're not, then you need to find out why. Defect? Or design? I'd bet it's defect.

[Ian McColgin]

I'm not sure from the description what you're saying. If you mean that both masts appear to have a curve with the hollow along the luff then either (or both):

1. The taper is all on the forward side and/or

2. The thrust of the gaff and pull of the peak hallyard have conspired to bend the mast.

If 2, then perhaps a little counter bending during winter storage and better use of the running back will fix it.

[imported_Ola Sylwan]

I agree with Ed and Scott.
Another problem with a wooden boat is that you can overtighten the shrouds to the point where you spring the garboards if the mast is stepped on the keel. This is not funny if it happens when you are out sailing in a storm. In my experience the rig should be set up so the lee shrouds go sligtly slack when sailing.

[HizzenanHern]

My error(s). Missed the stated fact about being gaff rigged; I defer to the gurus about which way flattens the sail, but refue to surrender my underlying point, that some masts are intended to be bowed/straightened for sail trim--even if ever/rarely on a gaff rig.

Now somebody jump in my stuff about suggesting a rigger inspect aloft as part of the survey process, and goodbye to this room.

[Bob Cleek]

No need to jump on your stuff about the rigging survey... but I'll jump your stuff for not mentioning it right from the jump. Bottom line is, if you are "looking at a boat" and can't figure out why the masts are bent in opposite directions, you don't know what you are looking at. Simple as that. You do get honorable mention, however, for figuring out that something might be wrong. HIRE A SURVEYOR if you are thinking about buying a boat. Hire one that knows something about wooden boats. You will need the survey for insurance anyhow. Ask the surveyor to inspect the spars. That's what you pay them for. Don't go by us. We are all only guessing. My bet is improper rig tension. No bout a doubt it!

[TomRobb]

Harry Truman was right. If you can't stand the heat, stay out of the kitchen.
H&H, getting your stuff jumped on is a fact of life here.
It isn't personal.
You may have percieved that there are lots of contradicting opinions here. What else might there be?
It isn't perfect, it's life http://media5.hypernet.com/~dick/ubb/smile.gif

[This message has been edited by TomRobb (edited 01-08-2002).]