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wooden mast strengthen


kaeptnr

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Hello together,

 

my selfmade hollow wooden main mast bend strong in guests and stronger wind.

So I like to make the lower part mast stiffer  with fiberglass strips or perhaps with fiberglass sleeves.

 

Has anybody an idea how many layers useful?

 

Regards

Ralf

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Hi Ralf,

 

Did you make your hollow masts by the birdsmouth method or by some other way?  I will start building my coresound 17 soon and was wondering which way to go, either hollow wooden birdsmouth or aluminium. What has everybody else done, wooden or aluminium spars?

 

Regards,

 

Alex.

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I think it has been clearly documented here that the strongest of the cost effective methods that are also reasonably easy to fabricate is aluminum sectional masts often topped off with a wooden section.  This is also what Graham specifies in his plans.  Some have gone with wooden masts 'cause they look pretty.  It has been found that they usually bend at lower winds than aluminum.  Some have gone and ordered carbon sections.  Some of these do not bend off at the top enough to function according to plan, but are stronger over all.  Some are experimenting with clipped/square topped sails and carbon masts, which function differently in strong winds by the top of the sail twisting off to dump wind.  This will likely prove the fastest sails in the long run, though not sure if they are there yet.  You should decide for yourself based on learning more about the options.  What some one else does is not necessarily a good idea, or the best one for you.

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Alex I made a birdsmouth mast for my CS 17, couldn't source Spruce at resonable cost so went with Fir. Long story short mast came in at nearly 30 lb, able to manauver horizontaly but trying to step :angry:

 

ordered the Aluminium items from Carla/Graham, came in at 12.7 lb before any hardware. At an advanced age still somewhat difficult to step main (wish there was tabernacle design) but doable.

 

MM

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Alex I made a birdsmouth mast for my CS 17, couldn't source Spruce at resonable cost so went with Fir. Long story short mast came in at nearly 30 lb, able to manauver horizontaly but trying to step :angry: ordered the Aluminium items from Carla/Graham, came in at 12.7 lb before any hardware. At an advanced age still somewhat difficult to step main (wish there was tabernacle design) but doable. MM

makenmend - with doug fir you should have reduced the scantlings. Opinions vary but one should be able to reduce stave thickness by 15% to 20% with fir since it is stiffer.
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Ralf:

 

When you say your mast bends, how much does it bend? Also, in how much wind does it bend? A little wind (less than 10 knots and no white caps) or a lot (more than 15 knots and whitecaps forming)? Unstayed masts are supposed to bend to a certain degree. The response to a gust of is for the mast to bend some, which flattens and de-powers the sail.

 

What was the thickness of you staves (assuming a birds mouth mast) and what is the diameter of the mast? What wood did you build it with?

 

It might also be helpful to have a picture that would show the degree of bend, and also, the location of snotter end of the sprit (mast end) to show the location up and down the mast. If located too high, you may be bending the mast more than you should be simply from snotter tension.

 

If they only bend in really strong winds, is it time to reef?

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Yep, both aluminum and wooden mast on this type of rig will "spill" wind when pressed. It's normal, expected and desirable. The scantlings Graham has on his birdsmouth mast will produce acceptable spars, though they will be less stiff then the aluminum spars he also spec's in the plans. If you are very performance oriented, then you'll want the aluminum sticks. If aesthetics are more important, then the well varnished wooden poles will be the ticket.

 

Lastly, covering the wooden spars with 'glass cloth, will not do much to stiffen them up. You'll need quite a bit of fabric and goo, to make any appreciable difference, which means the mast will weigh a lot more too.

 

Next time you're out, take a picture of the mizzen, as you sight up its length. Note the wind strength and point of sail and post it. We'll see how much bend is there and if it's overly so, for the wind strength.

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hokeyhydro, I used Graham's plan for the stave diametions and when rounded it was to the stipulated size. That fir is heavy.

 

 

Alex I made a birdsmouth mast for my CS 17, couldn't source Spruce at resonable cost so went with Fir. Long story short mast came in at nearly 30 lb, able to manauver horizontaly but trying to step :angry: ordered the Aluminium items from Carla/Graham, came in at 12.7 lb before any hardware. At an advanced age still somewhat difficult to step main (wish there was tabernacle design) but doable. MM

makenmend - with doug fir you should have reduced the scantlings. Opinions vary but one should be able to reduce stave thickness by 15% to 20% with fir since it is stiffer.

 

 

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Hi Howard, the point is, I've build the hollow masts with the same diameter (63mm) how is provided for massive masts.

 

the main mast bend nicely in all moderate conditions (less than 15 knots), please check out my youtube video,

after runtime 1minute you can see the main mast at work.

 

 

I build the mast simple from four square pine lumber, I cut the inner edges to save same weight.

 

I use the boat mostly on a lake near the Alps, often not too much wind, everything is fine with the rigg, but some times I use my boat on the coast,

this year I like to cross some open water between Stockholm and Helsinki and take part at Raid Finnland, I don't like to have a broken mast away from the coast.....

 

So my idea was to protect the mast from breaking with two layers strong fiberglass on lower two meters of the main mast.

 

Regards

Ralf

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I didn't realize that Graham included a square sectioned mast scantling in the plans, I'll go back and check, but you shouldn't have used birdsmouth mast scantlings, on a square sectioned mast. Typically, a square sectioned stick would have smaller scantlings and with the usually 18% - 20% reduction in scantlings for a Douglas fir species substitution . . .

 

In any case, Douglas fir is a fair bit stronger and stiffer than the typical spruces employed in masts, so combined with the oversize scantlings, you probably have little to be concerned about.

 

Generally, you want the masts to bend, so they can "unload" in gusts. If you stiffen them up, they will not depower and something has to give, which usually means you'll heel more or the mast will not yield enough and breaks. This would be especially true if you added reinforcement on the lower portion of the mast, making it stiffer, but let the upper portion cantilever over this stiffer lower section. The net result would probably be the mast will break right at the point where, your lower reinforcement stops on the mast.

 

Judging by the brief glimpse I got on your video, the main bend is much less then I've seen on other, spruce masts, so this confirms my belief you'll do fine on your Finland raid.

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From the brief glimpse of the mast, looked to me like the mast bend was about right. Much more wind, you may want to reef. Looked like you were cooking along nicely with that much wind and with more, you may not notice much loss in speed. Safer, and nearly as fast.

 

Also, it appears your sales are laced on, and to my eye, looked like you have some vertical creases along the luff. Normally, that would mean you have the downhaul tight enough but it also looked like there was some puckering along the luff. It might need more downhaul tension. To get a better sail shape, you might want to move the snotter end of the sprit up a bit along the mast. The foot of the sail looked like it was pretty much stretched to the maximum, meaning you would need a bit more downward angle to tension the luff to get you a better sail shape. Something to consider and play with.

 

Nice looking boat and what a nice looking place to sail.

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Taking another look, you may have the correct sprit angle, but not enough tension on the sprit? If that is the case, and your sprit is not long enough to apply any more tension to stretch the sail out, you might have to lower it (not a good choice if you have the correct sprit angle as is) or build a slightly longer sprit?

 

Someday, we need to start a "fault finder" thread on these unstayed, cat-ketch rigs. Photos of well set sails with the sprit in the right place and with the right tension, then the same rig with high and low set sprits, loose tension, taught tension, etc. to show how these differences create faults in the set of the sail. Would be a big help when troubleshooting any performance related issues with these rigs.

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 . . . Nice to know that problably now reinforcement is necessary . . .

 

How have you come to this conclusion? The video shows an extra stiff mast, compared to other wooden masts I've seen on this boat. The species used is also stiffer and stronger than the typical species used in mast making, so why the need for more reinforcement, particularly as previously described, which may just create a place for the mast to break easier?

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