Werzko 4.5 - 15' ply stitch-n-glue sail dinghy

[Vulkyn]

Have no idea in that matter, i am sure one of the experienced members will reply ...

[NoEyeDeer]

Originally Posted by Aharon

My boat plans require a 6.3m aluminum mast ("aluminum alloy spar, section approx. 57 x 73 mm, required transverse momentof inertia 14cm4, lenght 6300mm"). Please do not ask why "57 x 73 mm" because it looks round to me in the drawing...
Would you good sirs give me an idea of the dimensions for a mechanically equivalent birdsmouth mast? Should it be tapered?
Thanks!

I'd google up birdsmouth spars and email someone who actually makes the things. Ideally, the mast should be tapered. It will still work if it isn't tapered though, just not as well.

Originally Posted by Aharon

The plans I got show a cross section similar to the picture attached, with two kind of "claws" on the drawing (seen from the top).
Is this a kind of tunnel where the sail edge goes?
Does it run the whole mast lenght?
Do I need it at all? (is it some kind of alternative to tying the sail to the mast, thus facilitating putting it up or down?)

It's a groove for the bolt rope and is what holds the mainsail to the mast. Yes, it runs the full height. You don't actually need it and there are alternatives, but it's common on dinghy masts because it's simple and efficient. Lacing sails to masts tends to be a bit messy, and lacing obviously can't go past spreaders. Tracks and slides are extra weight, work and cost.

[Aharon]

The plans for the Werzsko dinghy I am building call for a 20’ (6.300 mm) mast. According to plans its approximate section is 57 x 73mm (2 ¼” x 2 ¾”), 2mm thick walled, Luff groove aluminum alloy mast, with a “required transverse moment of inertia” of 14cm4.
Looking for affordable, diy ways of getting a staff and boom, I learned about birdsmouth construction. While “lurking” and learning around, here and in other forums, I came about this:

“Here’s a simple calculator (http://www.engineersedge.com/calcula...re_case_12.htm) for the moment of inertia and section modulus of round tubes; you can put in zero for the ID of a solid mast.
This assumes that you don’t make the wall very thin; the failure mode is different in that case.
If you play around with it, you’ll find that the larger diameter and thinner the wall, the lighter the weight for a given strength. For example, a 4-1/2” diameter mast with a 3/16” wall has the same section modulus as a 3” solid, but 35% of the weight. That’s way too thin a wall in wood, I think; I expect it would fail by splitting along the grain unless perhaps you could find a way to make a hollow plywood tube.” (In woodboats by Mr. Wilson. Maybe he even cohabitates in this here noteworthy forum).

I think I have a solution to the problem posed by Mr. Wilson, and I intend to make my first mast like this, unless you say I am crazy.
3 stripes from a 240 (78.5”), ½” marine plywood board scarf jointed make one 20’ stave (1.2” wide). 24 needed for 8 staves.
The mast will be cylindrical (no taper, as in “kiss”). Two opposing staves to be protected with tape, to allow a two-part mast for hard points and anti-moisture treatment.
Once planed and sanded, a first 10 cm wide strip cut from a 3.00 mm “aviation marine-grade plywood” sheet is glued in an upward helicoidal fashion, clockwise. (see figure) The “step” of the winding is kept regular at 10 cm. A second stripe is then glued side-by-side with the first one. Then the same process is made, but this time counter-clockwise. The whole mast is tied (several methods available) and put in a straight jig to let the glue (epoxy?) set.
I believe the resulting “plywood tube” would be very strong and light. What do you think?

[Aharon]

Thanks to the big help I found here, I have everything figured out for the moment of decision: begin construction. This moment however is depending on an important news - the acceptance or refusal, by the Government, of a law declaring Sundays a day of rest like the rest of the world.
As an observant Jew, I keep the Shabbat, while non-religious Jews have this day to go to malls, make barbecue and relax, even sail!
If the measure is NOT approved (which is what I think will happen), I will weight the pros and cons of skipping one day every month to go sailing. Or taking sailing lessons in other people's boats. Or both. Or whatever!
It's good to say hi.
Aharon

[Aharon]

pistnbroke, I refuse to believe that you are calling me an ignorant. Religiosity or atheism are choices, to which everyone is entitled (at least in my democratic country). I regard your outburst totally uncalled for, also because I spoke about politics, not religion.
This knee-jerk reaction of yours is very suspicious - and I hope I am wrong.
Shalom,
Aharon

[Aharon]

This will be my last attempt before calling the moderator: yes, you dashed with a rant against "religion". Three phrases, same target. Useless waste of bits and good will.
Yes, "some" of the world has moved on - so what? Moved on to where? There has always been atheists, so what is new in yours?
I will take in account that you are closing in on 1000 posts, and try to enlighten your seniority about your mistake. An orthodox Jew today or 1000 years ago is the same kind of person. Without the Temple, our religion "moved on" and became centered on the Shabbat and on 3 daily prayers.
Today, Sunday, we have all worked our "first day". Should that law pass, I will become a captain too, and "then you will see what you will see"!
Cool, man, really.