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Poca Barta posssible error


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  #1 Charles Treichel

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Posted 11 February 2013 - 08:12 PM

Just finished lofting and believe I have found an error.  (Checked the first 8 pages and didn't find it)  Pg 61, new edition, Bow offsets, second line down shows x=4, z=2- 3/16.  Hope I am not missing something, but I think it should be 1-15/16.

Pg 33 shows the frames with stringers more or less flush.  Pg 34 and 35 show the stringers somewhat outside the frames, which is where I believe they were intended to be.  In any case there is no discussion of what the outside radius of the stringers should be, but I think I will be rounding them off to 1/4 or so radius.

I've been toying with the idea of making the stringers out of 1/2 x 1" white oak (partially because I have lots of it)  Weight would be about the same.  The oak is incredibly strong and bends nicely. Also wondering about the properties of luann (meranti???) molding which is sold in strips 1/4 x 1-1/2.  (I would laminate two of these to make 1/2".  Varying data and opinions on its resistance to decay.  Any comments on this would be appreciated.

 



  #2 Hirilonde

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Posted 11 February 2013 - 09:12 PM

White Oak weighs about twice that of Western Red Cedar.  So your 1/2" thick stringers will still be heavier than WRC.  I think Luan is junk, brittle, grainy and probably won't bend well.  Meranti is good stuff, but another heavy wood and does not bend well, though probably could handle the bend on a long narrow kayak.  Laminated stock would resist bending even more than solid.


Dave Finnegan
http://charlestownboatworks.com

1967 Pearson Renegade  "Hirilondë"

Spindrift 9N #521 -  many KudzuCraft SoF kayaks


  #3 Kudzu

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Posted 12 February 2013 - 08:29 AM

Just finished lofting and believe I have found an error.  (Checked the first 8 pages and didn't find it)  Pg 61, new edition, Bow offsets, second line down shows x=4, z=2- 3/16.  Hope I am not missing something, but I think it should be 1-15/16.

 

I spent some time this morning trying to see if there was a problem and I don't see one.  I checked the drawing I made to get the dimension and everythign checks.

 

I don't list all these in the book, just to much detail but I am showing the following:

1* 1.83

2 * 1.99

4 * 2.18

6 * 2.40

8 * 2.67

 

If your bending a batten around the points and your getting a fair curve and it doesn't fall exactly on the points that is OK. There can be some variations, that is normal. But as far as I can see the numbers are right.

 

As far the radius on the stringer it's really a personal choice. I have run them through my shaper with (I think) a 1/4 radius and I have just knocked the corners or with a block plane and some 80 grit to a very small radius. Nothing critical about it and only affects the looks and isn't that noticeable.  I have built them with nothing more than sanding the corners smooth.

 

I am all about keeping the weight down, so I have never used anything but cedar. I can't recommend cutting down the size of the stringers because I haven't tried it. Might be some unexpected problems so I never recommend something I have not tried.  


Jeff
Kudzu Craft SOF kayaks
www.kudzucraft.com

  #4 Charles Treichel

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Posted 12 February 2013 - 08:50 AM

It seems one of the problems with "luan" is that no one seems to know what it actually is.  Some say meranti; some say balau, totally different properties.   Anyway, I have ruled it out mostly because I am not sure it will hold up.   Although it is twice as heavey as cedar, it is also about twice as strong so I could appropriately reduce the cross section..  I'll make up a test piece and see how it behaves.

Here are some good websites (there are many others)  on properties of a wide variety of woods.

 

http://www.plantra.c...t-service.pdf 

http://www.fpl.fs.fe.../chapter_05.pdf



  #5 Charles Treichel

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Posted 12 February 2013 - 09:59 AM

I am working from the 2011 edition of the book.  Pg 61 shows the bow offsets in inches. Pg 63 also shows them also in inches, not mm.   The patterns are coming out looking like the picture on pg 57, using my judgement as to what the z dimension should be at x=4, 1-15/16, not 2- 3/16 which creates a 1/4 dip where the picture shows as straight.  No problem, but I am worried about other possible errors.

The stringer notching is charted on the stern upright, but not on the bow; I'll just notch it for what the stringer turns out to be.

 

On pg 43 you show tabs on the stern upright.  Do the loftings allow material to do the same, or is this just for the kit plans?

 

 



  #6 Hirilonde

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Posted 12 February 2013 - 10:00 AM

There are a lot of woods that are misrepresented, and often by the seller.  Meranti is Shorea Platycladus.  My only experience with Luan is the subflooring and hollow doors (plywood).  What ever it is it is coarser than the Meranti I buy as decking which I also use for lots of stuff.

 

Sea chest, um, err, toy box of Meranti for my soon to be born grandson:

Attached File  DSCN2265.JPG   96.01KB   2 downloads


Dave Finnegan
http://charlestownboatworks.com

1967 Pearson Renegade  "Hirilondë"

Spindrift 9N #521 -  many KudzuCraft SoF kayaks


  #7 Kudzu

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Posted 12 February 2013 - 10:29 AM

If you want the tabs you will have add them after you loft it. I did not allow for that. I think they are worth the effort to add. Makes assembly easier.

 

I am going to suggest you double check your layout on the bow. If I change it to 1 15/16 I get a hump then.  I drew it out in CAD software, then I created a grid and measurements of each point. I am looking at the bow full size.  I double checked it this morning and I can't find a mistake. Not saying I didn't make one, but I can't find it. All the dimension check.


Jeff
Kudzu Craft SOF kayaks
www.kudzucraft.com

  #8 Charles Treichel

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Posted 12 February 2013 - 01:41 PM

My mistake.  My copier smudged out a digit on the previous station making it look off by 1/4"  (I copy the offsets from my book to use in the shop).  Sorry for the confusion.



  #9 Kudzu

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Posted 12 February 2013 - 05:42 PM

No problem. Glad you found the problem.

 

Be sure and post photos. I only know of one other Poco Barta that was being built and the builder never followed up on it. So I don't know if anyone has built one. Lot of Curlews have been built though.


Jeff
Kudzu Craft SOF kayaks
www.kudzucraft.com

  #10 Charles Treichel

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Posted 14 February 2013 - 06:45 PM

Will do.  This is my 5th small boat.  I am building it because I want to try something different.  My last boat built from plans by Harry Bryan was a decked canoe.  Fiddlehead 12'.  I got a little carried away on materials and it weighed almost 60#!

 

 

 Attached File  Fidddlehead.jpg   22.29KB   5 downloadsAttached File  Fidddlehead.jpg   22.29KB   5 downloads



  #11 P Douglass (WA)

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Posted 15 February 2013 - 08:50 AM

pretty!


P Douglass
1st build - Curlew