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Have been working on building the crossbeams for my Tiki 21 and have started making fillets.  The radius on the plans seems large - will require a lot of epoxy which will add a lot of weight in the end.  Just wondering if they need to be that "stout" to weld everything together.  Looks like it will take four liters of expoxy to complete as per the plans.  What have other builders done?  Stuck with the plans or made them a bit smaller?

Cheers

ScottO

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Hi Scott,

I am not really an expert, but from what I read, the stability of the cross beams is crucial to get a safe boat. You find some scary pics in the web where people seem to have modified the beams. So, I would build them as they are designed.

Martin

I felt the same way, Scott.  We ended up using smaller (~2cm) radius fillets (and a mahogany top plank) and after 2 summers use I've seen no failures or cracks in the beam fillets.  Be sure to use a strong/bonding filler like microfibers.

Here is one of many blog entries that discusses our beam build and an associated photo gallery:

http://econscience.org/tiki/2010/03/09/testing-polyurethane-and-sea...

http://www.beamreach.org/gallery/v/User+Albums/scott/tiki21/constru...

And for god's sake, don't forget the Nielson no-sanding fillet trick!  Dip gloved fingers in high-% rubbing alcohol and massage fillet when firm but still tacky until it is evenly distributed and glossy smooth.  Use a small square of brillo pad/sponge dipped in the same to clean up any extra epoxy/filler beyond the edges of the fillet.  Presto!  No sanding required in all those (*&#$_! interior corners.

Or you may glue (epoxy) a triangular stringer where the fillets should go, the stringer should be smaller than the fillet, and finally make the fillet on top of the stringer. That way you will archieve the required radius with less epoxy.

I would think this is structurally equal to the all epoxy fillet, but I am no engineer. Maybe someone might comment on the pros and cons of this path.

Thanks for that info Scott.  Yeah, have been doing 2cm radius because I found out the ply in the crossbeams is 19mm instead of 15mm so am very confident of its strength.  I bought the "work in progress" and just discovered the use of 19mm, which the previous owner/builder had used when he cut out the ply.  Imagine 15 mm wasn't available to him.

Looking forward to going through your blog for other bits and pieces too.

Cheers



Scott Veirs said:

I felt the same way, Scott.  We ended up using smaller (~2cm) radius fillets (and a mahogany top plank) and after 2 summers use I've seen no failures or cracks in the beam fillets.  Be sure to use a strong/bonding filler like microfibers.

Here is one of many blog entries that discusses our beam build and an associated photo gallery:

http://econscience.org/tiki/2010/03/09/testing-polyurethane-and-sea...

http://www.beamreach.org/gallery/v/User+Albums/scott/tiki21/constru...

And for god's sake, don't forget the Nielson no-sanding fillet trick!  Dip gloved fingers in high-% rubbing alcohol and massage fillet when firm but still tacky until it is evenly distributed and glossy smooth.  Use a small square of brillo pad/sponge dipped in the same to clean up any extra epoxy/filler beyond the edges of the fillet.  Presto!  No sanding required in all those (*&#$_! interior corners.

That is a great idea that I didn't think about.  However, already started filleting with smaller radius fillets when I discovered the ply in the crossbeams is 19mm instead of 15.  I am the second owner/builder of this Tiki and I guess the original owner didn't have 15mm available when he cut out the crossbeam pieces.

Cheers Ricardo



Ricardo Aráoz said:

Or you may glue (epoxy) a triangular stringer where the fillets should go, the stringer should be smaller than the fillet, and finally make the fillet on top of the stringer. That way you will archieve the required radius with less epoxy.

I would think this is structurally equal to the all epoxy fillet, but I am no engineer. Maybe someone might comment on the pros and cons of this path.

Hi Martin,


Thanks for the prudent advice.  I discovered the plywood for the crossbeam to be 19mm instead of 15mm the plans called for.  I purchased the work in progress from someone else who had already cut those pieces out.  I am guessing he couldn't get 15mm ply.  So with the added strength of the ply I have lessened the fillet just a bit.  They still seem large and strong - only use will tell.

Cheers

Martin said:

Hi Scott,

I am not really an expert, but from what I read, the stability of the cross beams is crucial to get a safe boat. You find some scary pics in the web where people seem to have modified the beams. So, I would build them as they are designed.

Martin

please forgive my ignorance , but what is wrong with aluminum crossbeams . a 3 x 3 x 12 foot beam with a 1/4 wall thickness costs roughly 200.00 plus shipping . The strenght is much greater , the maintaince almost non existent and they are about the same weight at 38 pounds . I have also wanted to make this a hard connection ( using turnbuckles  ) to secure the beams in place of lashings . does anyone have any thoughts reguarding this ? I certainly would value your thoughts .

Another good idea.  Thanks Chester.  However, even with almost non-existent maintenance, I prefer the aesthetic of wood and am actually using Doug Fir with a bright finish.  

chester mcintire said:

please forgive my ignorance , but what is wrong with aluminum crossbeams . a 3 x 3 x 12 foot beam with a 1/4 wall thickness costs roughly 200.00 plus shipping . The strenght is much greater , the maintaince almost non existent and they are about the same weight at 38 pounds . I have also wanted to make this a hard connection ( using turnbuckles  ) to secure the beams in place of lashings . does anyone have any thoughts reguarding this ? I certainly would value your thoughts .

Aren't the beams curved as drawn in the plans? You would have to get the alloy bent somehow. I think there is a Tiki 21 in San Fran with alloy beams, but I thought they might be custom welded jobs.

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