I BEAMS Poltruded Fiberglass (EXTREN)

[carlosproacarlo]

Hi
I wanted to know if anybody had any experience or opinion on using poltruded fiberglass I beams for akas or outriggers. I have information on a company called Strongweld and their Extren I beams.

I am designing a low cost no frills coastal 40 ft pacific proa for the Miami area and Fla keys. I got a quote for an I beam of 20ft in length, 12x6x1/2 inch I beam. The price per foot is $41 - so around $800 per aka and the weight per foot is 9 lbs.

Since this is a pacific proa - there will be very little stress in the aka/ama connection as the ama is a wave piercing design.

Flexural Stress Length Wise is 30,000 psi and Flex module is 1.6 x10**6 psi

Flex Stress Cross Wise is 10K psi and module is 0.8x10**6 psi

I am trying to get away with the smallest I beam I can - the one mentioned above maybe over-specs

Any comments?

[nero]

seems heavy. Can you make a wood I-beem/keelson for less weight (and the strength were it needs to be) for less money? Of course this would take more time.

[carlosproacarlo]

I was consideing a modified Simpsom type of beam. I saw also from a video of Kurt Hughes a more streamline beam. Both using wood stock and ply. I guess I will have to carfully compute the overall weight of each beam but the I pultruded I beam seemed about 50 lbs heavier

[Chris Ostlind]

Carlos,

Take a look at this boat, the Multimarine L-7 trimaran, and ponder the use of pultruded beams. http://multimarine.com/L-7/L7.html

Chris Ostlind
Lunada Design

[miked2006]

How well does the sliding beam system work? I like the simplicity of the idea.

I have a Tremolino and while the consensus is that its a mistake to try to convert a Trem into a folder, I had this nagging idea about a sliding conversion,
aka the L7. Probably a mistake for the Trem, I dont claim to understand the dynamics of the Trem's flexing structure, but idea's are cheap
Mistakes are the expensive part.

Thanks,
Mike Davies