Design of wood epoxy trimaran beams

[Adrian Baker]

I'm looking at a fairly simply attachment plan something like in the pic of Dragon fire

 

[IvanAntun]

Thanks Adrian this info is great. Especially the example, it illustrates further the well-known principle of simplicity being the generally best way to go. Slightly raised glassed grooves, two brackets, bolting, and voila.

Have you already started with other components except the beams?

 

[redreuben]

Have a look in the Buccaneer 24 builders forum for a boat called Capricorn. He built gullwing beams to replace tubes and wire.

 

[bruceb]

Adrian, I have been watching this, I have some experience to share. I had a Buc 24 with a tall rig that I still help maintain, I currently have a modified Dragonfly 800 with fixed beams and I am just finishing a refinishing project on my Buc 33. I have "improved" the beam on my Fly from 19'6" to 21' and I use dyneema waterstays with a better attachment system at the beams. I have raced it pretty hard for the last three years and I really like the extended beam and the dyneema stays. My stock alloy beams had some salt water damage where the waterstays attached so I cut them in half, turned them around and extended them about 18" with an old Hobie cat mast section in the middle that fit well inside them. I am very pleased with the result, I do get some creaking but every thing has held up well and the boat is fast and more forgiving with the extra beam.
I wish I had extended the beam on my 33 to 26' or even 27', much closer to modern tri's ratios. Before you finalize your design, take a look at modern tri's, Bucs were designed a long time ago!
On another note, I did a lot of research several years ago trying to design a folding system for my 33. I decided not to rebuild it that way but I did get some good feedback on this forum. Look at my threads on the Buc 33 rebuild and some on the Buc 24 thread also. I will try to post some more soon.
Bruce

 

[Adrian Baker]

Hi Bruce, could you describe how the beams are attached to the mainhull and floats on your dragonfly with fixed beams maybe a photo or 2 would be great cheers

 

[bruceb]

Adrian, the main hull has the beams stuck through it. At the front beam there is a ply/glass side to side box tied into the deck , DB trunk and a built up area at the hull/deck join. At the rear the hull and deck are just built up some where the beam goes through. One 3/8" bolt is used at the outer deck flange each side to locate the beam side to side. Remove the bolts and the beam slides out for transport. The Fly seems like a little more flexible boat than my old Buc 24. The Bucs use a three part beam with the middle section well bolted to double cross bulkheads in the main hull.
The Fly floats have a saddle with a thin stainless strap bolted over it to the rail lips of the float. The Euro Fly's have a glass sleeve on the float deck that holds the end of the beam. Both designs seem to work, the strap design seems easier to assemble, the glass style looks more durable if the glass is strong.
The float beam saddles on the Buc's have proven to be a very leak prone design with water getting down the bolt holes and rotting the wood inner structure. They are very strong when sealed and in good condition.
I will try to take some photos later this week and post them.
Bruce

 

[Adrian Baker]

I find so many threads end in a dead end with one not knowing what ended up happening . So I'll add a few pics as I finish this beam part of the build. I made half molds of the beams and glued one half to the deck the other half will act as a clamp once I add bolts ect.

 

[Adrian Baker]

Well after alot of jigery pokery I was able to set the boat up and glue the fiberglass sockets to the float .I now have to put it all apart and glass it all up

 

[nueva30]

In a plywood and wood crossarm, what carries most of the load, plywood or wood? I'm assuming the wood? Would thicker plywood on the vertical webs help with stiffness and load carrying ability? If the crossarm section were made larger to separate the timber carrying most of the load farther apart, would it benefit the stiffness and structure?