Mashup Trimaran (continued)

Discussion in 'Multihulls' started by Bigfork, Feb 17, 2021.

  1. peterAustralia
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    peterAustralia Senior Member

    Yes, just use bathroom scales, add the weights. The exact same method is used to weigh light aircraft (heavy aircraft too I believe). They put a bathroom scale under each wheel and add up. Have seen youtube videos of this for experimental planes and they want to check the weight after construction is completed. As to beam thickness, my guess would be 4 inches or so,,, but would have to do some maths,,,,, maybe give me a short time and I can give it a go
     
  2. Bigfork
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    Bigfork Junior Member

    Greetings wise people!
    Pictures are of the aft box beam, minus the closing layer, and upside down.
    Also need to install blocking for hinges/fixatives to main hull aft mount.
    In boat profile drawing you can see the beam colored black.
    Questions for the powers that be:
    1. Do i put a wee fillet on each of the web sections or just epoxy em in place?
    2. Do i paint the raw interior w an epoxy coating before closing off?
    (If the section is deemed too weak for the task, i can incorporate water stays. I think a rear facing aero foil section would also help to strongback the beam.)
    92D8818F-9497-46A3-AC4D-885BA7885DB6.jpeg 8D7BC293-68F0-4225-882D-162E4F60DBBD.jpeg 833C04B9-D55C-4DFE-8E74-2B9F55939C3A.jpeg
     

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  3. upchurchmr
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    upchurchmr Senior Member

    Put in your wee fillet, or maybe not so wee.
    Coat the inside of the beam, unless you want it to rot and give you a chance to change the design later.
    Looking good.

    On your fixatives for the beam on the inside of the hull, you might put in fillets with some glass to beef the up.
    All the bending load in the beam is going to be concentrated in the beam bolts and hull structure.
     
  4. Bigfork
    Joined: Dec 2009
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    Bigfork Junior Member

    00299330-9FDE-49F8-A489-885D84BA200D.jpeg 6BE5B3EA-7A35-48DD-BDE6-8C5F526A98E0.jpeg B377DAFB-9A96-42AD-8044-F239B0F5A69F.jpeg 2A47310E-526A-4127-B08E-83660BD6572C.jpeg
    I realize it’s been a while… but still tootling away. Now that sailing season is done in Montana, I can continue w my folly.
    Update on some pictures:
    Bottom couple are the fore box beam (bb) getting wrapped up. You can see the “aero” section added to force spray down and strength to bb. It’s 4x5” by 7’ (before foil). Weighs 18.5 pounds total before final glass fabric…not bad I think.

    Top 3 pics are the 3’ bb sections finishing from the main bb to the float (the 3’ section with float attached will hing up for travel.
    You can see a front view doodle in the last post to relate to. Pictures of the bb stringers getting glued up in curved jig. As the front view doodle shows, the final 3’ section must curve.
    No shortage of questions.
    I’m off the map but am still moving forward. Aiming for a spring float test which will tell alot. I’m in for only 600$ or so and lots of time. I don’t count the time as pittering in the garage is good fun!

    Couple legit questions:
    You can see the internal structure of the bb. The web bits (on 8” centers) have a “breather” whole to allow air to move throughout. Is that necessary?? On the fore bb, I skipped it. Essentially, each bay is totally sealed once sheated.

    2nd question: does 6oz glass sound appropriate to wrap bb in?
    Once the blocking is added for attachment, and the hinges fabbed, it will be time for a mockup!

    thanks folks!
     
  5. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    Looking good BF!
    No, but you made your boat a little bit lighter. Make them bigger.
    Yes, but multilayer where needed.
     
  6. trip the light fandango
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    trip the light fandango Senior Member

    Looks great Big fork, I'm a bit puzzled by the thickness of the pink triangular bracing blocks, they could do with some dieting/ holes. filleting adds heaps of rigidity, at least 2 coats of epoxy internally,I been reading here about how condensation is a problem, bags of moisture absorbing stuff were mentioned ,Mr E I think. I would have thought that you would need to drill each brace for even air pressure with a valve somewhere mb to release pressure, I suppose there isn't that much air in there though, just don't paint the beams a dark colour.

    Gary Baigents stuff is quite similar so I would be looking at his Frog for inspiration on technique, strength , thicknesses. I really like your deck joins, nice curves, his stuff is super light.
     
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  7. Bigfork
    Joined: Dec 2009
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    Bigfork Junior Member

    Trip, the pink blocks in the foil section are just Home Depot purple house foam, 1”.
    Its just for compression support as the 5mil skin was too soft over span.
    For better or worse… I have snuck that stuff here and there: The sole of storage lockers in the floats are 5mil skin over 1” foam (makes a surprisingly stiff laminate), the “joists” under the main cockpit sol are filleted vertical foam, and I have used it w fabric on top of it to fair one component to another (in a non structural sense). I will likely use the cloth/resin/foam as filler to make the beam ends-to-float more seamless; I can bond layers together, stand vertically, scribe, and shape or carve as desired.

    I do have a bonding question:
    Can I use old fashioned water proof wood glue to bond surfaces that will never see the light of day (or water)?? Knowing the whole lot will get a resin coated, encapsulated?
    I have the west system bible but can’t find any solid discussion of this.
    Does every wood to wood union need to be epoxy bonded? Everything?

    And another question:
    Can glassed over spray foam ever be used to fair things, (for example beam ends to float). It is so easy to shape in a strictly cosmetic sense.

    thanks folks!
     
  8. trip the light fandango
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    trip the light fandango Senior Member

    Polyurethane glue like Gorilla grip is waterproof and fine, [and pretty toxic to handle] the issue with joins and timber and foam is water vapour ,so really each piece of timber needs 2 coats of epoxy so it can't absorb water. From what I've read here, the expanding foams have a habit of absorbing water over time and don't have much density,strength, if the foam can drain freely into the bilge it will hold less water., If the boat sits on a mooring for a while it will get heavier.. I haven't seen or used that pink skinned foam so can't comment, The polyurethane foam I have used gets a little heavier but isn't too bad, it's like the foam in surfboards hope this helps cheers.
     
  9. Bigfork
    Joined: Dec 2009
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    Bigfork Junior Member

    beam to float mount drawing.jpg

    Greetings folks,
    so a question for you guys who check sites like this every day (people like me :)).

    So in the near future is the beam-to-float connection. As you can see in my doodle (ignore the actual coffee stain and imperfect scale) you can see the micro and macro drawing. All four mounting points (2 on the aft and 2 on the fore beam) are relatively the same. The end of the beam is solid blocking of cedar. The mounting surface of the float is 5/8s ply, glassed up and ready to receive the arm. I was planning on using 1/4 stainless all-thread with a lock nut/washer below and above; top can obviously be reached easily, with my long arms I can reach inside the float through a hatch to secure the bottom nut.

    How do I do this next bit? Do I oversize the hole through the cedar to 3/8ths, temporarily cap the bottom and fill with epoxy, then re-drill for 1/4"?? Everything I read says don't let the steel touch the wood; over-drill the hole diameter and fill with epoxy so steel touches poxy and not wood. I'm not drilling the actual float mount surface till I do a final pre-fit because surely there will be adjustments to be made.

    The 8 bits of all thread (all 4 mounting points) will add up to some steel weight... Once I've bedded the float arm in epoxy and sucked it all together with the all-thread, part of me wants to remove the hardware entirely. I could brace glass fore and aft to the top sheet of the float, reinforcing the connection.

    I either plan on the steel staying in there, or remove it after the "fit" has been finalized. Leaving it in there requires proper bedding and steel to wood relationships (which I'm a little grey on) or removal. If removed, I can simply drill for the 1/4 (with a 5/16) , achieve final fit and bonding, and then pull steel and simply plug holes up. I'm quite sure the arm to float relationship will be permanent, even if the floats get used in another fashion.

    Use the steel as a temporary fixative while bedding sets......or
    Keep the steel in there (in which case it needs to be done 'right')

    Thanks people! You are super helpful! This thing is going to float this spring, one way or another :) I'm beginning to see the light at the end of the tunnel or at least the test float tunnel.

    cheers.
     
  10. trip the light fandango
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    trip the light fandango Senior Member

    I think 1/4 inch is a little light but you haven't said how long the longer one is, the washers need good surface area, otherwise it sounds right to me, judging from what I've read. Go with the size the H18 uses probably.
    Looking good.
     
  11. BlueBell
    Joined: May 2017
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    BlueBell . . . . .

    Your decision unfortunately.
    I prefer removing fasteners and filling in with thickened epoxy forming composite fasteners essentially.
    No over drilling, filling, redrilling, then sealing
    You could also use dado's and/or wooden pegs with lots of thickened epoxy.
    Consider your loads and design accordingly.

    The big washers Trip is referring to are often called "Fender Washers".
     
  12. trip the light fandango
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    trip the light fandango Senior Member

    If you don't need to separate the hulls from the beams you have far more glueing/ epoxy/ glassing surface bond area as you mention. Bolts are concentrating the load area, hopefully I've used the correct terminology here..eek. shearly,..sorry. ha. Threaded rod suggests the length is more than standard bolt lengths.
     
  13. Bigfork
    Joined: Dec 2009
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    Bigfork Junior Member

    Inkedbeam to float mount drawing 2_LI.jpg


    Greetings gang,
    Related to my last post....So I plan to do something like the doodle shows as far as aero-fairing and bracing (in green). It will eventually wind up and follow the beam down to the main hull. The aero-foil section will help send spray down and add additional strength to the beam. The neon green shows the web bits of the foil, not yet sheeted over.

    As I showed earlier, I planned on using 1/4 bolts w lock nuts to secure the beam to the float but then there's the wood-to-steel issues. On the "toe" of the mount, the thickness is about 2", on the "heel" of the mount the blocking is about 4.5" thick. The bracing down from the beam to the float will be filleted and tabbed in both directions (against the float and up the beam).

    Now I'm having second thoughts about the fixatives. If the level bonding surface is about 4x12", and I plan on bracing fore and aft (aft one is optional (?)...), do I need the hardware at all? I could use the bolts to "clamp" the float to the beam during curing, but with the bonding surface and bracing, maybe I don't need to leave the steel. And that leads to another notion.... the cedar blocking in the beam is sort of heavy! Maybe a 1.5 lbs per! If I forgo the steel pinning, perhaps I don't even need the cedar blocking in there at all. The cedar blocking was simply for compression strength for the bolts...

    Sort of thinking outloud- but now I'm leaning this way:
    Get rid of heavy cedar blocking
    Get rid of steel fixatives (other than for prefit and bonding pressure)
    Add bracing down to float, filleted and tabbed both directions

    yes, unless I'm convinced otherwise, no metal fixatives, no heavy cedar blocking.

    thoughts?
    cheers.
     
  14. upchurchmr
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    upchurchmr Senior Member

    You are designing by guessing.
    Not a good method.
     
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  15. trip the light fandango
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    trip the light fandango Senior Member

    Yep the cedar is a bit of weight.
    If you increase the glue area to include your green beam support brackets [they could be foam with a few layers of matt, they help stop beam twist] and that is glassed in that will help. The way a chainplate spreads load into the hull sides is what I would be thinking about. Glassing strapping that spreads out diagonally each side of the beam inside the hull for instance. Non woven uni directional, [I've seen carbon used for this in this forum]] like rovings.
    It's a pity my descriptions aren't particularly correct in terminology, but still. Think of load paths.
     
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