Shear-web ?

Discussion in 'Multihulls' started by BobBill, Feb 28, 2020.

  1. fallguy
    Joined: Dec 2016
    Posts: 3,567
    Likes: 505, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    A piece of 1708 would be plenty methinks.
     
  2. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Whatever! It is a boat...your choice but passengers/crew count!!!
    There is nothing wrong with simple in the beginning, in any case.
    Seems simple is best in the beginning and always best later...
    Just assume what the corrections might cost and proceed.
    I, for one, prefer to handle paper one time only - never desired winning a Darwin Award.
    Safe is healthy...as "unmasked" dodgers of sound mind admit.
     
    Last edited: Nov 20, 2020
  3. fallguy
    Joined: Dec 2016
    Posts: 3,567
    Likes: 505, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Did you ever even specify the size of the ama?

    A bunch of pink foam glued together and encased in glass is pretty stiff.

    That blue one in the linked photos is a Dierking version. Just go to Menards and get a piece of Roseburg 1/4" ply. Might want to scarf it.

    When I said use 1708, I was guessing at your sizes.
     
  4. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Fall, the outrigger (ama) is 16,' LOA as in "Hobie 16"... "starboard hull side" noted above... avatar is boat and in the photo bin here. No asymmetrical ama rudder needed.

    Boat specs are: 19' LOA, Beam 8'/10.' SA = 2202, no battens. Loose foot, hook and loop to carbon/6061T spars, conventional tack-end attachment. (no levers etc.)

    Stiff it might be, but I have the old H hull too and do not wish to deal with ship cost etc...Plus, would 1708 be stiffer than half the Hobie hull?

    Am figuring 2 8' foam sheets is more than enough material for 16'...ama plan is for on 12" asymmetrical 14" deep shape. And, if more needed, easy pick up.

    Also need to have sturdy attachment for 6061T pylons which bolt to shear to attach to fore/aft akas, plus the (unplanned) chainplate forward. (Plan was to have unstayed mast, but Hobie 19 hull too flimsy, per here, and safer is smart. Sort of a PIA but doeable, so far...

    Ama must be stiff enough to handle crew/cooler and moi, besides chop and heel pressure when on starboard tack. reach or beat...
     
    Last edited: Nov 20, 2020
  5. fallguy
    Joined: Dec 2016
    Posts: 3,567
    Likes: 505, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Order a piece of 1/4" Roseburg marine ply from Menards.

    scarf or butt block the seam with epoxy

    one piece enough for two amas
     
  6. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Fall..., Thanks...while you make sense, at this stage...no rush. And seein' as I have the Hobiecat hull, why should I not use its slab side as both shear and ama hull side? I imagine it will be a bit wiggly, but should hold the pylons. Seeing I already have it...should do it...I kinda like the idea of salvaging i

    BTW, the rig is affording lots of experiments, even using a seldom seen Clamcleat Bollard. ..and have yet to install the sprit and the wee jib...will likely do in August if still on the hard, and boat is not broken. I have yet to run it in a gale...chicken me.

    I forgot one spec, weight...350# rigged, no crew or cooler, soon to be 300#.

    BTW, if you do on-line sear for "Popular Mechanics Malibu Outrigger Build," (sorry, thought was Mech Illus) you'll see the ply ama...I worked off original MO plans toc fashion salvaged plasti rig as close to Seaman's venerable original rig as possible. (Hobie used the MO as idea for his cats)...

    Those MO originals are now very rare, and likely only place to find long spruce spars etc. Malibu effectively shut off the beach to outsiders, but might change as population density lessens. Only two reasons for C-19: (Population density and population density.)
     
    Last edited: Nov 21, 2020
  7. Tom2x4
    Joined: Nov 2017
    Posts: 5
    Likes: 3, Points: 3
    Location: Philly Area

    Tom2x4 Junior Member

    u could try corrugated plastic sheet, brand name Coroplast, same stuff political signs are made of.
    (if i'm reading this right and you are using as shear web between XPS foam)
    its polypropelene..u might need to test that your glue makes a good bond, and/or scuff up/score properly.
    pic attached $20
     

    Attached Files:

  8. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Tom thanks.

    The ply shear is easy, and has been proven...only thing is replacing the dusty mess of foam sanding with/by wire cutting and epoxy-less fairing with long board.

    Am looking hard at the product you note for other uses.

    Also, have the "shaped" Hobie hull side to used and keep from landfill. (Did you know cured epoxy does not breakdown...? I only found out about that last year. But, landfills are better than water for these hulls.)

    Truly, my only serious concern with this rig, was the weak Hobie 19 main hull that forced me to abandon the unstayed mast (ala Wyliecat17), but no wishbone boom. Rest, including current ama, was fine...but new, lighter foam ama has been planned since I bought and devoured Dieking's book.

    Thank-you again! For the info...
     
    fallguy likes this.
  9. fallguy
    Joined: Dec 2016
    Posts: 3,567
    Likes: 505, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    The dusty mess is a good thing. By breaking the surface of the polystyrene, you create more surface area for the lamination.

    if you hotcoat it with thickened resin; it will be less likely to shear and delam from the foam...you cab also buy denser pink or blue board and they have better shear as well, but weight tradeoff
     
  10. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Try cleaning garage of foam dust...
    Try a hot wire...works very well, even if soft glue used and no mess, just a smell.

    AND, has added benefit of semi-sealing foam at joints.

    Besides, if the foam holds together, who cares?
     
  11. fallguy
    Joined: Dec 2016
    Posts: 3,567
    Likes: 505, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    you want the foam dust; laminate is better

    use 40 grit; entire surface; it probably increases the bond area by about 33%

    plus, impossible to hotwire to fair

    I have tested this out.
     
  12. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Fairing awaits...There are always gives-and-takes..foam is still best lightweight ama choice..

    Dierking might not agree, but bet he loves solid foam o'rigger...
     
  13. fallguy
    Joined: Dec 2016
    Posts: 3,567
    Likes: 505, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    solid versus what
     
  14. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    To me, composite is soft, unless, a matrix like glass in resin...cured. The hobie hull is thick and will hold bolts...that is solid.
    Will try to post pic of H-16 hull cross section I have. Plan to use the flatter side, post cut.

    I might add the pylons in the pics weigh and replacements are much much lighter.

    Consider weight reduction at 16' will be near 75 lbs with no concerns re moisture, draining, etc.
     

    Attached Files:


  15. BobBill
    Joined: Oct 2009
    Posts: 750
    Likes: 13, Points: 18, Legacy Rep: 157
    Location: Minnesotan wakes up daily, in SE MN, a good start,

    BobBill Senior Member

    Aside from being a bit heavier than 3/16 Okuma, for the foam shear-web, seems using half the Hobiecat 16 hull is wise choice, and using 2" OC or Dow foam is pragmatic...not to mention low cost.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.