Testing wood species to determine suitable strength?

Discussion in 'Materials' started by abosely, Jan 4, 2019.

  1. abosely
    Joined: Mar 2015
    Posts: 190
    Likes: 2, Points: 18, Legacy Rep: 10
    Location: Big Island Hawaii

    abosely Senior Member

    After not being able to do any boat building for good while, I'm back to building. Because of a bit of problem with my ticker, was offered to go back to school for while, paid for, so thats what I've doing for while. So that now thats wrapping up, I can return to boat building!

    Life has changed a bit and then my wants/needs in boat has changed some also. Don't really need/want a semi-live aboard, long distance cruiser, but something a little smaller now.

    I'm building a Gary Dierking Ulua, that Gary was kind enough to scale up 135% & stretch to 8m.
    Just finishing the strongback and molds today and will be ripping strips for it next week.

    Sorry for the long winded explanation. But that brings me to the testing wood question.

    I'm using what the sawmill guy called Albizia chocolate heart right by me thats been milled, kiln dried & planed in 1" clear boards for really $3- $4 board foot, less than a mile from me. When I started ripping some strips for Ulua, I noticed this is pretty darn nice wood. It actually seems as strong and a little harder than DF, just from messing around with it a little.

    To me it looks like Albizia, Tanga Tanga, the chocolate heart I've had & cut is more of a milk chocolate color and rather soft and fairly light.

    Specs from Wood Data-Base for Albizia, Tanga Tanga
    Average Dried Weight: 38 lbs/ft3 (605 kg/m3)
    Specific Gravity (Basic, 12% MC): .52, .60
    Janka Hardness: 1,020 lbf (4,530 N)
    Modulus of Rupture: 11,990 lbf/in2 (82.7 MPa)
    Elastic Modulus: 1,581,000 lbf/in2 (10.91 GPa)
    Crushing Strength: 7,160 lbf/in2 (49.4 MPa)
    Shrinkage: Radial: 2.7%, Tangential: 4.6%, Volumetric: 7.4%, T/R Ratio: 1.7

    From playing around with it this seems much more like the wood I've got.
    I know its a little heavier than DF, but wonder how much heavier than good tight straight grain DF preferred for boat building?

    For the Ulua Outrigger it's rather heavy, but the beaches are a bit rocky so should be durable.

    I'm going to start building a Wharram Pahi 31 stretched with 4' added in center of hulls, the hulls there are dead straight. Using the Tiki type I-beam crossbeams and 3 not 4 crossbeams. not using dagger boards as general consensus is they don't really work so well and incorporating small skeg keels, cabin top hatches will be done a bit different.

    Cheers, Allen
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