Stringers

October 29, 2014  Hours spent building to date:  283

I took a break from fairing to add the small fore-and aft stringers in anticipation of putting in the big, beefy engine stringers which take the stress of the engine and run half-way through the boat.  As I scarfed short pieces into boat-long pieces and glued them in, the boat seemed immensely stronger.  Then I put I clamped in the engine stringers to check the fit, and the structure became virtually immovable as the “egg crate” effect began to make itself apparent.

Intellectually I could always grasp how lots of pieces of small, tough materials locked into one another with epoxy and glass would be very strong.  But seeing it and feeling it was quite another thing.  My 22,000 pound motorsailer Memsahib was tough purely because of the weight of its materials — a one-inch thick teak skin, 2-inch square frames holding the skin, 3-inch floors tying the frames to the keel.  Memsahib could stand a lot of compression stress (getting whanged against a dock in a storm) and what I think is called tensile stress (bouncing up and down waves without breaking in two).  But torsional, twisting stresses (confused waves or rigging stress from high winds) would cause her to “work”  as all the pieces tried to twist away from one another at their edges.  That would lead to leaking, not uncommon in conventionally built boats.

As I look at the stringers going in, and I can see how the egg crate works.  No matter which way you try to bend the structure or push the structure or twist the structure, there seem to be about the same number of pieces taking the stress.  And they are all held rigidly against one another — very rigidly by epoxy and glass.  I’m going to add yet another layer of strength by using a lot of “biaxial” fiberglass tape with the stress lines running diagonally to all the other structural members.

When Tardis occasionally launches herself off a wave and comes down, I know it will sound like a base drum and scare me half to death.  But I doubt that any water will get in, and that’s a good thing in a boat.

Fore and after stringers tying the whole structure together.

Fore and after stringers tie the whole structure together.

I'd say this is a Hermes-quality scarf (ignore the one in back of it).

I’d say this is a Hermes-quality scarf (ignore the one in back of it).

"Egg crate" starting to form.  Resists stress from all directions.

“Egg crate” starting to form. Resists stress from all directions.

Aft end of engine stringer.  Very high on both ends, and I don't know why.  Fine everywhere else.

Aft end of engine stringer. Very high on both sides and I don’t know why. Perfect on the bottom side and close everywhere else.

 

Stringers are starting to define the shape of the boat.

Stringers are starting to define the shape of the boat.

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One comment on “Stringers

  1. Harry
    November 2, 2014 at 10:19 pm #

    Nice tidy work , love the boat too

    Like

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