Undoing tack welds?

I'm building a Shearwater 17.  I have tack-welded the forward half of the deck to the hull, but I'm not satisfied with the fit and alignment, so I have decided to separate the assemblies and re-do the process.

I was thinking of using a heat gun and starting at the cockpit area (the aft-most part that is tack-welded) and working my way forward using a heat gun to soften the epoxy.  I plan to wedge a piece of wood between the top and bottom and move it forward as I go in order to provide some separation force.

Any thoughts on the above, or recommendations?

For re-assembly I was thinking of using CA glue instead of thickened epoxy to tack weld, the idea being that I could fit the parts together more precisely, then apply a few dots of glue working on a small secton at a time, rather than running a long bead of epoxy along the top edge of the hull (as the manual directs) and trying to align the whole mess at once.

Comments and/or suggestions appreciated.  Thanks.



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RE: Undoing tack welds?

Yep, heat gun. Used carefully. Work slowly on one or two welds 'till you get a feel for how close to hold the gun & for how long. Too far or short you risk splitting the ply's veneer, too close or long you risk charring if your heat gun's anything like mine.

Few months ago I was mortified to discover I'd bonded - BONDED - the decks of the two amas I was building for my Waterlust canoe on upside down. These things are asymmetrical in every aspect & I wasn't paying close enough attention to the plans.

Thus I was faced with getting them off the completed hulls before I could remake a pair then bond those on, this time properly oriented.

(Complicating things a bit were the non-metallic brads I'd used to hold them in place as the epoxy cured. The deck ply was thin enough that most pulled right through it, the rest pulled free of the sheerclamps fairly easily.)

Took me about 45 minutes getting each deck peeled off. Would have been hours using a pull saw or other means had I not had that heat gun from back in the early '80's when I was making custom countertops. And the resulting surface left on the hulls' sheerclamps wouldn't have been as undamaged as what the heat gun let me achive simply by pulling the decks up then running a putty knife into the heated seam.

RE: Undoing tack welds?

Hi air dog, 

I have built the shearwater 17 before.  its a beautiful, amazingly good performing boat.

i am a bit confused about your description and approach.  you describe that you have tack welded part of the deck to the hull (e.g., the deck was completed and the hull was completed....and you are now mating the deck and hull?).

the reason i say this is that usually these elements are not tack welded.....but they are temporarily held together with strapping tape....and fully aligned....then taped together from the inside.   not really tack-welded in the traditional sense of how the term is used.

that said, if you need to seperate a hull from a deck my first approach would be a thin-kerf saw like: https://www.clcboats.com/shop/products/boat-building-supplies-epoxy-fiberglass-plywood/booth-tools/beading-saw-with-woodpecker-tooth.html

i have done a lot of 'undoing' things in my experience.  sometimes heatgun, sometimes a saw like this.  based on what you are describing here... a saw like this is thin enough to typically fit into this gap so you would not end up losing any wood.  a saw like this will cut through an epoxy tack very fast...faster than a heat gun...and none of the risk of a heat gun in terms of effecting an already glassed hull/deck.

as you are undoing the tacks, you dont really need any 'force' to seperate the pieces.  i would avoid force.  if you need force, you have not cut the tack and that is what you need to do.  the woods natural spring will seperate the pieces as you work your way forward.

hope that helps....


RE: Undoing tack welds?

hi air dog,

just read your description again....and do want to suggest, that after you get hull/deck seperated, that you reach out again on how the hull and deck get joined.  

the process for joining the hull and deck of the shearwater should be very low drama as everything should be held togther tempoarily with strapping tape.....giving you plenty of opportunity to check/confirm alignment before any epoxy comes into play.

while not a shearwater, here is a picture of what i mean by strapping tape to temporarily attach the deck to the hull:

and here is a picture of my shearwater:


RE: Undoing tack welds?

   Thanks for the replies, folks.

To clarify, what I was doing was mating the upper half of the boat (deck and shear panel assembly) to the lower half (hull).  I did this per page 47 of the manual.  Summarized, it says:

1. Place the deck on the hull, separated by two sticks supporting the hull. 

2.  Stitch the deck to the hull loosely.

3.  Mix some silicone-thickened epoxy and apply along the top edge of the hull (this is what I'm referring to as "tack welding").

4.  Remove the two support sticks so the top is resting on the bottom.

5.  Tighten the stitches.

After the tack welds have cured, remove the stitches and proceed with fillets and fiberglass tape on the inside of seams.

My halves fit together nicely before I fiberglassed the underside of the deck, but apparently I managed to distort the deck as I had a tough time getting it aligned during the above tack weld process.

I will separate the halves using a heat gun, saw, axe, or dynamite.  Then I will re-mate using the tape technique instead of tack-welding. 

My list of "things to differently next time" continues to grow. :-/

Thanks again for the input.  h, your Shearwater is beautiful.

RE: Undoing tack welds?


Per your suggestion, I'm back.  Hull and deck are separated.  Next step is to clean off all the excess epoxy and sand the mating surfaces (top edges of hull, bottom edges of shear panels).  Then I'll be ready to mate the two halves again.

I'm open to suggestions on technique.  I think the idea of using filament or strapping tape to hold things together, then using fillets/figerglass tape on the insides of the seams sounds like a good plan.  Should the outsides of the seams be filled with thickened epoxy?  Any other input would be most appreciated.


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