David Tyler. I'm sure your correct with your longitudinal construction of Deck Beams aand stringers. When we were building relatively high speed planning Launches in timber, if the longitudinal members of the hull (Chines, stringers, etc were let into the bulkheads, we had problems with broken stringers on occasions, when a Launch fell off a wave at speed. When we ran the longitudinal timbers of the hull over the top of the bulk heads, we did not experience these failures as the bulkheads could not create a hard spot to the same degree. Pretty much the essence of Cold Molded Multi Skin Construction. However, Annie's approach is the traditional method for plywood decks and boats I was involved with building 40 years ago using similar construction to Annie's's are still going strong. As with all things Boat, Timely Maintenance is the Key.   

  

Annie wrote:

Graeme wrote:

I think you did absolutely the right thing, and I disagree with your remark that it was “hardly necessary” to cover the 6mm butts.

By coincidence, just this afternoon Marcus and I were discussing the failure of the plywood deck on the old scow I built 50 years ago. (I did not make the deck, the next owner did it). It was a single skin deck, with butt joins landed on bulkheads. The bulkheads are actually 3.5 inches thick so no butt straps were used. 40 years later cracks appeared at all these joins – and later, rot set in. Bulkheads are hard spots of course, and I think the joins would have been better between the bulkheads, and done with plywood butt straps. To make matters worse, the deck was then just dressed with canvas and paint.

I think we are, perhaps, at slight cross purposes here, Graeme.  What I meant was that I didn't believe that staggering the joints would make the deck stiffer or more stable. I don't think that in a reasonably flat (fore and aft) deck, the bulkheads should be creating  a hard spot.  I would have thought that is more of an issue in the curving surface of the hull.

What you appear to be talking about is water ingress in the joints.  From my reasonably extensive experience and ownership of plywood boats, my conviction is that the difference between plywood boats that rot and plywood boats that don't, is epoxy, carefully and correctly applied.

Still, 40 years is pretty good going!

I think that a large part of the problems with Graeme's plywood joins over the bulkheads is that there would have been inadequate landing for each plywood sheet, There must be a formula somewhere which states how wide the butt strap should be for a given planking thickness. But as way of example the designed butt strap width for the 6mm thick plywood on my little catamaran is 120mm, so a landing of 10 times the width of the plywood. As the plywwod is worked and walked on with Graeme's scow, movement within the joint would result, which would lead to the cracking and degradation of the joint. I don't know that even the use of epoxy would have helped in this situation. 

Having seen the deck that Annie is building I very much doubt there will be any degradation of the plywood joins for many years. In fact Annie you can probably give a genuine 'lifetime warranty' with your creation.

Well done Annie you are making great progress.

I want to pick up on one sentence from your blog, in which you refer to laying strips of 4mm ply over a first layer of 6mm:

I laid them out to cover the butts in the 6mm, but in truth, as those all landed on beams and stringers, this was hardly necessary. 

I think you did absolutely the right thing, and I disagree with your remark that it was “hardly necessary” to cover the 6mm butts.

By coincidence, just this afternoon Marcus and I were discussing the failure of the plywood deck on the old scow I built 50 years ago. (I did not make the deck, the next owner did it). It was a single skin deck, with butt joins landed on bulkheads. The bulkheads are actually 3.5 inches thick so no butt straps were used. 40 years later cracks appeared at all these joins – and later, rot set in. Bulkheads are hard spots of course, and I think the joins would have been better between the bulkheads, and done with plywood butt straps. To make matters worse, the deck was then just dressed with canvas and paint.

I realise your laminated deck is not quite the same thing and a better proposition, and I have no doubts about your “workmanship” (gender error) – but from what I see now, I think it is good that you lapped over the butt joins with your second layer, and I do not think beams or bulkheads should be regarded as butt straps.

That’s my tuppence worth. I think you are doing a great job.

Annie Hill wrote: Don't hold your breath, David.  I have found that a lot of wooden boat lovers are somewhat elitist about including plywood under the category 'wooden boat'.  I've even heard the Carrs' Curlew denigrated as no longer being a 'real 'wooden boat, because she'd had two layers of wood cold-moulded over her! 

Call it Gopher wood: "In the Concise Oxford Dictionary 1954 edition under the word 'gofer, gaufre, goffer, gopher, and gauffer see also wafer' it speaks of a number of similar things ranging from wafers as in biscuit making (layers of biscuit) or in a honeycomb pattern, to layers of lace in dressmaking, and hence goffering irons to iron the layers of lace."

Gopher wood seems to have a long tradition in wooden boats...

Thomas wrote:

I'm waiting every sunday to see any update of Annie's blog, and it's a real pleasure to see that the boat is closed ! As usual a very good job, I'm a little more impatient for launch date !

I usually write on alternate Sundays, Thomas, so I'm sorry if you feel let down when I don't!  I can assure you, that I am even more impatient for the launch date than you are.  However this boat is not going to be launched until she is finished, and with everything on board, right down to the fresh food in the lockers!  When she is in the water I want to enjoy her, not spend the rest of my life working away at things I should have done when I was building.