I'd like to poll Weekender builders on their building technique. Stitch and glue versus stringers and screws. Post reasons for your choice.
Dave
Stitch & goo requires a fairly heavy investment in epoxy and a higher level of quality control that I'm probably capable of. Additionally - in my opinion - some of the structural bits of the boat benefit by having a solid piece of lumber behind them. I'm thinking specifically at the stern where I used shaped 2X4s rather than bent stringers to ensure a heavy-duty connection.
Thanks, Andrew....just the kind of feedback I'm looking for. The boat is a compromise between structural strength and aesthetics. Sometimes the balance is the best you can do. I'd like to have no interior stringers to spoil the aesthetics, but I think they're needed to maintain structual integrity. Am I wrong?
Dave
The plans as drawn do not provide for a true taped seam (stitch and glue) construction style. The conversion is possible and I'm making this conversion for some one now, but unless you have a fairly good understanding of the conversion process, not something I think the average Weekender builder would (or should) attempt.
For what it's worth, a true taped seam build, rather then the glue and screw method shown on the plans, will save a great deal of weight, build effort, materials cost and the number of pieces necessary for assembly.
For example, all of the bottom gussets, joiners, stringers and bulkhead framing shown in the plans could be eliminated, in a true taped seam conversion. These are pieces that wouldn't be necessary and you'd not have to build them, install them or buy materials for them.
On the other hand as Andrew mentioned, the "goo factor" (my term for lots of epoxy work) goes up dramatically. Money wise, you'll spend less on the extra epoxy and filler materials then you will on lumber (and the saw blades to cut or paint to protect) or any other pieces the epoxy replaces. Considering that most sheath their boats and do a fair bit of epoxy coating anyway, it's not much of a stretch to step up to the next level in construction methods. Yes, your first fillet attempts will look like crap, but it'll eventually dry and you can grind it down to a manageable ugliness. The nice thing about these taped seam builds is you can screw up pretty badly, grind back to good stuff and try again with little harm.
You see the reason designers and engineers have jumped on these monocoque, homogenous construction methods is simply because wood to wood interfaces (joints), even well designed and with solid, big fasteners, transfer less then 1/3 of the single stick wood strength (before things start breaking). An example would be two 1x4's lap jointed to each other, at a 90 degree angle, along the 4" edge, forming a long "L" shape. Â But an epoxy fillet will transfer all the loads from one piece to the next. This is the huge advantage these methods offer the designer. Structures can be lighter, yet stronger, both of which you pay for when you buy materials and use the completed yacht.
I wonder, if the plans need to be revised anyway in order to do a stich and glue version, (the fillet transfers all the load? that's PFM man!) what would a weekender with a V bottom hull sail like?
(07-15-2009, 07:10 PM)Paul Riccelli PE,NA link Wrote: [ -> ]Money wise, you'll spend less on the extra epoxy and filler materials then you will on lumber (and the saw blades to cut or paint to protect) or any other pieces the epoxy replaces.
Keep in mind Paul that you are coming from this with an American perspective. In other parts of the world - including Canada, epoxies are relatively expensive and being a lumber producing nation - and living in a lumber producing region, wood is cheap.
I plan to build my Vac in stitch-n'-goo, which is why I've had to properly draw up plans and lines for her. The problem with stitch n' goo is that you need accurate measurements of everything, offsets, deadrise, sheerline curvature etc. so that you can pre-cut the pieces to fit beforehand.
I have built an s-n'-g kayak before (during shop in HS), and from my experience it is actually a very facile method of building boats. The really nifty thing is that once you have "the box" built, you can use incremental adjustments of the tension on the wires holding it together to fair the shape to an extent not possible with screw-n'-goo.
When we were building the kayak, we first built a set of female "ribs", set out at regularly set stations, whose inner profiles matched the outer hull offsets. These help align and hold the panels being sewn together. This is, I believe, called a basket mould, but it is not necessary, just helpful if you don't mind the extra scrap plywood or aspenite butchery.
My $0.02
Marcin, drop me an email when you're ready for scantling modifications. There are areas you will need tape and other places where just a fillet will do. It's important to identify these locations, to save effort and money.
Are you going to build over station molds?
(07-16-2009, 06:35 AM)Paul Riccelli PE,NA link Wrote: [ -> ]Are you going to build over station molds?
I am thinking about it, because I'm unhappy with the "average bevel angle" of 27 deg. as per the plans. What I would actually like to do is use either a block plane and chisel or a router to adjust the straight cut deck and bottom to a proper angle for said station. It seems to me from my drawings that the angle of the deadrise changes bow-to-stern by several degrees, which actually leaves quite a gap in some spaces. It would then be a relatively easy (I think) procedure to draw in splined pencil lines between the stations and pare them down as well.
Of course if building over station moulds, this begs the question why stitch most joints at all, when you can just tack onto the station moulds tehselves.
I realise that this may be more trouble than it's worth
But I am at the happy planning stage, and this year I will likely only either make up the station molds and cut the skin, or else just cut the skin. Little babies are so m'uch fun, aren't they?
Building over molds usually means you can skip the stitches for the most part. Stitches are just one way to hold things in alignment as you apply goo. I've gone away from stitches completely, preferring a well placed tacks or clamps. If well planned out, you can make your seam fillets in one shot, which saves a lot of work.
Don't worry some much about the gaps on rolling bevels. It doesn't matter at all on a taped seam build. In fact you're better off if the gaps are sloppy. Most joints I "under cut". By this I mean the inside edges, where they meet is radiused back so there is more room for goo and less wood to wood contact.
I was just discussing this on another site the other day. (
http://www.boatdesign.net/forums/wooden-...28193.html)
Attached is a sketch of three planking joints. The top row is as you'd see planking in the forward sections of a V bottom, the lower two rows the aft sections of a V bottom, which was the discussion at the time, but the principles are the same.
[attachment=1]
The far left column is just the wood to wood interface. The top one shows what I mean by "back cutting" the joint. The middle row is the way I do near 90 degree joints. I let the bottom run out past where it should be a little. The bottom row is the way most tell you to do these type of joints, with both edges flush.
In the center column, you can see the inside of the joint has been filleted and taped (2 layers). It's easy to see why I back cut the joint now, as there's lots of room for the goo, which forms a plastic (rot proof) longitudinal stringer along the joint and protects the eng grain (the most vulnerable part of plywood). The middle row, I don't back it out as it forms a natural cavity that gets filled.
The right most column shows the finished joints. The top is slightly rolled to make the 'glass lay down nice and no end grain is exposed. The middle row has some end grain exposed, but only half as much as the "usual" method and you don't need to apply filler on this side of the joint, just grind back a radius, for the 'glass. The bottom joint requires more filler to fill up the joint (another step), then has to be radiused over for the 'glass.
These steps may seem trivial, but when you have hundreds of feet of fillets, taping and general goo work, any short cuts are welcome.