I’ve just got hold of some Birch ply, 20mm thick, 13 layers - decent stuff!!
I wondered if some of the longer sections could be used for a stringer. I know 20mm is a lot thicker than the norm but is there any reason not to? I could rip it down thinner but seems a bit of a shame to…
cross grain will plane down like shit.
When using plywood for a stringer I have shaped the stringer first before glue-up, then shaped the foam down to the stringer. But I have also done it the standard way, shape the stringer with the board. I used 3/16" plywood, and it wasn’t too bad to work with.
Many layers of that plywood are going to do absolutely nothing for strength, likely the exact opposite, simply add unecessary weight, and will cause extraordinary amounts of cursing when shaping planing and sanding. The 90 degree grain of some plywood layers will rip out with hand or power planer, dull blades quickly, and cause smoke filled burning glue curse fests among tool throwing curse fests, and you will regret ever even considering the possibility of a thick plywood stringer until they roll you into an incinerator or bury you underground.
The grain of plywood which also winds up perpindicular to the surface to be laminated, the end grain, will drink SO much resin, that there will be dry white spots if not outright bubbles blown through the lamination, unless you take the extra steps to saturate just the stringer, many times, before actual lamination.
Laminated stringers are nice, as one layer at a sight different angle to another layer will bridge any inherent weak spots in any particular layer, but plywood is largely 90 and 0 degree, rendering half of the layers absolutely pointless in a surfboard stringer application, at least if the board is actually going to be surfed.
I had to go back and double check myself. I have done boards with pre-shaped stringers, and I have done several plywood stringers, but as far as I can tell the only plywood stringer on a foam board was this 6’ 7" stubby I made myself. The other boards had typical stringer wood, or the plywood stringers were on wood boards, a different animal.
But this board definitely has a plywood stringer, and looking at the pictures I would say it wasn’t pre-shaped, it was shaped with the board, and it wasn’t a big problem for me. I went back and read through the build thead, and nope, nothing at all about the plywood stringer being a problem. I used good quality plywood, and the exterior laminate layers of the plywood were lengthwise, so the opposing grain was bordered by wood layers, not next to the foam, which is typically how plywood is sold, the lengthwise layers are the exterior layers.
Its been a while, so I can’t recall all the details, but I think I probably used a sander when working near the stringer, or maybe I set the planer on very shallow cuts, but at any rate I have no recollection of it being a big problem in shaping, or in any other way. Maybe I just got lucky? Be interested to know if the dire predictions of problems are backed by photos and actual experiences, or just hypothetical??
I’ve No experience with a 20Mm wide multi layer plywood stringer, or shaping it near foam so my hypothetical predictions of doom and frustrating tool throwing curse fests are without supporting data, but I’ll stick with my opinions regarding the attempting of it.
So many plywoods will be called birch or oak, but that is only the very outer veneer, and some many plywoods have considerable voids which will appear in the worst possible spot because murphy said so.
Now if were aircraft grade plywood being considered…
I’d still pass.
Birch Plywood … is It Finnish Birch, or Russian?
I’ve got a finnish birch plywood skateboard deck and tuning the outline with a sharp low angle hand plane was a no go. Anything but sandpaper was to be avoided
I get it now, 20 mm is the problem. I would agree thats asking for trouble. I just looked it up, thats like 3/4", way too thick.
I thought it might be a no no but I don’t mind asking daft questions rather than just assuming. Thanks guys!
It just looks so good though!
(I’ve used some previously to make a skateboard deck)
Oh and interestingly I came across this while browsing other stuff last night.
http://woodenshipsbyjcherry.blogspot.com/2010/06/bigger-wood-97-1962-hobie-template.html?m=1
3" stringer! Balsa though so much easier to shape but looks great.
Looks like 13 ply cabinet grade plywood. It would be superior to typical sheathing grade CDX or even A/C ply, as it’s much denser and often void free. The main thing about cab grade 20mm is the weight. 3/4" ply of that type is pretty dense and weighs a lot compared to luan ply and other types. The stuff is often used in high end speaker cabinets due to its density. Many concert grade speaker companies advertise the use of “13 ply, void free, baltic birch plywood”.
As with any other choice in materials, you often sacrifice weight for strength.
As mentioned, many types of plywood that specify the wood species have a very thin veneer of birch, oak etc with poplar or some other softwood in the other layers.
If I was going to do a 3/4" stringer I would do three 1/4" strips of the same wood with the grain running opposite. Basswood or spruce being common as a stringer material.
It has been said that increasing thickness in the vertical dimension of a stringer adds more strength than width will provide. IOW, the thicker your board is at the stringer, the less prone to snapping. Adding width to a stringer when the board thickness stays the same yields almost no gain in strength. Might as well do a three stringer board with offsets. Similar to the old Edwards and Hynson models of the 60s.
I’d use it for a board if I had it lying around.
Chamber it and I’m sure you can knock the weight down by half if not more.
If it’s not going in a board that will see large powerful surf I highly doubt you would run into issues with strength even if you run into a little void here or there.
Nice proper glass job and you’ll be off to the races
I’ve used plywood and I’ve also made stringers by gluing up layers of short wood to get the length I need. I try to start with a stringer that already has the rocker and profile set, but leave a little in case I have problems and for the final sanding. It can be a mess when you start planing it down to get a really nice smooth finish.
I would take the planers you have and try planing it a just a bit to see if it tears, and if so how badly, then you can decide. Thickness doesn’t matter, weight would. I have made solid 1" stringers and used 2 in boards.
A comment for the picture in number 8. I have used plywood (lines going rail to rail) for a couple of tail blocks.Looks nice and some guys will always ask, “What kind of wood is that ?” When you let em know it usually gets a second look and a smile.
Tailblock seens a more logical use of it than a stringer.
I’ve seen entire boards made with chambered out plywood as the blank - no foam at all.
If it’s going to be all wood then there are better ways of doing it than stacking a load of ply sideways then chambering it out. I’ve built a couplf of hollow wood boards but just fancied this as a side step.
You haven’t been around long enough,
youve no idea what swaylocks is capable of!!!
You could make nice fins out of that. Easy to visualize foil with all those plys.
I’m just picturing a board looking like a massive end on piece of ply now! It wouldn’t surprise me if someone did it, but it won’t be me (on this occasion! 
)
