My ol 15ft canadian canoe needs a rebuild. The hull is very floppy n flat thru the middle. I use a 25mm pipe to induce a V shape into the keel line, supported from the 2 thwarts. Id like to make this shape (rocker n V) permanent.
1. Would carbon on inside of hull covering floor be of any benefit?
2. What could i use as stiffener inside hull along the keel line? (Maybe a pipe cut lengthwise)
3. Must be a light weight fix. As i lift this over my head onto roof racks. Already weighs 30+ kg.
Any ideas guys?
Only a guess as its a little hard to visualise (you are using a bit of pipe vertically to push the keel down?)
I'd cut a bit of 5 ply to the correct rocker you want and stand it up in the bottom - so it will look like a surfboard stringer....
Push the hull to where u want it with the pipe/s
Pour resin around the wood and let it set
Remove structure that was holding the rocker in- as by now your glued in stringer should be supporting the shape
Glass over /around your keel stringer
Carbon too expensive, and flat laminating over the floppy hull may not keep the shape you want.
Mark, yep vertical pipes push down from thwarts to hold keelson pipe on centreline of hull. I want to make a glass mini 'I'beam kinda thing to set rocker n V permanently. Beam can only be about 15mm high. Width doesnt matter.What other material besides ply could i use. Needs to be fairly stiff over 3m length.
Hey Olskool, have you thought about maybe a couple of ply bulkheads glassed in to act like ribs? Maybe even shaped to become thwart seats 
Paddles, yep ive already stiffened around gunwales. Ribs/bulkheads would be great. But i need most of floorspace open longitudinally to stash my crabpots fishing rods etc. I fish solo from the middle adjusting my seat position according to trim requirements. Its also gotta seat 3 for tribe outings. Hmmmm.....
You could make it really stiff all kinds of ways...... expensive ways........
Ply stringer and drowned in resin will be cheapest, and still very stiff in the vertical axis.
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hey olschool i sent you some photos of the box that fits in to my canoe also can plug in 1 of the out riggers to stabilize it and stand up paddle the box holds the bottom from flexing
Grich, thanks mate. Did you make it? But i need open cockpit space. So the ply stringer idea is probably the go.
So 15-20mm vertically is about max thickness for stringer. Any particular width? 50mm? Taper the edges. So glass easily conforms to shape. Chopstrand or cloth? About 300mm wide under length of stringer. Then a few layers over the top? Lay it all up in one go?
www.bunnings.com.au/knauf-insulation-50-x-600-x-1200mm-xps-multi-use-foam-board_p0811028
This stuff might be the ticket if you don't wanna use ply. Turn the bottom of your canoe into a "sandwich" construction. Some shaping may be required.
Can we have some photos to bring meaning to the thread.
Maybe one one with a mast attached ;-)
I built many kayaks and canoes back in the '80's. Waaay too many really. 
The most common method for stiffening the bottom of a fiberglass canoe was to use something cylindrical, or better, half cylindrical, down the centre line inside, and glass over it with a couple of layers of fibreglass, usually CSM. The core is incidental and just there to form the shape. It could be a bit of rope, or better still a shaped piece of PVC foam, but usually I used thin plastic conduit tube about 3/4" to 1" diameter and sliced it in half to make a upside down half cylinder shape. Don't forget to thoroughly sand the bottom of the boat to help the resin adhere to it.
On lightweight competition Kayaks, I often used a stip of 4mm Corematt with a layer of glass or carbon cloth over it to make a sandwich, but I think a PVC foam stip, a feww mm thick would probably be stiffer and absorb less resin, and be even stiffer again if it was shaped in a half cylinder. This was often done in conjuction with transverse ribs of the same construction in the widest part of the hull. One consideration is how stiff you actually want it. On whitewater kayaks we didn't want to make it too stiff as the hull needed to flex a bit over rocks etc. That is why we used a flatter rib profile and Corematt. If you make a rib too stiff it may delaminate from the hull if it gets loaded too heavily.
Glass fiber is very good in compression so don't get too carried away with other exotic materials. Just make sure it is thick enough to give the shape the required stiffness.
Edit: I just had another thought. It might be lighter to use a slice out of a sheet of corrugated fibreglass roof panel to form the shape. Sand it well on the side you are glassing over though!!
Jirvin4505, camera lens on my phone is cracked atm. Will see what i can sort. Imagine this (Ive got it set up as giant slalom. Well over 400l volume. 1m wide. Footstraps outboard n mast position just fore of centre.!! Bloody thing still wont plane,but glides like nothing else.)
Will get a pic of the 'War Knu' asap.
Sailquik, im a sparky so the half conduit sounds great. Non porous non corrosion lightweight. Awesome. 40mm cut in half should be the go. Im on to it. Thanks.
Oldskool I have a snapped 100% carbon sdm mast that you are welcome to use if it helps
Select to expand quoteMrA said..
Oldskool I have a snapped 100% carbon sdm mast that you are welcome to use if it helps
Now thats a great idea!!! Rdm top would be ideal. See what ive got in the stockpile. What ever i use has to be rigid enough to induce the rocker into the hull, without flattening itself out while the glass cures. I dont want to have to make a jig up to support it while curing. Quite a bit of force needed to get desired shape.
It's polystyrene so you need to use epoxy.
I've got a few sheets I'm using for a project and am planning on epoxying over it, but yet to do any. It cuts nicely on the CNC, as well as with a hot wire cutter.
I checked the specs of the above foam more, and being XPS foam it should be fine with epoxy resin.
But it can offgas badly which makes it delam, needs to be rough sanded and left in sun for a few days then laminated - and heavier lam than usual to be safe.
Safer with a high density EPS...
After successfully repairs to his new light wind weapon-
Oldskool was seen testing his latest Ezzy sail at GB
