Female Canoe Mold Questions

Hold on a second there fellas.

The original post said the thing was made with ply bulkheads and foam stringers with a 6 oz skin. It only revealed a 6oz skin and not even the strip materials. A stringer is not a strip.

How about everyone agree a 6 oz skin and no strips is insufficient and we start over?

Can you share the tds for the xps you used? The shear rating is probably not high enough for you to part well without plug destruction. But maybe that is okay with you. I think the 1.5" xps while not ideal would at least support builidng the mould.

If the plug needs to be used more than once for making a split mould; it may be trouble is all. Xps is a very weak bond and will pull apart super easy is all. I don't know the shear ratings of expanding foam either. But same story...

 

Having recently had a debate on this forum where it became clear that using one type of unit for CSM and a different type for cloth are regarded as normal in American usage,it would be helpful to know whether the laminate weight of 7oz is per square foot or per square yard.A 6oz per square foot laminate is sufficient for a canoe and in any event if the surface doesn't yield to a 15lb weight it ought to be rugged enough.Different considerations apply if the plug is of a size or type that might have six or seven laminators walking around on it.It also helps that a canoe hull has enough curvature that it is an inherently strong shape that resists distortion.Plug building isn't a "one size fits all" business and the normal commercial imperatives dictate how much time,effort and material can be allocated to a project.Sometimes a hobbyist's fear of failure leads to overbuilding and a lack of experience is a contributory factor.It can be revealing to talk to those whose hobbies are aeromodelling or model boat building.

 

Typical woven glass used on canoes in these parts is 6oz per yard.

So, he used 1.5" thick xps to build the strips and 6 oz woven cloth.

The xps itself on transverse male stations and stem and stern stations is fine. The problem is xps has terrible shear and compression ratings, and so this plug is not going to be great for even two parts. It will not tolerate any prying whatsoever as the core is likely got a 25 psi shear/compressibility rating.

I would either A, make the skin thick enough to reduce skin deflection and the likely shear under any tool pressures to part the mould from plug and not damage while adding stiffeners.

Or B, expect a single shot plug or maybe two shots with excellent wax work all by hand, no machines, and use of partall spray. This is for a half mould split at the keel that would be relatively easy to part from the male with very little tool pressure, if any. Some creativity with air may help like perhaps a couple air holes built ?somewhere? so he can shoot some low pressure air in. But keep in mind, air nozzle from a tank will be over 25 psi typ., so even that may damage the plug, but for a two part plug; you could shear one side better than shear at the keel.

More trouble when you put mould stiffeners. One bump from a chunk of ply or a bit of torque will crush the core and delam the glass.

I did some testing with xps as I wanted to use for the core for a livewell. I could not use peelply in the vac process because the pull of peelply damaged the part and delaminated the edges.

The skin was 12oz per yd db and it sheared off with an effort similar to tearing paper. I ended up making the skins heavier and accepting delamination as a potential for the sides and top and for the bottom of the well, I switched to marine foam so I could dump ice in it if desired.

I'm not a mould making expert and don't profess to be. I know the limits of xps and spend a few days each year in in the bwca. And I've made a couple simple female moulds. I also built Dierking inspired amas for my canoe with xps and 6 oz glass. They are good enough for what they are, but if they delam, I don't care.

 

I have yet to make a plug that needed a second mould taken from it,but I have had to amend a few so that a new mould could be made that incorporated refinements which use of the original item had indicated to be beneficial.If we want to play a game of mine is tougher than yours then I would immediately recommend a solid piece of epoxy tooling block,5 axis machined to the desired shape and I have made a few hundred of those for autoclave cured carbon prepreg tools and components.For an enthusiast who is developing his ideas,the process described earlier in this thread will work well enough.I'm no fan of polystyrene in any form other than insulation for an icebox but given the right level of preparation,which seems to be the case here,it can work.I have used slabs of polyurethane foam as the armature for such things as instrument pods and given a good skim of polyester filler,they worked beautifully.If we find ourselves in a situation where there may be several hundred components over a long period then it isn't unusual to go through two stages of tooling.first of all the preliminary plug is produced and a mould taken.An initial set of components may be made and put through the manufacturing process to produce a pre-production prototype that may indicate where refinement is needed or alterations needed.Any changes may be added to the original plug and a second set of components can be produced to verify the revision and then a secondary mould made-from which a component is produced with a heavy laminate and sufficient bracing to hold it's shape.This is then worked on to achieve a finish that is utterly perfect and a first set of production moulds can be made.In one instance I know of,the first set of production moulds was used to produce two epoxy master plugs,one for creating additional sets of production moulds and one of which is stored in a secure underground facility as insurance in case of disaster with it's twin.Any time a new set of production moulds is needed,the master plug is used to produce a new mould.

At the other extreme,I know a radio control sail racer who made a mould,pretty much as described earlier in this thread and took off a mould with a 5oz layup and he was quite happy with the result which behaved as he wanted it to.To learn more about non mainstream methods of plug building one can do worse than reading Alan Byde's writings on the ways he produced kayak plugs.I remember coal and concrete featuring in some.I also know of a few concept cars that were made using moulds taken off styling clay.There is usually more than one viable way to proceed.

 

I've simply stated the plug is pretty fragile.

The OP mentioned he needs to make a split at the spine.

I'm going to bow out and let you help @wet feet .

And Joe; if you want a roll of 1708 tape, dm me; it'll be free. You can use to stiffen the foam on the mould, but I would not use xps. I'm in the SE metro.

Good luck, please circle back and give some pictures to the forum.

 

Thank you all for the help! I've finally figured out how to post photos. Ill take some more when I get some more work done this weekend.

I totally understand that this is not the strongest plug in the world. I wont be pulling more than one mold from it. If it doesn't go well I am prepared to strip the plug down to the bulkheads and start over. However I feel this will be adequate. I've always used Partall #2 paste applied in 8-10 applications followed by Partall #10 film sprayed. I've never had any release issues with this system. I do think the air holes are a good idea. It actually looks like that Wenonah photo posted earlier shows their molds have air ports. I think I will give that a try.

On the topic of XPS I totally agree. Its definitely not the best foam. However its inexpensive and readily available. For the foam that will be incorporated into the mold, does anyone have any suggestions? Polyurethane seems like it may be a good option?

fallguy I sent you a message!

 

Polyurethane foam will work but if you have any offcuts of the better PVC foams that would be a little better.Normally a business that uses cored laminates will have a box of offcuts somewhere.Whatever you use it will be a good move to ramp the edges down to avoid hard spots.One thing that I don't see is a flange around the sheer and there are reasons why having one is a good idea;first it stiffens the mould and second it defines the line that you trim the part to.If you get it right it is quite a lot easier to green trim the partly cured laminate than it is to attack a cured laminate with no clearly defined trim line.Some parts are laminated with overrun and a line scribed in the mould surface for this line to be apparent.

I'm not totally sold on air injection points as they will need temporary blocking to prevent the gel creeping into them and this leads to additional finishing work.I would expect that simply pushing a wedge between the flanges would release one half of the mould and the exposure of the other flange should allow you to remove the other mould section.

What will you be doing at the sheer?Is thereto be another moulding incorporating thwarts and decks?

 

That is a good point on the air injection points. I also have seen the air wedges which I could always try if need be.

I will be adding a flange to the sheer. I am getting my final shape for the plug then trimming the sheer and adding a flange. I thought this would be the best way to get the sheer line I desire.

There is no decking per say on a canoe. There ar flotation tanks which will be added after the canoe is molded and gunwales attached.

 

I used the term decks because the stripper canoe people use it to describe what I would call breasthooks and I wouldn't be shocked if there were a channel section joining them to stiffen the sheer.You could leave it as a raw edge and use wooden strips to save making tooling.I agree with your approach to adding a flange as it is a bit easier to fair the surface without an obstruction in the way.

 

Most canoe sheer in these parts are made with a piece of ash lumber radiused both edges and screwed through the hull both sides or an inside blocked version of same. The aforementioned Wenoe wah uses ally.