Female Canoe Mold Questions

Hello!

I am new to the forum. I am an avid BWCA canoeist and have started construction of a male canoe plug this winter. This plus is constructed of plywood bulkheads with foam stringers. That was then sanded and a single layer of 6oz fiberglass epoxyed over. I am now doing body work on the plug and getting it very straight and to a high quality finish.
My intention is to create a multi part female mold from this plug. I then plan to lay up multiple Kevlar canoes from this mold. I know the preferred way for new builders is to lay up the canoe right over the male plug. However I want to make numerous canoes for my BWCA groups, and do some experimenting with different material layups. I do have some extensive experience with composites and have made many female molds in the past. However I have never made anything as large as these molds will be. So I am looking for some guidance in my layup plan. I am still in the initial stages of planning so bear with me. Here is what I am thinking as of now:

1. Spray gelcoat in two applications, when tacky lay up a single light weight stabilizing layer of CSM.
2. Once (1) is completely dry lightly sand it in preparation for further layers.
3. Lay up 4 layers of CSM and let completely dry.
4. Sand previous layer and lay up another 4 layers of CSM.
5. Repeat (3) and (4) a total of 3 times.

This is where I am looking for some help. What thickness should I shoot for this mold? I'm considering using some core material to add thickness and rigidity but I've never done this before for a mold. Does anyone have any experience with this? Any other guidance in construction of a mold this size?

Thank you all!

 

When you mention CSM what weight will your CSM be?For something with the curvature of a kayak hull I would estimate that a total layup of around 3300gsm would be about right and then you will need some sort of framing to stabilise the mould while you work on it,since you won't want it rolling around.You can also add foam stiffening sections with a couple of plies of CSM to improve the stiffness and perhaps reduce the overall laminate.

Does your previous experience include planning where items need to be split to facilitate release?I have seen several kayak moulds that were in three sections;the bottom being in one piece and the deck being split around the cockpit rim to allow for a spraydeck to hook over the rim.

 

I was planning on 2.0oz CSM. I was planning on a simple 2x4 frame to stabilize the mold while laying up the canoes.

I do have experience in split molds. I think I'm planning on 3 parts split bow to stern. This is a 18' 6" canoe so I need to be able to store it properly. The center of the canoe has a very slight negative draft so I may need to split along the centerline of the canoe as well, but I think it might be possible to release the plug from the mold without it. I don't think I would have any issues removing the actual canoe as it will flex a fair amount.

Any suggestions on using foam as a stiffener?

 

I wouldn't recommend attempting to flex the mould for it's release from the plug.It ought to be too stiff for that and you may find yourself having to decide which piece to sacrifice.When you mention a slight negative draft,in which direction are you viewing?I would regard it as fairly normal to split the mould at the widest point of the assembly,even if there is an amount of sheer to take into account,and as I mentioned the other likely point would be the narrowest section of the cockpit opening.

Foam can be a handy material for stiffening the mould and a strip applied beneath a layer of glass will help to avoid the frame from showing it's location.Foam strips in the hull can be helpful and don't need to be much bigger than 3/4" square before the corners are sanded to a radius.Applying foam in sheet form to stiffen the hull may be a bit difficult due to the curvature.I wonder why you are looking at Kevlar as it is a nightmare to work with although there are benefits if your boating is done in rocky rivers.

 

Actually looking at my plug it's a pretty significant negative draft. I certainly will need to split the mold down the spine of the canoe, as well as at the half way mark. I'll upload some pictures to make it clear.
Kevlar with be used along with S glass in the finished canoes. This is very common in canoe tripping as it makes a durable yet light canoe. Look up wenonah canoes.
My main concern is getting the thickness and stiffness of the mold right, as I feel very confident in the other aspects of this project.

 

You're going to have some significant warping based on what you wrote. The plug needs to be super strong. Remove the foam and strip with 1 inch thick oak glued solid. Fair this. fix any low spots with automotive body filler, then prime, then paint or gelcoat.

When you go to make the mold, do one layer per day - not three. Use tooling gel and special low shrinkage tooling resins. If the plug has negative draft, shrinkage is a huge trouble maker. You'll be pulling the mold off the plug with a sledgehammer and great big wedges. For a canoe, I would part the plug, and finish the pieces to make the separate halves of the mold. Trying to part the mold off a single plug and then add the faying and locating surfaces to the halves seldom ends well.

 

What makes you say I will have trouble with the mold warping the plug? It is very stiff with the glass applied over the foam. I certainly could build a few more layers of glass over the plug if need be. I've not had issues using this same technique in the past. Although as stated before never anything this large.

 

I have never encountered inch thick oak as a plug material and don't actually expect to as it has several disadvantages;cost and toughness being just two.We used to use gelutong strips as it is light,comparatively cheap and a pleasure to work with and 5/8" was adequate for lots of hulls.I look forward to seeing pictures of the project as that will make it easier to understand.A sketch of the proposed shape of the gunwale would be useful too.

 

Wenonah Canoe manufactures canoes and paddling accessories for paddle sports enthusiasts. https://www.wenonah.com/

Here is an interesting background shot from Wenonah's website:


How they are made video:
Wenonah Canoe :: How It's Made TV, Wenonah Aramid Canoes https://wenonah.com/HowItsMade.aspx

 

That clarifies things,a simple centreline split in the mould ought to suffice.I would have built those support frames a little differently,with a taper in plan view to improve access.I'm still interested in understanding the gunwale detail and thwart attachment details.

 

Your plug is waaayy too weak. It will result in a mould that may tincan.

I'm not doubling down on PhilSweet either; it was my first thought.

I have only built two female moulds in my life; they were far simpler than what you have planned. The female mould can be stiffened with plywood or foam after you skin the plug. I would make transverse and longitudinals so the mould can sit upright and flat. Use a laser to set the stiffeners and when you flip it off the plug; you can verify the thing is true.

But start off with a plug that is strong enough to support making the mould. You cannot put transverse members over a 6oz cloth skin and if you only place stiffeners reverse of plug stiffeners; it may not be enough.

I'm not here to disagree with Phil, but somewhere in between a 1" white oak strip and 6 oz cloth is rational and 1" wo is more rational than 6 oz cloth. I'd think 1/2" to 5/8" strips would make a good plug.

Let me know your location in Minnesota and maybe I can give you some supplies for mould stiffening if we are closeby. I recommend some 1708 biax tapes on the bottom of the mould and the long ts and transverse stiffeners. You tab to each side just like tabbing a bulkhead.

 

If you are making a female mould; it needs stiffeners and must sit upright. Those stiffeners need to basically be the length of the hull and wider than the beam and stable enough to never twist or warp. Think 3/4" plywood maybe 6-8" wide or 12mm foam with biax both sides to keep it lighter. All that weight is applied on top of the skin of the female before removing it from the plug and will sag the plug. Then when you tab the stiffeners to the back of the mould; you will have stiffened a deforemed mould and need to start over. The foam will not be very strong for long ts either...

 

Also, something you said above does not make sense.

This does not make sense. Did you strip plank this thing? What did you skin over? Just foam?

Maybe our confusion is just omission.

The plug ought to be able to have a 5-10 pound barbell weight set on it without deflection.

 

Would it be to much too ask the advocates for super tough plugs to explain what forces they believe the plug will be exposed to?Once some numbers are forthcoming,it will be simpler to understand their point of view.As things stand,it seems the plug is close to being complete and I would be surprised if there is a huge amount of enthusiasm for starting again.

I stand by my suggestion of about 3300gsm of mat and a foam stiffening section,similar to that in the picture above,and enough ply/OSB/MDF framing to stop it falling over and ideally glassed over with a couple of plies of mat.I would recommend using proper tooling bushes to hold the sections together with some kind of accuracy.

 

I am having issues posting pictures to this thread, but I'll try to clarify how this plug has been constructed.

I started with a 2x6 strong back in a T. Cross sections (I call these bulkheads) of the canoe in 5/8" plywood were then screwed to the strong back every 16". Bow and stern profiles were then shaped of 5/8" plywood and attached. 1.5" XPS foam was then stripped over these bulkheads and glued with gorilla glue. I like gorilla glue because it foams and bonds extremely well to the foam and plywood. This was then sanded to a consistent shape I desired. Gaps were filled with an expanding foam. And sanded again. Following this 7oz (I think it was around there) fiberglass was layed up over the entire canoe in one sheet and epoxyed with a laminating resin. This has now been sanded and some feather-rite has been applied to begin to body work the surface.
I hope that makes sense. I too wonder why I would need a stronger plug. While aggressively sanding the plug there is no deflection. I can easily lay a 15lb dumbbell on the surface with little deflection when it is positioned in-between bulkheads.
I don't have a problem modifying this plug if I need to. But I struggle to think this would not be a strong enough plug to support the construction of the mold.