so I have a female canoe mold… right now I use coremat. I’m going to use 1/8 h80 on the next canoe… Can I just put that in the mold and go or do I need to thermoform it??
I am worried about pulliing the canoe out of the mold and the sides wanting to straighten out… It’s only 1/8 in so it’s flexible but I would rather here from someone who knows then trial by error and waste all that material and time…
A few options here.
I think you could layup your first fibreglass? in the mould, let that cure and then vac bag your foam core only in with some additional resin/paste. Then layup the inside skin once the bag is removed.
You could also try to vac bag the foam core directly onto your wet outer fibreglass skin, this could be messy or difficult and as above it may also be hard to hold the sheet foam in place. I imagine that if your hull is a nice round shape that the foam could be held down at the mould flanges with something temporary??
Or if you have access to an oven you can use your mould to heat form the foam first. Place the foam in your mould and vac bag down, then heat the whole mould in an oven under vacuum to 100 deg C, let cool still under vacuum and the foam will stay in that shape. Then you can remove the foam and further tailor the edges etc and it’s ready for a vacuum layup with the wet resin system. I would still only bag the outer skin and foam in the first bag. This heat forming works well and I have made many boats like this.
Also, the foam might snap when bent into shape. Thermoforming might help.
Probably thermoforming is the best option, but you need to have a mold that support 100 ° C It can be a problem.
What’s happen when foam break? It shouldn’t affect the mechanical properties, right?
Regards
No, the mechanical properties are not affected, but fitting broken foam into a mould is a tedious job.
The thermoform mould can be a more or less sacrificial mould, the shape of the foam does not need to be 100% perfect.
I have found that the cracks are often not a problem. If the crack does not go far? the foam will still be formed in the moulded shape and the crack will fill with your resin when the job is done so no structural issue.
You can probably get away with 80 degC, I know 90C is ok too.
well I don’t have an oven… I do have a paint booth… 160f (70c) I’m in the autobody field ( panel beater in australia)… I do have heat lamps if that would help… I can only do a 4 foot section at a time is my guess… the canoe is an outrigger canoe so its 23 feet long ( 7 m) and 15 in wide ( 391 mm) I’m not sure if the mould can handle high heat… it’s your old school tooling/polyester resin mould…
when you say a skin on the foam. are you talking thin like 3/4 oz… that is an easy option… I really want this to stay light… we are shooting for just over a 1lb (.45 kilos) a foot…
This is only 1/8 in (3.2mm) so cracking is not a major problem… Here is another ?? I was no going to have the foam all the way to the nose and tail… where the foam stops and it’s just carbon and kevlar. Is there going to be a transition issue at that spot ?? since i’m vaccing I’m guessing it will be ok… I could see that if you used thick core and did’t pay much attention to that spot… but at 1/8 ( 3.2mm) I can’t see that …
Thanks for the help so far guys
I stand corrected The booth will go to 199f (93c) so I can uses it as an oven. So will my mould work in that’s Its just a tooling gel and polyester resin/cloth mould and its old like 15 years . What if I baked the foam and then put the hot foam in the mould to cool. I could pre cut the shape I need so all I would need to do is hold it in.
Hey fasta, why should I only do the out skin of carbon on the first vac instead of the whole sandwich?
It’s just a bit tidier to do it that way especially if the foam is not heat formed you can imagine trying to do a layup on top of foam that is sitting loose. Plus with a wet resin you will be under some time restraints so just getting the outer carbon and foam down first will be faster and done within your gel time. It’s reasonably common practice to build sandwich hulls like that. A single carbon each side of 3mm foam will be very light. This is the same layup I use on my 3.3m sailing dinghy hulls, except mine are 4mm foam with 1 x 200g pre preg carbon each side. This panel weight with pre preg is about 1.1kg m2. Finished painted hulls weigh 9.7kg.
Your polyester resins are pretty good for about 80 deg but doing the vac bag may be a lot of hassle if it is something you have not done before? But then you will need to bag the foam core in anyway.
I would consider just doing the outer carbon layer and let that cure, then bag in the foam with a resin coat. Then layup the inner carbon with or without a vacuum bag.
With the typical rounded canoe this should be fine to bend without breaking except near the hull ends but you will not need foam there anyway as the shape will be plenty strong enough with an extra layer or two of the carbon.
Another option for foam could be a contour foam, I used to use a 5mm one called termino that had just 10mm squares so this could easily be rolled down onto a resin slurry and no vacuum bagging required, but then slightly heavier with the fine cuts and thicker foam.
I think your heat lamps could work but you would really need to be sure that it soaks the foam well with heat 100% all over, checking with infra red temp tool along the way. If the mould really is a simple shape and you can think of an easy way to temp hold the foam down at the flanges then I would just bag in the flat sheet foam.
And lastly you cant heat the foam and then put it in the mould because it cools super quick in the open air, like 5 seconds quick!
If you are in Perth I am happy to show you some of the materials and tricks etc.
I think I will try the carbon outer skin and foam in the vac bag in one shot, then the inner skin on round 2… I will probably vac that as well… I need to glue the hulls together and foot pedal rails in… I have made a few canoes already. we can go from start to vac pulled in about 1 1/2 hours…
If I do this in two sets will I still need the perforated foam or are plain sheets fine? ( vac bagging of course)
I always just perforate the plain sheet foam with skewer roughly 150-200mm apart.
Also I have always found that laying up on top of the foam is often not so nice to do on the textured foamsurface. After bagging the foam in I would then also screed the inner foam surface with a filler slurry really nice and flat with a wide blade and let that cure. Then sand any dags off and do the layup. It’s always no much nicer to work with the cloth that way and probably lighter too.
I don’t do this screeding step with pre pregs though.