Could a plywood coated with epoxy canoe be used as a mold?

[yoram]

Hi guys
This forum is amazing and the amount of knowledge here is much much beyond my level. I spend at least an hour a day reading here and enjoy what ever I can understand. I have a small sailing boat, 21 feet which I sail in a fjord in Denmark. I also, with the encouragement of some good people in this forum, built a canoe and I think I got “infected” by the passion of building boats (I can not really call it boats after building one simple canoe but one can dream…). So I am entertaining all kinds of ways of boat building in my mind and thought to use the canoe I built as a mold for other canoes. Meaning, to turn the canoe up side down, coat it with plastic like duck tape, put the fiberglass mat on top and start purring epoxy.

What do you think about it? It sound very easy and simple to me, basically too easy, so there must be some things that I do not see. Will you help to shed some light on that matter?

The canoe I built was from plywood, stitches and glue system and the fiberglass tape only in the seams, both in and out. I am writing this point to say that I do not have much experience in the subject in general and particularly in working with fiberglass.

All answers are welcome

Thanks

[PAR]

With some minor modifications to your plan, you could produce a boat, from a boat, though it will be heavier for the same strength as the plywood version and you'll be sanding 'glass through at least half the build. It would likely be more costly then the plywood canoe and lastly you don't use mat with epoxy, just cloth or knitted fabrics. Also I do think you are grossly underestimating how much fabric, goo and sanding you'll have to use to produce a canoe this way.

[yoram]

Thank you, par, for your answer. The answer raises some more questions in my mind.

Where lays the difference between putting a cloth (300 g/m² ) and epoxy on a plywood, when it is built in plywood-epoxy system and on a mold from the point of view of sanding the exterior part?

How many layers of cloth do I need, in the mold system, to make it relatively strong? Or is it better to do minimum layers and strengthen the canoe in specific points, after removing the mold? (420 cm canoe )?

Does it need serious sanding in between one layer of cloth to the next one or it is enough to sand when the last layer is saturated and dry from the epoxy?

Could you please estimate roughly how much cloth and epoxy I would need or if it takes long time to calculate the estimation, could you please guide me to a place on the net where there are tools to do that?

Another question, not directly on the topic; when I built the canoe, I used epoxy putty on the seams that were stitched with plastic bands (I am not sure I have the right name in English for them but they are the one usually used by electricians) every 20 cm or so and about 1-2 cm from the rim. In the instructions it said that it is recommended to put the glass tape on the wet putty. I could not see a proper way to do so when the plastic bands were in the way. What is the proper way to do it? I tried to look for an answer in many web sites that explain stitches and glue but could not find an answer.

Thanks

[pistnbroke]

elastic bands = cable ties.
Putty between the cable ties then remove them .. 150mm apart holes 10mm in from edge
See www.epoxy-resins.co.uk the boat Morgan has step by step photos.
Google Hannu's Boatyard for lots of information

[yoram]

thanks, pistnbroke.
still, if i do what you say, then i can not put the glass tape on the wet putty because the cable ties is still in the way or there is something here i do not see?

or put the putty in between the cable ties and let it dry and then remove the cable ties and apply putty again and only then lay the glass tape on the wet putty?

[pistnbroke]

putty and tape between the ties ,,when gone off remove the ties and putty and tape the spaces where the ties were . If you look at Morgan you can see its a mess as he left the ties in ( bumps and air pockets)

[yoram]

ok, thanks.
i though it is important that the tape would be in one piece and not cut to pieces, or i was wrong?

[rwatson]

The usual technique is to put 'tabs', or epoxy/filler of putty between the ties. so you have epoxy/filler almost all the way along the chines ( inside).

This will hold the hull rigid enough to remove all the ties, and then you complete the inside fibreglassing, which is when you apply the missing epoxy/filler sections ,and only then cover with FG cloth ( tape).

Plastic ties are good, but in some situations, you need a bit firmer control over the panels. I originally tried ordinary garden wire, which I found very hard to bend and awkward to use. Copper can be good, but its not as strong, and a lot more expensive. If you go to an industrial supply shop, and got the 'tie-wire' that is used for wiring steel re-inforcing in concrete pours. This is much, much easier to bend, and is really useful in tricky, hard to hold hull areas.

Never leave the metal or plastic ties in the boat, as they will work their way out through the epoxy over time, and leave voids.

[pistnbroke]

Some people like to do the glass and filler both wet ...I dont think it matters about it being in 150 mm strips as the epoxy bonds so well with the wood and you have a continuous length on the outside ...BUT see morgan the outer glassing looks bad unless you sand and fair out well ( morgan builder did not ) personally I dont glass the outside on small projiects...faster to finish and better looks...dont forget to notch your baulkheads so the taping is continuous and easy to do ....

[yoram]

thanks guys, it is clearer now about the stitches and putty.

i still would like to hear PAR about my questions from above. i am really curios. it is relatively a new area for me and every thing i managed to learn is really exiting.

[yoram]

i am not very proud of it but i am happy with it. i don't think i did an excellent work on it but we learn from mistakes.
i took it fro a short ride in the fjord and it floats
my priorities were to build for learning and then to do something that could go safely and not sink and then to make it easy to build and bottom of the list is the looks and the speed.

we would probably have class in the school i am working in, for building canoes, simple not professional building and i wanted to do it with 2 amas for first timers (the water in the fjord is really very cold...).

so i am trying to upload photos of the canoe.

[pistnbroke]

can I use it as a mould??? yes if you built it as a mould not a canoe..as an extreeme example I took 4 sheets of australian tin shed ...600 x3000 screwed them together into a 1200 x 6000 sheet and bent the ends up aborigonie style and bent it to shape with an external frame ....coated the inside with canola oil and glassed it internally .....took out screws and popped the tin off .......should have done it in ply ...HEAVY...

[yoram]

if i understood right what you wrote, pistnbroke, you have used the banded tin as a mold? if so, my questions still stand:
Where lays the difference between putting a cloth (300 g/m² ) and epoxy on a plywood, when it is built in plywood-epoxy system and on a mold (in your case from tin)from the point of view of sanding the exterior part?

How many layers of cloth did you use on the tin mold? and how much epoxy?

Does it need serious sanding in between one layer of cloth to the next one or it is enough to sand when the last layer is saturated and dry from the epoxy?

Could you please estimate roughly how much cloth and epoxy I would need or if it takes long time to calculate the estimation, could you please guide me to a place on the net where there are tools to do that?

[pistnbroke]

If the inside of your mould is smooth and coated with release agent and you use POLYESTER not epoxy and mat then it should come out ok ...as your design is simple why not make your mould in a shiney plastic with an external frame ??? I think you can get ply with a shiney coating on one side ...someone will let us know what it is called ...

[yoram]

i think i mean to use my canoe as a the male mold and you used the tin and talk about the female mold, is it right or i got it wrong?