i see alot of people here trying to mold thier own hulls. first i want to congrats. to all those who try to do this. is sounds easy . but i can tell you from experience . it aint. i was wondering if anybody here has tried to make false bulkheads in thier hulls? now what i meen by false. is you get your mold. and it is perfect. just the way you like it. then you wax is 3-4 times. you then put down a coat of pva. let it dry( now this is where i get alot of flack) i put down a second coat of pva. i just am paranoid that way. then when it comes to laying up a hull. i put down a coat of resin. and while it is curing. i press fit my cloth into it. but not as 1 piece i use 12 cm strips. that over lap each strip by 2 cm. that 2 cm will act like a bulkhead. then when the first layer of resin is tacky. i just add a coat of resin to make sure everything is soaked. so far everything has worked out well. i end up with 10 bulkheads. also i add some chopped up strands of cloth to the foot of the bow. just for strength
what do you all think? am i nuts or just canadain:zbeer:
I’m Canadian, and I’ve done similar.
The key is, your experimenting.
Most professional composite shops, have a weekly “R&D” meating, to discuss methods tried, what succeeded, and what has failed.
So, keep up the craziness:devil3:
Cougar
Do you just use the one layer of pieces or do you put more on top? When I first read your post I thought that the overlap would just add weight but if you only use the one layer you might be on to something. What weight cloth do you use? I’m just about to lay up another hull so this is timely. If you look at the Fibertek site thet say that if you’re spraying the PVA to use 4 or 5 light coats.
http://www.fiber-tek.com/Bulletins/Plug.htm
Thet’re Canadian too
Don’t eat to much turkey
Don
don
turkey done. stove done.lol thank god for the bbq.
what i have been playing around is using 8 0z cloth cut into 14 cm strips. starting at the bow. brush on a coat of resin ( no cloth) and when that is tack . you work fast and lay in your strips. every 10 cm wil have 1 layer of cloth. but you will end up with an overlap 20 cm of cloth. sure you are adding a liltte wieght. but you will also brush out most of it out. when you wet out your strips. and as for pva. the reason i do more pva than wax. was during a seminar i went too. i was at the sub reggatta in carmel indaina. (I know model subs dont they sink.) i play with them too. but they get together to share secrets. and this one manufactor put on a demo. and he made a very good point. your first mold. will have 7-10 layer of buffed out wax. then 2 layers of pva. so you have a good barrier against joining. when you lift your part out. it will take 3-4 layers of melted wax as well as the pva.
so next part you will wax agian 7-10 times. and pull second part.only this time because of the wax left in the mold you will have ( techincaly) 14 layers of wax then 2 layers of pva . ect. so what he suggested was the waxing was very important for the first 2 pulls. then pva will do the trick after. i came and tried to pull a hull from a old mold. using 1 layer of wax and 3 layers of pva. the hull popped right out
the layer idea is just that. i had a problem with the hull being flimsy. but after trying the idea of the falsa bulkheads. it seemd to help
i use only 2 layers of 8 oz cloth. and my boats seem to work fine
There are as many ways to layup, as there are people doing it. You can use PVA, or you can use can wax (I prefer the latter) it depends on what you like and what you want. For me, time is money in HUGE letters… PVA just slows me down. I want the part to come out of the mold PERFECT and that means finish as well. For me, PVA doesn’t produce that finish. I can buff out the mold, and wax it, and the finish on the part will be mirror perfect.
You can skip cloth/mat and go to the next step which is impregnating the material (which also means skipping pre-preg/oven) you can put in resin, put in glass, saturate and THEN put in the mold… they ALL work… with the common goal of 100% wetted out resin laying in the mold with no airbubbles/voids. It is critical that you lay in the material without repeated movement if you are working on a gelcoated mold. The resin actually eats into the cured gelcoat, and bonds with it… so if you have too much traffic… you will disturb the cured gelcoat into a 3rd state (called RUINED) This typically happens around angles, (we call them 'returns" because of the turn in the mold) where the material will not lay in as desired.
The choice of the method to follow, is usually based on the desired result, mold type, and results desired. Such criteria as weight of finished part, finish of finished part have imact on the best way to do things. As you remove limitations such as above, and/or time, money, strength etc… you are allowed more flexibility. Then comes those problem areas where you can not get the material in without some luck, or extremely small hands (hey kid… come’mere a minute)
Personally, most of the time, I spray the mold with gelcoat and let it cure 100% and then some. (gives me more time on difficult molds) some guys spray and lay… as in… once the gelcoat is kicked off (about 20 minutes in the Summer ) and dry to the touch… buddy… the are getting it done with the resin and cloth coming right behind it. (I can do this on a deck for instance… essentially a flat piece and goes FAST) I cut my cloth for fit but oversized, I am good at leaving my gelcoat just a bit tacky so the 1st layer of glass stays in place, I smooth it onto the mold carefully until it is perfect, then mix the resin. I pour on the resin (pre-measured/weighed on weight critical parts) and brush (cloth) roll (mat) the resin in place until the first layer is saturated. If I am feeling fruity and in a hurry, sometimes I lay the 2nd ply of glass on top of the first and wet them both out at the same time.
Laying in the 3rd ply is usually the most tricky, (getting it into the wet sticky mold) and an extra pair of hands is always welcomed here. Once the whole piece is wet, I begin to squeegee out any excess resin, and then do the whole part for uniformity. Then go back and add any wood backup blocks, reinforcement strips, labels, etc and let it cure in the hot Texas Sun.
Everyone does it a little different. One thing I can tell you about molds and making molds… is do yourself a favor… and make the mold FLAT and leave yourself atleast 1" splash around the part. Do NOT put a return or lip on the edge of the mold… as it will just cause you grief when the glass doesn’t want to lay down into the 90 degree corner. Also, if you have any openings in the part (deck for instance) you can make those holes correctly on your mold and lay up over them. Once the resin begins to kick off… it goes through a rubbery phase where it is neither liquid nor hard… and just PERFECT to cut with a sharp blade. If you have your mold flat… you can run a utility knife around the edge of the mold (outside) and it will cut the part out clean and perfect. Same thing with the holes/openings. It will make them as perfect as you made the holes in mold… and it takes seconds to do. It cuts beautifully, and then the part comes out of the mold trimmed, and ready to ship/mount.
Good luck with it, PREP is EVERYTHING.
PS… I do of course use PVA when I am working “backwards” and have the gelcoat shot on top of something and is curing while exposed to air… instead of being underneath the layup and consequently sealed off that way.
:zbeer:
i hope you guys back up your gelcoat. depending on the type of gelcoat you should be able to layup the rest of the boat/mould once it has fully gone off. a rule of thum i use and has been taught to me by the best boat builders in the world is that the max amount of glass wet out at one time is about 3 layers of 600gsm choppy as if you do more than this you will get exotherm.
larry your coment about cutting off the excess glass is actually called green triming, as the resin is what is actually called “green” this is a great safety practice in building boats as well as it gets rid of the sharp bits of glass that can cut really easily.