Anyone around these parts had much to do with it?? Looking at utilising it as a construction method for a hardtop build in an attempt to minimise weight. I will only be doing it manually as I don't have access to vacuum bagging gear. Talking to the guys at Cruisecraft, they have gotten their tops down to a weight of about 15Kg. If I can get within cooee of that I'd be stoked.
My stink boat is foam core, and the hardtop is also foam composite. The hardtop has a minor amount of sag, probably because of the type of foam and possibly the layup was insufficient over a core that is likely to small to span the area. Interestingly, it was the only part not laid up by a professional boat builder. The newer v-grooved/slotted and/or perforated foam cores are so much better. Its about as tough as you can get. The slotted stuff creates a beam to increase shear strength, and the perforated stuff does more or less the same thing by tying the 2 skins together.
You can also get pre-manufactured foam core panels, all you have to do is seal up the edges! Might be wroth looking into those as its less work and you will have a better finish, and you will know the panel weight before you start. You will also get the added benefit of having the composite finished in an autoclave which increases the temperature before the resin starts to soften (Glass transition temp). Although most modern epoxies wont go soft even on the hottest day in Brisbane!
As for weight, my racing cat (sailboat) is epoxy over foam. Its 22ft long, hull and rigging the boat comes in a 670kg. Nice having a light boat, but alas its far to light, and far to buoyant for the good old morten bay chop, especially if going to windward!
Cheers Andy. I looked at thermolite / Coosa etc and while they would be great strength wise they were heavier and won't really play the compound curve game all that nicely. The plan is to have a top that more or less mimics the curve in the existing stainless targa so hopefully sag won't be an issue. Some sheet thickness stiffening beams can be built in underneath if necessary. Working out the numbers using Divinycell 80 the foam came out at less than a quarter of the weight of Thermo lite before adding "glass". I know it will need a heavier lay up and I am still investigating lamination schedules so until I get that nutted out I won't know the approximate weight. I may end up using a sheet of slotted stuff for the main body of the top and strip plank around the outsides yet...….too many options for someone who's never really played with it before
Did, this.. no reason it wouldnt work for a hard top.
http://www.ausfish.com.au/vforum/sho...ng-a-kill-tank
Regards
Honda
Scottar i would go EPS foam or Polystyrene not Styrofoam as the core it weighs nothing but as long as your not planning on standing on the hard top u should only need 2 maybe 3 layers of 400g double bias cloth as long as u get wet on wet layers you'll save a ton in weight if u go one layer let it cure than the next you'll use more resin because the cloth is hard to wet out, going wet on wet i saved probably 30-35% of resin over a wet-cure wet-cure layer
if u peel the laminate of double bias off say for instance plywood sheeting the laminate is flexiable if its 2 layers but super strong to the point if u try to snap it into two pieces the laminate will just bend unless u put a lot of force on a very tight bend than it will snap
Divinycell is good. Both of my boats use it. What the approximate area?Originally Posted by scottar
I think mine power boat is mainly 12mm foam, and 10mm for the non structural bits. I reckon the roof would be 10mm, but I will check that for you. I'll have a yack to my fiberglasser and see what he recommends, he is working on my boat at the moment so I should see him over the next few days.
If you want to get the weight down even further, you could use a layer of carbon fibre and save on glass density. You need deep pockets for that stuff though.
Thanks Andy, that would be great. I was looking at 10 or 12 mm for core thickness. Top is 1.8 x1.8 roughly - will depend on exactly what happens with the screen. I'm almost ready to pull the trigger on a new full height screen from Alfab. Just sorting out whether I need to modify the combing around the front. If I do I'll straighten out the side combings where the Victory has the curve as well. If not Alfab can add an alloy filler to compensate for it.
Cheers Gazza. I remember reading somewhere the weight of resin used to wet out is roughly the same as the cloth weight. Was that about right with yours?
Yeah that is about right i mix up around 300mls of epoxy than i need a further 100-150mls per square meter its kind of hard to judge in the cold weather because the cloth doesn't adsorb the resin like a tissue u really need to roll in the resin and keep going back over the same spot every few minutes untill it turns translucent,in a rush because resin goes off quick in the heat i found smearing the resin a head of where your working than going back and forth gets u better coverage instead of sitting right on 2 square foot of space waiting for the resin to soak in but don't bite off to much at once
you'll think by people sayin "wet out the cloth" its not exactly that easy unless u pour the resin on if your on a vertical job the resin doesn't absorb into the cloth as u would imagine like a tissue in a bowl of water it takes probably 10mins for the cloth to go translucent without adding to much resin, you don't want to much resin as it makes the job weaker, i found once u have the first layer wet out than u lay on the second layer of cloth wet on wet the second layer only needs a small amount of resin u can work in the second layer of cloth with what resin u have on the first layer just roll over all the cloth it will stick really well and it will absorb the excess
for me the above works on the second layer and i only need to roll over it quickly to wet out that top layer it will suck all the resin from the first layer strait thru just the cloth is not like a towel after a shower give it 5-10mins and it will go translucent
if u go with thicker cloth that 900g double bias i used omg my wrist were absolutely caning from all the rolling trying to wet it out i guess u learn with practice
Scottar as u would know i made a mistake on my transom with the air bubbles if u can shape your foam or core than put on a layer of resin only let it cure than said than start with the glassing this way there is no chance of off gassing from your core as my plywood off gassed causing those bubbles under the glass
A few notes to add to your thoughts.
The chamber of the roof adds to the stiffness of a panel. Putting the panel under compression the further distance the reinforcements are apart the better the panel. So 18mm foam is better than 10mm.
The best guesstimate you can make of resin to glass ratio is approximately 1.5-1.7L per kg of glass using wet layup techniques. Depending the fabric choice and core material properties. The open pores of the foam does soak a little resin too.
The attachment points will need a high density core to take the fasteners. Solid core slugs can over come this if engineered big enough. Compensating plates from solid glass laminates can be inserted into the area to replace the foam.
Epoxy resin is a good choice for its flexible properties, water resistance, and core adhesive strength. Vinylester resin is not far behind though. Epoxy resins have an anime blush that forms on the surface, which can be overcome with a peel ply sacrificing product. He amine blush doesn’t dissolve with acetone. Soapy water does dissolve it though.
You can add different fabrics to the laminate to add your strength. Things like double bias fabric, uni directional, triaxial glass etc. if you can align fibres correctly. That’s the difficult part, Anticipating where the loads are going to be. Carbon fibre is a great product when used for weight reduction and correct load paths. But you can get the same strength from standard glass fabrics with a little extra weight. The percentages only measurable on destructive testing.
Your roof structure is more about shade and being strong enough to resist the impact loads from landings with a 2.5t object in rough conditions. So the attachment points are as important as the weight savings.
Hope this gives you some ideas to null over, ask any questions you like.
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Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
You guys that are sanding back fibreglass, ask for your resin without the wax in it. That way, when it goes off there is no need to sand it. Just a wet coat n then your mat. Just remember to add the wax when you apply your final layer..
Cheers Damo. 12 mm is going to probably be my absolute max foam thickness due to height constraints (must remember to measure that - it is that close. I can already give the rocket launcher a nudge on the shed frame if I'm not careful about getting it perfectly in the middle. I've got no idea as to how thick a lay up to put over the foam and have a rather nasty tendency to over engineer stuff when I build it - going to have to control myself. Weight reduction is going to be important as excessive movement of the windows may result in a shattered screen. I intend getting the existing targa cut and plates added above and below the top. I know the lads at Cruisecraft use aluminium bedded into the right spots for attachment points for the window frames and had anticipated doing similar. I hadn't thought too much about the areas that will be where the stainless supports are - a solid lay up pad in these areas sounds easy enough though. I will probably add a second layer of foam in a flat section down the centre on the top adding to stiffness with the vertical edges and giving me somewhere for a small radar at a later date I will also want some hand rails so I will add some pads for these too. If I'm not entirely happy with the stiffness I can add some foam thickness bracing underneath.
From everything I had read, everyone seems to use epoxy with foam due to superior bonding. I've worked with polyester a little bit but never vinylester or epoxy. The only exposure I had to foam was helping a mate build an esky years ago - we put so much resin into it because it kept soaking it up that the ting weighs a ton - you could use it as a bomb shelter though. As far as research goes this site seems to be about the most comprehensive available
http://bateau2.com/howto/foam1.php
Probably my biggest concern is the initial layer and making sure my resin uptake into the foam isn't ridiculous. Gazza's suggestion sounds good - what about amine blush in the resin though. I would assume that washing foam with only a resin coat would present a rather large risk of having it get into the gaps (if any - sure there will some) or possibly the foam itself.
Scottar i ran into the amine blush problem at the beginning of glassing and was advised to use a wet sponge to wipe off the amine blush i tried it and my bucket of water went cloudy strait away so i looked a little into AB and i found out it forms a layer over the outside of the job when epoxy resin is curing in a damp location or where night air is present its the moisture in the night air that does it
just a simple wipe with a moist sponge wipes it all off when u squeeze the sponge in the bucket u will see it turn cloudy if it doesn't turn cloudy your conditions are warm and dry enough u didn't get AB when curing
mixing up the epoxy is a breeze i use 1200mls painters mixing cups i think they cost me about 28c each they have 1-1 thru to 10-1 ratios on the side just find the 5-1 ratio (some epoxy resins are 3-1) fill her up with resin top it up with hardener give it a good mix and its ready to use
i also use the mohair rollers they hold a nice amount of resin, don't use foam rollers they break down and foam sticks all over the job, i use the thick plastic paint roller trays from bunnings for the mini rollers so once the left over resin is cured in the tray i can twist the tray and the cured resin pops out and goes in the bin
. If you want yo vacuum bag you can use an old fridge motor. The bag and tape from fg suppliers
I done that its not a very cheap set up i had to run the pump plus i had to add on a car 4x4 vacuum adjustable switch and some relays, the vacuum switch was adjustable and allowed a pre set psi on the vacuum so it should turn on and off the first compressor mine cost me like $300-$350 to set up
if u run the pump on its own u have no way of controlling the vacuum pressure and it can easily warp the job
a really down right cheap way of vacuum bagging is to use some aquarium air pumps but its a lot of DIY'ing
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