Help with fiberglass

Let me introduce myself I am new to the forums here. My name is Steve I live in the US Virgin Islands I spend every moment that I’m not at work on the water fishing or sailing with my friends.

Now for the reason I am posting. I need some help with building waterproof troughs for baitfish retention. As I have been searching the web for answers I keep ending up at this site, it appears this is the place to find answers to fiberglass questions.
The design is simple the troughs will 150’ long, 8’ wide and 10 inches deep, built from plywood with an inverted V in the middle rising about 5 inches. They will be supported every four feet down 150’ axis.
I was thinking that 3/8 or ½” plywood with fiber on both sides would be strong enough to support it. How many ply’s and what kind of resin would I need?
Also someone suggested to me that a chopper gun would be much faster to use as we will be building 30 or more of these but I’m concerned about strength with a chopped fiber.
I don’t want so say money is no object but they will be holding 10” sea water indefinitely and, they will need to last for many years so I don’t mind spending a little more money if it increase’s service life. Also this will be indoors so there will no UV damage

 

With the price of resin and fiberglass today, the reduced labor of using a chopper gun will probably not make up for the extra materials cost. Vinylester resin gives better adhesion and is relatively easy to use at a lower cost than epoxy and a bit higher than polyester. Thicker plywood will be stiffer and the extra cost will not be huge. If the underside is not immersed, it is not necessary to fiberglass it. I would go down the sides though. Also, the top edges will need some stiffenning; maybe a 1X2.

 

I'd skip the plywood all together and just make a polyester laminate. I'd make a mold of a section that was comfortable to work, say about 10', then laminate up trough sections as needed, bonding each together, end to end. Of course you'll need to mold over or in something, but this is where some cheap plywood can be used. You''l use the mold to make each section, popping them out as they cure. This sure beats dozens of sheets of plywood, goo and fabric. For local reinforcement, I'd cast wrapping paper tubes (cardboard tubes) into the laminate, which will act as a temporary core until the goo and fabric setup. Once cured, the tubes don't need to hold anything and can rot out all they want with little harm. Cheap, simple and manageable.

 

sounds like an aquaculture project...

making 30 of these, it would be WELL worth your while to learn and implement a resin infusion strategy. Google "resin infusion" for more info on this method.

Ply wood is expensive, use a bulker material like soric to infuse a homgenous resin and glass fibre tank... i take it the surface finish is not important? - what difference to the fish know? So the mold will be cheap and easy to build, look into a hole dug into the ground, shaped with earthmoving equipment and sand, then lined with builders/concreters plastic as a mold etc

You are talking about a large surface area, so material cost and labour cost need to be carefully considered in your method of production....

 

Infusion will jack the costs way up and add considerable, unnecessary complication to the project. Making it in the ground, full length seems a good idea initially, until you have to dig it up and move it.

Simply put, work in manageable sections, using a simple jig/mold and laminate system, so you can replicate them as needed is the logical way to proceed, if intrested in meeting all of your listed goals.

 

Thanks for the insight.
I will look at the infusion method I can build a male mold and do it upside down build the mold out plywood then fiberglass and gel coat it, it would not necessarily need to be faired perfectly as one might want a boat hull. Seems as though from what I’ve been reading the past few minutes it would be fairly simple to use that technique once we go through the learning curve. Maybe do 12 or 16 foot sections.

Steve

 

Though I am infusing my boat, I wouldn't infuse this project either. I'd do the male mold in the small sections and just tape them together later, like PAR is suggesting.

It will take much *much* less time to slap cloth on a nice male plug, grind any edges, then tape (using biaxial fiberglass tape) the sections together to make any length you want.

One real advantage is you will be able to make them in any increment of 10' or whatever size you decide to make the sections from.

I think that's how a profitable company would do it, so I'd go that route.

Infusion is great, when you need a certain type of perfect laminate - especially over a core - but if they are just regular glass tanks using vinylester or even epoxy, you'd save a fortune just slapping the glass over a short section of male plug and wetting it out.

 

Didnt see your post while i was replying.
I thought it would easier because i would be laying up dry material then infusing, I want it to work correctly but keep cost under control as it will be a hugh project if it all works as well as the biologists are suggesting 300 to 5oo units total if it works.

 

Well, it depends on how many layers of glass you will be laying down. I don't know what is required for this type of tank in terms of glass thickness. Anyone care to make a guess on that?

If it is one or two layers (even of really thick, 34oz or more), it would be so much easier to just use paint rollers and epoxy.

You would have a section of tank done by hand in less time than it takes to set up your vacuum pump and infusion plumbing. Wet out the male plug (after mold release), drop some glass on it, wet that out. Use really thick glass so you only have one layer to deal with.

I have an idea... take a look at the pricing on the infusion materials you'll need if you go that route:

http://www.fiberglasssupply.com/Product_Catalog/Vacuum_Bagging/vacuum_bagging.html

And... I'm not against infusion. In fact, I'm using it right now. It's just that it is kind of over kill for this project, IMO.

 

id suggest infusion if you plan on doing things on a large scale.... can you imagine wetting out by hand the quantities of cloth required for a project this size? Its a phenominal amount... infusion will lower the labour component substantially.

If you just want to build 1 unit to start with, then sure hand laminating it in smaller sections would be the go...

Small infusions are expensive, however once the laminate gets large enough, the extra expense of the infusion consumables is offset by the increased resin usage and other tools like paint rollers etc of hand laminating. For my purposes and the consumables i choose to use, this break even point is about 1000gsm per side of a sandwich core. Youd have to run the numbers on your laminate to check viability, but at a guess id say you would be at a similar material cost with infusion using a "through laminate infusion media and bulker mat".

Theres other advantages also, like virtually zero styrene vapours, lower health risks, better laminate quality, and faster production.

 

Making 10' trough sections and bonding them together as needed or as the project expands, is the only reasonable way to go. Infusing then bonding, just seems self defeating, not to mention costly. Infusion has benefits, but none of them really are in play with this type of project. These troughs still need to be dragged to where ever they're going to live, so the sections need to be man handed, then bonded.

 

That is probably the best point of all.

Make the 10' sections, then truck them to where they need to be assembled and tape the sections together *on site*!

 

Why would you bother to tape sections together??

I'd make the mold such that, at each end of your section, you flare it to a flange. Then you can make the sections up and just bolt them together with 1/4 inch bolts and big fender washers. If you need some additional support in the flanges you could put some plywood in the flange area. The flanges will stiffen the segments and you likely won't need much other reinforcement.... The flanges can act as feet and it will support the trough and get it up off of the floor.

You can use a silicone goop to seal the flanges and it will be much easier to set up at a different location. For the ends you can just make up a end plate that bolts onto the last section...

Keep it simple...

 

Agreed the flange idea is worth considering, though it seems he wants to have along, continuous trough, which might complicate the flange idea. Without more input from the original poster, it'll be difficult to continue.

 

As a second thougth I'd put an outward flange on the top too. this will stiffen the side lenghts and prevent the sides from bowing out. When coupled with the end flanges you'd have a suitable amount of stiffness and it would be easy to make..