Building in Fiberglass – part 1

From Doug’s Workshop:    If you have ever owned a  boat, chances are  at some point, you had one that was made in fiberglass.As far as productions boats go, fiberglass is the most common material used in the last 40 years.
Unless your home was the Sahara desert, then most folk grew up with at least knowing someone who owned an frp vessel or even owned one themselves.It was because of this “wonder of plastics” invention that affordable boats were built for the common man. It is both a boon to mankind and in some ways a curse. but I’ll get that later.
early fiberglass boats - Google Search.clipularAs a boatbuilding material, fiberglass, or frp(fiber- reinforced plastic, sometimes called grp in the UK) has come a long way since its inception in the late 40’s as a way to produce a vessel.Today there is so much being done in so many areas its hard to keep track of.  We have  Carbon fiber, Kevlar, and many new high tech materials that I cant even pronounce the names of.Even more,  exotics are now being accepted into mainstream hull production, techniques  such as  “coring” and vacuum bagging, which even the amateur can produce.
These methods are in fact widely accepted in many other areas other beyond  yachting.

Areas including the manufacture of windmills and many other products that need high strength to weight ratio’s.

So, as this incredible and quickly expanding universe of  understanding of plastics increases, so do the options one has available to them. It also stands to reason that these same materials can be used to build a shanty hull if one so desires.

the problem of the information age…

Sadly, to the best of my knowledge, there hasn’t really been an up to date book for creating a modern hull in FRP written since ” Fiberglass Boat Building for Amateurs”  by ken Hankinson which was written in the mid 80’s. That book has been considered the bible on the subject by pro’s and  amateurs alike for many years.

But it is now badly outdated. Don’t get me wrong, it still has merit. The trouble is many of the techniques and materials have become more mainstream that aren’t really covered in depth by any book I know of today. One would think with all the info available out there on the internet that perhaps someone of great distinction in the boatbuilding world, would decide to write at least a pdf on the subject that covers in depth the production of a one-off frp hull. But as mentioned I’m not aware of one. Of course, I’m not a internet archivist so who knows, maybe there is some great work of note from some modern genius in the field, that IS up to date? all I know is. I wasn’t really able to find much. Somehow it seems that this topic has gotten lost between the cracks? or perhaps there is so much “piecemeal” knowledge base on the internet, that  the master builders/designers assume that people don’t need one?…who knows.

My point is…if your going to build an frp shantyboat…where does one start?


why frp?

I think the next logical question to ask is; why build in frp?

Well I outlined some of the pro’s and cons in my big essay on the matter of materials on this site late last year. Please have a look. I will once again though, outline the pro’s and cons for a quick overview.

-plastic is forever!
– easy to work
-low skill involved
-quick learning curve
-easy to obtain
-fast to build, once mold completed.
-impervious to rot and borers
-can create a monolithic hullform
-good strength to weight ratio
-can be molded to any shape
-easy to repair(depending on the type of layup and hull type)
-can have an outstanding finish if done with care

early fiberglass boats - Google Search.clipular (1)
– plastic is forever!(they just don’t break down and go back to nature…ever!)
– can be very messy to work with.
-to maximize strength, frp almost always needs to be formed to some curvature.
– more expensive than other methods, perhaps most expensive.
– one shot pour(i.e. if you make a serious mistake, your stuck with it)
– fumes can not be inhaled and some people are allergic to epoxy fumes.
– a method of forming is needed, usually some type of mold which  constitutes a great deal of work and money  to get correct
–  information on building  is not easily obtainable if using exotics
– polyester resins are not fire-resistant.
– vacuum bagging requires at least some expertise

There are more for both but I’ll stop at that.

One of the great things about frp is that pretty much anyone can do it, if building in standard layups.
The problem is, that nowadays, there isn’t a standard layup. Sure you can go and get the “bible ” mentioned above, and use standard cloth and roving, but it just is not going to be as cool, or as good as what you could build today, and the costs won’t be much different in the long run for other types that are more new tech.

In the olden days, when polyester and cloth was the way to go, it was pretty straightforward.
You made a mold, you then double checked the mold…and then again.
then you would start your layup. This would have been simply laying the cloth over the mold , stirring up some goop(polyester in most cases) and spreading the goop, over the cloth, laying down more cloth, more goop, more cloth, more goop, and  Voila! you have an instant boat, tough strong, and high tech at the time.

Today, its a bit of an assache to try to decipher just what would be best with regards to frp materials in a given type of vessel.

Because of this, the amateur for the most part shouldn’t try to attempt his own layup schedule without some serious thought on the matter.

A layup schedule, is very important to the function of the vessels intended purpose. After all just how thick is thick enough?…too thick and you pay too much. not thick enough and you hole your new hull on the first docking attempt, or the whole thing vibrates like a guitar string on every wave.

vintage damaged fiberglass boat - Google Search.clipular

For this reason, an amateur would be advised at the very least, to spend many hours researching each type available in the area, and what constitutes a good layup.

I do disagree with the notion that a Naval Architect MUST be consulted here. But I would say it would be very sound advice to go that route and save you some big time hassles, and in the end perhaps the project.
Unfortunately, it will be a little more out of the pocket book.

cloth types

This article is a two part series. “Coring” is beyond the scope of this article,  thus, I will focus on what is known as a “single laminate”, or standard layup.

 laminate: def. a series of successive layers of fiberglass material, sandwiched between coats of epoxy or polyester resin, to form a stiff, strong, composite homogenous material. 

For this procedure, you will  be using some type of resin, (epoxy or polyester), and  cloth only.

i.e. one of the types of cloths listed below or ones that aren’t, but should have been.
In other words what you will have when you are finished, if you build a hull in frp is a solid one piece fiberglass hull(panel), that is about the thickness of  plywood, depending on the size of the boat and materials used. (see! i told you it isn’t easy to figure out.)

There are many types of cloth, there are biaxials, triaxials, double bias, standard cloths, weaves, stitched, Carbon fiber, Kevlar, dynel, and many more types out there. Many are just becoming known and even some were super high tech 40 years ago and somehow faded into the night, never to be seen again.



The resin is the goop, or the glue holding the fiberglass fibers together creating the laminate or  skin.
The resin  hardens by way of “exothermic” reaction, which is a fancy way of saying it produces its own heat when mixed with some type of catalyst, usually methyl ethyl ketone or MEK for short  if polyester, and a “hardener” if epoxy. The heat generated from this chemical reaction cures the resin to a hardness usually expressed scientifically as a “barcole” hardness.

There are two types of resins used in a hull.
polyester and epoxy types.

People seem to get confused about this. “give me the facts ma’am, only the facts!”

Epoxy is different chemically than polyester. I’m not going to bother explaining what that is, simply because I don’t know(nor do I really care too much whether I do know or not).

I do know it has something to do with the molecular chains formed when the substance hardens or something like that…

Nevertheless, Epoxy is considered superior. It has  better hardness properties yet is resilient to stress more so than polyester which tends to be more brittle, in comparison.
Epoxy does not absorb  much water in what is called “osmosis” or water entry into the laminate, through the resin. Whereas, this can be an issue with polyester resins.
Also, epoxy will stick to anything, even your Teflon frypan! Polyester will not stick to anything , other than itself. For example, you can laminate your cloth with epoxy over polyester resin, but generally not the reverse.

The more common term for  water migration into the laminate is called “boat pox” due to the similarity to your boat being covered with some unknown boat attacking  strain of infectious chicken pox. They are literally water blisters. And they are a costly and labour intensive malady to repair.

Epoxy is also more expensive too, but has come down in price enough that since the “Hankinson” book, epoxy is  now used more so than polyester. However be forewarned an epoxy hull will be in the area of  double the costs of resin than if using polyester, again, depending on where you live and who your supplier is.

also be forewarned, some epoxies are better than others. Once again due diligence is the key to finding out the best epoxies available. Make sure you get it from a reputable boatbuilding supplier.

There is also the issue of mixing.
Epoxies come in numerous varieties of mix ratios. The standard ones are 2:1, 3:1, 4:1, 5:1, and yes there are 1:1 too, but some builders will not use these types as they are may not be suitable for laminates, and more suited as coatings over plywood, since the mix ratio has some bearing on the hardness/flexibility of the cured epoxy. Once again, trying to sift through this information can be a daunting task.

what about shantyboats!?

Ok so, the last question remains, would it be good to build my shantyboat in frp?

Well, I am not going to say what is a good idea and what isn’t. I’ll leave that to you, but I will offer up my two cents…( should say “five cents” since  pennies are now extinct here in Canada ).

For starters, I personally, don’t like frp for a flat bottomed hull. now, this is a slippery slope. Some may say it is perfectly fine for that. But my response to that would be, yes, but…

You will need to reinforce the bottom of your hull quite extensively, even if cored.(coring adds greater stiffness, and strength).The reason as stated earlier, is that flat bottoms are not a well supported plane especially if a chop picks up. There will be a vibratory wave , built up in the hull as it gets pounded. This wave is an undulation that is caused by the flow of the chop under the vessel. This wave will cause the whole vessel to vibrate- trust me, I have felt it first hand and it is very unsettling, when  to say the least.
So the only way to solve that is to build in a LOT of reinforcement, in the way of what are called stiffeners. These are basically longitudinal stringers that are attached to the inner hull once it has been laminated. There are many types, but they have to act like I-beams, by resisting vertical forces. These members, which can be  made of many different materials,  are attached with the same cloth material used to build the boat, and attached at the bottom. It is the same idea as building in steel , there are “longitudinals” spaced at specific intervals, throughout the hull to provide resistance to forces acting on the hull, and keep the vessel, “stiff”To maximize the strength potential of frp, curvature needs to be built in. This is why you see so many round bottom sailboats. Its not so much the fact that they are more hydrodynamic, -they are,  but the frp needs less stiffening when there is curvature. If building a hull in frp this :stiffening needs to be well thought out, and it is time consuming. To my knowledge there are no flat bottomed barge plans out there for frp. Because of this, it might not be cost effective or realistic to try to do an frp hull. The upside of a frp hull would mean little maintenance, and a nice finish. it could be very strong too, especially if you bypassed the “stiffening process by simply increasing the thickness of the hull at the bottom, although this will be costly, it will require much less stiffening. Of course, it will still need some.
All this begs the next logical question, why build in frp at all when it comes to a barge?
This is where the argument for an frp hull in a flat bottomed shanty boat falls apart.
It fails for a few simple reasons…the main one being, that wood is simply easier, faster cheaper and probably just as strong on a lb. for lb. basis.  There are many plans for wooden hulls and they can even be cored for added strength. So why would one go to all that trouble?
BTW in case your wondering why  frp might be a curse?  Well, its just not cool these days to build a boat that just won’t ever decay. Frp is forever, unless you burn it,  which isn’t such a great idea. Its very much like building a giant plastic bottle that eventually will end up as landfill. What do you do with something like that, after it is past its prime, and outdated?
In the end it all becomes a personal decision. I personally would not attempt an frp hull for shanty since a wooden one, even cored, will be much less expensive.
Perhaps a frp cored hull, might be the answer though as you will see in the next installment, people have solved the “stiffness” issues in frp by use of “core”…this however is also highly controversial.
But who knows, maybe you will start a trend?
Douglas J.Westover

Originally posted 2016-01-05 04:35:37.

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