Boatbuilding Can Be Risky
It has recently become apparent to me that most boat builders do not know where the risks actually lie in boatbuilding. Later in this essay, I will tell you what you need to be most worried about.
This was kicked off by an article titled "TAPE & GLUE Assembly" (link) here in Duckworks. Nothing unreasonable there. Only thing I disagreed with was the "messy" comment. In my experience I have found a huge variation in "messiness" for the same process among
different first time builders. He found the original method messy. With his new method he is less messy.
Who can possibly argue with that! I wonder which method I will be more or less messy with? How about you?
Later, in a discussion of the article on the Duckworks Forum, someone made a remark about the threat of Bisphenol in epoxy?!? A number had read that it had similar effects to Estrogen - the female hormone - with effects such as making your voice higher, reducing body hair, growing breasts and the shrinking of testes. Sounds like the typical hobby boatbuilder to me!!! But seriously ... later I will tell you whether this is a significant risk.
Boatbuilding is full of items that are really bad for your health if used the wrong way. Paints, glues, solvents, lead shavings or dust, some wood dusts are particularly bad. We all hear that endlessly ... blah blah blah. But what are the real risks and how do you manage them?
The Problem with Epoxy
Most research seems to indicate that a quality full solids epoxy system (ie one with no solvents) is one of the more benign boatbuilding materials - much safer than polyester resin for example. One of the necessary epoxy ingredients (for modest priced stuff) IS an allergen. It upsets some people - not many, but definitely some.
Allergen means that some people's bodies react badly. I am allergic to horses because of tetanus injections when I was a kid. If I get horse hair in my eyes or breath some in then my throat closes up, I get a red painful rash, my eyes puff up and close. Sound familiar? This is exactly the same physical response for someone who is allergic to epoxy (or anything else). IT IS THEIR OWN BODY'S RESPONSE. It is not any type of measure of the quantity or effects of the material under consideration.
So if someone is telling you epoxy is "TOXIC" it is a load of tripe. It is probably less toxic than cedar dust with a much better long term outcome for routine exposure. Remember it is an allergy and not a toxic effect. The fierce affect is the body's response - to some epoxy component or horse hair or cedar dust or apricots or dust mites or peanuts or whatever.
The quantity is almost irrelevant in the size of the effect. Where the quantity is important is in the sensitisation process.
I am allergic to horses because that schools immunisation program gave me three shots of the horse based tetanus antigen when I was a wee kid. Last one took me out of school for 3 months.
Pretty direct way to build up an allergy, eh! So how are you injecting epoxy into your system?
With observing hundreds or thousands of cases of people doing boatbuilding over the years it is interesting to me that the ones that became sensitised were older men who were working in poorly ventilated areas and also that they were not working particularly cleanly. Also all the projects were large builds. Two were trying to boat build in winter and had worked out a shelter to keep the worst of the weather out but the fumes in and a couple were using heat to set off the cure.
But it still is a low number. Hmmm?!?
I do know of one or maybe two cases in these thousands where the people were working clean and carefully and still got sensitised.
So there is some marginal chance of fate intervening.
Why Epoxy is Good
Yes, I am biased in that I only really use epoxy. However I have used some of the modified crosslinked PVAs in recent times for specific processes.
The history of plywood boat building in Australia and New Zealand is interesting. A bulk of the work was started by Kiwis for sure .. but we share a very common small boat heritage and there has seen huge cross pollination across the Tasman Sea .. because we really like to beat each other. The only people we both like to beat more are the Brits!
The problem was that our small populations make it difficult for fibreglass boats to be produced economically. So we kept developing plywood boats at the top level of racing craft until the mid '80s at the least and some classes still continue today.
Our plywood raceboats were and are the lightest, fastest, strongest wooden boats on the planet. Our hullweights average between 8 and 10 lbs per foot with excellent reliability (within some limitations described below)
Two examples from us antipodeans...
12ft skiff/Q-class - 12ft long ... hullweights around 90lbs in 4mm (5/32") plywood. Two crew on trapeze. Mainsail and Jib ... about 300 sqft ...spinnakers about 550sq ft.
12ft skiff/Q-class - 90 lb hull! Just think of the loads!
90 lb hull! Just think of the loads! In recent years the efficiency has gone up resulting in some reduction of sail area. Also the timber has disappeared completely - all composite of course - with the reflected price rise.
International Moth - scow hullform in wood - now replaced by very narrow skiffs (12" wide with hydrofoils). But at the end of the Scow moth development this 11ft x 4ft6" scow hull would typically weigh in at around 28 to 32lbs. 0.7mm (1/32") plywood hull and 1.2mm (3/64) cockpit.
International Moth - This boat is from the second last generation of the type and would have had a hullweight of around 55lbs
photo reprinted with the kind permission of Tom Dunderdale of Campion Sail and Design - click to enlarge
This boat in the pic is from the second last generation of the type and would have had a hullweight of around 55lbs ... the hullweight still had to be halved from this point.
The first advantage of epoxy is that it is gap filling. There is no other commonly available glue that is so gap filling. Big gaps ... no problems. They also don't require much clamping pressure - too much is a bad thing in fact.
The other advantage of epoxy is it sticks to wood. Unlike polyester resin that makes up its own mind whether it is going to stick or not and in many cases is only loosely attached to the surface.
This is why I specify epoxy for my designs ... It means building the boats it totally foolproof and the results are completely repeatable.
Other glues such as the modified PVCs and the moisture cure
polyurethanes are not gap filling. Their instructions always say that
joints must be tight fit and clamping pressure should be moderate.
This comes from the manufacturers own technical pages.
The Best of the Non-Epoxy Construction
Now what construction methods were used during the heyday of the light
and high performance boats I mention above. Well ... the common ones were urea formalehyde and resorcinol and
includes the ever loved "Selleys 308". All these glues are non gap filling as well and require high clamping
So the method that evolved was to use the 308 or one of the others in
the joints, use heaps of clamps and then glass tape all the chines
with 2" glass tape in polyester resin.
The exact modern equivalents of these glues are the common modified "exterior use" PVAs and the moisture cure polyurethanes. These are infinitely more convenient to use than the old style glues above as all of them require close fits and moderate clamping pressure.
So these structures of the non gap filling glue and the glass tape have almost been completely replaced by epoxy in the OZ racing classes that still use wood. No-one would ever consider going back to the old methods.
Epoxy makes the building a lot easier with a much smaller amount of equipment.
The old method results in a significant amount of maintenance. A repaint of the boat every two or three years and replacing the polyester glass about every two repaints to try and stem the ever increasing leaks. This was typical for our raceboats when we used those methods.
Build them with epoxy ... and they never start leaking in the first place. Coat them with epoxy and it does mean adding some pounds but it is less than the water soakage over the race season for many boats ... or the timber structure is lighter than the class minimum so the epoxy coat is carried instead of lead weight correctors.
Painting becomes 1 time in 5 or 10 years for this type of small boat that can be stored out of the sun. The first Goat Island Skiff is coming up to its 14th birthday without a repaint ... and far from being mollycoddled it has spent extended periods under a cover in a yacht club boat park often with puddled water inside which would get bailed out every month or two. The set below is from around the 13 year mark.
To navigate the images below, hover near the top and bottom of the picture
or just enjoy the slide show
If you cannot see the slide show above, click HERE
to go directly to the Flickr page.
The water has gone through the varnish but has been stopped by the epoxy coats under where water spent long periods pooled under the covers in tropical Queensland. How do I know ... there is mildew or fungus growing between the varnish and epoxy. The wood is in perfect condition under the epoxy.
This is completely typical for hundreds (thousands) of boats I have had something to do with while working at Duckflat running schools and in my career (intrans: to rush in an uncontrolled or headlong way) as a designer since.
Epoxy Is Not For Everyone
There are swings and roundabouts. If you have a boat that you want to build VERY cheaply and want to economise on every detail and you are happy if it only hangs around for 5 years ... then non gap filling glue and polyester is a rational choice. It may hang around a lot longer than that ... but no guarantees.
If your feeling is that you want the boat for a lot of years and that it is a beautiful thing with some value (however you personally measure that) ... then consider epoxy.
Finally the Engineer's Creed: "Materials are not good and bad or weak or strong ... it is how you design and make the structures."
Cost is one of the factors to consider in the achieving your aims.
BUT to achieve your aims - YOU NEED TO KNOW WHAT THEY ARE AND WHETHER THE MATERIALS CAN DELIVER!
What You Should Really Worry About
Back to the original topic!
The items that we all need to be most careful of are the hydrocarbon solvent group: Acetone, petroleum, styrene, (large quantity in polyester resin), all the fancy lacquer and two pot solvents, through to the milder turpentine and alcohol.
This is where the biggest single risk is in both toxicity and quantity of contact.
Don't worry about growing breasts from bisphenol ... worry about headaches, dizziness, excessive fatigue, cracked fingers ... all signs that something serious is on the brew.
Everything you can do to keep solvents away from your body is a good thing. The news is ... if you proportion this risk properly and are careful with contact with solvents then it will protect you from all the other nasties that people are talking about.
But guys ... also be careful of wood dust. Particularly any timber that has good rot resistant properties. If you want TOXIC ... that's the place to look. Or if you want NASTY ... colloidal silica.
But keep it in proportion and take care for solvents all the time and dust when it is present - clean it up quick.
All you need is good workshop practice. I'd say the most important single item for protecting your health is a portable dust extractor and powertools it can connect to. This is assuming of course that you are using the correct handling methods for solvents and other liquids.
Best wishes and keep enjoying the boatbuilding! I know I enjoy watching you all!