Building a boat for the first time

What about the boat builders from the middle ages? What did boat builders use before epoxy wasn't around?

EDIT: Caulking was the method they used, right? And the modern day equivalent is still popular, right? How about using 3M 5200 as a sealant, then putting on some good oil-based paint all over the boat? Would that do?

 

Most recently, resourcinol was (and still is, but fits must be near perfect).
Middle ages? Tar and pitch I guess.
I've seen PAR (who appears the most experienced in this area) recommend polysulphide sealants for seams, and there are polyurethane formulations that are made for lap seams. It's no problem sealing seams with a non-hardening adhesive caulk, but epoxy makes a more rigid structure, and obviates the need for ribs.
If you use a caulk type adhesive, you may need to stiffen the hull with ribs to compensate for that loss of rigidity.
Often, changing the construction method entails a redesign, usually by a good designer who can analyze structures.

 

Up until relatively recently all wooden boat structures relied on a structural support system that permitted some "movement" of the various pieces. This movement allowed neighboring structural elements to share common loads and spread them throughout the framework.

This building method is tried and true, but not without good and bad points to consider (like everything else in yacht design). The good things are surprisingly light, strong and long lived boats can be built this way. The bad, all this movement eventually leads to leaks.

Leaks where a common aspect of all boats, from the day they were launched. Log books from the late middle ages, when Columbus debated crossing the ocean, clearly show how much leaking was accepted as "normal". A new boat, not yet over worked could be expected to have to have the "pumps manned" for 5 to 10 minutes every hour. A well worn boat could ask for 30 to 45 minutes per hour of pumping. This was noted in the log and was part of "ship's business". In fact, The Santa Maria required 30 minutes per hour during her crossing. The Pinta was a new boat, considered a fairly high tech departure from the current trends in caravel merchant vessels of the era. She required 5 to 10 minutes of pumping during the same crossing.

They used a number of things in the seams of these vessels, most less then satisfactory, by modern standards. In short, if you want a traditional build, then don't be surprised if you find you have to bail it out every so often.

With the advent of better glues in the later half of the 19th century, structures could be engineered differently. Molded hulls, strip planking and other construction methods took hold.

Once truly water proof glues came to be during WWII, everything changed. Now truly "homogeneous structures could be built with tremendous weight and frame member count savings. These types of builds rely on entirely different engineering methods and the two aren't very compatible. As a result, a design from the very start is determined to be one or the other.

Designing a small boat may seem a fairly easy prospect. It's deceptively not so. Small craft are very weight sensitive, even if just used in a swimming pool. Engineering structures strong enough to support itself, the folks sitting in it and the water pressure outside the hull from crushing it like an egg shell, can be an intimidating set of convoluted complexities, especially if you want to be able to lift it by hand.

It would be nice if it floated where you painted the waterline, for example or with the trim (bow up or down) as you hoped. Developing enough internal volume to carry the folks you want it to, without flipping over and getting everyone wet would be an extra nice feature as well. Even in a pool, all the hydrodynamic requirements apply. Will you be able to climb over the side or step on the rail, without being rewarded with a clunk on the head as it flips belly up and other stability questions should be a major consideration.

Do I think you can do this? Well, frankly no, at this point you're education on the various subjects isn't sufficient. Can you? Well of course you can, but you'll need to do some basics, possibly with the help of a designer.

The other option is to down load one of the public domain designs and staying very close to the shapes, modify it to suit your needs.

 

Hmm... interesting. I definitely don't like the idea of constantly bailing out the boat.

I am beginning to realize that it's difficult to build even the most basic of boats, as things like wood rot, proper sealing, and structural strength must all be considered, even if it is just floating in a still pool. I'm still going to continue with aiming to build this boat without a complete set of instructions, but I guess I may choose otherwise if I find this too impossible. I am finding this very good for stretching my brain, and once again learning that things that seem simple are often far from it.

So, just to clarify, are the only two methods that would be suitable for this construction stitch and glue, and caulking the seams? I'm interested in the caulking of the seams, but I'm not sure how the rest of the wood would be water proofed. One would paint the entire boat with a latex or oil based paint, right? Is that actually sufficient waterproofing? I remember reading that moisture does actually seep through paint...

 

No paint will seal wood effectively from moisture penetration.

You can engineer a build method in any fashion you like. Lots of different methods have been employed, some better then others. Having a grasp of the engineering principles and the physical properties of the materials you'll use is another matter, which I don't feel you currently own. Without at least a fundamental understanding of the hydrodynamic concepts and basic engineering abilities, you're shooting in the dark.

 

So what does properly waterproof wood, aside from epoxy?

I know this is a bit of a shot in the dark, but over the past couple of years I've managed to pick up a bit of a feel for overall engineering ideas (I think), and I'm looking at studying engineering in university, so I'm not completely clueless when it comes to designing structures. I guess we'll see if I actually do have a grasp for that stuff or not.

 

I went to my local hardware shop, and of the things I saw, I found epoxy PC-7 and PC-11, which both look like very strong waterproof glues/sealants. I may go with PC-7 for sealing the cracks, as it's cheaper, but looks as if it'll still do the job. However, it's quite rock solid, so I'd be looking at a boat where all the parts hold tight and don't move, right?

I also saw some acrylic sealants, which advertised that they were waterproof, but said on the back that they shouldn't be used below the waterline, so I don't think they're truly waterproof.

I found Titebond II, would that be any good for sealing?

So I guess I only found stuff that would be useful for sealing the joints, but nothing that could coat the entire boat. Currently I'm thinking of joining the wood with the sealant, and probably screws for added strength (then covering the screws up with the sealant), and then coating the entire boat in some sort of waterproof paint.

So then, how are the products that I mentioned for sealing? And once again, what could I use to coat all the wood to properly waterproof it?

 

Those epoxy products are, I believe, repair formulations that are not at all useful for boat construction.
Your best bet on a first build would be to get a few cartridges (caulking tubes) of seam goo and build in plywood screwed to a skeleton frame in the traditional way. The right epoxy is often hard to obtain in some parts of the world, or at least it is very expensive.
A boat built that way will last for many years if well taken care of.
It's not a good idea to spend much on a first build. Epoxy is a messy thing to deal with, and it tends to take over so that you end up serving the epoxy rather than it serving you.
With plywood, you can epoxy/glass tape the seams and be done with it, and it won't leak at all. You might use a quart and some hardener of West System epoxy, available by contacting West Marine or Hamilton Marine or a lot of other suppliers.

 

Yeah, I was thinking of something like that. So I'd make the wooden structure of the boat, and have it all solid using screws, and then I'd line the seams with seam goo? What stuff should I use? And then after I line the seams, what do I do about the rest of the plywood surface? It's not waterproof as is, right?

Oh, I'm in Indonesia by the way, so I have very limited access to things.

 

I think I should actually go with epoxy for waterproofing the whole boat. Is there any variation in types of epoxy, other than ratios? I'd have to do a bit of a search around my city to see if they got it here. What would I coat the epoxy with, and once again, what would I seal the seams with?

[EDIT: I'm having a lot of trouble finding a polysulphide or polyurethane sealant here, so I'm thinking of just skipping on the sealant for the seams, and just using epoxy over the whole thing, and have nice, tight joins. Would that work?]

And just to kill 4 birds with one stone, is there any alternative to using epoxy for general waterproofing of the boat? The boat only really needs to last a couple of months, as I'm moving after that.

 

If you build a plywood boat using chine logs, seperate stem, etc., and you wish to omit epoxy, the seam compound should be applied to frames before the plywood is screwed on. Unlike carvel method, there is no crevice designed in to accept any caulking after the planking is hung.
You also want to have compound in any crevice down low, where frame parts join, such as where bottom, sides, and transom meet. The idea is to prevent places where rot can take hold by eliminating water traps.
I've used LifeCaulk form BoatLife, a polysulphide you can probably get anywhere boats are serviced.
If you want to epoxy the whole boat, there's a lot to know. A lot can go wrong. If you're going to use that volume of epoxy, it would be one suitable for laminating, like West System 5:1.
It would be best to add cloth for abrasion resistance and for reinforcing seams on the hull exterior. A lot more money to glass/epoxy the whole hull of course. The question is, is your first boat worth the expense?
For example, will it be used in salt or fresh water? Will it be trailered/carried or left in the water year round? Is the climate hot and humid, or cool and dry?
A boat left in the water all the time in a humid and warm climate, in fresh water, is most likely to suffer from rot.
If the climate is cool and dry, and a boat is only seeing four months of use in salt water, it will last a long time without the use of epoxy.
Good grief---- I am suddenly reading that you are building the boat to last for only three months?
Frankly, why not just build it out of cheap plywood with latex caulk for the seams and house paint? Why on Earth would you consider epoxy at all? For what? Even crumpled-up newspaper will float for a while.

 

Ok, I'll remember to do that for my build.

Haha, yeah, that's nice to hear. I think I'll go with house paint for this boat. For the sealant, my three options are acrylic, silicon, and Titebond II. What would last me the longest? I'd love to use something better, but I just haven't found it.

I'm thinking that I'll build this boat just for a bit of fun, and won't expect a whole lot out of it, then maybe later on, when I move back to Australia, I may build a nice stitch-and-glue dory, or even a good-sized skiff.

Oh, and I think I'll use some cheap, ordinary 6mm ply. That'd be ok, right?

 

Don't go farther from shore then you can swim back to in this contrivance, Andrew.

 

For sure, I doubt I'd even take it out to the ocean/sea, and a lake would also make me uncomfortable. Don't worry, I'm going to be completely safe in using it. To me, it feels as though it has the potential to sink at any moment, so I'd never rely upon it for being seaworthy.

 

I'm not talking about sea worthy, just common sense. Titebond II is a type II non-structural adhesive. It's not even close to waterproof. It'll melt after just a few minutes of emersion. Please do some research before you elect to use different techniques and materials for a boat. Silicon has only one use on a boat, to seal windows to their frames, that's it. Acrylics generally are worth a damn either.