II. Selecting and Gathering Materials

Building the Core Sound 20

Choosing and gathering materials is one of the most difficult (and expensive) steps in the boat-building process. Aside from the logistical difficulties of obtaining the plywood and solid lumber, novice builders are also sure to encounter the frequently heated debate over what materials to use in the boat's construction. I won't rehash that debate here, but in the tradition of this website, I'll give you the carefully-reasoned opinion that I've formed after talking to a lot of talented builders and after building two previous boats of my own.

Please feel free to disagree with my views, and do not construe these comments as criticism toward those who make different boat-building choices.


All plywoods are not made equal. Many folks claim you can build plywood boats just fine using the ACX- and BCX-rated exterior plywood found at most big-box lumber stores. Frankly, they're right. To make ACX or BCX plywood suitable for a marine environment, however, you must sheath the wood in fiberglass (on both sides) or the surface of the plywood will "check" (raise the grain unevenly, ruining the painted finish and allowing moisture intrusion which leads to rot). Merely epoxy-coating the wood is not sufficient to prevent checking. Some folks claim that even fiberglassed ACX plywood may "check," but in my experience, if the wood is properly sheathed with 5 oz. or heavier cloth, it fares quite well in a freshwater environment. (I didn't sail my previous boat in saltwater, so I can't address that issue.)

So why all the hype about "true marine-grade plywood" (typically, Okoume or Meranti) rated to British Standard 1088 specifications? Well, BS1088 specifications reflect an appreciably higher standard of quality than the American Plywood Association's (APA) rating system. Most builders agree that the quality of American plywood has declined dramatically. American marine plywood is made with Douglas Fir faces and is supposedly without voids. Unfortunately, Fir can check, and many folks have reportedly discovered voids, inferior glues, or other irregularities (varying ply thicknesses, misaligned plys, etc.) in APA-rated "marine" plywood. BS1088-rated Okoume or Meranti (purchased from a reputable wood supplier), on the other hand, is much finer and more consistent in quality: The plys are bonded with a truly waterproof phenolic resin glue, the plys are all made of the same wood species, and there are few or no blemishes or defects (knots, cracks, fillers, etc.). This makes the plywood much easier to work with throughout the building process, allowing for smoother cuts, less filling and fairing, less sanding, and so forth.

Because Okoume and Meranti are not prone to checking, they also don't need to be fully sheathed in fiberglass to protect them from the marine environment. Some builders use no fiberglass cloth, but coat the wood in epoxy. Most builders, however, recommend sheathing the exterior hull in fiberglass, then coating the interior surfaces with three coats of epoxy to provide waterproofing. Many builders also add fiberglass cloth in strategic areas of the interior (such as the cockpit floor) to increase wear-resistance.

Since Okoume plywood is fairly lightweight, it is particularly attractive for boat-building. A 4' x 8' sheet of 1/4" Okoume weighs about 18 lbs., whereas a similar sheet in Meranti weighs about 24 lbs. Meranti, however, is denser and more rot-resistant, so some builders favor it over Okoume especially if they sail in shallower waters where running aground often is likely. Either plywood is perfectly suitable for boat-building, though for weight-sensitive designs, you may want to check with the designer before opting for (heavier) Meranti over Okoume.

Our last sailboat was built with ACX exterior plywood, and I have little doubt that (with proper care and storage) it will last for a decade at least—possibly twice that long. But when I think of all the time and effort spent prepping (filling, fairing, and sheathing) the plywood to make it suitable and long-lasting, and compare that labor to the far superior workability and durability of the BS1088 Okoume and Meranti I'm using now, I realize that the "savings" of the cheaper ACX plywood were not nearly as significant as they seemed at the time.

For one thing, the resale value of a boat is much higher if built with BS1088 Okoume or Meranti. We sold our last (ACX) sailboat for barely more than the cost-of-materials, making no profit whatsoever if you factor in our labor. Even so, we felt the selling price was fair since we understood that knowledgeable buyers would not be willing to pay as much for ACX-built boats (and we considered the building labor to be "fun," not "work"). For another thing, Okoume and Meranti require less epoxy and fairing, so their higher cost begins to save you money (and time) elsewhere once the building process is underway.

A more difficult advantage to quantify (but still noticeable) is that BS1088 Okoume and Meranti sheets are a joy to work with—especially the Okoume. The Meranti is more prone to splintering (and slivers) while cutting, but is every bit as workable as the best ACX plywood I have used. The Okoume, meanwhile, is as nice as it gets—I love working with it. Moreover, the BS1088 rating gives me real confidence in the quality of the wood I'm using. The sheets I bought are beautiful: easily the finest, prettiest sheets of plywood I've ever seen—head and shoulders above anything I've ever seen on the ACX racks at local lumber stores. Is that a big deal? Well, not necessarily, but if you're a perfectionist like me, it gives you peace-of-mind to know that these plywood sheets probably truly are "void-free," and therefore not likely to have problems with condensation-related rot problems later. If I ever build another boat, I'll definitely buy BS1088 plywood again.

Our Choice: Boulter Plywood BS1088 Okoume and Meranti

In our case, we opted for BS1088 Okoume for most of the boat (12 sheets of 1/4" thickness); however, we ordered BS1088 Meranti (a.k.a. "Hydrotek"; 4 sheets of 3/8" thickness; 1 sheet of 1/4" thickness) for the bottom of the hull to benefit from the added abrasion- and rot-resistance of Meranti in case we ever do run aground. The Meranti will add perhaps 20 lbs. to the design, but all located down low, where it won't adversely affect performance and we'll probably never notice the difference. Choosing Meranti also meant that the most expensive sheets (the four 3/8" thick sheets used for the hull bottom, plus one 1/4" sheet for the curved forward hull) were slightly cheaper because Meranti sheets cost less than Okoume. We saved about $60, which we used to buy one spare sheet of 1/4" Okoume (just in case).

I purchased my plywood from Boulter Plywood in Somerville, Massachusetts. They provided superb customer service and had my wood delivered to my doorstep within six days of placing the order. Many places quoted me a $300 - $400 shipping fee, but Boulter covered all shipping and handling for $170. When the shipment arrived (by FedEx semi truck), it was beautifully packaged with extra sheets of (ordinary) plywood on the top, bottom, and sides to protect my BS1088 Okoume and Meranti from being chipped, gouged, or cracked. I will definitely order from them again if I ever need marine plywood in the future. Their prices per sheet were also as good as the eight other suppliers I called (indeed, much better if you factor in the savings on shipping).

Solid Lumber

Here, too, you will encounter conflicting opinions about which lumber to use. If your local big-box store carries Douglas Fir and has a lot of straight, relatively-clear pieces to select from, you may be able to cut everything you need out of their stock and scarf the pieces together to the appropriate lengths. Frankly, on a boat like the Core Sound 20, this approach should be more than sufficient, and I've met a few folks who have built very fine boats this way. You may, however, want to save the best pieces (or track down a few "select" pieces) to use for submerged parts like the keel, where denser, older-growth wood is preferred for strength and rot-resistance. You will also have to be pickier about the wood quality if you're building your own wooden masts, which we may decide to do.

Our Choice: Pratt-Dudley Douglas Fir

In our case, living in Georgia, the big-box lumber stores carry a lot of "Southern Yellow Pine" (SYP) and little to no Douglas Fir. We had to look around for a source of clear Fir and most of the places we called in the state told me Douglas Fir is very hard to come by. Fortunately, we found a source right here in Augusta, GA, about 6 miles from our home: Pratt-Dudley Builders Supply Company. They sell their Fir as "C or Better," but most of what they have is very clear, very straight, very nice wood. We placed an order and all of the pieces we got were perfectly usable. Not all of it was the ideal "quarter-sawn" wood, but again, in this boat, that shouldn't be a concern as long as the wood is structurally stable (no cracks, stresses, severe warpage, etc.).

Epoxy and Fiberglass

There are many fine brands of epoxy and sources of fiberglass. Some of the most popular and well-known include West Systems and MAS. Any of the well-known brands will be fine choices, as long as you use epoxy resin (not polyester).

Our Choice: Raka Epoxy and Fiberglass

Since my last two boats were built with epoxying supplies from Raka, Inc., and since their prices are so reasonable, we decided to stick with what was familiar to us. We're using Raka 127 Resin and the 606 Slow Hardener. We also bought a gallon of the 350 Non-Blushing Hardener because we're fairly certain that we're going to finish the deck "bright" (varnished, not painted) and the 606 Slow Hardener is a structural hardener not recommended for clear-coating applications. The plans call for seams to be taped with 3" wide 10 oz. fiberglass tape, but we're using two layers of 3" wide 6 oz. tape instead because we got an excellent price on it from Raka. For thickening agents, we're using Fumed Silica for most of the epoxy fillets, but we'll switch to maple wood flour when we work on any fillets or joints that may get clear-coated (such as around the cockpit coaming, etc.).

Paint and Varnish

In the amateur boat-building world, there is an ongoing debate about what sort of paint to use. Generally speaking, marine paints dry to a harder, finer, more durable finish, but many backyard boat-builders will tell you that a premium-quality exterior-grade 100% acrylic latex house paint will work just as well and cost significantly less. Certainly, there is no denying that latex house paint is less expensive, as marine paints seem to cost, on average, about three to six times more per gallon than the most expensive exterior-grade latex house paints. And, on our last sailboat, we tried the latex paint approach with very satisfactory results. It held up very well, even when keeping our boat in the water as long as 5 days at a time, and was very easy (and cheap) to touch up.

The downside of latex paint, of course, is that it doesn't produce that high-gloss "factory finish" which really makes a boat look professionally painted. It also doesn't hold up quite as well to the abuse that a boat receives when it is loaded on and off a trailer, or when it scuffs against objects like docks or underwater obstructions. Theoretically, latex paint also isn't intended for long-term submersion, so if you take a sailing trip for longer than a week, you may arrive back at the dock to find that your hull has started to peel and needs to be repainted—particularly if you've been sailing in saltwater.

Since this boat will see its fair share of saltwater and may spend as much as two weeks at a time in the water, we decided to finish it with true marine-grade paints. Although costly, these paints can stand up to years of abuse and because they yield a harder finish, they also do a better job of protecting the epoxy-coated wood. They also represent a fairly small portion of the total costs associated with building a boat. Better yet, if you prepare the painting surfaces carefully, they look terrific.

Our Choice: Bottom Paint - Interlux VC Performance (West Marine)

For the exterior hull, we chose the two-part, teflon-impregnated epoxy paint made by Interlux. We considered an anti-fouling bottom paint, but since most of our sailing will be done in freshwater, and since our boat will rarely remain in the water longer than one or two days at a time, we decided against the ablative (shedding) or biocide-impregnated paints which require more regular maintenance and tend to rub off on the trailer. The VC Performance paint has no anti-fouling chemicals, but its slippery teflon finish discourages marine growth from attaching itself to the hull, and also reduces the friction of the hull in the water (encouraging more efficient sailing at a slightly higher speed). We don't plan to race our boat, so we don't really care about achieving the utmost level of hull smoothness, but we liked the idea of a very hard, low-maintenance bottom paint that can stand up to the abuse of riding on a trailer. We spoke to three folks who have used this paint on their boats and they raved about its durability and its excellent resistance to water-staining. We found the 2-gallon kit to be sufficient to spray 6 thin coats onto our hull using HVLP equipment.

We purchased our paint from the excellent staff at the local West Marine store here in Augusta, GA. If you're in the area, you won't find friendlier or more knowledgeable folks than Bill, Carl, and Cameron. Besides helping us select our bottom paint, they have also become good friends and trusted resources throughout the boat-building process. Always warm, helpful, and patient, they helped us with hundreds of other questions about stainless fasteners, bilge pumps, rigging solutions, GPS/sonar units, lifejackets, oarlocks, cleats—too much to list! We can't say enough about how fortunate we felt to have their advice and supplies available to us locally, whenever we needed them. Besides their professional expertise, they took a genuine interest in our project and even came out to the lake to see us on one of our first test-sails. If you stop by to visit them, tell them Wes and Anna sent you!

Our Choice: Interior Paint - Systems 3 WR-LPU and Silvertip Yacht Primer (Hamilton Marine)

For the interior, we chose the two-part, water-reducible polyurethane paint (WR-LPU) made by Systems Three. We were impressed with the finish on other boats painted with this paint, and we liked the idea of a paint that is water-reducible, and which lacks the noxious odors and solvents often found in other polyurethane paints. These qualities make it safer and more pleasant to apply. To prep, we used the associated high-build primer also manufactured by Systems Three. We found the best price on these products at Hamilton Marine. Each quart of WR-LPU yielded 1 to 1.25 coats on the interior, and we used 3 quarts total. This yielded excellent coverage and color consistency when applied over the top of 2 coats of the Silvertip Yacht primer.

Our Choice: Varnish - Z-Spar Flagship Varnish (Hamilton Marine)

For the bright-finished deck and our spars, we chose the excellent clarity and UV-protection offered by Z-Spar Flagship Varnish. Having used this varnish on a cedar-strip kayak, we were already familiar with its properties and the outstanding protection it offers for epoxy-coated wood. We received a discounted price on quart-sized containers by ordering them from Hamilton Marine at the same time as the Systems 3 topsides paint. We found 2.5 quarts to be sufficient to put 7 coats of varnish on the deck, hatch covers, thwart, and sprits.

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