Mostly retired spend all my time working on or thinking about boats and outboard motors :)
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Follow our project from start to finish

 

Lumber/Plywood

If you get 10 wooden boat builders together, nothing will start an argument quicker than "what's the best" - lumber, glue, you name it.

Lumber:

What to use? The designer suggested Sitka Spruce or Mahogany for all the frame members (alternately, White Oak at some weight penalty). Other "suitable" woods that were readily available in our area included Black Locust, Spanish Cedar and Douglas Fir.

Ultimately, we decided on Douglas-Fir for all major structural components.

Two factors led to this decision (since I had almost purchased Black Locust for the frames). First, it was less than half the cost of Sitka Spruce or Mahogany in similar dimension and secondly, quality stock was available (somewhat) locally.

At this time we still have not yet selected the variety of wood we will use for the sole and interior cabinet work. Cherry is right up there and am considering Ash for the rub rails. I will update with our decisions when they are finally made.

However, I have picked up a few beautiful pieces of African Mahogany (Khaya) that will be clear finished and used for the deck, dash and windshield frame.

My advice. Check locally. You will be able to find suitable lumber at a decent price. Many woods can be substituted for the more popular ones. There are numerous resources to help you determine the viability of the type you are considering.

Plywood -

You will hear "I know this guy who used plywood from a big box store and the boat it perfect" - well maybe it is. But when I'm out on Lake Huron and the weather gets rough I'm sure going to be glad that I spent the extra few bucks on Marine rated Plywood at least for your major structural components.

You have three major wood choices when it comes to plywood and a couple of minor ones. The most commonly available are -

Douglas Fir Marine Plywood
Meranti, in both 1088 and 6566 British Standards, and,
Okoume (Gaboon) - ditto the BS numbers

The Fir is decent if it will be covered in fiberglass cloth and painted. It does have an issue with “checking” – fine crack lines developing in the outer veneer which can result in a poor finish. Fiberglass covering mostly alleviates this.

(note - my transom is constructed of Fir plywood. Over the course of the winter some very significant "checks" developed on the (outer) layer. Fortunately, this will be covered by mahogany veneer in the finished product, but it certainly reinforced my decision to use a marine mahogany on the other surfaces)

Meranti, which is a tropical cedar (actually any of approximately 500 different species) and is often referred to as Philippine "mahogany" or Lauan. It is also suitable if painted. In general it sells for a few bucks more than Fir, but you may find it on par or even cheaper in price than the Fir depending on your location.

If you want to do a clear finish or are looking for the lightest possible weight, then Okoume (referred to as African Mahogany or Gabon) is probably the leading contender on the market when using plywood, and is the lightest weight of the three, if weight is a consideration.

Of course that is reflected in the price, with the Fir and Meranti being the most economical.

All three are readily available with a little bit of looking. There are a couple of other options. Sapelle and Tiama look outstanding when clear finished, but is double to triple the cost of the other options. Additionally, these are not rated to Lloyd's standards (at least none that I have found) and may not be suitable as structural sheets.

Our choices -

We will use the Meranti for the bottom of the boat since it will be painted in our case. It is heavier plywood, so it makes sense to put the weight below the water line; and, we will also use Merati for the sides since I will cover them with 1/8" Khaya veneer and clear finish. Okoume will be used for any visible bulkheads since we plan on "clear" finishing those parts as well.

(note - I ended up getting 1088 Okoume for the sides and bottom. Found a source that sold it for 10 bucks less a sheet than Meranti so opted for the better quality at the lower price - you can never stop looking for deals even after you have decided on a particular product)

Any plywood that is totally hidden, under sole bulkheads, inner transom laminations etc will be built with Fir - just as strong and a little cheaper than the other two options.

I will wander a tiny bit here and talk about fiberglass cloth - partly because this is kinda where it belongs since it will be used to cover the plywood panels.

To provide abrasion resistance we will cover all the panels (exterior side only) with 6 oz fiberglass cloth. While this will add some weight we believe that is outweighed by the protection it gives the wood.

The fiberglass is NON-STRUCTURAL (although to save an arguement, it does become structural once applied since it adds an "extra ply" to the plywood. This makes the panel a little stiffer than it would otherwise be, but it is included for abrasion resistance, not to compensate for using "thinner" plywood. Your plywood alone should meet the structural requirements of your build).

This is not a fiberglass boat built of multiple materials sandwiched together to try and mimic the strength of plywood. The structural strength will be provided by quality plywood and solid frames.

Using more than 6 or 7 1/2 oz cloth with do nothing more than add weight to your boat. No, you can not cut back the thickness of your plywood and add more fiberglass to "build it up".

(note - Jan 2010 - after doing some "winter reading" I came accross some tests performed by the "G" brothers, inventers of West System. They have shown that by sandwiching a layer of cloth in a multi-ply layup that you can significantly increase the integrity of the entire panel following an impact such as a rock etc. Since my bottom (hull) is to be built from two layers of 1/4" plywood (according to the designer), I am now considering a layer of 4oz cloth in between which would be in addition to the 6oz that will be used to cover the outside. I still have to do the cost and weight change calculations before I fully buy into the idea, but ultimately think I will err on the side of caution and use their method to improve my hull integrity).

And besides, fiberglass is heavier than wood. A 25-26 foot "glass" boat, kitted the way we intend to do ours will weigh in at approx 3500 pounds dry weight - ours will be less than 1400 (best estimate at this point).

That's the reason why we will power with a single 140 horse motor instead the pair of 150's or 200's you see hangin' off the back of that Whaler down at the dock. We will obtain a similar speed at less than half the gas consumption because we are pushing less than half the weight of the other rig. So yes, use the fiberglass sparingly to protect your wood, but don't buy into the misconception that it's stronger than the underlying wood and use it in it's place.

End of my sermon, back to the plywood :)

We are fortunate that Noah's Boatbuilding is within commuting distance. They are a major supplier, on a world-wide basis, of quality marine plywood - that made some of our decisions easy. The bottom line is, you should trust the source of your plywood. Anyone can throw a Lloyd's stamp on a substandard sheet and charge you big bucks for it. Deal with a place that has a solid reputation and will back the product they sell.

If a dealer’s price is significantly lower than the "going rate", there has to be a reason – beware you may be getting a deal or you may be getting garbage....
 
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