I understand these material more than most, including those on this forum. I am a licenced professional engineer with 30 years experinace designing structures for aircraft, automotive, buildings, bridges, towers, marine engineering, and consumer products in metal alloys, composites, wood, concrete, steel, fabrics and plastics. I have designed to ultimate loads, cyclic loading, thermal loading, vibrations, live loads, dead loads, seismic loads, winds loads, dynamic loads, hydraulic loads amoung others.
Be it aircraft rated lumber, marine rated lumber, or contruction grade lumber, all have allowable design stress and detailed engineering properties for specific applications. Whether a boat hull or aircraft stucture, or building, or bridge, whether designing in steel, aluminum, or wood, you always design to the properties of the material you are using. To fail to understand this means you fail to understand the design process. Consider that the first German jet aircraft had laminated main wing spars and plywood skins, and they worked.
Yes you have have to carefully select and remill from stacks of low cost lumber to get what you want for specific applications, or make up your own laminates in controlled conditions. But it is possible, I have done it. With that I have designed and built over 14 small boats.
Please do not lecture me on materials.
>>>>>>>>>>I'm sorry to have missed this thread as its a subject very close to my heart. But not to worry, it appears to still have some life in it.
A few things, Last time I was in WA, I bought a sail from a sailmaker in Rhode Island ( I think) . Its a Force 5 sail, cost about $165 including freight, its a practice sail a tad bigger than a Laser sail but similar, and it appears to be of very acceptable quality.
http://www.intensitysails.com/gearforforce5.html
Most people would be hard pressed to make a good polytarp sail for that!
Carl Cramer and I have been chatting about a kitsettable budget racer suited to guys who want a reasonably fun boat that is suited to us older grey haired types who no longer have the fitness to cope with a full day in a Laser type boat, and who dont want to get wet too often, who still want a boat that will plane, and have commitments that obviate large expenditure.
So we are you and I looking in a similar direction.
I figure that a plans built boat to the rough I have drawn out, using stock aly tube spars, that cheap "practice" sail,
www.duckworksmagazine.com or EBay second hand fittings, and medium grade exterior rated plywood, could be built to a good standard for about US $1800, $2200 for one built from a pre cut kit.
If you look at the price of a new Laser or similar, thats the bargain of the year, and it would be a boat that will cater to a much wider demographic than the sailing ironing boards.
I'll watch to see how this thread progressess, I'd love to see a similar one on coastal cruisers as well.
A note on epoxy sealers. I've been building plywood boats since the 1960s, some have had their interiors epoxy coated as per the book with three coats of epoxy lovingly applied, some have been painted with two coats of primer, two of undercoat, and two of topcoat. While there is not a lot in it I have the impression that the painted ones are doing better.
A note too on the "Duck" racers, the class originator had a row and I am formally divorced from the class, but did sail in the 2012 "Worlds". These boats are a lot better sailors than you'd think, and on short courses can be great fun. A properly thought out and built one can be a formidable little boat, and some have badly shown up competent kids in Optimists.
John Welsford
But do please contribute helpful ideas.
Should I scrap the allowd use of epoxy as a sealant?
What do you think is a reasonable cost limit for a "low cost" boat?