I completed a second study of material costs and I've decided that my Scarab 650 will be built using plywood instead of foam. I just can't get myself to pay three times the cost of plywood to build this boat in foam. I found good prices, but I found even better prices for plywood. However, prices aside, the decision was made based on a conversation with a fellow boat builder who owns a composite material buisness. I was speaking with the owner of Express Composites in Minnesota about trying to get a better price on marine foam when he started asking me quesitions about why I wasn't considering plywood. I thought this odd since he could potentinally loose a pile of foam buiness. I found out during the conversation that he is a serious wood boat builder, power boats, not sail. He suggested that prior to applying the wood parts to the strongback, I should coat both sides and all edges with epoxy and allow it to cure. This seals the wood completely. I agreed that that would be a great idea. He also told me that doing so will easily make the plywood last 25 to 30 years. He then asked if thought I would still be sailing this boat in 30 years. I did the math and agreed it was highly unlikely. I then asked him about damage. I asked "what happens if I hit the dock really hard or run aground on a gravel shore and bust up the fiberglass that will cover the plywood?" He then told me that the repair to wood would be less work compared to the same repair on a foam boat. He said with wood, the damage will remain close to the site of impact. With foam, you can experience delamination sometimes 8 to 10 feet away from the impact site depending on how serious the impact. It was at that point I decided to go with plywood.
The plans call for 34 sheets of 6mm plywood for the majority of the hull parts. Not wanting to spend that much money right now, I picked up 25 sheets of 1/4" which should be enough to build the floats and the lower hull. Here is the pile
The next challenge was coming up with a way to make the scarf joint along the 4' side of the sheet. I will need to bond 3 sheets together to form a 4' by 24' sheet. I did quite a bit of internet research and found many different ways to join the panels. I really like the way Chesapeake Light Craft joins panels in their Kayak kits but the method requires laser cutting or 3 axis routing. The second best method I found is to angle the end of the sheet with a slope of 7 to 1 based on the thickness. Some builders use planes, sanders or circular saws. I decided to use the cicurlar saw method. I figured if I made sure the blade was square to the fence that is attached to the saw, I would need to tip the saw about 7 degrees to angle I need. My plan was to clamp the sheet to my workbench with the sheet flush with the end of the work bench. I would then build a fixture that would attach to the end of the bench that will guild the saw and provide the tilt I need to make the cut. Here is what I came up with.
Attached to the end of the workbench
I did a test cut on a scrap piece of plywood and fixture works great! I can't wait to start bonding the plywood. However before I start that step, I'm going to build the prodder tube assembly.
Until next time...fair winds.
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