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the garboard measures more than 4 feet wide in places, more like 4' 2". This measurement includes the distance from the middle of the keel to having a 1/2 to 3/4 lap under the first plank. The plywood is 4 by 8. I was told the facotry was using 5 x 10 plywood. what do I do? Did the boat beam spread over time?

Shop around. You can probably find sheets in the demensions you need. I would expect an 8 foot sheet wouldnt be long enough either. If you cant find what you need, or a non-standard size is too expensive, you could scarf sheets together, or perhaps even install two planks instead of just the one (lapped over as you would any other plank/strake)

I just went out to my boathouse and measured a number of lapstrake boats made by Thompson Bros. Boat Mfg. Co. at Peshtigo. None of them had garboard planks wider than 36 inches. On the 1962 Sea Lane Cabin Cruiser with her 22 ft. length the garboard is no more than 36 inches wide. On the 1964 Super Lancer it's about 25 inches. Same on the 1959 Off-Shore Cabin Cruiser which is 18'-8" long and my 1957 Sea Lancer.

I dug around and determined you have a 1960 Peshtigo Sea Lancer.

I restored a 1961 Peshtigo Sea Lancer a number of years ago. I had to replace a portion of one garboard. I know I used standard sized plywood.

If you need wider than 48 inches, scarfing pieces together to get the necessary width is an option. Plywood larger than 4' x 8' can be acquired, but it will be difficult to find and will cost a pretty penny.

Andreas

sorry, long day when i sent the original email. from the center of the keel to the first plank is also about 25 inches. 50 inches when you add the two side together, thats the problem as the plywood width is only 48 inches. I was hoping to use the 8' to run a long scarf, now I have to use the 8' wide to cover the 50 inches and I will only have 4' long scarfs. This cretes more scarfs. I hope I am expalining this correctly.

You use separate pieces of plywood on each side of the keel. One to the port and one to the starboard. The pieces butt together at the keel/centerline of the boat. Therefore you need plywood about 25 inches wide.

Andreas

This drawing may help. this is for the 1961 Thompson Bros. Boat Mfg. Co. model 605 Lap-Chine. But the basic construction is the same for all models.
Andreas

A 1962 model year drawing of the Sea Lancer. Showing basic construction.

Andreas,
I think they were looking at getting 2 pieces out of 1 48" sheet of plywood. At 25" each that won't work,obviously. Those drawings are great. They break down the construction of these boats to something simple.
Bill