Strake Thickness

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Strake Thickness

Postby PeterZ » Tue Feb 07, 2012 3:06 pm


Thought I had this figured out, probably not. I measured the strake thickness on my 65 Thompson Offshore where parts of the transome used to be, using calipers. I measure 7/16" thickness, on both sides of the boat. To me this is close to 1/2" as 1/2" plywood is typically a bit thinner by 1/32nd or more. However I have been reading from other posts that people are saying the strakes are 3/8" Doug Fir plywood. So the 3/8" strakes might be a little closer to 5/16" I would think, not thicker!!!

I am curious now, my boat, given the year, has a phenolic paper overlay on the strakes. So could they be 3/8" + the overlay to make them 7/16".

Sorry to nit pick, but how do I scarf in replacement plywood if the thickness dimension does not match with 'new' plywood? One of you, I think its Capt Dan from TX gave a great tutorial on this forum on replacing parts of strakes near the transom. Dan, you mentioned that you had to have a woodworker plane them down to match on your Cruisers Inc. boat. Did you start with 1/2" and plane down? How do you plane plywood!!?!?! Not much there to plane.

Advice needed, do I use 3/8" and fair it in with some kind of filler, or 1/2" and plane it down somehow (how????).

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Postby PeterZ » Tue Feb 07, 2012 3:10 pm

Follow up question

What is the Mahogney deck plywood material thickness on these boats. I want to replace the deck on my boat, it currently has vinyl over some kind of plywood. Did they use 3/8" or 1/2" plywood.

As you might be able to tell, ... I wanted to start ordering some supplies and of course these questions come up. I don't have the luxury of walking up to a plywood dealer and investigating all the options, I have to order it.

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Postby JoeCB » Tue Feb 07, 2012 9:57 pm

Sorry ,I can't answer your questions, have to wait for the experts to chime in. However , a word of caution. I believe that much of the marine plywood these days is imported and as such is in metric sizes. So consider that 12 mm = .472 and 10mm = .394 , now even with these conversions I do not know if the actual wood thickness if "full" or "nominal" sized.
Joe B
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Postby LancerBoy » Wed Feb 08, 2012 5:44 am

The 1965 brochure for Thompson Bros. Boat Mfg. Co. of Peshtigo, WI indicates that planking was 5 lamination plywood of 13/32 inches thickness. That's a little less than 7/16 inches and a bit more than 3/8 inches.

Plywood for decking was probably the same thickness.

I know I used the equivilant of 3/8 inch plywood on the 1965 Sea Lancer that I restored. I had to replace some of the garboard plank on the port side. I don not recall any variation in thickness between new and old material.

And yes, today's marine plywood is imported and in metric sizes.

By the way, stained and varnished plywood for decking and covering boards was an option vs. the vinyl covering on the 1965 models. I opted for the former when I restored the above boat. I had the replace the deck plywood anyway becasue of problems, so why not go for the better appearance???

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Postby PeterZ » Sun Feb 12, 2012 1:40 pm

Thanks for the inputs all.

Well I did find out that the 1/2" Doug Fir is pretty close to 1/2". I also took some more measurrements on my 65' offshore. The Garboard ends must have soaked a little water as they are thicker than the side strakes, ... again measuring at the ends where the transom is. The garboards measures 7/16" (or about 11mm). The thickness of the strakes, measured with calipers at the transom end of the boat seem to be 3/8"+, or 10mm+.

As Andreas said, the brochure mentions 13/32", which is 0.406". Most marine plywood that I investigated carries 9mm (or often referred to as 3/8") which is 0.354". Given that 12mm ( called 1/2 ") is 0.472", sounds like the 9mm is the closest to thickness and I will have to 'fair' it in somehow if needed. Since Andreas used it on his 65', I guess that is what I will go with.

Sorry to be so anal about this. In building my house I second guessed about every board, nail, and electrical box I put in knowing that somewhere down the line there would be an issue if I made a mistake. I can just hear it now, .... 'you used 9mm and not 12mm in replacing the garboards, ... well thats why your boat lists to one side and vibrates at 28.4 mph and thats why your trailer pulls sideways as the wind whips over that 0.052" of difference in the plywood" .... :D LOL!!!!!!

regards Peter
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