ErikLane Posted July 30, 2011 Report Share Posted July 30, 2011 I am new to boatbuilding, so I don't know a ton about boat stuff. I am building a Weekender, I have purchased the 1/2" and 3/8" plywood. It is voidless and uses water resistant glue. the guy at the plywood shop builds boats too, he said it would work just fine after fiberglass and epoxy. He said he wouldn't leave any exterior surfaces un-epoxied (which I planed on doing anyways) Now on to the 1/4" plywood. He didn't have anything that was more than the 3 ply stuff with the inner core that looks like the luan stuff. He recomended 1/4" underlayment at Home Depot. My biggest concern is it seems flimsy. One thing I thought of is not using plywood for the sides but stretching fiberglass planking like C-Flex and epoxying that, builing it up to 1/4" and calling it a day. To have 1/4" marine plywood shipped to my door would cost $300, a bit much! So any thoughts? concerns? Quote Link to comment Share on other sites More sharing options...
Frank Hagan Posted July 30, 2011 Report Share Posted July 30, 2011 The 1/4" ply does seem very flimsy until you attach it to the bottom and put the deck on top. Then it becomes very strong. A comparison would be a shoe box, something that is strong enough for a kid to stand on, but an individual side of it would bend under its own weight. In woodworking, its called a "torsion box". A hollow core door is usually 1/8" plywood (or even thinner) over a frame, and the door is very stiff. Same idea. The Weekender is a boat-shaped torsion box. Water resistance is less of a concern if the boat is going to stay on the trailer most of the time. If you're planning on leaving it on a mooring or in a slip then, yeah, I would avoid using anything but the best marine grade materials. If the boat is on a trailer most of the time you can use any exterior grade plywood. You can expect 5 - 10 years life out of a construction grade material boat. The main enemy of these boats is rot from the inside when leaves or other debris, or rain, is allowed to collect and sit. Keep it covered and you'll be fine. And, I'll add not to glass the keel. The Stevenson's knew what they were doing by leaving the keel un-glassed. Because of the construction of the keel, the seasonal wood movement causes gaps between the glassing and the wood, water collects and the keel rots. Keep the keel un-glassed and just paint it. Quote Link to comment Share on other sites More sharing options...
Jim Stumpf Posted July 31, 2011 Report Share Posted July 31, 2011 He recomended 1/4" underlayment at Home Depot. My biggest concern is it seems flimsy. To have 1/4" marine plywood shipped to my door would cost $300, a bit much! So any thoughts? concerns? I have used 1/4" luan from Home Depot in the past without any major issues. I had a 16ft Bolger Pirogue pushing 10 years old that held up very well. Last summer I built a Bateau Cheap Canoe and I have to repair pieces of delamination every time I use the boat, the outer veneer just lets go, I would certainly think twice about using the crap that HD tends to sell as of late. Where are you located maybe someone has a source for better quality materials at more reasonable prices. Jim Quote Link to comment Share on other sites More sharing options...
ErikLane Posted July 31, 2011 Author Report Share Posted July 31, 2011 Where are you located maybe someone has a source for better quality materials at more reasonable prices. Jim I am in Green Bay, WI. Home of the Super Bowl champions! Oddly there are not a lot of companies dealing with plywood, considering the majority of business north of here is lumber mills. Frank, thanks for that info. The guy at the plywood shop said the plywood I bought is often used for exterior finish projects like sofit and such. What about abrasion resistance on the keel when beaching? We have a lot of rocky beaches here (I should say, razor sharp zebra mussel shells) Quote Link to comment Share on other sites More sharing options...
lewisboats Posted July 31, 2011 Report Share Posted July 31, 2011 here are a few places that deal with boatbuilding woods...the ones that have PW sell plywood. You could also try a contractors lumberyard and see if they can get you Plyfloor underlayment in 4x8 sheets. It is baltic birch with 5 plies, no voids and exterior glue. Pretty good stuff really and about as rot resistant as occume...which is to say not very. It is a bit heavy...around the same as hydrotek meranti plywood. Caledonia - Kettle Moraine Hardwoods, 195 S 27th, 414/835 9212 - L (4-00) Green Lake - Norton Boat Works, 535 Commercial Av, 54941 414/294 6813 - L, PW Hartford - Kettle Moraine Hardwoods, 5261 Aurora Rd, 53027, 414/644 8119 - L (native & mahog.)(4-00) Madison - McCormick Lumber, 3156 Milwaukee St, 53714 608/244 4741 - L, PW Plum City - Grange Hall Hardwoods, Inc., W2326 US Hwy 10, 54761, 715-647-4544 - L Quote Link to comment Share on other sites More sharing options...
Frank Hagan Posted July 31, 2011 Report Share Posted July 31, 2011 I am in Green Bay, WI. Home of the Super Bowl champions! Oddly there are not a lot of companies dealing with plywood, considering the majority of business north of here is lumber mills. Frank, thanks for that info. The guy at the plywood shop said the plywood I bought is often used for exterior finish projects like sofit and such. What about abrasion resistance on the keel when beaching? We have a lot of rocky beaches here (I should say, razor sharp zebra mussel shells) The exterior ply should work. I used a pretty low grade of exterior ply; one side of it looked like the surface of the moon. I put the good side out, and just filled/painted the insides. Glassing the keel has led to a lot of problems, but you can put a "shoe" on the bottom of the keel without too much trouble. One builder used a strip of UHMW plastic, while others have used aluminum and stainless strips screwed to the bottom. BTW - this solution can be done after you sail it for a while, and see what kind of wear you actually get. You can get some issues with screw holes starting to rot, but they are easily filled with epoxy and re-drilled. If you really wanted to get fancy, drilling 1/4" holes for each of your screws, filling them with epoxy and then pilot drilling them for the attachment screws would eliminate that problem. But its a lot of work for a boat that is usually kept for about 5 years, and then given away (there are exceptions, but most people get "bigger boat fever" after about 5 years). Quote Link to comment Share on other sites More sharing options...
Johnny Socko Posted August 28, 2011 Report Share Posted August 28, 2011 I used allot of luan from HD. Big mistake. I had to replace most of it this spring with a better grade. The epoxy seams to soak into the ply but it really only soaks in to the very outermost bit of the wood. So when you epoxy luan the onion skin on the outside get tough but the bond between the outer layers and the inner layers is not improved at all. I have literally removed all of the outer layers on my boat. About the keel. I built up the bottom of the keel with thickened epoxy. The boat is yet to get wet so I don't know how well this will work. Quote Link to comment Share on other sites More sharing options...
Frank Hagan Posted August 28, 2011 Report Share Posted August 28, 2011 I used allot of luan from HD. Big mistake. I had to replace most of it this spring with a better grade. The epoxy seams to soak into the ply but it really only soaks in to the very outermost bit of the wood. So when you epoxy luan the onion skin on the outside get tough but the bond between the outer layers and the inner layers is not improved at all. I have literally removed all of the outer layers on my boat. About the keel. I built up the bottom of the keel with thickened epoxy. The boat is yet to get wet so I don't know how well this will work. A lot of the luan isn't really "waterproof". Its always recommended to test it by boiling a piece of it first. I used exterior grade "ACX" plywood; the "A" is the grade of the first side (pretty good surface), the "C" is the grade of the second side (unfilled knot holes, rough surface) and the "X" stands for the core, which in this case is of unknown species. I think our information in the Wood and Plywood FAQ still applies. Most of the "Exterior" plywood at home centers is really "Exposure 1", meaning that it is OK for exterior construction, and can be exposed for a little while before being finished with a protective covering. It shouldn't de-laminate if protected from weather by glass and epoxy. If you're planning to leave it unglassed, and just cover with epoxy, I think you're better off using marine grade ply (well, you are always better off using marine grade ply, but there's a cost/benefit equation to consider). I've heard of people using luan "underlayment", that is graded for use on a concrete subfloor under tile or hardwood, and having success. I would still boil a piece of it to see how it reacts. Quote Link to comment Share on other sites More sharing options...
Al Stead Posted August 29, 2011 Report Share Posted August 29, 2011 I used ACX from Menards. It is very inexpensive. So inexpensive that I used 4 whole sheets to make up my hull sides. This allowed me to cut the shear to suit me and not worry about fitting the piece over the joints either top or bottom. Don't worry about the apparent strength of the plywood. Once it is on the boat it will take a pretty fair amount of force. I dropped my weekender on her side in the shop with no ill effect. I glassed the outside but painted the interior without a base of epoxy. That was probably a mistake, but unless she sinks, I don't expect any problems. As far as the zebra mussles go, mount some kind of skid plate to the bottom of your keel and don't worry too much about the bottom of the hull. If you run her up on a beach, the keel will be about all that will touch down. Al Stead Weekender Jumping Duck Quote Link to comment Share on other sites More sharing options...
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