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new here. I am building a classic design runabout with 1/4 plywood over hardwood frames. my question is that is it really necessary to fiberglass or epoxy the hull. just to run up and down the river a few times a month. I realize the added strength that this would give but............
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Brian,Welcome to Hydroracer.net!
We'll need a little more info to be able to make suggestions of much value. Is this an older design racing runabout or a family runabout with 2 or more seats? Will you leave it in the water for several days at a time? Hardwood? What kind of plywood? Will you 'carry' the boat? Drag it up on the beach, or trailer it in and out of the water?
Sounds like it may be a bit OVERBUILT if you are using plans from an older design racing runabout. Most of us us Spruce or Obeche for frames and thinner 4-6mm Okume for bottom/side panels. These are built very light for speed and very few are Epoxy/fiberglass reinforced. Whichever, I'd recommend using thickened Epoxy instead of Weldwood or some other marine glue. I didn't note where you are located but I'll bet there is a boat builder/racer not too far away for advice and maybe hands-on help. Mike Raceboat61-S -
building a runabout
it is an older design called ATOMITE I will be in it alone dont plan on driving it on the beach . and it will be on a trailer that I have modified from a john boat trailer with wood bunks carpet covered. and it has been glued with resorcinal glue. I dont know about being overbuilt. I would say that the hull weighs less than 100 pounds. I have an old kf7 mercury for it. it is sheethed with 1/4 marine ply. smoothe the seams and screw holes with BONDO. I also have asked the local dupont dealer about urethane auto paint. they say that if a good urethane primer is used that the auto paint will be good. but I have mixed feelings on that. being that wood shrinks and expands with the humidity. I live in Anderson Indiana. I dont believe that there are any racers near me. Thanks for the help. BrianComment
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runabout const
Originally posted by brians306 View Post
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I presume that the marine ply you are using is fir. The lateral spacing between the bottom stringers will determine the flex the plywood will take. If clear space between stringers is too wide (greater than about 5 inches) the fir ply will flex too much and will check the grain and result in a crack at the surface of the plywood directly below the stringer outer edges (been there done that with first hydro built from MI plans Scat Cat
). This action will not be prevented by most finishes. I would fiberglass the last 4 ft of the bottom with 9oz cloth and epoxy then paint hull with a good marine enamal. This will give you a more stable bottom where it counts an keep that fir from checking. IMO Auto urethane is overkill for your use. Go with the more flexable coatings.
"Keep Move'n" life is catching up!
No man's life, liberty or property are safe while the legislature is in session.Comment
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Brian, there are 2 of the best race boat builders within 50 miles of you. Steve Roskowski is in Mooresville (near Indy) and Jason Dirksen is up near Auburn, IN. Give me a call 740-319-5040 and I'll give you their contact info. MikeComment
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1/4" = 6mm
I think you are fine with the plywood, 1/4" plywood is just about the same thickness as 6MM.
My suggestion to you is base to fiberglass or not on the water you are going to run in. Clear of debris ? Not planning on beaching it or bouncing on a few rocks while sitting at a dock ? If none of that is possoible, don't glass it. If any of that is possible, glass it. Given the engine you plan to use, the speeds should not place an unusual amount of force onto the plywood, as long as the framing is sound. If you followed plans, I assume it is.
Have fun with your project, and don't forget to post up some pics !!Dave Mason
Just A Boat Racer
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