striperick Posted July 19, 2014 Report Share Posted July 19, 2014 I have a 4" fracture that goes perpendicular to the stem that happened during gluing the bottom on the port side on my OB 20. It is below the waterline and is roughly 4' aft of the bow it is on one side of the scarf joints I did on the the bottom . It did go completely through but I did epoxy the outside of crack to fill. This does not have glass yet (inner or outer). Will this be ok or I am looking for trouble to continue to glass both faces ? Quote Link to comment Share on other sites More sharing options...
Peter HK Posted July 19, 2014 Report Share Posted July 19, 2014 A photo would help with recommendations but remember there is no problem that can't be fixed with epoxy and glass. Usually if you can fill the crack with thickened epoxy and glass either side there will be no problem...it would likely be stronger than the original ply Cheers Peter HK Quote Link to comment Share on other sites More sharing options...
Ken_Potts Posted July 19, 2014 Report Share Posted July 19, 2014 Yes - Pictures would help. If the wood moved (seems like it couldn't NOT move) you might want to try to bring it back into position before glopping it up and glassing it over. Quote Link to comment Share on other sites More sharing options...
striperick Posted July 19, 2014 Author Report Share Posted July 19, 2014 The chain of events is that my dad an I scarfed and glued up 2 each 20' long panels. We templated the boat and shaped the starboard side and glued down no problem . We then shaped the port side and started working fore then aft and saw we were over stressing the panel. We already had the fore 4' clamped up and had a pretty good area all epoxied epoxied aft (panel and stringers) and moved forward right or wrong. It is a 4" crack running perpendicular from the stem that goes through the thickness . I have filled the exterior of the crack during fairing process and haven't touched the interior. The crack has not spread but is this a weak point that will be an issue later on? Quote Link to comment Share on other sites More sharing options...
PAR Posted July 20, 2014 Report Share Posted July 20, 2014 Brace, wedge and curse it back into position, then grind out the back side a touch with very rough grit (40 or less). Next wet out with goo and apply a few layers of biax. The biax will replace the broken the wood veneers in the plywood, so consider this when deciding how much biax to employ. These things happen, just move on and no one except you will know. Quote Link to comment Share on other sites More sharing options...
Wile E. Coyote Posted July 20, 2014 Report Share Posted July 20, 2014 I'm no expert, but as I understand it, it almost doesn't matter what's between the two sheets of fibreglass. Even large boats can be built with soft foam between the fibreglass - the strength comes from the high tensile strength of the glass sheet, and the stiffness is a function of the space between the sheets. So another vote for fix it up and you'll be fine. Sent from my iPad using Tapatalk Quote Link to comment Share on other sites More sharing options...
PAR Posted July 20, 2014 Report Share Posted July 20, 2014 Actually, it matters a bunch, what's between the 'glass skins and this boat isn't a cored composite, so even more important. Because the sheathing provides little more than abrasion resistance, while the plywood the strength and stiffness, typically you disregard the strength and stiffness value of the sheathing schedule in design calculations. The only time this isn't true, is on very light weight designs or racers, where every ounce counts. Quote Link to comment Share on other sites More sharing options...
Wile E. Coyote Posted July 20, 2014 Report Share Posted July 20, 2014 Fair enough, I suppose it's not that surprising that plywood construction is different to strip construction! Nevertheless, whether it's in the design calcs or not, is it not fair to say that glassing both sides will add considerable strength and stiffness to the structure? Sent from my iPad using Tapatalk Quote Link to comment Share on other sites More sharing options...
Dnjost Posted July 21, 2014 Report Share Posted July 21, 2014 I had a crack in my CS 17 at about the same spot. But, on the CS, it is where the bulkhead, CB case come together and therefore many layers of goo and glass are supporting it. Photo attached. I had forgotten about it until I sorted out my photos today. Quote Link to comment Share on other sites More sharing options...
Ambler Posted July 21, 2014 Report Share Posted July 21, 2014 Striperick, I don't know the details of your boat but I had an ugly fracture near the stem when building my Spindrift 12. Tried sandwich-patching etc but it broke 3 times! (I blame it on substandard plywood.) I eventually rough-shaped a wood block to fit the inside face, bedded it in thickened resin and screwed it in place through the plywood - pulling the broken edges into approx where they should be. Finished by filling & sanding outside. The wood block is inside the fwd flotation chamber so no one but me knows about it Maybe that approach isn't an option on your boat but I thought I'd share the "technique." Good luck with your boat and I hope you enjoy both building & sailing her. Quote Link to comment Share on other sites More sharing options...
Doug Cameron Posted July 21, 2014 Report Share Posted July 21, 2014 From my days of building and patching fiberglass whitewater boats - Use a small patch first, just larger than the injury, then put bigger and bigger pieces outside of that. That way, there is not an abrupt change in flex modulus at the edge of the patch. Quote Link to comment Share on other sites More sharing options...
rattus Posted July 21, 2014 Report Share Posted July 21, 2014 Chinese plywood, no? Quote Link to comment Share on other sites More sharing options...
Ambler Posted July 21, 2014 Report Share Posted July 21, 2014 Chinese plywood, no? I don't know where it was manufactured. It's marine Okume and was advertised and labelled - but not stamped - as "BS 1088." That standard was already "no longer supported" by BSI; but some manufacturers claimed (and still do?) to produce material that adheres to it. I think mine did not quite measure up, as the face veneers looked thinner than the cores; and I partly blame that for the fracture, which propagated straight along a line of the face grain. If you're interested you can read the whole sorry thread at: http://messing-about.com/forums/topic/1926-spindrift-12-setback-plywood-fracture/ (although the ugly photo attachments have been deleted.) I found no evidence of core voids although one sheet had a kind of slight hump across it, possibly at a splice in one of the veneers. I think my repair is brutally strong. After several years of not-so-gentle use It hasn't shown any sign of distress. Nor have any other areas of the plywood. Quote Link to comment Share on other sites More sharing options...
russell Posted July 22, 2014 Report Share Posted July 22, 2014 Thought I'd add a bit from my newly gained knowledge, I bought some "marine plywood" for my present build of OB24 #2. I couldn't find any Jobert any where near by so I found a dealer for "marine Ply" in south Fl. We had planned a trip there so I bought a supply. All has gone pretty well until the past few weeks, I found near the bow of the boat, where the greatest bends are, the plywood cracked in the tightest bends. I have some Jobert so I cut it and found it bends much easier and does not crack! I beleive the filler layer must be much better and/or is layed in a different manor. (it would have been a better idea to travel to B&B to get the best wood!) Just another lesson learned the hard way, tou'd think after 70+ years I'd know better. Quote Link to comment Share on other sites More sharing options...
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