Island Time 1,235 Posted November 25, 2015 Share Posted November 25, 2015 PF, That pic pretty much shows the same story - the cracks are where the hull is struggling (and now failing) to support the actual loadings. Shows Martin's analysis to be pretty damn good I'll leave it to some of the others with better layup design knowledge than me to recommend exactly which cloth, orientation, and how many layers, but it does not look like a difficult repair/upgrade to me. Quote Link to post Share on other sites
MartinRF 53 Posted November 27, 2015 Share Posted November 27, 2015 It is easy to impress by using computer generated graphics I think it does a good job of illustrating where potential problem areas are. Unfortunately it does not offer a way forward to determining proper laminates. The reason is I don't have tools for modelling composites - I have used homogenous, isotropic materials and composites are layered and orthotropic. What I miss is something like this: http://www.ansys.com/Products/Simulation+Technology/Structural+Analysis/Structural+Technology+Leadership/Technology+Tips/Efficient+Workflow+for+the+Design+of+Thin+Composites+Structures It is possibe to make do without this helper add-on by 'drawing' the layers and creating the local coordinate systems manuallly but it would be very time consuming. But all hope is not lost. Back in 1986 I engneered both boards and hull reinforcements using pen, paper and pocket calculator(*). I actually found my notes the other day and have scanned them for your enjoyment. Structural_engineering_of_daggerboards_in_1986.pdf The engineering assumptions are crude but they worked. The boat is 30 years old and we have had no problems with boards or hulls. The original boards where all glass/epoxy and weighed 15 kg a piece. I built deeper and slightly thinner boards in 1995. Using carbon in the main spar of the boards the new ones weighs 13 kg a piece. I still stick to the same basic engineering principles with few improvements related to better understanding of fatigue limits of composites. See http://hem.bredband.net/b262106/Boat/dagger.html and the documents linked to this page. I will try to write an explaination to the hull exit reinforcement engineering of 1986 asap, maybe this weekend. It isn't exactly 'rocket science' so it shouldn't be too hard to grasp. /Martin *) Martyn Smith once told me he used those tools and no other to engineer the composite structure of Formule TAG. Quote Link to post Share on other sites
MartinRF 53 Posted November 29, 2015 Share Posted November 29, 2015 Here is the 1986 calculations explained in English. This is kind of brief but I hope it makes sense. DaggerBoardLoads.pdf I tried to attach the LibreOffice spreadsheet as well but that was not permitted. It is my current understanding that real composite experts do not design reiforcements looking like this but it may still be the best option for paxfish. (The presence of the floor calls for a modification in the laminate scheme though.) One thing not addressed here is how to avoid locally crunching the hull laminate. /Martin Quote Link to post Share on other sites
paxfish 5 Posted November 30, 2015 Author Share Posted November 30, 2015 So, I'm a do-er. Armed with Martin's excellent analysis and a warm day, I forged ahead. I removed the floor in that area, and any damaged glass. On the inside, I layered uni, DB and Triax where it seemed appropriate (certainly Martin's presentation was in my head), I also wrapped 150 strands of heavy uni between the back of the case and the hull, wrapping them around fore and aft, and then let the strands splay like outstreched fingers in several directions. This will further support the board on the opposite tack (though there was no apparent problem there. Another layer of glass, replaced the floor, a couple of layers over top. There is no horizontal beam in addition to the floor as yet. It doesn't "feel" like it is necessary (sole is sufficient now, with the heavy glass extending from there to the dagger board exit 2cm above it.) I added about 5 pounds of material overall, but removed about half that previously while grinding. I removed 31 pounds elsewhere and my net will be negative! Once everything cured, I ground out any remaining bad glass on the outside, and will soon re-glass there to clean everything up. (need a warm day!) Meantime, back at the house, I'm starting to tackle the dagger repair. Eventually, I will build a mold and make new ones, but for now, I am repairing it. Quote Link to post Share on other sites
MartinRF 53 Posted November 30, 2015 Share Posted November 30, 2015 Photos or it didn't happen Here is one I created just before bicycling home today: This is for the floor-less case with the board pushing on the left side of the hull opening. Red arrows show material in tension and blue arrows to the left of the hole shows the material is in compression. The red 'ball' is just an indicator showing the centre of rotation when I was manipulating the view. /Martin 1 Quote Link to post Share on other sites
paxfish 5 Posted November 30, 2015 Author Share Posted November 30, 2015 Very cool. Intuitively, I would expect to see some red arrows near the ball. i wish I had taken a couple of photos while laying glass. But I was busy! Quote Link to post Share on other sites
MartinRF 53 Posted November 30, 2015 Share Posted November 30, 2015 The red ball is on the unloaded side of the dagger board case -- where the board isn't even touching the case. /Martin Quote Link to post Share on other sites
paxfish 5 Posted December 1, 2015 Author Share Posted December 1, 2015 The red ball is on the unloaded side of the dagger board case -- where the board isn't even touching the case. /Martin Gotcha - Of course! Quote Link to post Share on other sites
paxfish 5 Posted September 6, 2016 Author Share Posted September 6, 2016 Just an update, Guys. With your good advice, my repairs to the dagger and the dagger trunk opening have been water tight and rock solid this season! Thanks for the help! Quote Link to post Share on other sites
MartinRF 53 Posted September 7, 2016 Share Posted September 7, 2016 Good to hear that. /Martin Quote Link to post Share on other sites
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