Carbon Lay-up for Racing Dinghy

[CloudDiver]

I have become the Steward of a mold for the International 505 racing dinghy. I'm not going into business for myself, but I would like to pull one hull for my own enjoyment in sailing and in practicing the craft. I have the shop space and tools (mostly) for vac infusion. I don't have an oven, but I can post cure by warming the space to around 150 degrees f if required.

I have the complete hull mold and the centerboard case mold. The transom, foredeck, and seat tanks will have to made one-off for each hull (also centerboard and rudder). To figure out a build plan I need a lamination schedule which I'm not sure I have the know how, but some of the members here have assured me the math isn't as difficult as I imagine.

You can google the specs on the 505, but shortly it is 5.05m LOA (16.6 ft), 1.88 m beam (6" 2"). Total weight for class rules is 127.4 kilos (280 lbs), but that includes all spars, hardware, and rigging but not sails. Main/Jib sail area is 174 sq ft, spinnaker is 220 sq ft. Class rules specify alloy mast only, but boom can be carbon.

I am envisioning a 3mm PVC80 foam core but not certain on that. I would do it in all carbon because for a boat this size the limited amount of cloth isn't going to be murder on the wallet jumping from S Glass to carbon, although having the less expensive lay up as an option could be attractive. FYI, the only place I know of building new 505's is Parker of UK, new cost is over 8K GBP up to 18.5 K GBP in nomex honeycomb core, 70 kg completed hull only. I am not trying to beat Parker in weight & tech, I don't have that capability... I dunno, I might be able to pull off a nomex core. Anyway, I think the catch 22 to keep in mind in that I have been told by racers that these expensive boats almost always have lead corrector weights to meet minimum racing weight.

Any help or advice would be appreciated. Thanks!

 

[jorgepease]

Is that core thick enough? Why not go thicker, weight on core is nothing and your stiffness will increase greatly. For oven some styrofoam insulation and drop cloths and a bunch of halogen work lights, with switches to ramp the temp up correctly. I'd even put a fan and don't point lights directly at hull.

 

[CloudDiver]

Is that core thick enough? Why not go thicker, weight on core is nothing and your stiffness will increase greatly. For oven some styrofoam insulation and drop cloths and a bunch of halogen work lights, with switches to ramp the temp up correctly. I'd even put a fan and don't point lights directly at hull.

Not certain about 3mm, it was just a rough guess. I imagine I could go as much as 6mm.

 

[jorgepease]

I googled the boat and see what it is now, I would use around 16 mm core. If you build the thickness with the foam, not the glass, you will get a very stiff boat and easily meet the weight spec.

 

[CloudDiver]

I googled the boat and see what it is now, I would use around 16 mm core. If you build the thickness with the foam, not the glass, you will get a very stiff boat and easily meet the weight spec.

I can get some 1/2" nome honey comb for about $150 per sheet (4x8). I may need 5 sheets if I include creating the foredeck, transom, and seat tanks. I've never infused nome honeycomb and wondering if that is too thick and/or beyond my capability.

 

[jorgepease]

It's not a good core for infusion, it's got all those open cells that will fill with resin and defeat your purpose, corecell is considered a top of the line foam and about the same price. But you could go with a decent pvc foam for much less and it would work fine.

 

[CloudDiver]

It's not a good core for infusion, it's got all those open cells that will fill with resin and defeat your purpose, corecell is considered a top of the line foam and about the same price. But you could go with a decent pvc foam for much less and it would work fine.

I watched some videos on honeycomb layups. You are right, infusion is not used and there are multiple steps involved. To avoid resin filling the cells the first laminate is in infused in the mold, after curing the outside laminate layer is rolled with epoxy and the honeycomb is laid on and vac bagged until cure. Again, bag removed and a single laminate of e-glass applied to seal the cells, but it its a wet lay-up and vac bagged so the breather cloth absorbs any extra resin. Now the final laminate of the sandwich can be laid up and infused with the cells sealed closed. So that's multiple bags to do a honeycomb sandwich rather than a single go at infusion which would do both sides with the core in place. Lots of extra labor for that superlight core. I guess its worth it for doing your own boat to be competitive. I can see why anyone pulling these hulls for customers can command such a high price.

I have some sources, other than one I mentioned above, to get 1/4, 3/8, and 1/2 inch nomex honeycomb at lower prices than corecell.... much, much lower. Not sure if all the extra vac bagging steps would be worth it. My local supplier of genuine corecell is quite pricey. They gave me a nice box of samples but have ignored my emails for quotes, they used to publish prices on the web but their site has been broken for over a year. I have another source for Air-X that is pretty competitive and I have a U.S. manufactured foam from a small company in VA; very price competitive but they only make 4lb density and then jump to 6 lb density... no 5lb? For this racing dinghy I think I could get away a lighter density foam.

Anyway, I still need to figure out a lay-up schedule.

 

[jorgepease]

Give these guys a call, they ship - Boating Supplies - Norfolk, VA - Eastern Burlap & Trading Co. http://www.easternburlap.com/ very good core prices. A sheet of 4x8 corecell is extremely light, I can pinch it between a finger and thumb and carry it around. Get it scored and perf'd for two sided infusions. I love infusion because you aren't exposed to the resin like in hand layup. You can take your time getting it all perfect and then open the valve and 20 minutes later or so, you have a hull. Your probably going to end up needing those handicap weights in the end ))