For those contemplating building or converting a trawler, I have just completed the construction of the pilothouse and saloon(salon in my circles) on my 42' downeast hull and will pass along my experience with vacuum bagging the side walls (bulkheads?) and other flat panels. I am not a fan of fiberglass over plywood but I am fond of my money so as I approached this effort I concluded that cored construction hit the budget a bit too hard. Forced to a less expensive alternative I investigated vacuum bagging as a means of getting the most effective bond possible between the glass and a ply substrate. Early investigation of vacuum bagging, principally on the internet, proved daunting in that they specified a menu of expensive separator and breathing materials, elongating membranes,valves etc. Fortunately, I stumbled across several sites that essentially said "get a pump, some polyethylene and have at it. Further research revealed the availability of "Marine Tech" plywood manufactured by Plumb Creek Corp. At About $35 per 3/4" 4X8 panel it is considerably less expensive than conventional marine plywood. If you search on Marine Tech you can find it's specs and a number of recommendations for it's use in boat building. I had to purchase mine in New Orleans and found a number of boat builders in that area that are using it under fiberglass with good result. Plumb Creek also produces Marine Tech in pressure treated form for a bit more that is dried after treatment and proven in tests to accept fiberglass laminations as well as non treated. This product caries a "lifetime guarantee" and I used it in the bilge areas. Armed with these and some hints on building a flat mold I jumped in and have been very pleased with the outcome. There are probably numerous ways to achieve the same result but here's mine. Begin by making a sturdy and flat! low table approximately 10'X6'. Contact cement white smooth "Tile Board" ($11 per 4X8 at Lowes)to the top of the table. Shop around for the fairest board. Some have minute pimples but no big deal in that the final product will be sanded, primed and painted. This applies to the panel joints as well. They protrude on the final product and are easily sanded. Wax the surface of the tile board 3 times with quality mold release wax. Lay out with 2" masking tape the part to be made leaving a inch or so margin. Mask off the remaining table area with cheap polyethylene to protect from over spray. Spray the part area with "Partall purple release film". This step is not essential but it makes releasing the part quite easy and improves the finish. Allow the Partall to dry thoroughly 10min-2hrs depending on humidity. Spray or paint on the Gel coat. I highly recommend spraying and the purchase a "Cup Gun" (you put the gel coat in a paper cup and throw it away when finished leaving only the top and simple spray nozzle to clean) about $135 and worth every nickle. Allow ample time for the gel coat to cure, overnight if possible. If not cured the jell coat will "alligator" with the application of the resin. Now begin the lay up of the fiberglass. I used 3 layers of 1 1/2 oz mat then coated the 1/2 plywood liberally with resin and placed it carefully on the wet lay up. Remove the masking around the part and apply 1/2" vacuum bag sealing tape(several internet sources @ $3.50 per 25' roll) around the part leaving about 2 inches margin around the part.. Place a small vacuum chamber (an inverted metal 1/3 cup measuring cup with 1/4" hole dirled in the bottom) Carefully! place a good quality 4mm polyethylene sheet (visqueen)over the part sealing one edge and preferably with help, pulling gently and diagonally on the far corners while lowering the sheet on the tape. The tape is very sticky so do not let the sheet touch the tape until in position. Press the sheet into the tape vertically around the edge taking care to work out and little folds that might form. Do not run your fingers along the tape. The poly will stretch and form folds. Buy, rent or make a vacuum pump from and old refrigerator compressor. Do not use 6mm poly. It is too stiff and you cannot work out the inevitable minute folds. Insert a !/4' copper tube through a bird feeder suction cup, spit on the cup, stick the tube thru the poly and turn on the vacuum pump. You made need to hold the tube in position a minute or so as the vacuum builds. I usually was able to achieve over 20 inches of vacuum which is on the order 10 lbs per sq inch of vacuum/pressure or 1400lbs per sq ft. When cured remove the poly and tape(if possible before resin is fully cured so you can scrape off any resin that migrates to the back side easily) Apply one or two layers of fiberglass on the back of the plywood while still on the mold. For 3/4" inch panels cover the sharp corners with poly or cardboard to protect the poly cover. Listen carefully for leaks and daub them up with the bag sealing tape when found. The result is a very fair and very flat and ridged panel that is essentially ready for final finish. To install them I milled back 1"x 1 1/2 layer of the fiberglass surface with a router then butted and screwed the panels to a 1X3 white oak batten. This essentially makes a "drywall" joint that I fill with 2-3 layers of 8oz 2"cloth tape and fair with filler. The seams are very stable, easy to finish and invisible. I made about 500 sq ft of panel this way with good results. All in all a relatively simple and less expensive process. Foam core or honeycomb would have cost more than double and presented challenges in screwing things together which I like to do. For HOW TO references I recommend Fiberglass Coatings http://www.fgci.com/ for their quite complete free catalog of fiberglass products and tools and fair prices. It also contains a very succinct primer on making molds, using gel coat and laying up fiberglass including estimating quantities. For bulk resin and other fiberglass products I recommend, if possible, you suck up to a local boat builder or fiberglass repair service and give him a small fee (10%) to buy at wholesale through them. Major savings there like 50+%. I used 5/8" Core-Cell core and related family of products to lay up my 12'X11' roofs. In my opinion an excellent system. The roofs are about 1" thick ,are unsupported and quite ridged and strong. For Core-Cell products http://www.atc-chem.com/. Also an excellent brochure on E-mail request. If anyone is interested in more detail please feel free to E-mail or call at 850 581 2000. I also can provide detail on fairing my wall to hull and roof joints which also came out well if anyone is interested. Usual disclaimers and such. Larry Ropka "Charis" abuilding Ft Walton Bch Fl

That is a great post. Some good ideas and sources for the materials - a big PLUS! I vacuum bag using a shop vac, 10 mil plastic sheet, and a 1/2 I.D. plastic hose with holes drilled in it for the header (sometimes I just snake a 1/4 " piece of line around the area being bagged.) Lay a smaller piece of plastic sheeting between the piece being bagged and the header if you need to prevent epoxy from oozing onto your header material, then use a larger piece to form the top of the "bag." If need be, you can bag right to an existing structure (such as a deck, hull, etc, by using duct tape around the edges of the plastic sheet - horizontal, upside down, vertical - doesn't matter; the sheet forms the top side of the bag and the deck, etc, the bottom. Don't have to buy the expensive stuff, as you discovered, and a shop vac has other uses! Tape the rectangular floor tool (from the shop vac) to the surface of the plastic, with a slit cut in the plastic under the tool - hook up the hose leading to the shop vac, and you're in business. Once you understand the concept, you can create your own system with little expense. At 09:37 PM 10/9/2003, lropka <lropka@cox.net> wrote: > For those contemplating building or converting a trawler, > >I have just completed the construction of the pilothouse and saloon(salon >in my circles) on my 42' downeast hull and will pass along my experience >with vacuum bagging the side walls (bulkheads?) and other flat panels. <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> Bob McLeran and Judy Young Manatee Cove Marina M/V Sanderling Patrick Air Force Base Hampton 35 Trawler Melbourne, Florida