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Tom Lathrop

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Everything posted by Tom Lathrop

  1. There is probably some case where Gorilla Glue would be preferable to epoxy but I don't know what it would be on a wood boat. The stuff is very expensive, has short shelf life, foams on drying. is messy to use and is of questionable waterproofness. My own tests show it to have inferior gap filling strength. I do remember urethane glues similar to Gorilla being used for applications needing flexibility years ago. Heck, even Titebond ll yellow wood glue sets up a good joint faster. Maybe I'm missing something.
  2. Ambler, A break like that looks like a plywood problem. Maybe the face plies are thinner than they should be. An interior void could also cause that but you said there was nothing obvious. Anyway an exterior batten would have solved the problem. Usually, the break is very ragged and over a much larger area, not straight across. The hot water tortue method also works.
  3. I agree Charlie. Can't see any reason to use peelply on an epoxy only finish. John, as I stated in my post, peelply does work ok on glassed surfaces. It may be a bit hard to understand this unless you have tried it. What normally happens is that the first coat of epoxy on a fiberglass surface leaves the surface pretty rough with glass fibers standing proud when it sets up. No big deal though since adding more coats of epoxy will smooth it out, after sanding or scraping of course. What the peelply does is force the glass to level out more, so that when stripped off, the surface is much smoother than without the peelply. This allows a smooth surface with less epoxy, less weight as well as less sanding and zero chance of amine blush. We usually use a serrated metal roller to roll the air pockets out of heavy glass layups or peelply but, in this case, the serrated roller should be followed with a smooth roller to avoid the ridges that will be left in the final surface by the serrated roller. If all this has talked you out of using peelply, that is ok since you can get along just fine without it.
  4. With all respect to John Blazy, I can't endorse the plastic leveling technique for the whole side of a boat. There are two major problems. The first is that the plywood deforms in making the twists found on the panels of our boats. The amount of this stretching/compression becomes very clear when we attempt to lay a sheet of stiff plastic over the plywood. The plastic will not take even fairly simple twisting movements without buckling and refusing to follow the surface of the plywood. It might accept following the side panel of some of our boats but, if you have to torque the plywood even a little, the plastic will not follow smoothly. The second problem is that it is very - very hard to get the air bubbles out. In previous uses, I had applied a dollop of epoxy or gel coat to a small repair and laid the plastic sheet on. Then the epoxy was rolled toward the edges and the large (relatively) blob of goop would chase the bubbles out completely. This is not possible on a large area. Maybe if several workers were used it could be easier. After the plastic sheet is removed, the surface looks just as good as the one on Blazy's website - from a distance. Beautifully smooth and fair. Up closer, the bubbles become craters and they are there by the hundreds, if not thousands. Getting these things covered is at least as much trouble as fairing in the usual way. If someone finds the secret to these problems, then this may be a worthwhile finishing method. In the meantime, I am going back to normal epoxy coating with a foam roller and dry brush for plain coating and peelply for fiberglassing which does work and does not have these problems. That's my story and I'm sticking to it -- until someone shows me otherwise.
  5. Too bad about the break and hope that it will work out fine next time. I am sure Graham is right about the building method but there a couple of things you can do to prevent breaks when bending plywood. All breaks start at some weak point in the ply so the idea is to stop the fracture from beginning. If the surface of the area to be bent is sanded on the outside of the bend and then squeegee on a THIN coat of epoxy, the epoxy will bond the surface fibers and stop a fracture from starting. You can also attach a batten on the outside of the bend will spread the stress out and prevent the fracture from starting. I have used both methods and they do work.
  6. Roger, There is no doubt that the technique works. Many of us have used it for repairs for many years and I saw it being used in manufactureing on a large boat in the 1970's with gel coat and celophane plastic. I got the material from the nearest supplier of Cadillac Plastics in Raliegh, NC. It is too early for me to give any pointers or advice but on the topsides of most of the boats we discuss here, it should do very well. I may try it on the topsides of this boat without the layer of fiberglass.
  7. Funny you should mention John Blazy's site and technique. I am currently doing that on a small classic style runabout. Getting the 30 mill polyester material was fairly easy although it had to be ordered. Fishing out the bubbles is the most difficult part of the process and I found that chasing them to the edges with a small wood block held on edge was better than the roller. One concern is getting enough epoxy over the fiberglass to prevent early print through of the fabric. This will eventually happen anyway but I'm trying to work out a way to get more epoxy over the cloth before laying on the plastic sheeting. Time will tell how it works out. There is definitely a learning curve.
  8. Rule number one: As soon as you start to build a boat in a garage, it becomes a boatshop and the car stays outside. We have owned several "garages" and the only time a car has been alowed inside is when it needed to be worked on. Now, if you are building the boat in the dining room, some concession may have to be made.
  9. Wow, I expect that this amount of interest in scarfing means tha lots of begining builders are just a little apprehensive about the job. this explains all the interest in jigs of all sorts to take the worry out of it. My advice is to forget the jigs (especially the router ones) and just give it a try with a well tuned hand plane. When I first joined Graham's class about 15 years ago in a project to build a 20 foot trimaran for the World 1000 race, he gave me the job of scarfing up 5 sheets of 3mm ply on end to make the wing mast. I'd never done a scarf in plywood before and being ignorant of the possible pitfalls, just forged ahead. After a few hints from Graham, it turned out not to be any big deal even though the multiple sections had to be rolled up because there was not room enough to lay out a 40 foot sheet of ply, even in the school shop. We devised the jig that he wrote about above that, with a few modifications, is still in use today. I think his estimate of 100 scarfs is probably conservative. One neat thing about the screw/plank method of clamping is that it can be done on the boat if needed. I did this recently while finding the limit to which 6mm ply can be twisted in the sharp bow of the little speedboat I'm now building. One side literally exploded while being stressed beyond it's limits. After splicing in a new section, I backed up the plywood with temporary external stringers to prevent stress concentrations and it finally worked out just fine. Main thing is to just do it.
  10. I hope that your panels came out all right but it is not easy to get much clamping pressure with weights. Figure out the PSI that you obtained and you will find that it is very low. Epoxy does not like a lot of pressure but you need to get the panels to conform to a proper glue line. Unless I am doing panels that are to be finished bright, I clamp the scarf joint with a board on each side screwed together with drywall screws. Drill holes in the top clamp board so that the screws draw the panel tight. The small holes left by the screws are easy to fill later. I also use the finish nail idea to keep the panels in alignment.
  11. Gary, As you have discovered, it's no big thing to make scarf joints and your method is a completely acceptable one. I question the need for 12 to 1 bevels though since I have never had or seen a failure on 8 to 1 scarfs which are much easier to do. Some designers set the length of a boat to fit the max length that can be made using a minimum number of 8 to 1 scarfs, so longer scarfs might require an extra one.
  12. :idea: I have made it a Cardinal rule that I will not sail if the wind is higher than the temperature. The rule was violated only once and as punishment, I received near frostbite in my gloved fingers. Hurt for a year. This rule applied even with ice boats.
  13. Since the 4th is on Friday, the race will be on the 5th and 6th and starts in Oriental at or about 9am. I assume you have read the article on the race on Graham's website. The Bluejacket "Liz" has been mother hen for the last two races and, assuming that I'm around here, will be again this year.
  14. I'm sure that neither I nor Graham meant to scare you off with our tales about the "Great Race". There should be several boats built by these forumites, from the BRS 15 to the CS20 that could sail this event. First to finish of every race since its inception has been won by one of these boats. So, If you hanker for something a little different and more challenging than a Sunday afternoon sail, think about making plans while watching the playoffs and waiting for the epoxy to set in this cold weather.
  15. The Fein is a great little tool even if a bit pricey. The basic tool is not too bad but the attachments, like the saw blades, are way over priced. When you need it and nothing else will work, you kind of forget the cost. As an aside, the saw blade with the section cut off that will allow cuts right up to a corner, was a eureka discovery of your eminent designer, Graham. He broke a blade cutting some oak flooring and discovered the new ability by accident. Told Fein about it and they added it to the list. Got a full set of new attachments but no royalties.
  16. Wood flour is an excellent filler for filets but: If you wait until the epoxy sets up, you will have a rough surface on the filet that requires lots of sanding. You will need to use silica in any case for the usual reasons. I use a mix of half flour and half silica. The rough surface is caused by the flour absorbing epoxy which shrinks back a bit from the surface/ or the flour particles absorbing epoxy and expanding proud above the surface. I don't know which, probably both. I try to make my filets in one step, including the glass tape so that minimal or no sanding is required. It is best to let the epoxy filet get a bit set so that placing the tape does not disturb your perfectly shaped job. If time is critical and you are careful, you can do all this at the same time. In any case, sanding is to be regarded as a sin when possible. Care and neat work (clean up drips, smears, etc) really pays off with epoxy. Sanding is drudge work, especially if you the only drudge available.
  17. John, Their correction puts the weight only slightly more than occoume at 0.103 lb/mm/sq ft, which is lighter than fir. Send us some and we will be glad to try it for you. Especially at those prices. Is the face fgrain as nice as it looks in the photo?
  18. Hopefully there will be a "great Race" in the two day format this year. I asked about the race at the fall TSCA meet and the Museum folk said that it was on. I expect to be available with "Liz" this year instead of cruising in Canada like last year. No knock on the Penobscot 14, but I think it could be a hard slog in average conditions and downright gut stretching in more wind. The Sunday leg starts with a typical 22 mile beat to windward into a freshening wind that gets reinforced by the sea breeze. In a boat that requires much hiking to keep on its feet, your gut better be in good form. I expect that the museum might be receptive to opening the race to more kinds of boats but I personally will vote not to let the event be taken over by racing types. The character of the race depends on keeping to the traditional nature of the format. That said, I'd like to see more participants from outside the local area.
  19. Just looked at both weights they gave you and there is some problem there. The sheet of 9mm should be 50% heavier than the 6mm but is given as only 35%. The heavier figure is probably more accurate, but who knows? Tom
  20. After weighing quite a few sheets of occoume (gaboon) marine ply, I use the figure 0.10 lb/mm/sq ft to calculate weight of boat panels. This seems to work out well for all thicknesses. There is some variation but not much. For your ply, this would work out to about 0.115 lb/mm/sq ft. This is probably about the same weight as marine fir here in the USA. Tom
  21. I use a home built styrofoam box with a hole in the removeable top to fit the small SOLO brand plastic cups. In summer, I put water and ice cubes it the box to keep epoxy cool. In winter, my shop is warm enough that I don't have to resort to drastic measures if the epoxy is fairly warm to start. I think some warm water in the box would work fine in winter. I used to have a small bar refrigerator left over from my son's college days that I used to keep left over batches of mixed epoxy in the freezer until I needed them. Saves a lot of mixing time and waste. This is especially good when there are a lot of small gluing jobs to be done in one day. Hurricane Dennis got the fridge 1999 and I got another from a garage sale and used the first with a 40W bulb in it to warm the epoxy in winter time. Hurricane Isabel got the second one this year and I found another smaller bar fridge. Rust got so bad that I canned both earlier fridges and built a wood box under the workbench which works just as well with the light bulb. Life goes on. Tom
  22. Greg, I may have the answer to your problem with the gypsum leaking problem. A while back, a group of locals, including intrepid designer Graham, built a 20 foot trimaran which was raced in the World 1000 race from Ft Lauderdale to Virginia Beach. The bottom of the center hull was coldmolded with juniper laminations that were stapled until the epoxy set and then several coats of epoxy applied. On the big launching day with local news cameras running, the "Oriental Express" was taken out for a sail. While the cameras did not show it, she proceeded to take on an alarming amount of water. The cause was water leaking through the staple holes. Graham and I surmised that surface tension of the low viscosity epoxy prevented it from sealing the holes. This is completely normal and should have been forseen. Surface coatings hate sharp edges and will always draw back from them, leaving the edge exposed, or hole open, in this case. Thickened epoxy or a fabric sheath will solve this problem. I had a result just like you when my wife bought a pottery bowl that proved to be porus and leaked. I tried coating it with epoxy but it still leaked. Takes a lot for some of us to learn from our mistakes. Adding some cab-o-sil to thicken the epoxy solved the problem. ------------------------- (quote) I do not trust air tight voids to remain free of water, so use the blue foam. To those who keep stating wooden boats float and do not need floataion, they should look at the history better. Wooden boats and ships sank and still do sink all the time. The Great Lakes are littered with thousands of them in just the last 200 years or so. (quote) ------------------------------ This is a bit out of context. As I stated, I do use the waterproof blue foam quite a bit for floatation. My comment was mainly an attempt to give a jolt to the novice's belief that all floatation tanks must have foam or something else in them to make them work properly. 'Taint so, at least for the unballasted wooden boats here. I advocate multiple air tanks for the small unballasted boats that this forum is about. I like to make all my small boats so that they will float with any air tanks punctured, however that is achieved. In the Bay River Skiff that I built, there were four sealed air tanks plus the two "almost waterproof" sealed lockers in the sides and the large locker forward. To say that foam should be required in the tanks as well seems excessive to me. This boat, like all Graham's unballasted designs, will float and hold its crew up if all the tanks are flooded. That's my story and I'm sticking to it. Tom Lathrop
  23. Charlie, you're too rough on B.C. You just gotta remember that he is secretary of Ludites International and has to keep up appearances. Many of the old fishermen refused to learn to swim based on similar reasoning. Natural selection has somewhat remedied that situation. I'm a pretty fair sailor and all my small boats have floatation and self bailers, with no appologies to anybody. Happiness is that gurgling sound from the bailer when the spray is coming over the side. Tom Lathrop
  24. These boats do not need any foam or other "floatation" materials inside the air tanks. If you don't build the tanks to be watertight, you will have more trouble if there is floatation stuff inside than if there is only air. Pour-in foam is not waterproof and should never be used in a boat. Lots of waterlogged glass hulls around to prove that. The ports in the tanks should be located so that all parts of the tank can be reached with your arm if they are to have anything stored in them. One nice idea for small stuff like glasses, wallet, etc. is to have a bag with a drawstring attached to the port cover so it can be retreived easily. Graham is using a new port with a large easy-open cover that he says is very good and maybe waterproof.
  25. Somehow, my profile has been magically straightened out so I can post under my own name. I agree completely with John that the best way to smooth out glass on a hull is to use a soft dusting brush. I use a draftsman's brush and find that it does the job without snagging the glass on wood fibers. With the proper care, lightweight glass cloth can be made to conform to some fairly compound surfaces without puckering. The tighter the weave, the less compound curvature will be possible. If the weave of the fabric is loose enough, I use the dry application method. If it is dificult to get the resin to flow through the fabric then it will be necessary to wet the surface first or epoxy and sand before applying the cloth.
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