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Polyester vs. Epoxy resin

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  • Polyester vs. Epoxy resin

    I'm redoing a keel on a small 17' power boat. This is a performance enhancement and I'd like to stiffen up the hull and provide a skuff/impact barrier on a thin glass boat.

    I'll be doing this project on blocks and in an overhead configuration. I plan on using a double bias type material on the keel line with matte and cloth to tye it together laterally. I'm see the whole project running about 7-8' and about 4' wide up near the bow.

    I will then surface sand and bottom coat with black.

    So should I be using standard polyester resin or epoxy resin to bond to old fiberglass to new?

  • #2

    The answer is epoxy, especially for improving performance on a small boat. Go with the West System Marine Epoxy. It is what many builders of the Tolman Skiff use for their boats. Polyester resin is much less expensive for many reasons. The biggest enemy is going to be inflexibility and uv resistance. You'll have to paint over polyester and if you do not it will give a light bluish haze to the glass underneath. Epoxy lets you lay down glass with a beautiful clear finish over top. Consider a place like this for your fabrics. Lots of cool patterns and colors if you want to show it off.




    • #3
      Thanks, I visited the site and sent an email seeking advice and a price quote. Lot's to consider for this project.


      • #4
        I second epoxy, and also second west system two part. I've been working with both for almost two decades. Go with the fast set hardner (201) for quick work like mods, or repairs. Go with the slow set hardner for big projects. I'd quote you a famous boat building book regarding how "sorry" you'll be if you use something in substitution of real epoxy, but I'll leave it be. Like wise, S-glass is ur best bet for real boat work. If you want to laminate dissimilar materials like kevelar, s glass, or carbon fiber, building a vacuum sealing station over your mold may be nescasary to regain all of the attributes and rigidity the laminate can offer.

        Just because you use good materials though....doesn't automatically make it the best.

        It's like taking the finest ingredients (a $50 dollar steak), over spicing it, and over cooking fcked it up in the end.

        If you'd like to chat about this further....PM me.


        • #5
          I agree with the epoxy too but beware that it tends to run in an overhead or vertical situation. Seems like there are some additives that might help. Of course vacuum bagging would be best and it wont be an issue.



          • #6
            I don't understand this "Vacum bagging" technique?

            What kind of additives could I use to thicken? How much work time do you think I'd get with the fast set 201 hardner?

            I project my work area to be about 4' x 8' with tapering towards the bow of course.

            Does Kevlar come in a double Bias type matterial for a quick thick lay up for the keel and cloth for the perimeter?

            Thanks for your help.


            • #7
              Vacuum bagging is where you stick the object to be laminated into a large "bag", seal it, apply a vacuum, and then let the weight of the atmoshere hold everything together as the glue dries. For a boat hull there are many ways to accomplish the task. The most common for your project wold be a sticky putty/tape rim seal with an overlay of plastic film and several ports for the vacuum lines to pull an even vacuum. One of the best tutorials I have seen was by a surfboard repair shop. Don't have the link anymore, but the tech details were pretty awesome for how to build a bag from scrap.

              Thickeners available to the retail user are sawdust, cabo-sil, micro-ballons. They won't help you with getting the glass to stick to the hull. Think of them as making resin into custom bondo for filling holes. If you use thickened resin on cloth the weave won't be filled and you have wasted your time and money.

              Personally I hate overhead work for anything but patches. Handling a piece of cloth nearly the size of the hull will be a tough project. Once you wet out the cloth gravity will start to pull it off the hull surface. If you wet the hull and then let it nearly cure before sticking the cloth to it you will then have areas where it might be too cured to stick and start pulling away.

              Mechanically the best way to stiffen a hull is from the inside not the outside. Hard to do on a boat that is not being gutted.

              I recommend building a cradle and turning the boat over. That is how much I hate working under a hull with resin dripping in my face.


              • #8
                I'm kinda torn here. If I was to drain the engine of oil. (It needs a change anyway) Could I invert the boat with the engine installed. It's only a 50 HP so not super heavy. I've got removable above deck fuel tanks I'd take out.

                I've got heavy beam rafters to work with in my space.

                I'd need heavy wide straps for this. What have you seen done for Cradles in the past?

                Gears are turning........


                • #9
                  Here is one example of how to turn a boat over.

                  If you read the text in the post you will be really confused. The photos don't match up with the text. Just stick to the photos.

                  the other way is to use straps and lift the boat from the rafters but then you need to make sure the straps are not going to tear anything off the deck as the boat spins. You can use a simple cradle to keep the boat up off the floor as you spin it and re set the straps if needed.

                  There is bound to be someone in Sitka that has flipped a hull before and can help out.


                  • #10
                    Ray, your photos or link didn't connect.

                    This boats gonna go over. I just won't waste my time trying the overhead work when I can do a better job with the boat layed over.

                    So Kevlar fabric, epoxy, and bottom paint here I come. I got new rub rail ordered too.


                    • #11
                      Found a way to copy the URL from that thread. The boat is a Snowgoose designed by Sam Devlin down in WA, built by Tod Osier on the east coast. He took everything off the boat and bolted a frame to the stern using the motor mount holes. He ran out of slack in his hoist and had to drag the boat a little when it was on its side in the third photo.


                      • #12
                        final photo of the series. He put it on the trailer so that he could move it around while making some repairs to the keels and what not.


                        • #13

                          That helps me tremendously! Rep point added.

                          I'll take some photos as this project developes and finishes.

                          Engine is comming off along with some other stuff.


                          • #14
                            rolling over boats

                            Bighorse, if they have copies of Wooden Boat Magazine at your library check out the following issues for examples. Issue 203age 60 is supposed to have many examples of several different types of boats. Issue 181age 34 might be a good example as well.

                            Sharpie: method for turning over, 22:30

                            Turning over boats: at Herreshoff Manufacturing Company, 33:50

                            Turning over boats: at Thomas Fabrication & Boatworks, 153:34

                            Turning over boats: commentary, photos, 203:60

                            Turning over boats: Didki 38, 154:84

                            Turning over boats: for classic sailing yacht restoration/Ed McClave, 189:78

                            Turning over boats: Redwing 18 (outboard camp-cruiser)/Bill Thomas, 181:34

                            Turning over boats: sharpie, 22:30, 33:36

                            Turning over boats: sloop Grey Seal, 129:84

                            AND....there is always Duckworks to turn to for some inspiration. This series of photos and videos should be very helpful if you don't have a wayt of lifting the boat.



                            • #15
                              I'll be going out to the boat yard and inverting the boat with a lift and placing it back on the trailer. I contacted a couple local outfits and that seems to be the practical way here.

                              I removed an old below deck fuel tank too. Now I've got a decking job to finish. Once I get the decking hole repaired. Is there a good one step deck finish I could apply?

                              I've used Tuff Flex but thats three steps and expensive. I still may do that but a one step sure would be nice.

                              I also got some ideas about the difficulty of saturating Kevlar. Can I use Acetone to thin my west system epoxy and get better cloth saturation? 105 and 207 combo.


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