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Thread: Re-building my Ketch Tonga (1960)

  1. #771
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    Default Re: Re-building my Ketch Tonga (1960)

    It's done, hope it doesn't cause inconvenience to anyone!
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

  2. #772
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    Quote Originally Posted by Dody View Post
    Awesome Phil, thank you heaps! If I make that out correctly, it is actually "only" a "normal" triangular piece of timber with the grain running paralell along the long edge. With "only" and "normal" I mean it's not made from a crook, and it's not laminated. Could that be the case?

    If so, I'm ready and set up to start. As it looks like I've got enough space under my stringers to bolt a nice corner-piece in on both sides, bolted to the beamshelf and the frame. Well, as I said "as it looks like ....". I'll better try this out now!
    Exactly right.

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  3. #773
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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by Dody View Post
    It's done, hope it doesn't cause inconvenience to anyone!
    Worked great Dody. Should be no inconvenience. The old links will just redirect here.

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    Default Re: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

    Quote Originally Posted by MN Dave View Post
    You can add me to the list of supporters who haven't had anything to add lately.

    Looking at the photos of the extended stern, I don't see limbers. It may just be the camera angles, but those areas do need to drain any water that gets back there. The standing water in this picture: http://forum.woodenboat.com/attachme...139898&thumb=1 reminded me to look for limbers.

    I was tempted to chime in on the Coca-Cola cleaner. There is a tiny amount of phosphoric acid in the stuff. I was just looking at water softener cleaners for my 11 year old resin and found that most of the liquid ones are pretty much 15% or so phosphoric acid. Some brands also have a little surfactant, so they might also clean some oily residues. It would be a decent substitute for Ospho as a rust remover. Naturally, I have no idea what is available in Nazaré. The dry powder water softener cleaner is often citric acid, which also cleans rust.

    I think I read somewhere that to change the name of a thread you have to move it to another forum like Designs and Plans. If that works, you can move it back with the new title. Once again, I don't know for certain, but someone will surely correct me.
    Oh, that's a very good point Dave, got to have a look with daylight tomorrow!!! Further forward they were always at the deepest point where the floors were joining the backbone, could we have forgotten about that?
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by Phil Y View Post
    Exactly right.

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    Awesome, great, thank you Phil! Didn't give it a go yet today. The moment I had my plank out of the workshop, table set up, circular saw out and electrics sorted a heavy drizzle started. Packed it all up, got the tarp over the stern and did the shopping I had successfully managed to avoid since last week.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Wood - Plywood - Epoxy bond, re-building my ketch Tonga

    Quote Originally Posted by Rumars View Post
    Attachment 41388Some back of the envelope engineering for you, plesse excuse my poor drafting skills.

    Don't worry about the planking on the bottom, just bore trough it with the countersink then put a plug over the bolt closing the hole. You are going to cover everything with plywood anyway.
    I still say the simplest thing is to make a plate knee out of steel.
    Quote Originally Posted by Rumars View Post
    Plate knee model and cuttting pattern. To be fitted on top of keel and inside fashion piece between transom planking and first floor. Web plate welded to base plate, all 4-6mm steel. Dots represent bolts.

    Attachment 41394Attachment 41395
    You've done an awesome lot of work for me, thank you heaps Rumars!

    I need more time to think this through. Both options.

    I've still got several meters of 6 mm mild steel roughly 150 mm wide - if I remember correctly - in my workshop, cutting is no big deal and Alec or ZeManel could theoretically weld it up for me in no time. I've got an old stick-welder which came with Tonga and is hideously heavy, but I haven't learned to use it yet, so it's got to be one of them for now.
    What I don't really like is using even more steel on Tonga in a spot where I can't re-paint it from all sides to prevent rust. Yes, I know, 6 mm is quite heavy and it takes a lot to have it fall to pieces. But steel today seems not to be the same quality as the steel they were using when Tonga was built. I could use stainless because it won't get in contact with mild steel anywhere (unlike my new ruddertube which is even welded to the steel-part of the backbone). Hm ...

    Using a wooden knee, after seeing your drawing, a few ideas hit me.
    For example: If I would manage to remove this bolt and replace it with a dowel (or how is this called correctly? I mean a round "stick" of wood banged into the complete hole?) to get rid of the obstacle I'm facing with the bolt holding the knee in an angle? The bolts I ordered to attach the planks with were meant to go through the whole lot anyway, so I would only need to install one to the right and one to the left of the backbone and I've got the same effect.
    You are right with suggesting to just plug the hole in the plank of course! I haven't got a plugcutter this big (yet, need to order it), but I'm sure Albertino has. I would need to drill in an angle from below through the plank, the backbone and the knee because at this point the planks meet in a V-shape and drilling through the center I can't plug a half-hole.
    I've been talking to Joao Paolo today, he'll call his brother Albertino to bring a crook if he's got one tomorrow when he comes back to Nazaré. He doesn't think he's got one, but if Albertino is here tomorrow we'll be able to work something out about a crook - or not, then the steel-option might get more attractive.

    Meanwhile I'll start with the corners tomorrow, if the weather improves.
    Last edited by Dody; 07-15-2019 at 06:07 PM.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Re-building my Ketch Tonga (1960)

    No problem Dody it was my pleasure.
    Steel today is even better then what was available then, but it all comes down to what you buy. After the war there was a lot of steel from scrapped warships wich could range from ordinary mild steel to some exotic alloys. Every once in a while one encounters a boat "buildt from the best U-Boat steel", or at least that's the story. Who nows what alloy Tonga got back then.
    But I get your desire to have less rusting boat pieces. Ask the local fabricators where you can get hot dipped galvanizing, I am sure they know and routinely send pieces there. Hot dipped and painted will last a long time. I would not use stainless for this.

    Yes you can replace the bolt with a dowel. Just put some groves onto it and bang it in with some epoxy or PU. Getting the bolt out without removing the frame is a little bit tricky and depends on what is now in there. If it is a threaded rod with nuts both sides or a machine screw or bolt it can be done. If it is a carriage bolt or finn head bolt and the bolt head is accessible it's a little bit more involved but possible. The way to do it is to pull on the bolt shaft while turning it so the nut on the other end stays put by friction against the wood. For that to work you have to weld an extension onto the shaft. Carriage and finn heads first need the head removed. Or you take the brutal approach and use a plug cutter that fits over the nut, basicly making a hole the size of the existing countersink. That's the only way if the head is on the inside. The cutter is made out of a steel pipe with teeths filed one end.

    To drill and countersink the holes trough the keel you drill from above then countersink from below using a boring bar. It's nothing fancy just a piece of round steel with a blade at a right angle. The bung you use is longer than the plank and gets cut to the plank angle, then you take a small saw or chisel and cut trough the middle along the plank and perpendicular along the keel on the other side. This way you plug a half hole with the required angles. Use some glue and cut after it has set.

    You don't need a crook, you have epoxy. Laminate in place using staples or on the bench with clamps. First you fit the upright post inside the frame. Then you cut the triangular filler piece with convex face and gue it to the upright. Then you continue with thin strips until you reach desired thickness.

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    Default Re: Re-building my Ketch Tonga (1960)

    Rumars, what is the reason you wouldn't use stainless for this?

    Hot dipped galvanizing is possible here of course, but it's something I can't get done in a day, it usually takes a week or a lot more than that. Which means a week or a lot more than that waiting till I can close my transom. I can get galvanized steel to fabricate the piece here, but that won't do coz you've got to grind off the galvanizing at the edges, otherwise you can't weld it. Painting galvi is a PITA as nothing really wants to stick to it.

    If I want a solution less than a month from now to close the stern galvi is not an option, and I'm not prepared to wait that long. Mild steel treated and painted: yes. Stainless: yes. Anything wood or plywood: yes.

    It's true, I could sort out the chaos in my workshop in the meantime, and there are a few other things I could tackle while waiting. My medical insurance for example, which will be discontinued by the company after the 31st of December this year. But I've got a deck to close before the next winter is gonna hit me and time is ticking. As much as I appreciate the qualities of good hot dipped galvi, it's not my preferred option right now.
    Last edited by Dody; 07-15-2019 at 08:43 PM.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Re-building my Ketch Tonga (1960)

    Cant see why stainless would not do just as well.

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    Default Re: Re-building my Ketch Tonga (1960)

    Make the knee from plywood like it was steel plate. One horizontal plate on top of the keel with ears to go around the existing bolt in the fashion piece, one vertical plate on top. Epoxy fillets and fiberglass tape at the joint, same for the joint to the transom plating. Requires you to do the whole transom plating in ply. The actual knee plates will be several layers of ply glued with epoxy and wrapped in fiberglass. Holes will need epoxy plugs.
    Or laminate a normal knee and try to fit the corner bolt at an angle so that it goes next to the existing bolt.

    Stainless on wood in warm waters and unventilated area = invitation to crevice corrosion. Works fine in Scandinavia, not so fine in the Med.

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    Default Re: Re-building my Ketch Tonga (1960)

    Having written all of the palaver below, I am leaning toward questioning the need for a knee or recommending this:
    Or laminate a normal knee and try to fit the corner bolt at an angle so that it goes next to the existing bolt.
    Stainless on wood in warm waters and unventilated area = invitation to crevice corrosion. Works fine in Scandinavia, not so fine in the Med.
    Stainless can have some corrosion problems that can be hard to understand. In general it is fine above the waterline, but there is always a few details to remember.

    Stainless steel is generally not a problem above the waterline as long as it has been passivated. It will stay passivated as long as there is enough oxygen in the air or water around the metal. Below the waterline, it is easy to run out of oxygen in tight crevices between stainless and wood or plastic. Cold water is much better than warm water. Once there are oxygen depleted areas underwater, things can go badly.

    Stainless resists corrosion as long as the surface is clean and coated with a very thin layer of chromium oxide. The oxide forms naturally on a clean surface, but getting the surface that clean is the hard part. Any time you cut, hammer, weld or otherwise scuff up a stainless steel part with a steel tool, you can leave a little steel smeared on the surface. When that rusts, the whole thing keeps rusting. That is why stainless steel fabricators routinely send the parts out to a plating shop to have them passivated.

    Passivation is a treatment to remove the smeared metal. Grit blasting with clean media can passivate stainless, but it is normally done with an acid bath, and the smoother the surface, the more rust resistant it will be. Paint and machine shops familiar with stainless usually send the parts out to an electroplating shop because they normally have the chemicals and equipment and know how to work with them.

    Galvanizing is the best coating for low alloy steel but logistics and economics can be a problem. Second best is arguably metallization. That is a process where zinc or aluminum wire is melted with an electric arc and sprayed onto a freshly grit blasted part. Quite the light show and an awful din. Finding an applicator in Portugal, or anywhere else can be as challenging as hot dip. Google says that https://anticor.pt/index-en.html does zinc metallizing about 180 km up the coast near Porto. I have no idea whether they will do one small part. They might be able to refer you to a job shop that takes small orders. There are also zinc rich paints which would be a good third choice. OK, fine, just get some decent epoxy primer and some coal tar epoxy if you can find it.
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    Default Re: Re-building my Ketch Tonga (1960)

    Passivating ... learned a new thing today, thank you Dave! I've heard about it before when it was about my ruddertube, rudderstock, propshaft etc. but couldn't really figure out what it means - and never took the time to look it up. I imagined something similar like de-magnetising or similar (well, we all know that using a magnet is how we can find out if it's stainless or just "normal" steel), as it was about currents which can develop under water between passivated and un-passivated stainless, but I didn't realize it's actually about the cleanness of the surface.

    Crevice corrosion I know about since friends of mine suddenly found this on their anchor-chain after 6 weeks in the water somewhere in the Caribbean many years ago and suddenly crevice corrosion was the subject anywhere in the boating community. There exist 2 other types of corrosion on Stainless, one of them makes the stainless turn into paper-thin leaves which seems to have to do with age and the type of stainless, the other one is fatigue as stainless can't deal with vibrations for very long.

    Metallization, Alec wanted to get a bit more into that and buy the equipment, should ask him actually what came out of it. And, I think, Nuno from Benedita has got the equipment. It's maybe 2 years ago we were talking about it. Benedita would be maybe 30 K from here.

    I still tend to use wood for the knee. Albertino was not here today, and I got sidetracked sorting out other stuff. The tiny bit of time I had on the computer I tried to find out a bit more about laminating a knee. Not very good with this. There was a video from one guy who did the laminating like one would build a flat pyramid and cutting it to shape - which is not what I was looking for and I don't think it's suitable for what I need it for.

    What I have in mind is making a jig, bending thin pieces of wood into this shape and gluing them together with Epoxy. The questions I've got is which kind of wood would be best, and which thickness should it have as a maximum? For example, I've still got quite a lot of scotch fir in 10 mm. Scotch Fir is not very rot-resistant and pretty soft, so I shouldn't really use it for this knee and I won't. Apart from this, I can't imagine it to be possible to get a strip of 10 mm of scotch fir into a 90º bend and certainly not any of the Kamballa if I had it in 10 mm. Whatever I use, it certainly has to be thinner than 10 mm. Which wood? On Wikipedia they mention white oak, hakmatak and something else. I can get white oak about 15 K from here if that's really what it should be, no problem. What kind of thickness would be suitable? There will certainly be a limit how thin the guys in Famalicao will be able to cut it for me. I will probably have to steam-bend the lams and I've already got an idea how to build a steam-oven from scratch, but of course I've got no idea how long I would have to leave the lams in there. I'm sure there is heaps about it here on the WBF, but I must be doing something wrong with the seach-function coz whenever I try to find something it offers me threads where the subject is mentioned, but doesn't give me a hint where in this thread I might find the information I'm looking for. While it's such a lovely, distracting and interesting thing to read all these threads it's also very time-consuming as some are 40 or more pages long. I'll have another look on Google tomorrow to see what comes up. There will be something for sure by the guy doing "Tips from a shipwright" and a lot of others also. We'll see!

    I didn't get the time today to check the lumber-holes, but it's on top of my list.
    fair winds, Dody
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    Download Gougeons book on epoxy boat building. Sorry I don't have a direct reference. Maybe 5mm strips?

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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by Phil Y View Post
    Download Gougeons book on epoxy boat building. Sorry I don't have a direct reference. Maybe 5mm strips?

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    https://www.westsystem.com/the-gouge...-construction/

    I had to read Uhlig's "Corrosion" from cover to cover, all 500 dull pages. We don't want to do that here. A 20 page summary for metal boats would be better.

    You left out stress corrosion cracking. I have seen a high strength PH stainless shaft let go at a stress only 5% of it's ultimate strength. Heat treatment error that time.

    I would like to see the paper-thin leaves. That sounds strange. Some aluminum alloys do something like that where it is called exfoliation corrosion.

    Fatigue is not corrosion. Each time the stress reaches a high enough level the cracks grow a tiny amount. Sometimes you can see the tiny lines that leaves if you happen to have a scanning electron microscope handy. https://slideplayer.com/slide/845543...Striations.jpg There is a combination called corrosion fatigue where it happens a lot faster in a corrosive environment.
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    Default Re: Re-building my Ketch Tonga (1960)

    That's a lot, Dave and I agree, 500 pages are a bit too much on metal! Will see if I can make a photo for you of this weird corrosion that left quite some people scratching their heads.

    Thank you heaps for the link! I remember I've read the whole book a long time ago, but too long ago to remember very much. So I started at the index to look for the key-subjects, flipped to page 74 - which actually is page 60 in the book, and what happens? It's the tools-section and my eyes get immediately caught by the sentence "... A saber saw is a little less accurate than a band saw, but it can do most of the same work and more. ...". Oh, whow, what??? Awesome!!! There's quite some things I've been wondering how best to cut them with the tools I've got. I've got a tiny little sabre-saw which is great for small stuff but it somehow never occurred to me that they might exist in big as well. Instead of going on with the book I started looking for Saber Saws. Didn't manage to buy one today but had a look at several brands in the shops around. Back home on Tonga I did some more research. At the moment all inside me is leaning towards the Bosch GSA 1300 Professional PCE, closely followed by the Makita JR3070 CT. Both have a very good vibration-control system, the Bosch-one seems a tiny bit better and the machine a tiny bit more accurate in operation, and the Makita a bit more powerful.

    Forecast is still a bit uncomfortable for tomorrow, so I guess I'll drive up to Leiria and Marinha Grande to see what I can get there and which prices. Whatever comes out of it, I definitely like it more than a chainsaw as an alternative. Dangerous this kind of weather, I always spend a lot of money when it's like this. But at least it's for a good purpose: tools

    o82161v54_GSA1300PCE_Dynamik.png

    Bosch GSA 1300 PCE
    JR3070CT.jpg
    Makita JR3070CT
    Last edited by Dody; 07-17-2019 at 07:42 PM.
    fair winds, Dody
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    Done and it works



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    Last edited by Dody; 07-18-2019 at 06:48 PM.
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    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Re-building my Ketch Tonga (1960)

    OK. I haven't finished reading all of Chapter 11 (Laminating and Bonding Techniques), but at least I got to where the application of Epoxy starts and some of my memory came back from reading it the first time. No idea if it will all work out, it's a first for me and I've got to give it a try. However, to get whatever material I manage to find in this corner of Portugal and get it cut - if needed - means, I've only got tomorrow (Friday) as most of them are closed on Saturday, otherwise it's waiting for Monday. If I want to get up earlyish, I need to stop reading now.

    The plan is:

    I wouldn't like to use the 6 mm Okume plywood I've got in the workshop, already cut in 14 cm (and 10 cm as leftovers) strips to be used for the hull. Although I had boiled it several times for 30 minutes and then dried in the oven for an hour without any complaints - meaning the quality of the glue must be alright - Okume is only medium density. I do prefer high density for this knee and as rot-proof as possible.

    The most import bit for me to start with is to find out which kind of radius would be the tightest necessary. Meaning: I've got to make a drawing how the cabin-side part of it should hopefully look like on the finished knee. Once I've got that worked out probably my feeling will tell me that I've got to use veneer.

    About 20 K from here is a pretty huge yard selling plywood, all kind of different timber in planks of various sizes and also veneer.

    What I'm looking for would be a high density timber that's as much rotproof as possible. I'll take my drawing with me and have a chat with the guys. Most of them have a surprising amount of knowledge and are happy to help their customers. But, as I said, I more than possibly will end up with veneer I guess.

    If it isn't going to be veneer it'll be a plank of white oak or something which I'll take over to the carpentry in Famalicão (4 K south of here) to have it cut into lams. Shouldn't forget some sticks of timber and some sheets and lanyards for my roofrack as Dave pointed out so nicely last time!

    I haven't got a clue how thin they would be able to cut this plank, but I'm sure they will be able to tell me if it's gonna work maybe or not. If not I can still try steam-bending, and I can increase the radius.

    Whow, I'm really curious now how this is going!!!
    Last edited by Dody; 07-18-2019 at 07:08 PM.
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    More or less like this, off to get the material now:



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    Default Re: Re-building my Ketch Tonga (1960)

    Nice 'Sawzall'.

    I think that you worried too much about laminating. Since it appears that you will have the laminations cut before you read this, you already know that you didn't have much to worry about. Use lots of glue. A mess is better than a lot of voids.

    It looks like I was mistaken about Uhlig. It was 1285 pages, not 500. It's been 35 years. I suppose that you do tend not to remember the unpleasant details very well.
    For the forum insomniacs, this will help you sleep:
    Uhligs Corrosion Handbook.pdf
    I do recommend reading the metals article metal boats.
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    I didn't buy oak but iroko. In oak the max. thickness they had was 78 mm and with lots of knots. 55 mm was the next down, looked really good but ... the employee suggested to cut it from the top down instead of slicing from the side. Wasn't sure about it and it was nearly lunchtime where everyone goes off for a meal. The iroko looked clean, was 80 mm thick, and drying in their shop for 3 years. So I bought this and another plank which was curved - something I might have a use for one day and desperately hunting for one. He was happy to have found a use for it and gave it to me for 1/3rd of the price.

    Have to go back to the shop on Monday to collect my invoice as everybody had gone by the time the planks were ready for loading into my car. Yes, into, because they were only 2.37 m long.

    After lunch to the carpenter to have it cut. All his employees were busy so the owner himself did the prep and cutting. He managed to go down to 3.1 mm thickness of the lams, we tested, and I still have to go for a bigger radius. Certainly my own fault because the plank wasn't as straight grained as I thought. One never stops learning, luckily!

    I'll leave them hanging over the flywheel of Alec's 18 HP 2-cylinder Lister for the night, maybe it helps a little. If not I still have the option of steam-bending.











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    Last edited by Dody; 07-20-2019 at 07:19 PM.
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    Cutting took an hour, I didn't even have to wait.











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    If you are having trouble with getting a tight bend, can you just make the bend a bit softer, the knee a bit deeper?

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    Default Re: Re-building my Ketch Tonga (1960)

    Iroko is good durable stuff.It also makes me sneeze and itch when working with it.I may be particularly sensitive and others may have less trouble with it.Once in the boat it will do a great job.

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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by MN Dave View Post
    Nice 'Sawzall'.

    I think that you worried too much about laminating. Since it appears that you will have the laminations cut before you read this, you already know that you didn't have much to worry about. Use lots of glue. A mess is better than a lot of voids.

    It looks like I was mistaken about Uhlig. It was 1285 pages, not 500. It's been 35 years. I suppose that you do tend not to remember the unpleasant details very well.
    For the forum insomniacs, this will help you sleep:
    Uhligs Corrosion Handbook.pdf
    I do recommend reading the metals article metal boats.
    Thanks Dave! I had to play with it straight away to try it out. It's a bit on the heavy side with 4 KG but powerful as I wanted it, easy to control and feels right when I've got it in my hands which I find very important also.

    Lots of glue, okay! The radius I used on my sketch is 23 cm. I took this sketch with me and after cutting the first 3.1 mm lam we tried if we would be able to bend it to this radius, but the lam broke each time. He couldn't go thinner, so I decided to have them cut anyway and use a bigger radius instead. We managed to bend it from corner to corner with a slightly larger radius and without breaking it, so there is a chance.

    Uhligs, whoa, this is serious stuff! More than 1200 pages about nothing else than corrosion. I actually downloaded it from your link, who knows if I ever might need to look something up in there. And thanks for the other link too!

    Quote Originally Posted by Phil Y View Post
    If you are having trouble with getting a tight bend, can you just make the bend a bit softer, the knee a bit deeper?

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    Yes Phil, this is what I'll probably do. It's still hanging over the flywheel and I was able to tighten the string quite a bit more this morning hoping to kind of pre-bend it a bit. I remember Albertino doing something similar on 2 planks we had to do again as the first ones exploded on us. We would install them as far as they would go fairly easy, get them under some clamping pressure and leave them overnight. Tightening the clamping pressure in the morning, again a bit in the evening and the next day we managed to get them in. The planks were Kamballa Oscura which is the same family like Iroko. So hopefully my Iroko will have kind of a similar memory-effect or how one might want to call this.

    Maybe I'm really overthinking this as I've never done it before, but in the Gougeon-Brothers book they mention that the more lams one is using on a tighter radius, the more clamping pressure is needed till it might not be possible at all. Sure, I will find out once I've built the jig and do a dry run.

    Theoretically, with each lam towards the outside it should be easier as the radius is getting slightly bigger. To get to my 60 mm height at the ends I would have to use about 19 lams (glue not counting) and add the rest of the shape later when this has cured. What is hanging over the flywheel are 10 lams and they don't like bending that much to start with.

    Quote Originally Posted by John Meachen View Post
    Iroko is good durable stuff.It also makes me sneeze and itch when working with it.I may be particularly sensitive and others may have less trouble with it.Once in the boat it will do a great job.
    Oh I know only too well what you mean John! I didn't have it with Iroko (yet) as they were having these dust-extractors, but cutting or sanding Kamballa Oscura was constant sneezing and blowing my nose! - And yes, I hope so if I get this laminating sorted somehow. Well, others have managed so it shouldn't be that difficult!
    Last edited by Dody; 07-20-2019 at 07:24 PM.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Little thinking-session at the beach ... when we tried to bend the lams at the carpentry we did that without supporting them on the flat side. Would this not be the same as with a ss-pipe one tries to bend by hand and one would eventually fold instead of bending (depending on the leverage)? Do the same, supported, with a pipe-bender and it works. Got to try out some stuff with the lams tomorrow!!!

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    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Re-building my Ketch Tonga (1960)

    Hey Dody, a couple of thoughts here:

    1. I don't know how well iroko would steam bend, but could you try soaking the lams in hot (boiling) water and then pre-bending them on your former. Let them cool and then laminate? I don't know if you are going to get a 23cm radius that way but you might get it to be tighter than what you have now. (I should add a disclaimer that I've never done anything like that so I'm just speculating).

    2. But I'm not clear on why you are laminating a knee at all? Is it just because you can't get a grown knee/crook and the available lumber isn't large enough for a sawn knee? I was really liking the fabricated steel knee idea myself. Simple, effective, fast. Tonga already has plenty of steel in other places so it's not like you are introducing a new element to the mix. I'm betting the steel knee would last at least 25 years, and we should all be so lucky if we are still here to talk about replacing it then...

    I'm just thinking out loud though. Good luck with whatever method you end up with!

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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by Dody View Post
    Little thinking-session at the beach ... when we tried to bend the lams at the carpentry we did that without supporting them on the flat side. Would this not be the same as with a ss-pipe one tries to bend by hand and one would eventually fold instead of bending (depending on the leverage)? Do the same, supported, with a pipe-bender and it works. Got to try out some stuff with the lams tomorrow!!!

    Sent from my SM-G900FD using Tapatalk

    Oh, and one further thought here... From my experience laminating the frames on Petrel I do think there is some advantage in supporting the laminates, although it's not quite the same as in bending pipe. If you made a former for the entire bend and supported it with even clamping pressure on the outside you could probably get a tighter radius before the laminates will crack.

  28. #798
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    Default Re: Re-building my Ketch Tonga (1960)

    Hot pipe bending


    This archery bow bending forum looks informative, but it isn't my problem, so I'm not feeling enthusiastic enough to read the whole thing to guarantee good in formation:
    http://www.primitivearcher.com/smf/i...?topic=60749.0
    Last edited by MN Dave; 07-21-2019 at 08:01 PM.
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    Default Re: Re-building my Ketch Tonga (1960)

    Just found this video on Youtube. Such an inspiration, I've really got to try steam-bending, even if I should find out it's not necessary when I try tomorrow (https://www.youtube.com/watch?time_c...&v=aAPD1SIeU_s)!

    Last edited by Dody; 07-22-2019 at 05:54 AM.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    I had to put quite a hard bend in the keel plank of a dinghy I built a few years ago. About 19mm stock. I draped hot wet towels over it and clamped it slowly over 2 or 3 days. It worked.

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    Default Re: Re-building my Ketch Tonga (1960)

    Hmmm, not a bad idea if I think about it Phil! I'm tempted to get me one of these sewage-pipes in a diameter big enough for the job, close both ends with a hose attached either at the center or maybe better at one end, the whole lot a bit inclined, and this connected to a kettle with water below on a stove.

    I just found a very interesting and informative video about the techniques which explains a lot - not that I am even thinking of using a press and all involved. But he nicely explains and shows the problems with the grain-runout (less than one inch of runout per foot in the grain) to avoid problems, and he explains and shows that the outside of the curve should not be stretched but the inside compressed instead. Lovely!

    Seeing this I don't think I should have the slightest problem to get my Iroko into any shape with steam-bending (https://www.youtube.com/watch?v=b9UPihp04xY).

    Last edited by Dody; 07-22-2019 at 05:54 AM.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    PVC plumbing pipe goes all soft and gooey at 100C.

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    Default Re: Re-building my Ketch Tonga (1960)

    Can you please post a link to the video?

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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by chollapete View Post
    Can you please post a link to the video?
    Ok, it's added in brackets on both posts.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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    Default Re: Re-building my Ketch Tonga (1960)

    Quote Originally Posted by Phil Y View Post
    PVC plumbing pipe goes all soft and gooey at 100C.

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    Good thinking, Phil! So it's got to be with steelwire inside or so, for it not to collapse.
    fair winds, Dody
    "They did not know it was impossible so they did it" - Mark Twain

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