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Ashcroft planking


Kennneee

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Hi All,

I am building an Outer Banks 26 and have been thinking about the glue and technique for applying the second layer of plywood when planking. I was reading Sam Devlin's book and he makes mention of applying a second layer of plywood with UNTHICKENED EPOXY. I know many builders trowel a thickened coat on.

There is more than one way to skin a boat and would love some discussion on technique as well as epoxy preferences. I have been using System 3 Silver Tip for the last 12 years with good results with my strip builds. Never have done Ashcroft before and wonder if anybody has tried their T-88 or Gelmagic for this purpose. Any input greatly appreciated. Thanks!

Cheers,

Ken

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I suspect most of us are using epoxies comparable to the T-88 and using thickeners like cabosil or wood flour.

 

The deal with thickeners with Ashcroft (overlapping planks) is in addition to filling any voids and gaps between planks, often times these planks are curved into a stressed shape, so clamp themselves tightly together. Without some type of thickener, the epoxy joint between the planks would be thin and it takes a bit of epoxy filled gap to generate the strength of the epoxy joint. Without that, the joints might be thin and dry, holding the potential for them to come apart under stress. The epoxy used need not be thickened so much it won't spread out. About like mustard or mayo.......not so thin it will run or flow, but not thick enough it won't compress and move around easy.

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Like Howard, I'm in the camp of mixing my own adhesives from resin and fumed silica (IE: cabosil).  I do this for a couple of reasons;  First I am cheap, I want quality but if I can achieve similar mechanical characteristics and save money then that's a winner.  If you're willing to use other epoxies, you can get you're per gallon cost to around half of what gelmagic costs.  Second, by mixing my own, I can vary the viscosity to meet my needs.  Peanut butter like for fillets, mayo for planking, a little thicker when it's hot, a bit thinner when it's cold.

 

As for applying planking with unthickened epoxy, If I could guarantee my parts fit up and where clamped perfectly I might consider it, but I can't, so I would be very concerned about incomplete bonding.  Straight epoxy will run out of joints with ease potentially leaving hollow areas or just as bad, starved areas in the planking.  Most (pro) builders will use glass or fumed silica on glue lines to hold the resin in the joint and provide some excess to completely join the planking where parts are not held together perfectly.  In the final analysis, I would prefer to have a little extra material (weight) in the joint and be relatively sure it was complete and sound.

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On molded hulls, the planking is "bent" on and places the contact surfaces in compression, most of the time, so straight epoxy can work. There are some considerations of course, the first is starvation. To solve this the wood should be previously sealed, insuring a good, continuous film, between the planking. This can be done in one stage, by wetting the pieces and waiting until you're sure it's all sucked up and the next coat will lay on the surface. Previously sealing the planking, before installation also insures no adhesive starvation. It takes some experence to go with straight resin and the hull shapes also can dictate if this is the best approuch. If the hull has any reverse curves in the planking runs, you'd be best advised to thicken it up a tad, as all of the planking will not be in compression as it's hung. The real advantage of the Ashcroft planking technique is you can apply multiple layers of planking at the same time. Unlike double diagonal molding, which requires you nearly finish the first layer, before the second can go down, Ashcroft only requires a few first layer planks be down, before the next can be applied. Naturally, the drawback (there's always something) is the molded results aren't as strong nor as stiff as a double diagonal molding.

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Hi Guys,

Thanks for sharing your collective wisdom. I am an old dog that has lots of new tricks to learn. I get into a way of doing things and have had a hard time trying something different. Been building boats for most of my life but never using the Ashcroft method of planking. Of course many techniquues work on different types of construction. There are techniques and products that have proven themselves over time and there is great value in that.

Most of my boatbuiding in the last 20 or so years has been strip kayaks and surfskis. I used WEST 105 and 207 for many years and it worked well for the glassing of the bright hulls. Around 10 or so years ago System Three offered to supply me with their SilverTip resin for one of my builds. I found it wet out easier and preferred it ever since. That got me thinking that other products might be worth playing with. I also tried another brand ( will go unnamed) and it was crap. Not all new things are a winner. I have a shelf full of powders that I have always used for thickining, filets, etc. They work fine. Again, got a sample of GelMagic a few years back and found it worked great for vertical and overhead glueing. That stuff just doesn't run and makes for a neater job. It is more expensive than mixing your own, for sure, but not that much is you can get it wholesale ( they just released an improved version). I tend to use this stuff a lot. I am pretty frugal but maybe getting lazy. I am open to trying time saving materials and techniques these days. System 3 just gave me a sample of their T-88 to try. It is a 50/50 mix and a bit thicker than most of their other products. I guess it was developed for the aircraft industry and is a bit more flexible that than their standard epoxies. That is the product their techs recommend for this application. Ask 5 boatbuilders and you have 10 answers :). I REALLY appreciate the feedback and help. I once thought I had all of the answers and have come to realize I have more questions every day. Thanks for the help guys! Please keep the advice coming.

Cheers,

Ken

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Ashcroft is a pretty old method and is just another way to do a molded hull. It, like most every choice you have with design and building, has good and bad things to consider. I use Ashcroft frequently on round bilge jobs (again) because of the speed you can apply two layers of planking stock.

 

I'd also recommend you consider one of the discount epoxy brands, which can be 1/2 to 1/3 the price of West and System Three. B&B has one, RAKA, EpoxyProducts.com, and Marinepoxy are the usual, lower cost choices. I'm not sure what issue you previously had, but 1/2 price is hard to sneer at.

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Almost all the epoxies I've worked with (except for West System) are 2:1 resin to hardener, and that includes S3 and all the brands PAR (Paul) mentions, and I've had good success with all of them. They are versatile and can be used to wet out glass, glue and fillet, all from the same jug. I know S3 throws cold water on that, and offers unique products for each of those applications. I eventually decided that was more marketing ploy than anything. Working with epoxy is not rocket surgery. Get the 2:1 mix ratio right and it almost always works out OK.

 

Seems I heard somewhere that 1:1 were the inferior products. I could be wrong about that.

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The epoxies I would like to learn more about are the supposedly less toxic varieties. Duckworks now has one that is claimed to be good in a milkshake and then there are the ones made from tree sap. I am reluctant to jump on that bandwagon until they pass the test of time. I have had a couple of bad experiences with paints and finishes that were the latest, greatest stuff. Anybody have experience to share about these products?

Thanks!

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The less hazardous formulations can be deceiving, unless you have a very good chemical background, to understand the various differences. For example, the new DMX stuff from DuckWorks is still an amine cure Bisphenol A formulation. A number of additives are in it, as well as difficult to explain chemical alterations, which offer some advantages, but you still have to use the same precautions, as the other formulations. The same is true of the non-blush formulations. If you're like most home builders, you can't control the environment well enough, to guarantee a real non-blush cure. Simply put, even the non-blush formulations will blush under some environmental condisions, so you should always assume there will be some blush and work from there, unless you're working in an environmentally controlled area.

 

I tend to stick with brands of paints that I know well, to avoid issues. One good way around issues, is a good epoxy primer. Technically, you can paint over straight epoxy, but some paints, particularly modified alkyds can have curing problems, so a primer is the easy cure to insure you don't have issues. A good primer also offer you something to really finalize your finish with. It's difficult for the novice to really see fair and smooth surfaces, especially if they're of various colors, blotchy with fillers and adhesives, etc. A continuous coating of primer serves to tie the topcoat to the substrate and gives a good idea of how fair and smooth the surface is, before you apply the shinny stuff. If it takes you an hour to paint a single coat on the boat, you'll have 10 - 15 hours of prep, getting this surface ready for the paint. Often the novice spends way more time on this, just to find it's wavy, when the shinny stuff gets applied. 

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  • 4 weeks later...

I am about to start planking an OK256. The plans call for the Ashcroft method and state that the advantages are being able to plank two layers at once. I have thought about how this might be possible and can't get my head around it. The plans show the first few planks of layer one held with screwed ply washers and strips. Clearly they have to go before layer two follows so the first few planks must have to be glued down. How is this a faster method if you can only glue a few planks down until the next day before you could start on layer two? Can't help feeling I'm missing something. I understand the advantage of access to the inside as you proceed along but that's as far as my thoughts of a benefit take me. Enlighten me please.

John

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Yep, two layers at once. You apply several planks of the first layer and then can start also applying the second layer, of course removing any temporary fasteners that happen to be in the way of the second layer. With a double diagonal build you can also do two layers at once, but you have to complete a much larger section of the inner layer and on a small boat, this means maybe 1/2 its length, before the next layer can go from centerline to rail.

 

Additionally with Ashcroft, you can do sections of inner planking, followed by overlays of outer planking, intentionally leaving gaps between the planked areas. This means you can do several areas around the boat, followed with outer planking all in one shot, which isn't possible with double diagonal planking. At some point, the patchwork quilt of planking areas will need to have the inner layer spiled, so you can complete it and install the remaining outer layer.

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There are a few different ways to spile a plank, some prefer more than others, so I guess it boils down to what you like. It's a subject covered in traditional boatbuilding books and classes and I only know of one that's a more modern approuch, though all are a little tedious. If the boat is to be finished bright, there's no easy method, but if the boat is to be filled and painted, there are faster methods, if slightly less accurate. I find the easiest is to make a spile board from stiff chipboard (a type of non-corrugated cardboard). It's cut with a knife or scissors, so it fits between the two edges or along side if just a single edge, with a slight gap. A divider can be used to pickup the distances across the gap, along with witness marks, so it can be repositioned. A Joggle stick can be used as well as simply rubbing a pencil along the edge of the plank you want to mate to and a tracing made (again with chipboard). The are a number of ways to skin this cat, but after trying several, you'll find you like one or two better. If the boat is to be painted, I don't worry so much about perfect fits, which speeds things up quite a bit.

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Thanks very much for your input and guidance. After a lot of thought we decided to fit our first layer of planking and glue down. This effectively eliminates any of advantages of doing two layers at once. So PAR, if you were me would you now proceed with double diagonal planking. You say that this is a stronger hull form. Can't see why we wouldn't - can you? Don't wish to deflect from the original question posed but for the sake of the discussion here is our rationale. Given the wide flare in the bow section of the 256 there is a need for spiling each plank. If we were to lay two or three first layer planks and then start on the second layer then the first would have only been temporarily screwed down. We would then need to remove those fastenings and have our pre fitted second ones spilied and ready for fitting with a batch of "hot" epoxy ready and then hope to get the first layer to sit where it should while we finesse the second slippery one in place. If we are only doing this for the speed of the process then I can sense a few dramas that would slow things down. We are working in the tropics so that is an important factor in any part of the build. It took the three of us a better part of the day to spile , lay and glue 90 percent of the side planking in one layer and I am happy that this is fast enough. Look forward to continuing commentary. John

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Double diagonal on a Carolina bow hull shape just isn't as fast as Ashcroft. You'll never "lay two or three first layer planks and then start on the second layer ", trust me, you'll need much more than a few planks. Given the length of the molded area forward, where this is done, you'll have to do nearly all of the first layer, before the second reciprocal angle can go down. Since you have the first layer down, you'd gain a bit of strength and stiffness if you diagonally planked the outer layer in the other direction. During this process you'll see how much inner layer planking you'll have to cover with a single outer layer piece.

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Double diagonal planking is an excellent method. The main reason that I use the Ashcroft method is that the planking has less twist in the direction as drawn compared the the opposite diagonal and the planking goes a bit easier as well as the afore mentioned, being able to work both layers at the same time. As for strength, the strength difference is marginal, when you consider the stringers and the fact that it is covered in glass.

 

To answer your earlier question about working both layers together. When you are working faster than the glue can dry, you just use permanent fasteners to hold the inner planking in place. They can be any non ferrous material, stainless staples, brass escutcheon pins or as we use, fiberglass nails shot from an air gun. I realize that you may not be able to go to your local hardware store in Vanuatu get them. With your big crew, the way that you are doing it is good.

 

There are two important points to beware of when planking. DO NOT EDGE BEND the planks to close up a gap between the plank edges. I would rather leave the gap and fill it later. Ply cannot stretch or compress and you cannot get rid of the extra material that you have just induced. I like to fasten the plank in the middle and work outwards so that the plank will lie down tight to the inside layer planking. The second point is drawing the planks together between the stringers. I typically use staples. It is necessary to have someone onside with a big piece of wood to buck up behind the inner planking to draw the two layers together. This is especially important when a staple hits near the edge of one of the inner planks and pushes it away instead of drawing it together. If you do not have staples you can drywall screw through both planks into some scrap wood on the inside. You might be able to get away with one row between each permanent stringer.

 

Good luck with it. It sounds like you guys are going like gangbusters. 

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well known Paul Gartside uses thickened epoxy in some of his double or triple planked designs.
I would first saturate the planks with unthickened epoxi and screw them a little bit later with thickened after the unthickened is in the still sticky state.
that will provide starvation of the gluejoints.
Some interesting pictures, is this the Ashcroft way of planking?:
http://www.gartsideboats.com/custom-boatbuilding/24-ft-cutter-design-ila-98.html

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