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21 ft Yawl Longboat for a Sixth Rate by vaddoc - Scale 1:10 - Plans from the National Maritime Museum

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First  a happy new year to you and your family Vaddoc. What an interesting thread to follow, your tenacity at resolving the details of the lines is admirable and point to the challenges of transposing working methodology. Think of any of the "Old Trades" and relate those to modern methods and technology and you run into all the same issues it seems from my few observations and experience. I used to watch my father mend our shoes on a three cornered shoe last, just as one simple example. finding a cobbler these days is a challenge in itself. your skills with the cad drawing are way beyond anything that I am capable of, I do know a little cad and am using an early generation Auto-Cad  which is OK for the engineering type drawings that I do but even so I think in a 2D pencil way while using it and still have trouble with splines curves in auto-cad. It is the reason I turned to a "drawing Program" Corel Draw for working out the lines of my boat model-work, I found it much easier to draw using the 2D mindset I had been taught with a pencil and paper, on the screen with the drawing program especially with the curves. As you have already realized in our attempts to make "accurate" models of vessels that were made in an earlier time using the "80/20" rule, it is difficult to work that way with our modern tools. It is as if we are forced to correct the slight errors to satisfy ourselves because we have been coached into thinking that perfection is the "holy grail". I suspect most of us fall into that mindset on some level. I can tell you that I struggle with it all the time, my little steam engine model is beginning to feel like I am watchmaking and it is becoming very challenging and frustrating, making and remaking parts to match the tolerances of the drawings without the "watchmaking tooling". I forget who said that the sight differences when we build the hull are easily corrected with a bit of 120 grit, are worth keeping in mind. I think it is our nature though to want to make it "Perfect" looking at you other builds I am sure that you will do an outstanding job on this model when you start making that "scale" sawdust. 🙂

 

Michael       

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Many thanks to all for your input!

 

Gary, I agree, pear is lovely. The problem I always had is that due to the pink-ish colour it seems to only combine with ...pear. But I am looking into your suggestion.

 

GL, I indeed remember our discussion very well and I am following your logs (not as often as I would like due to life pressures). The yawl however has a much more rounded bow and I really doubt that 2 mm steamed pear will be convinced to follow this curve, even steamed, without fracturing. Also, I guess the planks will need to be cut over a pattern with a knife to come out with a fair curve and pear is very hard. Still, I ll give it a try.

 

Michael, how right you are. I just received a copy of  "Boatbuilding" by Chapelle. What a lovely book it is! It describes how the various types of boats are built and how lofting is done with a pencil and ruler. This book is all about the 80/20 rule and finding the golden balance between being well prepared and having done a good lofting but also at some point start building the boat knowing you can correct miss-matches by taking more or less material. Today's CAD accuracy is a completely alien concept to Chapelle. There is actually a point where he advises, if the frame cannot be bent into place, "just use a shim"! I must say that in previous boats, the planking would actually correct design issues as the wood would want to find its natural fair position-then just had to be framed into place.

 

Back to the boat, I have finished designing all the temporary frames as well as the building jig. This will be a really big boy! I have also placed a rather large wood order but ordered only samples for the wood planking.

Not sure how the admiral is going to take it but she is busy getting new floor and carpets so maybe the timing is favourable.

 

I ll post new photos once the wood is in

 

Regards

Vaddoc

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I ve been thinking on the 80/20 rule and I would like to share some of my thoughts with you. I hope it is not too much of a boring subject!

 

I really liked Chapelle's book, the clarity of his thinking and the way he can communicate and explain complex issues is fascinating. So much so that I started CADing one of the boats in the book! Now, the following images I think really illustrate how ruthlessly (and unnecessarily) accurate CAD is.

 

The boat is a workhorse fishing boat with an engine, no sails.

20200105_183743.thumb.jpg.4fb413f448a7d26f061bcaad83d093bf.jpg

Now, the offsets are given in feet, inches and eighths. This is how fair the lines are just as they come out of the offsets. (The white lines show how fair the curves are, they should not have picks and abrupt changes in curvature)

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This is the boat with all waterlines, buttocks and diagonals. They appear looking at them to work very well together, they are all very close and intersect very closely.

1560221659_Screenshot(199).thumb.png.e55884bab8ba293ad8f7c2ea04b549af.png

Now, I faired all the lines but I did not do any true lofting at all, (although just fairing the lines is by itself a big part of lofting but it is a simple command with CAD). The next photo show how much more fair the waterlines are now compared to Chapelle's offsets.

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Now, based on these lines I produced the frames. These were also faired and just looking at the interaction with the lines, they appear very close. They are quite fair as well:

1926624530_Screenshot(204).thumb.png.a1b111df495e0763061e3f0e310ab88d.png

Still, the computer thinks this accuracy is not enough, cannot produce a surface and will not compromise. From experience, I know that this horrible dent in the stern is because the frames and lines are just not fair enough. But they already are more fair than what Chapelle intended them to be!

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Now, I can solve this but it will need a pretty gigantic amount of work which is I now realise unnecessary. It is already more than accurate enough to be built as is. Just as a comparison, this is how fair the frames of the Yawl are! (they are very fair)

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Of course,the most important accuracy is the one achieved with the saw and the files which is not going to be CAD like.

I will do some more work on the Chapelle's boat but will try and resist going crazy with the lofting. Maybe a little so I can produce a continuous surface to get the bevels of the last frame and the Transom. But I have no doubt that the wood will smooth everything out when bent on the frames.

 

Back to the Yawl, the plywood order has come in. There are 2 mm and 1.5 mm sheets, these will be used to laminate dead flat and very strong 4 mm sheets to cut the temporary frames.

 

I also received some cheap reading glasses (1.5x) from Amazon as a temporary measure. What a revelation! I can see!

 

I made 12 shackles without a single failure and without my eyes getting tired and blurred. I now have about 70 (I made a few more since) but I ll make another 30 as I do not want to come back to this during the rigging.

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The wood from Germany is coming in tomorrow, I ll post pics in a few days.

 

Vaddoc

 

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So, the wood is in!

 

First however, a couple of pics of the Chapelle boat. This was only a quick fix but I got a continuous outer skin, more than adequately fair, and offset the surface for a plank thickness of 2 mm to produce the inner skin. The rest will be done nearer the building time.

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Back to the yawl now, I received various strips and sheets of pear, and also sample sheets of ash, birch, alder and beech. Excuse my very poor photos, I only have a cheap phone! Also, I am not 100% sure that I got right which wood was alder and which was birch. 

 

Ash really has such prominent growth rings that it is of no use for modelling.

20200117_175921.thumb.jpg.1c43105aaf4bba6592ad99f44f421dad.jpg

Now, pear has a pink hue and really does not combine well with Birch Alder that has a yellow hue. Also I did not like much the black spots and streaks

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Alder Birch is a much nicer wood, although wood data base suggests is quite soft. It looked fine for planking but again, does not combine well with the pink pear

20200117_180504.thumb.jpg.eb37482262b6a96fd9ac81b281660193.jpg

Beech on the other hand has also a pink hue and looks really good with pear! I do not mind the spotty appearance. Beech is I think my favourite wood!

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Beech it is then for the planking! In the next photo all the sheets are shown next to the pear wood

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Now, I must say that this time I am not entirely happy with the quality of wood I received from Massive Holz. These are the pear sheets I received

20200117_180842.thumb.jpg.8402f4e88abbb39f334aa1ea488abfaf.jpg

Considering how expensive these sheets are, I would expect timber to be selected and such dramatic colour variations to be sorted. n my previous order, the colour of the sheets was much more uniform, the next photo shows two sheets I received many years ago, again from massive holz EDIT: This wood was bought from Arkowood

20200117_181623.thumb.jpg.df442d87ef33eb56042d04f33711a959.jpg

So all has fallen into place and I have no more excuses for not making saw dust. Both time and money though are currently in short supply so further posts will be at the usual snail pace.

 

Regards 

Vaddoc

 

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Hello Vaddoc, your comments about the wood quality are interesting. At my local hardwood supplier "Chanin Hardwoods" I went in looking for some straight clean grained Cherry, he had a couple of lifts of highly figured Cherry but no straight grained Cherry, his comment to me was "why would you want such a boring looking grain?" I occurred to me that model builders and the rest of the world who use wood have two different criteria and it has to do with the differences in scale, and aesthetics. Highly figured woods are desirable when juxtaposed well in furniture and mill-work. I am assuming that the supplies of clean fine grained wood is getting more scarce because of the reasons noted above. Ours is a marginal market compared to the industrial scale of the furniture companies who are the likely drivers of the hardwood cutters. It is only a guess on my part though, I am guessing that the suppliers of the wood for our models are at the mercy of the vagaries of the wood cutters.

Last but not least the good wood is getting used up through various practices of increased production and damage and wood grows slowly.

 

Michael     

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On 1/17/2020 at 7:09 PM, vaddoc said:

Now, I must say that this time I am not entirely happy with the quality of wood I received from Massive Holz.

Yes Vaddoc - I find myself shying away from remote suppliers because I am never confident about quality.

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I did some more research and reasoning and indeed I got it wrong. The spotty wood is Alder and the nicer one is Birch. Both have a darker colour as they are kiln dried. The bitch plywood I got is much whiter as wood is not dried prior to processing.

 

Another error is that the very nice wood I bought years ago, was not from massive holz but from Arkowood. That wood order was flawless, all strips dead straight, no knots and no colour variation. I emailed the chap to see if he has any beech sheets. His shipping fees are much cheaper as well.

 

Michael, certainly timber stock is now nowhere near what it was in the turn of the previous century but, at least in Europe, cherry and pear seem to be in good supply as they are used as ornamental plants. Here in Cambridgeshire these trees are everywhere! Beech seems to be also plentiful. I would expect wood to be selected before shipped, considering that each 2x100x1000 mm pear sheet costs close to $10.

 

GL, I never worried about ship worm in a model but how cool would be a log to replace worm-eaten planks in a model!

 

Keith, I cannot mill my own wood, not even cut strips from a board. The only suppliers I know that carry a variety of woods and can cut any size strip/sheet are the above based in Germany. Massive Holz charges I think close to £30 for shipping and Arkonwood about £15. If you know any UK based suppliers that offer similar products, even with more limited variety, please let me know. Cornwall models does not carry what I need considering I work in large scales

 

Regards

Vaddoc

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7 hours ago, vaddoc said:

Keith, I cannot mill my own wood, not even cut strips from a board.

Vaddoc - Ah! hadn't understood that. As you say, I also don't know any UK suppliers who supply milled "exotic" timber suitable for scale modelling, pity really but as Michael pointed out we probably don't create the volume of sales to constitute a viable market. If you ever need a bit of wood milling down I would be happy to do it for you

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Many thanks for the offer Keith!

Considering how slow I now work, it makes sense to get even very expensive wood orders as the cost spreads over many years. But it seems very attractive to get a plank and mill it. These would open up a whole new range of options.

How do you do mill your wood, do you have a professional set up or a more scale down one for example with a proxxon or Byrnes saw?

 

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2 hours ago, vaddoc said:

How do you do mill your wood,

Vaddoc - I have a Byrnes saw.  I can rip down wood of up to 3/4" thick using the carbide blade this has a .055" kerf. I limit my slitting saw blades to wood less than .250" thick. I typically use a .0315" blade. I usually get planks to within +/- .002" of the desired thickness.

 

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On 1/12/2020 at 12:29 PM, vaddoc said:

I really liked Chapelle's book, the clarity of his thinking and the way he can communicate and explain complex issues is fascinating. So much so that I started CADing one of the boats in the book! Now, the following images I think really illustrate how ruthlessly (and unnecessarily) accurate CAD is.

I'm probably stating the obvious for many, but for those who aren't aware, drawn lines are actually as much as 1/4" thick at full scale, if not more, depending upon the scale of the lines drawing. Offsets are, more often than not, taken from measurements made from the drawings and if taken from a half-model, the scaling issue is no different. (N.G. Herreshoff, perhaps the greatest American naval architect of the late Nineteenth and early Twentieth Centuries, rarely drew lines, designing his creations by carving half models and taking the offsets directly from his models. The loftsmen then lofted from those offsets directly, without any drawn lines or construction plans.) Theoretical accuracy is dependent upon the placement of the dividers' points and reading the distance between them on the scale. As the saying goes, "There's many a slip between the cup and the lip." A table of offsets generated manually from a manually drawn set of lines will never be sufficiently accurate to serve as CAD inputs directly and a lot of CAD "fairing" is always going to be necessary if the CAD drawings are to "work" the way one might desire, but that level of accuracy on paper was never necessary for traditional builders.  Manually generated offsets were never expected to translate directly to the loft floor and so produce completely accurate patterns. Rather, it was the loftsman's "eye" that was expected to fair the lines if not outright errors, in the offsets "right on the loft floor"and so correct the inaccuracies inherent in the manual technology, (And outright errors, be they in measurement or entries in the manually developed tables, are not infrequent.) In small boats, the "tweaking parameters" experienced are often measurable in inches, and in large vessels, easily measurable in feet.  You're right: The input demands of CAD's close tolerances can indeed be crazy-making. It's high level of accuracy is solely dependent upon the accuracy of the input data, which, if manually generated, will never be up to the task.

 

This was not so much a problem with model making in the days before highly accurate machine tools came into use among the modeling fraternity. What can be accomplished, and is being accomplished, by modelers today who are working to tolerances of thousandths of an inch is amazing, but a whole lot of the "machinists' approach" to modeling can be dispensed with by employing many of the fitting and joinery techniques of traditional full-size boat and ship building. There used to be a saying about woodworking tolerances: "The house carpenter works to the closest quarter of an inch, the finish carpenter works to the closest eighth of an inch, and the boatbuilder works to the closest boat!"  The experienced human eye is far more convenient a mechanism for discerning the fairness of a line and a sprung batten a far more user-friendly tool for generating a fair curve than any CAD program. Or at least that's my story and I'm sticking to it! :D 

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On 1/19/2020 at 8:30 AM, vaddoc said:

The bitch plywood I got is much whiter as wood is not dried prior to processing.

I think I had some of that same plywood a while back..😄

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1 hour ago, michael mott said:

I know but we still want it "perfect"

Indeed. IMHO, the essence of modeling is the exercise of striving for perfection. I certainly didn't mean to imply otherwise. My comments were limited to limitations with the use of CAD programs for drafting as a means to perfection, which is the constant in the equation. The work of a master machinist is a wonder to behold, but there's more to a "perfect" miniature than proper scale measurements. It's the minute, nearly imperceptible imperfections wrought by the free hands of man that give life to a true work of art.

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Bob’s post above is right on and explains why it is impossible to build as some have claimed, the “definitive” model of any wooden ship.  Using the same table of offsets, no two drawings or full scale patterns from the mould loft made by different individuals will be exactly the same.  This is because of the decisions made by individuals when plotting and fairing lines.  I even doubt if the same individual could produce the exact same drawing twice as he will make slightly different decisions each time.

 

While CAD offers a high degree of precision, I’m not sure that it is any better at transferring offset dimensions into the definitive hull shape because it too must make decisions when plotting curves.  I’m not sure that you the user know what those decisions are or if you agree with them.

 

Using offsets taken from a model or builder’s draught, you do not know what changes, minor or otherwise were made in the mould loft, adding another degree of uncertainty.  This also may account for the fact that different vessels built from the same plans perform differently, eg; The large 44gun American Frigates Constitution, United States, and President all had different sailing characteristics.

 

Your aim should be to produce a model that faithfully reproduces the characteristics of the real thing while realizing that slight variations are to be expected.

 

Roger

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All so very true!

Fairing lines is so easy with CAD but at the same time feels very artificial and indeed, the result is a compromise and seems that the computer is making decisions on its own. Much better to use a batten!

Building boats I find myself wearing two hats. One is the CAD hat, when I am trying to make all drawings perfect. Then the modellers hat, where I find challenging to even make all frames have the same height. In the Deben the tolerances between the CAD drawings and the actual result were abysmal, some frames were out of alignment by 2 mm and I did not like the lines at the bow so I let the wood sit at the angle it liked to sit and readjusted the frame to the new lines. No problem at all in the end!

Indeed some degree of lofting is needed to make sure lines are reasonable close and fair but thankfully the wood has its own self-fairing properties.

On a different note, I suddenly thought of another way to tackle the Yawl's planking which may work this time. I will try it when I have the time as I would like to have some idea of the shape of the planks. It will be a CAD exercise of course but I do not have any time to create actual wood dust so a good substitute for now. This is another side of things, CAD gives you the satisfaction of creating the boat although virtually. We do of course have our own CAD building section!

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I've just read through this thread and I'll be following along. I don't think I'd have the patience for CAD as I'm a hands on person and I took the lines for my 1:8 dinghy straight from the plans for the full size version, warts and all, built to a fair line rather than a measurement. Don't get me wrong, I appreciate what you're doing which is why I'm tagging along.

 

On the subject of wood supplies, business these days is all about minimum cost, minimum staff, minimum handling. You order two pieces and you get two pieces, you're lucky if the picker bothers to look and see if the sheet is in tact before packing it. I blame the accountants! Wood however is a natural product and is never uniform in colour or grain so the trick is to see it as the old ship builders did. It's a piece of material you are going to fashion into a boat, just do it and embrace the natural differences.

 

On the subject of the shapes of the strakes I would imagine on that boat they would look really strange, you should have seen the shapes on my dinghy. I just had a look with the idea of scanning them to show you but the lines are too faint. Crazy shapes though. I'd suggest maybe take the cad lines and cut them from card and give them a try.

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Many thanks to all for your very interesting comments! 

 

Now, I feel I may have actually managed to more or less define the shape of the planks. It has taken me overall many weeks of trial and error but this time the run of the planks looks ok. It is so much more difficult to do it with CAD, there were times that I thought of just cutting the frames out in cardboard just to be able to lay a batten! I fully admit it is a bit silly to do this on the computer but I am afraid it will be quite some time before I can cut wood and I really wanted to take it further and see the shape of the planks. 

 

Now, this is the carvel planking but the lapstrake will come out using the same lines.

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It is not perfect but I think it is pretty close. The largest blank needed is 57 cm, this would need either a crooked tree or a scarfed plank.

 

Regards

Vaddoc

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Amazing how you can do it with a computer, Vaddoc

Thanks to show all the strake shapes next to each other.

The shapes are very similar to those I tried to loft manually for my gaff sail boat. When I was doing it, it was always a surprise if they would fit or not. My longest plank was about 75 cm. As you see around the floor heads there the planks are very bent, you need a long and wide plank to make them. As I was a bit short of long and wide knot-free oak planks, I didn't want to spoil much wood. When bending the planks to place them, I cracked two of them, it was exiting to finish the job before all my oak was used.

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Thanks GL, It is interesting to see that the run of the planks is reasonable. The planking is not correct though and when the real boat is planked, the following changes will be needed:

 

1. The garboard should come higher up the bow, this will push the planks higher and maybe reduce the curvature of the planks

2. The width of the planks at the really curved areas of the hull and at the transom is far too much. This needs to be reduced and width gained at the flat areas.

3. I think 11 planks are too few, the average width is around 13 cm which is probably far too much. I suspect it will end up with 15 planks each side

4. There will be a 2 mm overlap for the lapstrake.

 

Due to the large scale, it is possible to do the planking exactly as it would be done in the full scale boat. The challenge will be access to the keel/planks, I was thinking of using a similar jig to yours but some modification will be needed.

 

Vaddoc

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Hi Vaddoc - 

 

This is an interesting project and I am enjoying following along.

I am fascinated with learning what CAD can do - and not do. 

I have done several lapstrake boats/ships and I have a few suggestions, if I may - 

 

1.  The garboard should not come up higher on the bow.  Bringing it up typically increases the bend required in the rest of the planks

2.  Try to plan out all of the planks before cutting wood.  You will certainly need to tweak the strakes as you install them, but it will give you a good starting point.

3.  A 2mm overlap is good.  I found that scribing the overlap on both sides of both edges of each plank kept me from wandering.

 

Here are some photos of my Gokstad ship under construction.  The overlap was just about 2mm and there were 16 strakes, so I hope it can give you some ideas. 

 

Best of success.

 

Dan

1799156603_Forwardplanking.thumb.jpg.542c086a232248033c51696bb8af51a5.jpg1521721069_bowexterior2.thumb.JPG.e210ca0c80cf49d3084bc17d8ea3b563.JPG126851343_bowinterior.thumb.jpg.a1b51158bbfd20a3e7a230e7e5f35da7.jpg

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I agree with Dan that the garboard should not extend up the stem. The other issue is that all planks are not the same width. As vaddoc points out, they are wider on the flatter cross-sectional areas of the hull and narrower on the more curved portions. CAD can take you so far with the science of planking, but does not account for the art of lining out!

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Sorry to butt in, Vaddoc, but I'd like to ask a question.

 

I've enjoyed this thread as it has gone into the difficulties of 3D design. It makes me ponder all the more at the work that goes into the various  3D designs on this site based on old plans (the fully rigged Swan class  3D model being one amazing example) which seem to have all the right parts in the right order in the right places (with acknowledgements to Eric Morecombe).

 

Like some others, I also use 2D CAD a lot to replicate parts of plans, design my own parts, double check dimensions etc., but I have often wondered how to use a CAD programme to 'straighten out' the planks to provide their accurate flat dimensions before bending. This seems a very useful function of CAD in order to be able to predict (albeit roughly) the width of planks to cut and therefore of amounts of wood to order.

 

So, as an aside, would you be able to provide a quick tutorial on how this is done, or point me to somewhere I could find out about that?

 

Thanks

 

Tony

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Apologies for the delay in replying, life went again into hyperdrive

 

Dan, this is a lovely model! What did you use for the iron nails holding the planks together at the lapstrake?

 

On 1/25/2020 at 4:44 PM, shipmodel said:

Try to plan out all of the planks before cutting wood.  You will certainly need to tweak the strakes as you install them, but it will give you a good starting point.

Will do, bellow is a relevant nice pic from the Deben:

1029578690_Debenplanks.thumb.jpg.5d3349c8a88d3d41a187b9591a0709c2.jpg

On 1/25/2020 at 4:44 PM, shipmodel said:

The garboard should not come up higher on the bow.  Bringing it up typically increases the bend required in the rest of the planks

 

On 1/25/2020 at 5:01 PM, druxey said:

I agree with Dan that the garboard should not extend up the stem.

 

Now, I would ordinarily agree with you. However, the following made me think that this may not always apply: 

1. Playing with the CAD, changing the height of the garboard had a massive effect on the plank shape, straightening some and making others more bent in a very unpredictable way.

2. On Youtube, there is a great series of videos on how to line off and build small boats, look under "traditional maritime skills, lining off planks (small boats)". On part No 4, the builder is commenting that the garboard seems to come up too low on the stem and he needs to change it so all the planks will be pushed up.

3. I am currently reading (very slowly!) "Lapstrake boatbuilding" by Walter J Simmons. In page 65 he writes: "...bear in mind that the whole planking job will go easier and look better if you allow the hood ends of the garboard to rise as high as possible, A narrow garboard is easier to fit, but one that is wider fore and aft will result in straighter subsequent planks and will thus make the remainder of the planking job easier"

 

I can tell you that indeed, in the yawl, pushing the fore end of the planks higher up the stem resulted in a more pleasing run of the planks. This does not apply planking a big ship, as the garboard really needs to be kept very low at the stem to minimise crowding of the planks and the use of stealers.  

Only way to tell is to build the thing! All in good time...

 

On 1/26/2020 at 2:20 PM, tkay11 said:

I have often wondered how to use a CAD programme to 'straighten out' the planks to provide their accurate flat dimensions before bending.

Tony this is the easiest thing to do. You just select the curved surface and you press "unroll". The computer thinks things over a tiny second and gives you your surface flat!

I would not rely on CAD to get the shape of the planks, it is immensely difficult to establish it. However, this is how I calculate the wood I should need for this boat: 

I expect I will have 3-4 planks each side quite curved and the rest more or less straight. So each 100 mm wide sheet should give me 2 curved planks and perhaps 4 reasonably straight ones. So if I end up with 15 planks each side, I ll need 4+6 sheets and with a 50% margin for error and wood selection, 15 sheets of beech 2 mm. This is close to £60 without shipping!

 

On another note, my computer suffered some catastrophic damage and packed up. I also managed to drop my laptop, it took a bend and I had to straighten some areas with pliers but still works just fine. I ordered a new desktop which should arrive in 2-3 weeks. I also took the opportunity to get a new monitor, chair, lamp as well as some peripherals. Although it is nice to get new toys, it takes a lot of work to set up a new computer and right now it is the last thing I wanted to do. Still, it has to be done!

 

An opportunity to go back to the Deben which at some point needs to leave the shipyard to make room for the Yawl!

 

Regards

vaddoc

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Just to add regarding the arrangement of planks at the stem, that is being placed as high as possible. There might be a connection with the issue of the "exaggerated sheer" (I think this is the term)

 

It is possible when designing a boat, although the sheer is fair and appropriately curved, when the actual boat is finally built, the sheer to appear flat at the bow. This is just an optical illusion due to the size and flatness of the boat and to avoid this, it is recommended to increase the curvature of the sheer at the bow, thus having an "exaggerated sheer".

 

Maybe this is why these people suggest to push the fore end of the planks higher, to get a more pleasing run of the planks.

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