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  1. #1
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    Default Little Red Hen - Clinker Dinghy

    Hi Folks,

    Chatting with a few fellow wooden boat enthusiasts some time ago, it dawned on me that many of us would like to have the experience of building a traditional clinker boat, without any of us necessarily wanting to add yet another boat to our fleet.

    Personally, I was driven by Andrew Denman's example. Wouldn't you love to build boats like that?

    The conversation, which progressed over several months, recognised that a group project would be one way to do this, but that there were a few obstacles. Firstly, how do you get a bunch of crusty 'old salts' to agree on the best plan from the best designer? That could take years to resolve. Then, where could you build it that was truly a shared experience? It could take quite a long time, and if it got built in any one person's garage it would become 'his' boat, and we couldn't have that. Next, how would we fund the project if nobody was going to 'own' the result (or, possibly, take responsibility for a disaster)?

    While we all agreed that it was a good idea it was going nowhere, so I decided to overcome the first obstacle by designing the boat myself. Having successfully designed and built our little stitch and glue, nesting dinghy Curlew, I thought I could take what I had learned about 'boat CAD' and design a traditional clinker dinghy of about the same size (10ft or 3metres), but with more 'conventional' lines.

    As I thought this through, and played about with FreeShip software, I started to see some other advantages. This was a way to get really engaged with the design process. I also wondered about the possibility of producing detailed dimension drawings of all of the individual components, so that each participant could make a part that suited their capabilities, in their own workshop, and they could all be brought together for final assembly. This would overcome the storage and workspace problem. If participants supplied their own materials it would also overcome the funding problem, at least for a start.

    As the design evolved I contacted potential participants to see if they would like to be involved in the project (which I named 'Little Red Hen' for motivational reasons obvious to those who know their folk tales). There was some scepticism regarding its feasibility, but general agreement and, after some consultation about material sizes etc, I punged into details of the design.

    Once the basic dinghy lines (below) were established I acquired a copy of TurboCAD Pro and started exploring the possibility of exporting the 3D hull shape from FreeShip and doing the structural design in TurboCAD.

    I'll add more posts about progress as time permits. And it could take a long, long, time.

    Cheers
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

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  3. #2
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    Default Progress

    Coming up with some more-or-less 'classic' dinghy lines is one thing, but it is not a plan for a boat. A true traditional boat builder could do it all from a table of offsets but we have no room for lofting, and no materials yet, so we are substituting CAD for lofting with the idea of producing detailed plans we can build from.

    When you build from purchased plans you get clear information about required timber sizes. If you start from scratch you must determine this yourself. I guess the proper way to do it is to do the engineering calculations about stresses and material strengths. But, if you're not an engineer, how do you do it. For a start, non-laminated wood is not a very predictable material so you would have to allow a greater margin than with manufactured materials like steel or carbon fibre.

    Well, this boat is hopefully going to use 'traditional' timber so we should probably adopt a 'traditional' approach i.e. 'Rule of Thumb". Curlew was the same size, used 6mm plywood bottom and bulkheads, and 4mm ply planks. She is extremely rigid so that provided a starting point. The next step was collaboration with other participants so that we gained from some collective experience and wisdom. For starters we agreed on 19mm for the transom and skeg, 30mm for the stern knee, 100 x 10mm for the hog, 50mm stock for keel and stem (hopefully a grown crook for the stem), and 6mm planking.

    It took a bit of figuring out how to transfer the lines from FreeShip to TurboCAD. I then started 'virtual construction' of the backbone, within the hull shape, according to the agreed dimensions.

    The pix below give an idea of the process but, as with anything to do with building your own boat, it was accompanied by much weeping and wailing and gnashing of teeth. At least when things go wrong there is no valuable wood being destroyed.

    Cheers,
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  4. #3
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    Default

    I reckon I've seen reference to some sort of scantlings schedule / rule book.
    One of our resident designers would know.

    cheers

  5. #4
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    Default

    Quote Originally Posted by b.o.a.t. View Post
    I reckon I've seen reference to some sort of scantlings schedule / rule book.
    I'm sure you are right. However, I am keen to use the inputs and judgements of the group of participants. They had plenty of ideas but none mentioned such a schedule. Right or wrong we will all have a strong sense of ownership of the outcome, and will learn from the experience.

    I'm sure we will find creative ways to justify any obvious mistakes.
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  6. #5
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    Default More Progress

    Questions arise about details like plank lap width and stem rebate bevel width. We've had a few emails and phone conversations around our little group and discovered a surprising diversity of ideas about what constitutes a 'Classic Clinker Dinghy'. My inclination is to use grown crooks for stem and knees, solid timber planks, and copper fastenings. Maybe even produce a 'hewn' keel and stem using broadaxe and adze (on a boat this size?) At the other extreme there are those who prefer plywood planks and a laminated stem on the basis that glued lap-strake ply would still 'look' classic. Then there are all the possible variations in between.

    Of course, it all comes down to availability (and cost) of materials. In the early 1900s there was an abundance of suitable timber for boat building in Brisbane. Great slabs of beautiful straight grained timber, in wide boards, from big trees. Just look at some of the old VJ wallboards from an old Queenslander. It's a bit harder to find these days.

    We are also hoping to keep the cost of this project under control by using 'found' or re-cycled materials so perhaps we can recycle some of those old VJ boards (130mm x 19mm) into planks. Will 130mm we be wide enough for Garboard and Sheer strakes? If not, we might have to use ply. Can we find a suitable grown crook for the stem? If not, we might have to laminate it.

    To help us get real about this, one of our group has made a very nice 10:1 scale model from the plans so far (see pic 1). This helps get us out of the 'virtual' CAD world and actually start bending strips of paper around he moulds to see how it behaves. Wonderful learning experience!

    We sort of agree that, with 6mm planks, the width of the lap and the stem rebate should be about 18mm. At least this will do as a starting point. The problem with testing this on a 1/10 scale model is that you can't realistically scale the thickness. So, it's back to CAD actually apply the 6mm plank width to the moulds in such a way as to end up with 18mm laps and an inner lip about 1mm (rather than a feather edge).

    The hull profile from FreeShip started as a new hull 3m long by 1.2m wide with 0.15m draft, then 'tweaking' until it looked more 'classic'. I paid no regard to the practicality of planking it. It turned out I had made the turn of the bilge much too tight a radius. This meant that the exposed plank width at the turn of the bilge would be about 36mm (see pic 2). This sharpish curve might be OK for strip planking but I worried that for a clinker hull it might look odd due to the great variation in plank width. So it's back to the drawing board. But first, we need a better understanding of the relationship between plank thickness, lap width, lip thickness, and bilge radius.

    As an exercise I drafted up an example (see pic 3). In both cases the planks are 6mm thick, the lap 18mm wide, and the inside lip 1mm. A plank width of 75mm thus generates a radius of 251mm. A plank width of 100mm generates a radius of 367mm. (Yes, I know they're lapped upside down, it's just an exercise). This is all probably blindignly obvious to everyone else, but I have my own ways of figuring stuff out. So, moving on.....

    Armed with this clearer insight I have 'tweaked' the curve of the bilge so that the narrowest exposed plank width is now 52mm and the planks are more similar in width (see pic 4). I still wanted to retain a bit of 'hardness' in the bilge for the sake of stability, so I haven't gone so far as to make it a simple arc as in the test exercise above.

    These changes have necessitated re-drafting the bevels on the keel, hog and stem. I thought I had better check the result for reasonableness, so ran a few splines arond the moulds to see how it looked (see pic 5 and 6). I think we'll go with that. It's a bit of a pain, but better than discovering the problem after the materials are cut.
    I guess that actual laying off of the planks will be whatever eventuates, but at least we have better understanding of the issues, and increased confidence that they will look OK.
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  7. #6
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    Default

    John,

    Good to see some progress!

    I wrote a long post in reply a couple of days ago and somehow it didn't post and I lost it all. Here's the guts of it though.

    Your scantlings aren't too bad but I would certainly increase the thickness of the planking to somwehere between 8-10 mm. For a boat this size the old guys were using 5/16 to 3/8". This will help with the number of planks and the internal width of the edge of the plank.

    I'd also take the transom out to 1" or at least 7/8" which will give it a fighting chance to be around in years to come. If you want to go thinner on the transom, then I would also use a transom frame or fashion pieces on the inner face of transom either side of the stern knee. This will allow you to get the fastenings in a bit further forward from the edges of the planks.

    Whilst grown crooks are nice, they are a lot more work than a stem made from several pieces. If you want to go traditional, just make up a 3 piece stem and bolt it all together with some bedding compound. you could easily make the bolts up at home from copper rod. If you go down this road, don't forget the stopwaters.

    something like this.



    If the boat is going to be rowed, I would probably increase the deadrise a bit to reduce wetted surface area. this would have the added effect of taking a bit of twist out of the upper planks at the stem.

    Whilst it is good to muck around with the computer, I would leave the lining out until the molds are up and yoou can really eyeball it. You could line out on the model as well.

    Keep the progress shots coming.

    regards,

    AD
    www.denmanmarine.com.au
    Australian agent for Swallow Boats, Bruynzeel Multipanel Plywood and Barton Marine Products

  8. #7
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    Default

    Great advice AD,
    My own opinion, for a first time build, would be to laminate the stem.

    Especially considering, one of the requirements is to use recycled timber in the construction.

    Also, glued lap ply construction is great. It has the traditional look you are after and there is lots of information on the net and in books on this build method.

    A few years ago we did a boat building program in my workshop for the local District School.

    Over 2 years we built 3 boats to an Ian Oughtred plan. The boys involved were 14 and 15 years old. They had no trouble with most of the construction of these boats. Apart from the sails and rigging hardware, everthing could be done on site with no problem.
    CLINKER PLYWOOD BOATBUILDING MANUAL. By Ian Oughtred, is well worth a read, before you make your final decision.

    For a first project I would definately recommend using plans from an established designer. All the work is done for you and you have backup if questions arise, especially if you use an Australian gesigner. Most designers are very happy to answer questions and help your project to completion. It is in their interest to see the job is done well.

    Cheers
    Paul.
    I FISH THEREFORE I AM.

  9. #8
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    Default

    Thanks for the feedback guy. All grist to the mill!

    There are so many boat designs out there, some great, some not so great. Why would anyone bother to design another one? My reason is that I just love the process and the learning and discovery that comes out of it. If you just want the building experience I would definitely recommend using an established reputable design. If you also seek the design experience it seems to make sense to design something that fits into a unique niche. The niche our Curlew nesting dinghy fitted into was very unique (i.e. the inside of our caravan). The niche for this Little Red Hen project is a bunch of guys with a limited budget, a random set of skills and experience, very little long-term available space, and a strong interest in building a traditional craft.

    Having learned a bit about the relationship bewteen bilge turn radius, plank width, and plank thickness, we are ready to apply our learning and progress a little further. The next step was to carefully dimension all the component parts so that members of the group could choose something within their capabilities. So, starting with the 'core' components I have drawn up the Transom, Stern Knee, Hog, Skeg, Keel, Mast Step, Breast Hook and Moulds. In the fond hope of finding a grown crook for the stem I have just drawn a profile template that I can slap against any promising piece of wood that might be on offer, to see if it fits. I'll take this (and a chainsaw) with me next time we go to our block in the bush, but even though there are many big trees, I doubt if I could find one big enough and suitable for the stem. We live in hope.

    Just to show that it can be done, my wife put up her hand to make the Breast Hook. And very nicely done too. Below are and overall drawing of the 'backbone' examples of some of the detailed drawings handed out to the team including the stem profile.
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  10. #9
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    Default

    Some of the CAD drawings I did of component parts are now re-appearing as carefully crafted pieces of assorted timber, depending on what each individual could lay their hands on. My wife Anne took an offcut from an old hoop pine board and turned it into a breasthook. This was presented to the other prospective participants as someting of a challenge for them to choose a drawing and go and make it. Ian Skeg found a nice piece of Meranti for the skeg. Chris Hog picked a nice straight piece of hoop pine for the hog. John Transom glued together a few planks of Huon Pine for the transom. Sam Moulds cut the moulds from some MDF. (Obviously the names have been changed to protect the innocent).
    I tackled the keel with a piece of Kwila. The wood was a bit too dark to see my pancil marks so I laid masking tape where the lines were to go. I've made the keel thicker in the middle to allow for the centre-case slot. I hope it won't be too difficult to remove.
    Well, it's progress. The next step will be a 'dry' assembly to see how well it all fits together.
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  11. #10
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    No luck finding anything remotely suitable in the way of a crook to use for the stem. One of our group let it be known that he had an old (100 years) hoop-pine mantel-piece that might serve if I want to build up the stem from blocks as suggested by Andrew of Denman Marine. A quick check of dimensions indicates that it might just do it. Next step on that front is to further develop my stem drawings so that I know exactly how to cut the timber, and to make sure that it will come out of the available piece.
    Meantime I have dry assembled the components that are ready so far, and it almost starts to look like a boat.
    Pic 1 - Keel, skeg & hog
    Pic 2 - Transom & stern knee
    Pic 3 to 5 - Moulds from various angles.
    Practically finished once I get the stem sorted out..
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  12. #11
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    Default

    This is becoming a really interesting process. Thanks for sharing it.

  13. #12
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    Default

    Looking good mate.

    If you already haven't thought of it, cut some holes in the molds (or screw on some blocks) to help with clamping up planks - particularly up forward.

    When you do get the stem organised, leave the rabbet "full" where the stem/keel join together until you are fitting the garboard as there is a tendency to take too much out here.

    It is great to see another traditional build going together - it's really not that difficult is it - just one step at a time. I wish more people would have a crack at it.

    Here's a bit of inspiration from last weekend. We provided a boat for a TV commercial at Dove Lake, Cradle Mountain Tassie - just a stunning location.



    Keep the pics coming.

    AD
    Last edited by bloggs1968; 1st April 2009 at 07:42 PM. Reason: added pic
    www.denmanmarine.com.au
    Australian agent for Swallow Boats, Bruynzeel Multipanel Plywood and Barton Marine Products

  14. #13
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    Default

    Thanks for the tips. I daresay there'll be tears before it's finished .

    What a stunning picture! (and boat)
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  15. #14
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    Default

    Hmmmm! That's a pretty tough act to follow.

    Well it's all very well to talk about traditional boats, but I don't suppose that's really legitimate with this project where all the design, drafting and lofting has been done in CAD, rather than with traditional lofting. Anyway, I decided to offer a bit more detail about the CAD process as I have applied it to this traditional style boat.
    I like to think of it as a unique convergence of traditional and modern technology.
    The approach I took was to create cross-sectional profiles for the whole backbone. Along the keel, skeg, hog, and horizontal part of the stem, these were based on station cross sections. On the vertical part of the stem they were based on waterline cross sections. I had to create a couple of diagonals for the turn of the stem.
    I then linked the vertices of these profiles with splines (as in TurboCAD splines) to generate the outline, then lofted (again using TurboCAD terminology) these into a solid. The first time I tried this I discovered a bug in TurboCAD where the lofted solid got all it's lines crossed over and it looked like the task would have to be abandoned. I was very impressed that when I took this up with TurboCAD they took it very seriously, fixed the problem, and gave me a free update.
    In all of this I had to separate the hog, skeg, keel and stem into separate components that could be dimensioned individually to be made by different volunteers.
    This is the 'virtual' stem on which I based my template to use in searching for a crook.
    Cheers,

    J

    ....

    Data isn't Information, Information isn't Knowledge, and Knowledge isn't Wisdom!

  16. #15
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    Default

    I've locked this into my favourites. Keep up the good work.

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