# Strip Planked Boat: Forms, the point where the Buttocks Plane meets the Waterline plane

Discussion in 'Boat Design' started by veekm, Jun 29, 2019.

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### veekmNew Member

Hello,
Total newbie - reading a book on wooden boat construction. Is anyone familiar with "Forms" (strip planked boats).
The point where the "Buttocks Plane" intersects the Waterline Plane creates a Forms Plane. You can then move the Forms Plane to create cross sections of the boat and then number those cross sections. What I don't understand is this bit: https://i.vgy.me/6dfo3s.png "7 inch waterline is a line drawn on the surface of the boat at an elevation of 7 inches above the datum water-line" <----- so if the boat's sitting in the water with me in it, it will sink in a bit thus creating the DWL and you want a 7" safety margin for waves and such - CORRECT? And THEN after that I don't follow ANY of it.. What's the CL? What the heck is a 3" Buttocks line? And his 0point definition is bonkers? Could someone clarify all that for me please He further says " Every time either a waterline or a buttocks line inter-sects the surface of the boat at a form location, the position of that intersection is noted ." But so far we only have one Forms plane? and Buttocks, Waterline PLANE.. if you move the Forms plane and cross section the boat.. you'll get an infinite sequence of planes.. he's trying to ..?

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### Mr EfficiencySenior Member

The 3" buttocks lines are vertical, longitudinal slices of the boat, at intervals of 3" across the width of the boat. Like slicing a loaf of bread, but lengthways instead of across the width.

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### waikikinSenior Member

Hi veekum,
The CL is the centreline. The whole scheme is simply a three dimensional grid with the intersection of the shape described to three views- http://i1.wp.com/www.themodelshipwright.com/news/wp-content/uploads/2013/02/hercules7.jpg . On a lines plan the transverse shapes are described by the "Body Plan" as "Stations- very often frames dont land on stations so can be drawn at the correct location on the full size lofting of the Plan & Profile- check this too as may help - Lofting Basics https://sandypointboatworks.com/wood-boat-school/boat-building-articles-journals/boat-shop-tips/126-lofting-basics
The forms as whoever calls them are the frame shapes. There can be a bit more to it if planking thickness needs to be deducted(bearding line) but a line/plane can be struck in any orientation through the drawing and that shapes intersection with the skin can be drawn.
Sometimes diagonals are drawn also- just another "cut" through the hull shape.
All the best from Jeff.

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### veekmNew Member

<i've nuked the rubbish i wrote earlier>
(thanks - the link really helped - it's kind of different from our typical coordinate system - need to think about it but it seems to be making sense now )

Last edited: Jun 29, 2019
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### rwatsonSenior Member

Hmm, perhaps you are just overthinking it.
Basically, if you put an object in space, you have X,Y and Z "Planes", and any point in space is fixed by the measurements within all three of those "planes"

For this boat, those "planes" are Z (up/down) is the "Waterline" Plane (sometimes the water is over your head, sometimes under the boat)
The Y and X plans ( one is Fore/Aft ( Form Plane or Frame Plane), and the other is the Width (Buttocks Plane)

Yes. The Planes he has drawn are either 3" or 2" - they are just handy divisions for the design process.

So, as you say, any point on the hull is referenced by the 3 points within the three planes.
You can think of the "frames" or Forms or Molds as Plane X divisions, (crossways saw slices) that provide the final "fixing" point in space after the Z and Y axis have been specified. They will probably be a couple of feet apart, rather than a few inches as you build.

I think its just the boat design terminology that has caused the brain-snap. Hope my stuff helps a bit.

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### JSLSenior Member

All the previous explanations are good.
One cause of your difficulty may be that you are transitioning from 'design to 'building' .
Looking at your sketch the 'forms' (cross sections) shown are called 'stations' when on a "lines Plan". Part of a Lines Plan has a view showing all the 'stations' and called the 'body plan' and are equally spaced along the DWL. All of these lines (waterlines, buttocks, stations lines, diagonals are at the molded surface of the hull, in the case of wood, to outside of planking. To build a wood boat you deduct the planking thickness to get the 'station molds', which are set up as 'forms' to build the hull.
That's my 2 bits worth, I am sure others can add more.

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### waikikinSenior Member

One of the best ways to fully understand is to manufacture a half block model at a scale- this when I went to technical college how apprentice Shipwrights were taught - shape the model then take off the lines & draw the lines plan- occasionally a boat was built to the plan with bearding lines bevels sorted and applied before stepping stem, transom & frames. Another exercise involved developing conical & cylindrical sheet forms with the application of triangulation- when done at scale the "learning by doing" comes at low risk & cost. Unfortunately and also fortunately the power of computers seems to have overtaken sometimes at the cost of a fuller & real understanding by the technicians applying.
Jeff.

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### veekmNew Member

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