Deriving station profiles from a drawing

[Kevin-the-lubber]

Morning all. I may be having a senior moment but for the life of me I cannot figure out how to derive station profiles from the drawing below. Am I being dense and, if so, what's the method? As a one time pattern developer many decades back, I'm convinced I should be able to derive them using projection but I'm getting nowhere on this.

 

I know plenty of ways of cheating here but that's not the goal - I'm looking for the scientific method, if anyone can help.

 

 

[druxey]

No, you are not having a senior moment! It would be difficult to do, as only the 'dead flat' in the end-on elevation drawing is given. Yes, you have the sheer (in elevation) and half-breadth (in plan) as well, but that tells you nothing about the changing sectional shapes. They may be inferred from the planking runs - if accurately drawn - but that is a s much as one can squeeze out of that plan. 

 

Perhaps a similar lifeboat drawing that has the station sections might help.

[Waldemar]

 

I would suggest the ancient method of whole-moulding, still being in widely use for small craft in 18/19/20th centuries. It is described in many works, such as the Steel's Naval Architecture, 1805 and also in many modern publications.

 

 

[Kevin-the-lubber]

Thanks both, there has been a little voice in my head telling me that I'm mis-remembering. I've just had a quick google on whole-moulding, don't fully understand it yet but it looks to be the 'scientific' approach I'd expect to find, especially for ships as opposed to little boats, where you could probably just get there by a bit of trial and error.

[Waldemar]

 

To possibly save time, you may simply go for the book Working Boats of Britain. Their Shape and Purpose by Eric McKee. Excellent study.

 

 

[allanyed]

Hi Kevin,

If you are not locked into exactly that boat, Google surf boats and monomoys.   While not exactly the same, especially at the stern post, they are similar in size and shape.

What year is the boat in your drawing from?   

Allan

[Kevin-the-lubber]

The aim of this particular exercise is three-fold - it's partly to make a better set of boats for the 1:96 cutty sark I'm building, via 3D development and printing; partly to have a set of 'stock boats' that I can tweak through scaling to get something reasonable for just about any ship that had clinker-built boats; but also to learn how to build hulls properly before I launch into building them for ships. I've already created the hulls for a jolly and a gig, see below; the two on the left come with the revell kit, the two on the right are mine, the gig is just a re-scaling of the jolly. I can of course re-scale and mirror (more or less) the front half of the jolly to get a quick result for the lifeboat on the left and probably will just to maintain progress, but that would leave me still not knowing how to develop the station profiles. I think whole-moulding and other ancient arts will be the way to go, I'll probably enjoy learning that as I love those old, often incredibly clever ways of doing things.

 

[Waldemar]

 

I like these methods too. Simplifying a bit, you can always use just one method/procedure, but by playing around with different specific values/parameters you can get distinctly different shapes to suit different needs.

 

 

[allanyed]

Hi Kevin,

Good for you in taking on this project!   Looking at build logs here at MSW, with one or two exceptions, stock boats found in kits are ghastly, so your idea could be salvation for kit builders.   

 

For your clinker project will you be basing the scaled series for the hulls only?  This makes sense as the number and scantlings for frames, thwarts, ears, and knees, and scantlings for deadwood, keel, planking, etc are not going to be scalable at the same ratios, if at all.

 

Allan   

 

 

[shipman]

Kevin, as I understand, you are a dab hand using 3D graphic projections, using the software for your resin projects.

That kind of computer witchcraft is a mystery to me but...

 

Could you not scan that plan, introduce evenly placed sections, then do your clever manipulations and by trial and error develop it until your new plan looks right. The 3D aspect gives you the magic where you can revolve the drawing through any axis you choose. After doing that and it looks right, what's wrong with that?

[Roger Pellett]

Ship’s boats, naval and otherwise are a particular interest of mine.

 

On a sailing ship like Cutty Sark, all of the boats that she carried were not “lifeboats.”  She would have carried  one or more transom sterned workboats for ship to shore service while in the harbor.  Actual lifeboats, number and design, carried by British Flagged vessels were governed by British Board of Trade Regulations.  I have a book published in the 1920’s that provides detailed design information for lifeboats meeting Board of Trade rules.  The name of the book is Ships Boats.  I’ll post the author’s name later.

 

The National Maritime Museum’s Branch in Falmouth (UK) recently built a replica of one of Titanic’s lifeboats.  I visited the museum in 2018 and talked to the boatbuilder.  He told me that they had been unable to find any drawings for the actual boats carried by Titanic.  The hull lines, the drawing that you need to determine the shape of the hull formers, were based on a drawing from an old technical paper.  I’ll post a copy later.

 

The size of a lifeboat was determined by the number of people that it was supposed to carry.  This determined cubic capacity: Length x Width x Depth x A Factor.  True lifeboats tend to have similar characteristics, whether very large like Titanic’s or much smaller ones that would have been carried on a ship like Cutty Sark.

 

Roger

 

 

[Kevin-the-lubber]

Hi Shipman, yes I could certainly do that, and a few variants, but it wouldn’t give me a “formula” for next time. CAD is a red herring here - for sure it can make it easier but a scientific method should always be quicker and easier than trial and error.

[Waldemar]

 

Among the many modern works that explain in a visually appealing and clear (step-by-step) manner the principle of the essentially non-graphical whole-moulding method is the chapter of a larger work: Capturing the Curve. Underlying Concepts in the Design of the Hull by Taras Pevny. Please take a look at pages 187–190. The paper was found in the public domain and I suppose it can also be uploaded here.

 

Pevny Taras - Capturing the Curve. Underlying Concepts in the Design of the Hull - 2017.pdf

Edited September 3, 2022 by Waldemar

[Waldemar]

 

It should be added that the version shown here, being suitable for larger vessels, is slightly more complicated than its simpler version sufficient for small craft such as boats. "Top Timber Mold" and "Splaying-Out Staff" can be dispensed with.

 

 

 

Edited September 3, 2022 by Waldemar

[henrythestaffy]

Kevin, i am not at home to try it out on fusion, but i was wondering whether the loft command would be of use. 
 

Paul

[Kevin-the-lubber]

5 hours ago, henrythestaffy said:

Kevin, i am not at home to try it out on fusion, but i was wondering whether the loft command would be of use. 
 

Paul

Hi Henry, lofting is key here. At present I’m lofting each plank/strake and using rails to hold the shape. Also using f360 by the way.

[Roger Pellett]

Kevin,

 

There seems to be two questions here:

 

1.  Can you produce an accurately shaped hull using just the information on the drawing that you posted?

 

Answer-  No you cannot.  The drawing does not provide enough information.  In addition to the shape of the midships section, you need more hull sections both fore and aft.

 

2.  How to design a series of ships’ boats to allow scaling up and down as needed.

 

Answer-  Difficult.  First of all what you want to do is highly dependent on period. The hull shape of a boat for Cutty Sark is much different from that of 100 years earlier.  For that reason Whole Moulding is inappropriate for a late Nineteenth Century vessel.

 

It might be possible to design a series of “Lifeboats.”  Only one boat in the photo that you posted, the double ended one is a lifeboat.  As I posted above these boats were designed to meet Board of Trade Rules, and post Titanic SOLAS rules.  The starting point was human capacity, specified to be 10 cubic feet per person.   The overall dimensions of the boat were then determined using the formula:  (L*(4A+2B+G))/12

L= Length In feet

A= Area of forward quarter length section

B= Area of midship section

G= Area of aft quarter length section

This formula provides the boat’s available capacity in cubic feet.  This capacity must be greater or equal to the number of people X 10 cu ft per person.

 

This still does not determine the shape of the boat and this is not entirely up to the designer.  The book,  Ships’ Boats by Ernest W. Blocksidge c1920 provides additional rules for hull shape, stability, and strength.

 

You need to solve a Naval Architecture problem, not a computer problem.

 

Roger

Edited September 4, 2022 by Roger Pellett

[Kevin-the-lubber]

I agree Roger, this has nothing to do with CAD, it’s a process question. What I’m asking is whether there are common methods for deriving the profiles and the answer seems to be yes, lots of them, and it depends on the type of boat, the era, and where in the world the boat is from. I think I’ll see what I can learn from the references but at 1/96 anything close to the sketches will be more than good enough.

[Kevin-the-lubber]

Gosh but this is getting a bit involved! For what it's worth, my experience of shop floor engineering, as a craftsman, is that very little was really done by eye. Back in the '70's we used to make 10 foot long, 3 foot diameter helixes on a forge and would swear blind it was all art, neglecting to mention the many templates used to get the right twist. So while it's perfectly possible that the cutty's boats were made by eye, many other boats would have been made using scientific methods like whole moulding. What I'm interested in is those methods, rather than getting hold of lines plans - I have enough info from the 3D jolly boat to produce the goods, but I'll be none the wiser as to how boatbuilders knew the station profiles to begin with.

[Waldemar]

 

 

 

 

 

 

 

 

 

[Kevin-the-lubber]

Waldemar, many thanks, that's exactly what I'm looking for, the logical projection method. I have forgotten so much over the years. Have you used a constant radius based on the '0' station? From a pattern developers perspective I think that is all that's needed to get a fair shape from these three views.

[Waldemar]

 

That's right Kevin, just two moulds are used for shaping the whole hull.

 

Or, this is how this boat of extremely simple, symmetrical shape was reverse-engineered by the most simple variant of the whole-moulding method (sufficient in most cases):

 

– original plan was checked and the worst distortions corrected (it sports quite many other errors anyway, although unimportant already),
– base lines were defined (keel, posts, stations etc.),
– shape of the main frame was reconstructed by two tangential arcs and a vertical line (outside the planking; also shown in the sketch),
– main frame "O" inside the planking was defined by offsetting the above curves by the planks' thickness (or so),
– just two moulds were defined in the process: the main mould (red) and the hollow mould (green); their names differ depending on the sources; hollow mould is just an arc of constant radius, sufficient in this case, but often/sometimes other curves were used, like parabola, hyperbola etc.,
– the attached drawing is self-explanatory on how to derive the other station sections (frame "1" omitted for clarity),
– normally, (narrowing and rising) floor curve should be employed for offsetting the main mould in order to get other station sections, but in this instance the sheer line (or greatest breadth) had to be used instead (the period craftsmen would had to do the same upon receiving this draught).

 

Good luck with your designs

 

 

 

Edited September 5, 2022 by Waldemar

[Kevin-the-lubber]

7 hours ago, Waldemar said:

That's right Kevin, just two moulds are used for shaping the whole hull.

Perfect, many many thanks Waldemar. I'll need to spend an hour or two properly digesting and playing around with this at the weekend and then compare the outcome with the quick'n'dirty version below, done as outlined in post #7. 

 

[Waldemar]

 

🙂

Out of sheer curiosity – please don't forget to show the result. And one more potentially useful advice: the whole-moulding method is both proven and universal in its field of application, nevertheless a slight, professional fairing touch at the hull ends is sometimes required, just as in the real shipbuilding practice.

 

 

[Kevin-the-lubber]

3 minutes ago, Waldemar said:

Out of sheer curiosity – please don't forget to show the result.

I will indeed. Don't hold your breath, these boats are fiddly to do and it might take me a while to get to the end point (though I hope not too long)

[Kevin-the-lubber]

And..... breathe

 

 

top = kit; bottom = mine

left = kit; right = mine

 

[Waldemar]

 

No comparison. I am referring to the hull lines. You can immediately see the hand of a skilled boatbuilder. 🙂

 

 

[Kevin-the-lubber]

50 minutes ago, Waldemar said:

You can immediately see the hand of a skilled boatbuilder

Credit where it's due, I think those were the hands of the original builders as all I've done is copy from the plans, with some important help from your good self. But it's surprising how chubby and crude the kit part looks against the 'plans' version, isn't it. This is the pick of the litter for me though, the gig, which has the most beautiful lines. I may make this one a little side project and do it separately at about 1/30 or 1/40. It would make a very nice windowsill ornament with all the trimmings. I'm hoping to find time to pop up to Greenwich next week for another photo session and this would be on the 'to-do' list.