Forums: The Deben 5-Tonner: station -5938 New Topic Post Reply
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GregH
Posted: Feb 20th, 2012 at 15:01   |   Subject: station -5938
Good Morning George.

I was going through some more ACAD sketches (and working out thoughts) at the stern and came into a wee bit of a problem. Could you please confirm whether station -5938 is correct? From what I can see, that would place the lower end (@ DWL) a few mm aft of the transom piece itself. If I understand correctly, this station would need to be at -5899 at the most otherwise it will interfere with the transom boards.

thanks!
GregH
GregH
Posted: Feb 20th, 2012 at 17:20   |   Subject: addendum
Sorry for this after-thought to my previous post. I wanted to say previously that the last station/frame would be better at about -5841. Not only because of the thickness of the transom piece, but also because of the siding dimenions of the transom fashion pieces which add to the overall thickness at the waterline.

thoughts?

Thanks again
GregH
debenriver
Posted: Feb 22nd, 2012 at 02:30   |   Subject: station -5938
Hi Greg

I'm away from my computer with the plans on it until the morning of the 24th – so I'll look into it then. Sorry about that; I only have an old laptop with me at the moment and the drawings aren't on it!

George
GregH
Posted: Feb 23rd, 2012 at 03:58   |   Subject: station -5938
No problem - life is pretty busy during the week anyhow :)

thanks
Greg
debenriver
Posted: Feb 27th, 2012 at 18:00   |   Subject: station -5938
Hi Greg

You mustn't confuse the Stations with structure. Stations divide the LWL (usually into 10 spaces – hence 11 stations). Their purpose is to provide a set of cross-section views of the hull in the laying off process and to assist with fairing the lines generally. Just as the waterlines provide a set of horizontal plan views and the buttocks provide a set of vertical profile views.

Think of it like a loaf of bread. Stations are ordinary slices of the bread – just 10 rather thick ones. Waterlines are as if you made horizontal slices down the length of the loaf. Buttocks are as if you made vertical slices down the length of the loaf. And diagonals are as if you made angled lengthwise cuts down the loaf.

Once the lines are drawn out and faired, we choose other positions for the structures of the boat. Those running across the boat (like the slices of bread) are usually called Sections.

In this instance, say, we need to choose positions for the laminated frames. So once the lines are faired, we set off the frame positions and get new offsets for the sections in way of the frame positions. There is no reason why the frames should come on the Stations – in fact they almost certainly won't.

And the bevel on the outside edge of the frame is found by drawing a section on the fwd, face and a section on the aft face. The difference will give us the bevel.

Bevels can be horizontal (on a waterline) or vertical (on a buttock), or even at an angle (on a diagonal).

Choosing an even number (or and odd number) of equally spaced stations derives from a numerical calculus called "Simpson's Multipliers" which will calculate the area under a curve of linears, or calculate the volume under a curve of areas – which is something we need to do. It does require that the spacings be equal. Hence dividing the LWL into an even number of spacings (so an odd number of stations) – because we are most interested in the volume (and other characteristics) of the underwater hull.

Simpsons is quite an old bit of maths – it used to be used a lot by surveyors to calculate land areas (odd shaped fields and so on), because all you have to do is to measure lengths from a baseline at regular spacings, in order to get an accurate area. Nowadays, it is mostly confined to ship and yacht architecture.

We haven't actually sorted out the frame positions yet. These do not have to be equal spacings, so we can organize them to fit with the internal layout.

George
GregH
Posted: Feb 28th, 2012 at 03:45   |   Subject: station -5938
OOOOOOOOOOOOOOOOOOOOOOH!

ok that makes total sense! LOL .. I WAS assuming the stations were also the frame locations. I can see how some frames MAY fall on the same location, but it's not a rule. As you say, deciding where they go will depend upon internal structure makes sense as well, as well as getting their offsets from the lofting.

For the lofting, what material would you recommend? I can get some 4x8' sheets of G1S ply (1/4 or 1/2")or masonite (1/8 or 1/4") or even 1/4" luan subfloor ply. I would paint the sheets white on the side I will loft on.

I think I will need 6 4x8' sheets to give me enough area. Does this make sense to you? For the frame lofting, I was thinking of using one more sheet for the forward frame halves (since 1/2 beam is less than 4') and another sheet for the aft frame halves. I would need to laminate each frame half one at a time from the one loft line.

Any thoughts?

Thanks
Greg
debenriver
Posted: Feb 28th, 2012 at 21:05   |   Subject: station -5938
I know – it does get a bit confusing! But the "lines" are only used to fair the hull. The the shapes of the actual bits of structure are derived from the faired lines. But they aren't (necessarily) the lines!

Any reasonable surface will be fine. Painted white is good. You need to be able to drive something like 30-40mm nails into the floor to bend battens around, so it really depends on the surface you are laying the floor on. If it is concrete for example, then you would want a minimum of 12mm ply or particle board – and I think I would actually go for 18mm. However if it is a wooden floor (and you don't mine nail holes in it) then 6mm ply or similar would be fine.

Our loft floor at the boatyard was simply softwood boards (typically 150-200 x 20). And they were a bit warped, with gaps between, so it was sometimes difficult to eye up the lines. But is was OK! But the flatter it is the better and the easier it all is. If you have a barn floor or similar that would be fine.

Again, to laminate the frames, the easiest way is to screw blocks to the floor to bend the laminates around and clamp them. So a reasonable thickness is needed (say 12mm minimum). You can laminate the frames right on the loft floor if you wish – just stretch and tape some polythene tightly over it to prevent the laminations getting bonded to the floor.

George