Understanding boat plans from table of offsets

So:
z = length*sin(angle)
y = length*cos(angle)

just insert the length and the angle given for that specific coordinate

 

That helped immensely. I was about to type a reply that I wasn't getting the same number for sin(10) - I was using the python interpreter as a calculator. Switched to normal calculator app and the numbers are same as yours. Now I will try making the sections and post my results. Also, need to see why math.sin(10) was giving -0.54 in python3!!

EDIT: In python, it was expecting radians and I gave degrees!!

Thanks

 

To expand a bit for the sake of clarity;i used polar coordinates directly as it seemed easiest not to go through the additional stage of converting to Cartesian format.The pale blue lines in my screenshot are the diagonals and the endpoints are located at the distances given in the offset table.It is quite common in mainland Europe for a comma to indicate a decimal point.I have encountered this in drawings from France,Italy,Germany and the Netherlands.Hand written 1's can cause a bit of head scratching,just as we might do the same with our 7's.

 

Thought so. I have seen the comma being used in place of decimal in several places from Europe.
I will try this method too and see if I make any errors.

On a related note, once I plot the shape, these can be used as formers/stations for building the boat right.

 

The table of offsets are normally to the outside of the hull, to make molds for building you have to subtract for your hull planking thickness. Which is done after lofting and fairing.

 

You also need to determine whether you may need to make allowances for a radius along the keel line.On some older designs there used to be a "fairing point" beyond the line in question to make the line fair and to allow for such things as a flat for a keel band.The sections are a valuable step along the way but only after you verify the fairness.The traditional way involved crawling around on the lofting floor but now much can be done with a CAD program and the zebra stripes or environment mapping will help locate unfairness.

 

Makes sense. Since this is a dinghy without a keel, i wonder if i can follow a batten or a French curve and see if i can join it with it's mirror image.

 

Good to know. Thanks

 

I would recommend looking on the class society's website for building information and recommendations, for example are there also the offsets for the stem given and minimum weight and what the weight distribution should be etc.

At least if you plan to competite you have to comply to the class instructions.

The hull will be measured with templates at the stations at the angles given in the table of offsets. This explains why the offsets are in polar coordinates.

But - since you are learning lineplans and stuff - first you should be able to draw the stations and after that making a linesplan with sections, waterlines and buttocks.

 

That worked!
I created the drawing with angle and distance and then checked with x,y coordinates. Both agree. Happy to learn something new today

Europe Roland table calculates to y,x coordinate set per each station as below.
[(14.15, 80.26), (28.9, 79.4), (45.25, 78.38), (64.28, 76.6), (88.86, 74.56), (122.11, 70.5), (173.37, 63.1), (261.96, 46.19), (399.0, 0.0)]
[(44.11, 250.14), (87.56, 240.56), (132.0, 228.63), (178.69, 212.96), (229.81, 192.84), (285.79, 165.0), (344.87, 125.52), (402.79, 71.02), (456.0, 0.0)]
[(66.51, 377.18), (128.94, 354.26), (188.0, 325.63), (244.26, 291.1), (298.76, 250.69), (351.61, 203.0), (401.72, 146.21), (448.09, 79.01), (491.0, 0.0)]
[(84.39, 478.62), (160.92, 442.13), (230.0, 398.37), (292.79, 348.93), (345.87, 290.22), (394.04, 227.5), (436.96, 159.04), (476.65, 84.05), (514.0, 0.0)]
[(97.85, 554.94), (186.91, 513.54), (264.5, 458.13), (329.11, 392.21), (379.96, 318.82), (423.49, 244.5), (462.33, 168.27), (497.33, 87.69), (525.0, 0.0)]
[(107.58, 610.09), (205.9, 565.69), (287.5, 497.96), (351.93, 419.41), (401.41, 336.82), (441.67, 255.0), (475.95, 173.23), (504.71, 88.99), (528.5, 0.0)]
[(114.17, 647.51), (219.75, 603.75), (305.5, 529.14), (369.92, 440.86), (415.2, 348.39), (448.6, 259.0), (476.89, 173.58), (502.25, 88.56), (522.5, 0.0)]
[(118.6, 672.62), (228.98, 629.12), (316.25, 547.76), (379.89, 452.73), (421.71, 353.85), (452.5, 261.25), (475.48, 173.06), (495.36, 87.35), (511.0, 0.0)]
[(121.64, 689.86), (234.28, 643.69), (321.75, 557.29), (384.07, 457.71), (423.62, 355.46), (448.6, 259.0), (469.38, 170.84), (485.02, 85.52), (497.5, 0.0)]

Image of the lines for station 1 and station 6 as below. Both x,y and angle/length agree.
Thanks for your help folks.

PS: Now, what is expected from reading these lines apart from fairing? The hull line stops at 10degrees. So, does one just add the remaining bit to connect to the deck since deck is above the baseline anyways?

 

Hi Thule, nice to see that it worked for you.

In the table of offsets you have two columns named "z" and "y". These are the measurements for the deck and you should add them to your drawings. Here is also "z" the height and "y" the offset or distance to the centerline. That done and your stations are complete.

For a complete linesplan you need a section view (where all your stations are visible), a plan view (making the hullcontour from above and the waterlines visible) and a side view (hullcontour from the side and some buttocks or sections in lengthdirection).

Divide the hull in waterlines with a logical distance and do the same for some (maybe 3) buttocks. If you know the depth at which the boat should float use this for a design waterline (also construct this line). Knowing the distance of waterlines and buttocks you can draw following grid:
-Sideview with waterlines (use your distance) and stations (use distance from table of offsets)
-Planview with buttocks (use your distance) and stations
-Section view: also draw waterlines and buttocks

Note: till now all waterlines and buttocks shall only be straight lines.

Now you can measure the intersections (waterlines with stations, buttocks with stations) from the section view and construct the waterlines and buttocks. I would probably start with the hull contour in the side and plan view and complete them with the stem contour. After that go further with the waterlines and buttocks.

Good luck!

Edit: for complete stations you need to draw the stations by connecting the endpoints of you lines (deck, 10°, 20°, ..., 90°) with a fair line.

 

Good progress!to complete the job you need to pass a line through the endpoints of the lines that have been created.the traditional way would have been to connect the dots using a pencil and a wooden spline.If you have a CAD program that can create splines it is easy and it still amuses me that somebody had to go to the trouble to make a computer act like a piece of wood.This though isn't the end of the process as you still need to go through the fairing of waterlines and buttocks (ideally diagonals too) to be sure there are no hollows or bumps.There may be a shortcut if you have access to a CAD program that can apply zebra stripes to show curvature or if it will allow you to Environment Map the surface to show reflections.I would suggest you try to discover the radius applied to the face of the stem as you won't want a knife edge there.

 

I have Freeship and Librecad. I can also recreate it in Blender, which allows for environmental mapping. Although, I don't know how to make blender behave as accurate as a CAD program. I can certainly try.
I think Freeship might be a decent option here.

What is the reason for not wanting a knife edge at the stem - is it in terms of safety on a small boat or does it create more turbulence d/t sudden change?

Thanks

 

Got it. I will finish the stations and add Z and the Y for the deck. Then I can start with plan and profile views. Thanks for the clear explanation

 

I can't help with Blender as I have never used it.Librecad will allow you to do a 2D lofting and that may be enough to give you a good grounding in the lofting process.Freeship will allow you to input a table of offsets and the X,Y,Z coordinates you have derived may be an excellent starting point.The older versions of Freeship-version 2.6- would allow an IGES file to be exported and maybe Blender could import such a thing.

A knife edge stem may well be outside the class rules as well as being very difficult to build.Furthermore,it would be ridiculously fragile in use.For practical purposes a line at the rake of the stem and offset perhaps 5mm to one side would be a good lofting or surfacing aid.If you wanted to refine the surface or even build the hull,a 4 to 5mm radius wouldn't be too great a task.