What is Michlet hull offset data form?!

[Dante]

I was trying to figure out how Michlets hull offset data actually works. All info given in Michlet manual says:
"All offsets at the bow (the first row) must be equal to zero (decimal). Stern offsets (the last row) may all be zero (no transom) or some non-zero if there is a transom stern of a shape determined by the non-zero offsets. The number of rows (cross-sections) and columns (waterlines) in the offset data must be the same as the number of stations and waterlines specified earlier. Offsets are separated by commas, and there is no comma at the end of each row."
So, rows correspond to cross sections (stations?) and columns to waterlines. Ok, as I see it, this produces side view of a hull, and numbers tell the distance from hull surfacfe to centerplane of the hull at each waterline/station, like coordinates. Correct? But this reasoning produces very strange looking hulls. Is this data for only one half of the hull, and other half is mirror image of first half?

As I am totally confused with this thing, I would be very grateful if someone could explain how this offset thing actually works and probably even give some picture or example with very low number (to make it understandable) of stations and waterlines.

[marshmat]

Michlet assumes that the hull is symmetrical about its centreline, thus you input offsets for one side only.
I'll post an example file for you shortly.
Free!ship ( http://www.freeship.org ) can easily generate a perfect Michlet input file for most types of hulls.

[marshmat]

Hi again,
OK, so here's some examples for you.
The attached 'example hull.txt' is a fairly conventional table of offsets for the default hull that loads when you start Freeship.
Now here's the offsets of that hull as you'd give them to Michlet:
# ============================ FIRST HULL ==============================
# Offsets
0.000,0.000,0.000,0.000,0.000
0.000,0.000,0.005,0.269,0.415
0.000,0.023,0.548,0.745,0.870
0.000,0.691,0.966,1.126,1.232
0.000,0.942,1.185,1.336,1.438
0.000,0.926,1.211,1.381,1.494
0.000,0.567,1.052,1.278,1.422
0.000,0.000,0.532,1.000,1.218
0.000,0.000,0.000,0.000,0.781
# Displacement Volume (cubic metres)
5.7960
# Length (metres)
12.0000
# Draft (metres)
0.5000

The first row is the bow. The next row is the station at 1/9 of LWL from the bow, etc. The first value in each row is the lateral distance to the hull surface, measured in the horizontal plane passing through the lowest point of the hull at design draught (always zero). The second value in that row is the lateral distance to the hull surface at, in this case, 1/5 of design draught above the keel.

It is important to note that Michlet only cares about the waterline down. Thus the five waterline planes (the columns) of the above table are equally spaced between base and waterline. Also note that you must always have an odd number of stations and an odd number of waterlines for the program to interpret it correctly.

(PS- Note to Jeff- any chance of adding .mlt to the allowed attachments?) << moderator's note 8/20/06: added to allowed attachments - thanks >>

[Dante]

Thanks, Matt! After all, it seems my first thought was correct, somehow it is difficult to get grasp of Michlet screens and prob that was confusing me...

So, using that notation and restrictions (first row of zeros) of it, can I create totally flat bottomed hull with horisontal sides, and nose tilted upward? Basicly that form is elongated and flattened cube with one section at nose cut off. Some short of planing shape. I know this hull shape is not practical, and probably Michlet should not be used to evaluate drag for that kind of hull, but CAN it be done?

What I tried was:
0.0000, 1.0000, 1.0000, 1.0000, 1.0000
1.0000, 1.0000, 1.0000, 1.0000, 1.0000
1.0000, 1.0000, 1.0000, 1.0000, 1.0000
1.0000, 1.0000, 1.0000, 1.0000, 1.0000
1.0000, 1.0000, 1.0000, 1.0000, 1.0000
This violates given instructions, but anyhow Michlet seems to start with this configuration. Anyhow, this does not produce shape I was aiming at, because result is sharp nosed seen from above (I wanted it to be rectangular from above).

For little bit more serious exercises I probably have to learn to use Freeship.