Pylot

Pylot is a helper application for Capytaine and, in the future, other BEM solvers.

It helps to develop and maintain a library of hydrodynamic data for a single vessel spanning multiple drafts, grids, heel and trim.

The whole idea is a follows:

1. define a base-shape for a vessel.
2. create calculation meshes for different "floating conditions" by cutting the base-shape at the water-surface and meshing (automatic)
3. run capytaine to obtain hydrodynamic data
4. store in a sqlite database

then, on the consumer side:

1. load the database
2. get the best matching floating condition (using surface probes)
3. convert into a mafredo hyddb1 for further use

to limit the python environment for the consumer side, the pylot package is split into pylot-db and pylot-bem.

run

uvx pylot-bem

pylot-bem

Write side of the hydrodynamic database: meshing, in-process Capytaine solving, assembly, a command line and a standalone application.

Pylot is a pylot_db.Library — it adds meshing and solving to the same object, so a file written here opens as a plain Library on a machine with no BEM solver installed. That split is the point, and a test enforces it.

Build a library

import numpy as np
from pylot_bem import Pylot, SolveSettings

d = Pylot.create_new("tanker.pylot", "tanker.stl", "stern, centerline, keel",
                     is_xz_symmetric=True)

condition = d.create_condition(z_origin=-12.0, condition_id="design")
mesh      = d.create_mesh(condition, pct=2.0)
result    = d.run_solve(mesh, SolveSettings(
    omegas=[2 * np.pi / T for T in (12.0, 16.0, 20.0)],
    wave_directions=[0.0, 45.0, 90.0, 135.0, 180.0],
))

print(d.validate() or "clean")
d.close()

Pylot writes the file in place. The application does not: it works on a copy, and so can pylot_bem.Workspace from a script — see docs/api.md. Opening and closing a Pylot rewrites the file's header even if you only read, so a script that only reads should use Library.open(path, read_only=True), which touches nothing.

Reading one back is pylot-db, which this package depends on and which needs no solver.

The application

uv run pylot-bem

A window for building and inspecting libraries: the tree, a 3D view in diffraction space, property panes, and tabs for Results, Databases, Inspect, Match and Validation. docs/manual.md walks through it screen by screen and assumes you already know Capytaine.

It works like a text editor. Open makes a private working copy of the library on your local disk, everything you do happens to the copy, and Save replaces your file in one atomic step — so a library the application has saved, in a Nextcloud or OneDrive folder, has no -wal or -shm files beside it, and the library file a sync client sees is always the old version or the whole new one. Closing or opening with unsaved changes asks first, and a crash leaves the working copy to recover from at the next start. See Saving, and where your work lives.

Filling a library overnight

Right-click the library → Batch…. A grid of drafts, heels and trims, and one line per mesh saying which periods it carries:

z_origin  -4.7 to -0.1 step 0.1     heel  -1, 0, 1     trim  -2, -1, 0, 1, 2

1 -> 1, 2, 3, 4
2 -> 5, 6, 7, 8, 9, 10, 12

705 conditions, 1410 meshes, 1410 solves — counted on screen before Start. A step that fails is logged and the run carries on, and starting the same job again resumes rather than duplicates, so a night that ended early needs no arithmetic to continue. When a run ends the library is saved for you — File → Save when a batch finishes, on by default, with the same check that the file has not been changed by someone else.

Save job… keeps the whole thing as a 29-line text file beside the library, so it can be edited, kept and run again. pylot_bem.batch is the same feature without a window.

Standalone executable

uv sync --group build
uv run pyinstaller packaging/pylot-bem.spec --noconfirm

Produces dist/pylot/pylot.exe — no Python install required on the target machine. Zip the dist/pylot/ folder to distribute it.

What is where

Licence

MIT. Copyright 2026 Ruben de Bruin / DAVE Lab.