A simple Boundary Element Method-model is implemented for ocean surface waves. The model is supplied with a framework for calculating source parameters, constructing boundaries, calculating sea surface elevation, and reflection coefficients at trenches or partially reflecting boundaries. The model is open source, and is based on the open source model for the acoustic Helmholtz equation developed in Kirkup (1998). It is implemented in Python and Rust, and may be installed as a regular Python-package.</p> <p>This type of models are suitable for domains that are separated by a sharp boundary (constant wave speed in each domain), like abrupt depth transitions (submarine trenches), coastlines and harbours. It does not account for refraction in the domain, but is particular useful for calculating the interference patterns caused by reflection and diffraction. This offers a complementary strength to ray-tracing models, which are particularly useful for modeling refraction. The model is a simple tool for computationally cheap exploration of wave propagation, and for studying the underlying phenomena which are often difficult to separate in more advanced models.</p> <p>We present the basic theory, and the boundary conditions for common situations like breakwaters and harbours, trenches (coupled with estimates of reflection coefficient), as well as partially and fully absorbing boundaries.