The Sisu boats were built in the 1970s and 80s by Sisu Boat Inc. of Portsmouth, NH. The hull designs were created by Royal Lowell. They were very popular, and many are still on the water today.
The term "sisu" refers to a common Finnish concept of "stoic toughness" or perseverance. The literal translation is "having guts" - basically, the spirit of will that survives and enjoys the harsh winters of Scandinavia. 'The Power of a Finn is the Sisu Within'
Most of the companies that provided components for Sisu boats have since gone out of business. We use Hamilton Marine as a great source for boat components.
The Sisu's windows were originally made of plexiglass, which has a tendancy to get cloudy. Replacement can be tricky because the windows often have a 2" corner radius, whereas 3" is now the industry standard.
Here are two companies that we know of who make windows that will fit for Sisu replacements. (Note: We don't recommend plastic windows.)
When ordering new windows, do a perimeter measurement and two diagonal measurements. (See the bottom of this page for an example: www.bomon.com/replacement.htm)
We have had good results with full-length spray rails for the Sisu round chine boats - this gives extra stability at higher speeds, while maintaining the smooth ride.