A .htm or html file is a file that is HyperText Markup Language. The language used to describe a web page.
If you goto the results page of the Sailwave site https://www.sailwave.com/results/ you will see a lot that have been uploaded by users.
Choose one of these and click on it and the results will be displayed in your browser.
then right-click on the displayed page and select Save as
This will download the file to your computer. Now open Windows Explorer and navigate to the file you downloaded and double click it.
It should open this in your default browser. Let us know what happens.