The first thing to note is that when Sailwave uploads results to the internet is does not upload your burgees as well. That is something you have to do yourself as a once only operation.
Once you have done that and you are pretty much always online, you can use absolute URLs in Setup+SeriesProperties to point at your burgees. They will work locally and when uploaded. For example http://myclubsite.com/images/clubburgee.jpg. Using absolute URLs like this also means the results is display corrently if also uploaded to say the Sailwave results folder. This is the preferred method.
If you are not always online you can use an alternative strategy. Put a copy of the burgees in the same folder as the Sailwave file and refer to the burgee by name in Setup+SeriesProperties. For example clubburgee.jpg. That will get the burgees showing locally, but when you upload the results to the web they will not show. To resolve that upload the burgee to the same folder that the results are in.
If you don’t want lots of burgees floating around because you use sub-folders for each year’s results say, put the burgee in the folder that contains the series sub-folders (locally and on the web) and refer to the burgee relatively in Setup+SeriesProperties. For example ../clubburgee.jpg.
If you use an absolute path to the burgee locally (e.g. c:\myimages\clubburgee.jpg) be aware that the burgee will not show when uploaded.