I tried something similar a very long time ago with a small USB WiFi stick and seem to remember that it did help a bit. I also tried various other designs of "Cantenna" type (Pringles style tube) and they also helped. I seem to remember that they weren't much use on the boat as they are highly directional (if they weren't then they wouldn't be worth using). So not suited to a boat at anchor.
However, that was a very long time ago (probably around 10 years) and I gave up with these when the original Alfa AWUS036H came out. It often gives up to 5mn range and I usually use it with the power wicked down to 10%.
You could try playing around with these DIY items but I think that the price of a decent booster is so low that it isn't really worthwhile. I suspect you'd get one for ~£25.