I've seen many anecdotal reports. The problems with these, no matter how well intentioned, is that they are not controlled:
* The person cleaned the boat, fixed some leaks, and sure enough, the mildew is gone.
* The odor wasn't mildew; it was the head, bilge, or some other source. The tea tree oil did make the odor go, which has value, but is not the same thing.
* I've read EPA and other studies that suggest that even dirrect liquid application of dilluted oil may have limitied effectivness and only create resistant bugs.
I've done some controlled testing, and if there is an affect, it must be subtle. My conditions my be too severe, while on the other hand I am using a smallish container that would consentrate the vapors (you wouldn't enjoy breathing it for long). Some sprayed liquid products are working very well (Concrobium--a TSP/baking soda/washing soda blend, washing soda/borax blend, other comercial anti-mold).
I find myself suspecting that anything that is strong enough to work will not be something you can live with, like mothballs (even before we learned they were toxic... which we always suspected). Additionally, we actively vent boats to control reduce moisture, removing any vapors. Nice smelling perhaps, but not actually a bio-stat. Clever marketing, but successful because actual performance is difficult to measure? Spray-applied products have been proven.
Please share anything quanititative and controled.
At the risk of sounding smug, because I enjoy your posts and think they are usually very relevant, I have to ask is your statement/ question of us amateurs who have provided the anecdotal evidence, to provide detailed quantitative and controlled evidence another way of saying indirectly we are just the dupes of a cleaver marketing scheme.
I would suggest you ask this question to the makers of Kanaberra gell or tree oils for instance and report back on what you find. I bet they have quantitative and a qualitative analysis done. You will do us all a great service in disproving or arguing for against its effects.
All I can tell you that I have used this product for 4 years now, and it APPEARS
to have a positive effect on our boat. I believe my answer will be the same as others who use the product. Others have often commented on their experiences also, although not done as a test study constitute and preponderance of anecdotal evidence that it is having a positive affect on their boats also. To me its not like being on trial for murder and it doesn't have to be proven within a shadow of doubt.
Until then feel free not to use it until proven to you beyond a shadow of doubt or until you can prove them to me just a mere marketing scheme.