TLDR; 20% muriatic/hydrochloric acid dissolves barnacle rings from HDPE with no apparent damage
For those fighting with barnacles on a Hobie Wave, Getaway / rotomolded cross-linked high-density polyethylene / HDPE which is what I understand these boats are made of,
I bought a 2002 Hobie Getaway and the previous owner left it on a mooring for a couple of months and it got covered in barnacles ( ps don't do that ).
He said they would just pop off and it would be easy with a plastic scraper......I tested one before I bought it and it did seem to come off pretty easy....but in my excitement to buy this awesome boat....I failed to notice that it left behind a small ring of cement like calcium carbonate. This is the natural glue these monsters produce to stick to anything....and its like scraping cement....
I tried (in a small area) to use a hard plastic ski scraper and that works but it scratches up the hull, dulling the finish and is a crazy amount of work so that is not a good solution (going to try and restore that scratched area with high grit wet sanding but have not done that yet...will do a follow up post).
After some research on chemical compatibility ( here is a chart
https://www.calpaclab.com/chemical-comp ... ty-charts/ ) and contacting Hobie to ask the question ( have not heard back yet)
<-(update a Hobie tech replied and said that 20% hydrochloric acid should not hurt the polyethylene hulls) I tested a small area with 20% muriatic / hydrochloric acid that you can buy at home depot / amazon etc. After repeated applications with a polyester rag and leaving on for about 1/2 hour each time and some mild rubbing.. this dissolves the barnacle rings completely leaving the surface clean and shiny without any apparent damage to the hulls. This seems to be the best way to go..e.g. knock off the larger part of the barnacle with a power washer on an angle....then remove any rings with 20% muriatic/hydrochloric acid by applying it liberally with a cloth, letting it sit for 1/2 hour and dissolve the rings and then rubbing it with a cloth/ more muria.
Important: Make sure to wear longs selves, pant and rubber boots, a resperator / mask, eye / face protection and rubber gloves as this stuff will burn your skin, eyes and the vapors are dangerous to your lungs.
best to do it outside in a well-ventalated area.