Extending slipping from 1 to 2 years and maybe more..........longest I did in prior yachts was 7 years but there was a lot of diving and scraping back then.
The normal waterline area fouling - ie waterline to (say) 75mm above it - is worst in the last metre to the stern where the typical black algae builds up underneath where no sunlight reaches. For the rest of the length it still builds up but slower, and is green.
Has anyone successfully used a hand squeeze trigger pump one litre type spray on liquid to remove this. The web throws up Starbrite and Boat Brite and numerous others - the videos mainly show small stink boats out of the water on their trailers with stuff all fouling on them rather a bit of slime which surely would come off with the garden hose and a scotchbrite scrubber.
So I haven't got cms of growth but scrubbing it with a stiff broom from the dinghy doesn't do much to it - the broom works well on the underwater hull surface sludge.
Was planning to try Exit Mould but this might not be environmentally legal.
Thanks.

I use Metal Gleam from Nowra chemicals. Mixed 5:1. It's basically phosphoric acid with other stuff added. I usually just do the whole hull slopping on with a soft broom from the dinghy. Leave it for a minute or so and bucket salt water over to rinse off. I have also done the waterline area around the stern snorkeling or just treading water with a mixture of Metal Gleam floating in an icecream container and a sponge/scourer pad, splashing the water to rinse off. It's harmless to bare skin but protect your eyes hence the goggles. Caution, the stuff running down will alter the antifoul colour. A squeeze bottle might be even a better way to apply. 5 litres is about $38 and should last a few years, even if you use it regularly to descale your diesel.

Thanks Ramona will give that some consideration.

I suggest you all check with your local regulations. In South Australia doing anything like this is prohibited under the Environment Protection (Water Quality) Policy. This is from the potential non target impact, however the much bigger issue is ignoring the fact that antifoulant coatings have limitations in terms of lifespan. Trying to extend their lifespan comes with many significant risks. Marine invasive species are moved through coastal areas by recreational boats, including yachts. Trying to extend the life of your antifoulant coating will increase the risk of transporting invasive species. There is evidence to suggest that recent incursion of pacific oyster mortality syndrome (POMS) into Tasmania was through a recreational boat and this has had massive financial ramifications on the industry and provided a foothold where it can then travel further including now into South Australia.

I have also personally seen the translocation of the European Fan worm into Kangaroo Island from a recreational yacht due to the poor condition of their antifoul.

These invasive species can devastate the beautiful locations we all go to with our yachts and try to catch fish from, snorkel in and enjoy. If you want to extend the life of your antifoul get in the water and do a full hull scrub regularly. Otherwise pay the money and renew your coating.

I understood the poster was talking about the hull just above the antifoul and below the boot line.
I also use oxalic acid once every six months with a soft haired broom and just fresh water broom monthly

Oxalic Acid pretty safe for the enviroment in my opinion
archive.epa.gov/pesticides/reregistration/web/pdf/4070fact.pdf
Environmental Assessment Environmental Fate EPA relied on data available in the scientific literature to assess the environmental fate and transport of oxalic acid used as a pesticide. Oxalic acid occurs widely in nature--it is present in the tissues of many plants and algae, serving both to excrete and store calcium. In water, its negative ion forms complexes with a number of metal ions; and oxalic acid is immobilized as a result of this formation of complexes. Both aerobic and anaerobic conditions biodegrade oxalic acid in less than one day

Thanks all I will explore oxalic acid obviously reasonably and sparingly.

Just found this for $15 at the big green shed so will give it a go and report back. It has excellent reviews. If it works will get the refill. Made in Canada..........

www.bunnings.com.au/concrobium-946ml-mould-cleaner_p4460772

www.bunnings.com.au/concrobium-3-78l-mould-cleaner-refill-jug_p4460773

www.concrobium.com/en-au/products/mould-control-spray/

r13 said..
Just found this for $15 at the big green shed so will give it a go and report back. It has excellent reviews. If it works will get the refill. Made in Canada..........

www.bunnings.com.au/concrobium-946ml-mould-cleaner_p4460772

www.bunnings.com.au/concrobium-3-78l-mould-cleaner-refill-jug_p4460773

www.concrobium.com/en-au/products/mould-control-spray/

I sprayed it on my roll-up dingy to stop mould and it worked great,,, so I then sprayed it over the underside s of the V berth mattresses and it seems to be doing its job.
So I went back and bought their other product to remove moulds stains.
I was pretty impressed with way the preventer worked on the dingy though.

The other solution suggested to me (instead of raising the boot line) was to use white antifoul on the original white gel coat strip between the (black) antifoul (up to the waterline) and the normal painted red boot line. Thus I've now got Pettit Vivid White (an antifoul) between the (black) waterline and the normal red boot line. More labour, but it works well without changing the apparent length/freeboard of the boat. You still have to rub the slime off (gently so as not to remove too much white antifoul) after a few months, but that's easy.

we use international tri lux as it is an aloy antifoul no copper so stays white