Hi all.
I am thinking about diving below my boat for the first time and giving it a bit of a hull clean as I am unable to get it out of the water at the moment.
I haven't had a in water clean/scrape before but thinking of doing it myself.
My question is, I am assuming that giving it a clean will remove any of the current antifoul that is on there and therefor really shorten the time until I need to haul it out.
Also, how long would I expect to get out of a in water hull clean? 1 or 2 months before the growth builds up again?
Thank you.
Bit difficult to answer as many unknowns in this including how long since slipped and the afouling type you have. In short (have done this off and on for 35+years) expect you will need a stainless scraper blade - round the 2 corners with 10mm radius to avoid digging in and damaging the gelcoat - to remove the small barnacles followed by scrubbing with one of those scourer pads - Whitworths sell them but you probably have one already. Expect the remaining current afouling won't be removed - just a bit of it depending if it is a hard type or softer ablative type. You will see plumes of afouling residue in the water after you scrape and scrub. So you will expose fresher afouling. Sounds like beneficial to do depends when you are going to slip next. Should get around a few weeks before slime starts, 1-2 months before small barnacles re-appear. Also depends on brackish water issues and if your yacht is in a good tidal flow area. Sorry if long winded and vague.
If you are in a strong tidal flow the shell will grow fast. If you have plenty of sunlight it will grow faster still!
Having some method of holding yourself to the hull while you apply pressure with the scraper is also important. Either one of the sucker grips that most chandleries sell or a taut rope under the hull would work.
My question is, I am assuming that giving it a clean will remove any of the current antifoul that is on there and therefor really shorten the time until I need to haul it out. (1)
Also, how long would I expect to get out of a in water hull clean? 1 or 2 months before the growth builds up again? (2)
Thank you.
That's two questions.
1, If you have barnacles, you will need to scrape and as the barnacles fall off they will take the antifoul with them.
If just a few, you will have a few spots. If many you will have large patches. If you don't have many barnacles, but mostly weed and slime, I suggest a kitchen scouring glove. This is a type of glove that has like a scouring pad on one side. Wipe off the slime and weed. If the antifoul wipes off down to the gelcoat or hull you have shortened the time to haulout.
2. The length of time really depend on how old your antifoul is now. 2 years is a pretty good stretch. After that it has NO EFFECT and scrubbing is just putting off the inevitable. As you have said 1 or 2 months and you will be foul again.
The other thing to consider is the condition of the propeller. A few barnacles there can make a hell of a difference.
So, dive under and have a look. Then you will see what you are up against.
gary
Yes what he said. Go for quick recce dive first & check it out. Cleaning a heavily fouled hull in water (even with scuba gear) is hard work. And potentially dangerous. And may get you in trouble with causing water pollution. Only dive under the hull in good light. Have a dive buddy on board the yacht to make sure you are OK & keep coming back to surface . Not sitting with head phones on drinking beer!! 
Aim for slack tides. Wear gloves - riggers gloves are good. And a wetsuit. And fins. You will leave some of blood in the water. Big bucket of fresh water for rinse after is desirable, and maybe a 1st aid kit for all the scrapes & cuts. Do you know if you have hard or soft (ablative) AF? Hard stuff will tolerate a bit of scraping. Soft stuff - well you are rubbing away what keeps marine life at bay. Scraper - I prefer to use those hard plastic paint scrapers rather than metal scrapers. A good stiff scrubbing brush (plastic or natural bristles) with a handle is also good. You will need to have ties on them, or a basket hanging above the water to store them.
In terms of bang for your buck (dives), do the hull in the following order:
* Prop
* Rudder
* Water line (ie what you can reach while still on the surface) - easy with just a mask & snorkel.
* Everything else.
Have a bottle of rum handy for when you are finished. We call it "dive rum". Take several swigs straight from the bottle when you are finished in the water. The bottle of dive rum should be stored with the boat cleaning gear so it looks suitably manky.
Good luck! 
And weight belt and ankle weights, or you will use all your energy just trying to stay down there and not float up.
Just out of curiosity, how much (roughly) would it cost to hire someone to do it?
Say on a 30 footer?
It's been a few years since I last had to have a diver to it - we sold our yacht a while back. I'm sure it was under $100 for our 36' ocean racer. But that's in a marina with good diver access, and a well maintained hull (ie: more of a wipe than a scrape...)
Typically the diver (its good to know who they are) will organise to do a whole bunch of boats at the same time, for obvious reasons, so it pays to be flexible with your timing and access. 
We always maintained our yacht in top order, I - with occasional crew help - typically cleaned the hull when required, and we only contracted a diver in special circumstances.
Be mindful of who you use as there is a bit more to it than just hacking at the hull.... 
Select to expand quoteMike367 said..
Just out of curiosity, how much (roughly) would it cost to hire someone to do it?
Say on a 30 footer?
Depends a lot on location of boat etc. Six months ago I was quoted $280 to do my 6.5 metre which is in a marina pen. I queried price knowing what daughters 43footer cost to be told it takes the same time to suit up etc irrespective of size . Got it done for under $80 by teaming up with boat next to mine.
I used a hardwood scraper I made up. 5x2x7cm with one edge cut at 45? This was screwed to a short broomstick about 70cm long. I was able to get most of the barnacles and weed off from the dinghy. I could probably reach nearly to the first meter under the boat. The handle keeps your hand well away from being scratched. The wooden scraper is pretty gentle on the antifoul.
Select to expand quotejohn24 said..
I used a hardwood scraper I made up. 5x2x7cm with one edge cut at 45? This was screwed to a short broomstick about 70cm long. I was able to get most of the barnacles and weed off from the dinghy. I could probably reach nearly to the first meter under the boat. The handle keeps your hand well away from being scratched. The wooden scraper is pretty gentle on the antifoul.
If you use a longer handle and tape a plastic drink bottle to the back near the scraper you will get more pressure upwards.
Select to expand quotewoko said..
And don't forget the 50/50 mix of isopropyl & vinegar to clean ya ears with
Woko, what does this mixture do? Shampoo and soap in the shower will rinse everything and remove/dissolve light oils and surfactants, but will the IPA and vinegar kill the bacteria/protozoa etc? Is that the reason, that it will kill any nasties inside the ear canal?
I fashioned ie. bent the alloy handle as per photo and attach a marine brush per photo. I give the hull a brush once a fortnight and interchange the broom head with a plastic spatula every month or so .
Select to expand quoteFabulousPhill said..woko said..
And don't forget the 50/50 mix of isopropyl & vinegar to clean ya ears with
Woko, what does this mixture do? Shampoo and soap in the shower will rinse everything and remove/dissolve light oils and surfactants, but will the IPA and vinegar kill the bacteria/protozoa etc? Is that the reason, that it will kill any nasties inside the ear canal?
A few drops on each ear does two things one it changes the surface tension I think it's referred to so the water is free to escape the ear canal, you know without all that hopping around while belting your melon about cocked sideways, and yes it kills nasties too boot
I use ear plugs to keep the greeblies infecting the ears.
Our 36'er can be cleaned fairly comfortably in two sessions if it has heavy weed and a few light barnacles. We have semi hard racing which is fantastic in terms of stopping bad fouling if you give it an occasional scrub, which hasn't been that easy the last few years.
Another albeit more expensive option is The Keelcrab - keelcrab.com/en/
Interesting promises but haven't seen one in operation.
If you're around port hacking I can clean for you as I'm back in the water from next week after some pretty nasty busted bones etc. Based in Gunnamatta Bay.
