Newbie question - bottom scraping

sgr143

sgr143

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In this my first year of boat ownership, I'm finding all kinds of things where I'm aware of the general principle, but utterly ignorant of the nitty-gritty detail. In this case, cleaning the grot off the underside of a hauled out boat and preparing it for antifouling... And even doing the antifouling, come to that.

Our Westerly Merlin was in the water when we bought her early this year, and has been in the water ever since. Slower and slower sailing, and inspection with wetsuit and snorkel, has shown an impressive and dismaying growth of weed down below. So fun times ahead when she is hauled out this week.

Questions : what tools does one use for cleaning up? Scrapers , wire brushes, sandpaper, power tools? How do you know when to stop? Is it OK to paint the antifouling on this side of winter, or wait till just before launching ?

If there's some publication that tells all about this (I've not seen one so far) then a pointer would be appreciated, as would any advice. Apologies for asking what to most of you will be the b'ing obvious... as I hope it will be to me once I've done it a few times : but that's not where I am right now!

Ta, Steve
 
arrange to have the boat power washed as soon as she is out of the water. The marine life is much easier to remove if it is 'fresh', and the washdown will then enable you to see if there's a build up of old barnacles which need hacking off with a draw scraper or oscillating tool.

I'd leave the hull cleaned up over winter, and apply AF before launch. You may wish to consider an epoxy primer such as Jotun's Vinyguard if you really clean the hull and blast off most of previous AF coats. If you are intent on keeping the boat for a long time, then remove all old AF and start with a primer, which you can then leave till you apply the AF.

If you are doing the water blasting yourself, you need to be aware of environmental issues and the need for PPE.


Is the yard propping the boat on logs and wedges, or do you have a cradle ? With the latter it is easier to remove a prop and clean/paint underneath it, by adding a temporary prop nearby. I really dislike removing wooden props one at a time.
 
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Be really careful if removing props - most yards are very very nervous of owners doing this. The usual MO seems to be yard will pressure wash on lift and chock off. You paint and the patches are dealt with whilst the boat is in the slings waiting to be launched. Speak to the yard. If you leave them a tin and brush they may well do it for you as part of the relaunch. Even if they charge you £50 to do it, it may be cheaper than driving down specially to do a 20 minute job.

Sarabande has given good advice if stripping it all off.

Advice if not stripping it all is to remove any loose flakes / remaining bits of growth with a handscraper. If you go back to bare GRP anywhere then you will need a couple of coats of something like Primocon on any bare patches, giving the bare GRP a quick rub with wet and dry first to provide a key.

Do you know what AF you will be painting over? Or what you will be applying? If you're not sure of the surface, you will need more primocon before sloshing on the AF.

Most cruisers seem to go for eroding paints which don't really need rubbing off every year. If you have a hard AF ( and are applying another hard AF) then you should really rub back to limit the build up of old AF on the hull. It's still a good idea with eroding AF but not really needed and most only seem to give it a token effort unlike the racers who will be fairing the AF like there is no tomorrow. I've not seen a publication as such but most of the AF manufacturers do provide good guidance but it's not rocket science - get a good surface, apply paint in accordance with the instructions on the tin.

Re A/F now. You can do it now - just look at maximum immersion times for whatever AF you choose and stick to it.
 
Thanks both - The deal at Wicor is that they pressure-wash on lift-out, so that should be a good start. The boat is bilge-keeled, so I don't have to worry about props and pads. I don't know what type of AF was previously applied, so I'll just have to have a look and see. Is there any way I can distinguish between hard and eroding previous coats? Also (really daft question!) when I'm scraping / rubbing off the old stuff, how do I know when to stop?
Steve
 
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You can stop as soon as you've got rid of any remaining fouling and any flaking AF. If there is a very uneven build up of old AF, you may want to scrape the thicker aggregations to achieve an overall smoother finish. Ideally avoid getting down to the bare hull but when i have done this in small patches, I haven't bothered with primers and the new AF has adhered fine.
 
Forgot to add that you want to protect yourself from any AF dust when you are scraping - it can cause skin irritation.
 
And be careful about sanding antifouling - it's apparently much more toxic to humans than the little *****ers it's supposed to deter - I and others have been made seriously ill, sensitised to the stuff, so do wear a dust mask.
 
The OP is right that there are many matters to do with cruising that seem straightforward until you get to the point of having to decide what method to use. The bottom will either be smooth, in which case a wet scrub with something like a Scotch pad is all that is needed, or it is rough and uneven with a lot of built-up A/F. In that case, I would be tempted to do the least necessary this year and plan for a full strip next year. I would start by going round with an ordinary scraper to remove flaking bits and bodging up the rest as described above. You will know when you have done enough because of a change of colour, though that might be a change of antifouling. You may also need to give attention to the iron keels, which will probably have areas of rust. There are ways of dealing with this and it has often been discussed here. The difference in speed between a smooth bottom and one that is a bit rough is not great, and much less than that caused by fouling.
 
Seajet said:
And be careful about sanding antifouling - it's apparently much more toxic to humans than the little *****ers it's supposed to deter - I and others have been made seriously ill, sensitised to the stuff, so do wear a dust mask.
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DO NOT DRY SAND ANTIFOULING.

Even if you are committed to the idea of suicide, those downwind may not be.

If it's coming off then use a chemical stripper specially for AF or dry scrape. Sanding should only be done by wet and dry.

A way to tell if it's eroding or not? Not really - GENERALLY an eroding one will be much easier to remove and you may get some off with a wet sponge as the sponge erodes it. It can also usually be rubbed off as a powder by your hands. That said - colour from hard can come off with a wet sponge, especially if it's been sanded so I wouldn't rely on those methods,

Best bet is to ask the former owner as even if you correctly diagnose it as eroding, then do you know which brand? Will your chosen brand be compatible? And we haven't even started on the slippery ones that CLAIM minimise fouling by being too slippery for weed etc to grow on by using Teflon etc.

As for removing old coats - if the previous colour ( or bare hull) is showing through then you've gone plenty far enough! All you're looking to do is to remove loose material to give a sound base for the new AF to adhere to. It's also a good idea to help minimise build up of AF if you can but don't go to town with it. Especially with eroding AF as the material is still good at doing it's job the whole way through so why sand off perfectly good AF to just replace with more? Hard AF is only good on the surface though so you may as well take it off if you have the patience.

When she does come out, have a look at where the additional wear is. You may find that the AF has eroded in certain areas - usually waterline, leading edge of the keel, rudder etc. Get an extra coat on those areas if you can. It makes tracking high wear areas if you use a different colour for alternate coats but you can end up with a blotchy bottom as the season progresses.
 
Steve

You don't say if you had a survey prior to purchase but if not you might want to look at the areas of rust around the join between the keels and the hull. In my experience on a fin keel the keel always showed signs of rusting and so that was area where the AF was most unstable and required scrapping and coating with eg Fertan plus a primer before re antifouling. I am sure though if you post on Westerly forum members there might have more specific on what to look for on a Merlin and when to have hull completed scrapped . What you tend to find is small patches of AF will in time drop off requiring repriming and filling if you wish but generally most AF stays stuck on so any need for wet (of course) sanding hull once sprayed down by yard is minimal. Our worst part is the line between the AF and the unpainted hull which can take time to clean and tape up. In the original days of Centaurs the AF was applied prior to launch but I suspect that might have been down to products used.
 
sgr143 said:
Is there any way I can distinguish between hard and eroding previous coats? Also (really daft question!) when I'm scraping / rubbing off the old stuff, how do I know when to stop?
Steve
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Easy to spot self-eroding anti-foul. Get a tough scourer and make sure the patch you're working on is well wet, a bit of scouring should be effective in dissolving the anti-foul in water. Wipe off with a sponge and rinse the hull.

Stop when you get to the gel coat or an epoxy layer - epoxy paint is hard to sand even (as I found out long-boarding a racer that had had the patches epoxy painted), gel coat is much softer, so take care not to scrape/scratch it too much.

One tip, if you do find thick layers of old anti-foul flaking off in patches, don't use filler on it - previous owner of my boat did. We eneded up spending six weeks going back to the bare hull because of it.

Another: if you find barnacles, they'll come off readily with a large flat bladed screwdriver without you needing to use much force, but they'll leave rings on the hull. Limescale remover will get rid of that - I just brush it on regularly until they're gone. Obviously, be careful near anything metallic, especially the prop or skin fittings.
 
I'll leave the niceties of scrapers and scraping techniques to others. My own view is that if you have to do this in winter and relaunch then best do as little as possible before anti-fouling, saving more serious treatment for better weather. If you have patches of bare gelcoat you could patch that up with Gelshield 200 but you'll need 5 coats with 5-10 hours between each; don't skimp this or you could solvent trapped which is generally held to be a bad thing. Also if the gelcoat is damaged you'll need to put something between the laminate and the Gelshield e.g epoxy filler. (Also make sure hull is dry before applying primer or could get moisture trapped - also a bad thing.) The annoying thing is that if you leave the epoxy primer more than a few days (well true for gelshield) you'll have to abrade it before applying anti-foul. I've also been advised to wash any new epoxy primed areas with washing up liquid before overpainting and drying to remove surface oil. Applying Primocon over whatever is a good idea - sticks to anything and has no overcoating time limit
 
Wicor will do a good job power washing when she comes out then block off. I've always left a tin of AF and a brush and they will touch up the bits once she is ready to be launched.
Good advice can be had there from resident engineer Rob Pope.

Derek
 
As others have said dry sanding antifouling is dangerous. Wet sand with 80 grit.

TOP TIP Buy a drwall sanding head like this and use with a 6 ft pole. It dramatically reduces the time and effort required to do a god sanding job.
drywall_pole_sander-300x261.jpg

If the antifouling build up is thick lumpy and flaking off paying a professional to soda blast it off is a GOOD INVESTMENT.

I find the best tool for removing barnacle feet is a sharp 1 in chisel with the edges rounded off with a file.

If during the year you have some fouling dry out and use the dry wall head on the pole with some green scrubbing mesh. Use gently you don't want to scrub off the liquid gold you painted on your bottom.

Do all the prep work and wait till spring before applying the A/F.
 
Thanks everyone for your advice... Really helpful and we now have a much better idea of the possibilities. I'll go and have a look in a week or so when I know the haul-out has been done. I'll make a list of other jobs to do so that if all I can do is look and go "ummm...", I can still have a useful day (it's about a 90 minute drive). I might take a few photos for your amusement and knowledgeable judgement.
Steve
 
Well done on getting in the water with wet suit. You should have given it a scrape down at the same time. I use a paint scraper (putty knife) and scotch bright pad. If you clean in water enough you can end up with much less scraping to do out of the water.
Sanding or scraping down the build up of antifouling paint (wet) is a terrible job. You start off with good intentions but end up giving up long before you do as much as you hope to do. don't be too dismayed about that. At worst you can slap on more a/f with little preparation or spend a lot of time and effort getting it perfect. A bad job only lasts till next lift out and in the long run enjoyment of the boat in service is the final aim. So for a new boat to you just do as much prep as you can then move on.
Most a/f makers say launch within 24 hrs of application. However I don't believe this is really critical as I have done up to 3 months ahead or relaunch. Application of a/f is easiest with a roller but inevitably with brush for the tricky bits.
Good luck with the new boat olewill
 
William_H said:
Well done on getting in the water with wet suit. You should have given it a scrape down at the same time.....
Good luck with the new boat olewill
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I did have quite a go at it on two successive weeks: mostly clearing up the prop and rudder. The first time round the prop was almost invisible! I came to the conclusion though, that the hull below water was too badly fouled for in-aqua attempts to have much effect - as the boat's continued sluggishness demonstrated. Had it been mid season, I would have grounded her for a scrub down, but with only a few weeks left till liftout, I thought I might as well leave it till then.

It's certainly been a year of learning... I hope next year will be more one of sailing!

Steve
 
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