Jump to content

Is it necessary to black the bottom?


Featured Posts

Had my boat blacked recently,but not the bottom,because the man said it would soon be scraped off and anyway the bottom won't rust because of lack of oxygen under the boat. This sounds to me like a load of horse manure,and I think he was trying to avoid crawling underneath and getting a faceful of bitumen.

Am I right? or is the man correct?  I welcome any input.

Link to post
Share on other sites

We always try and black ours, as its 6mm plate, and the boat is getting on in years. 

If we had thicker plate, we may find it less of a concern. Definitely worth it imo if you can be bothered and find somewhere with decent access to the baseplate.

 

Link to post
Share on other sites

He is correct about the scraping but the worst corrosion (galvanic )doesn't need bubbles around to rot your boat. 

It is difficult doing baseplates,  not many yards get boats up high enough (especially if a dry dock), and you still have a strip where the boat is supported left unblacked

Link to post
Share on other sites
15 minutes ago, Furness said:

Had my boat blacked recently,but not the bottom,because the man said it would soon be scraped off and anyway the bottom won't rust because of lack of oxygen under the boat. This sounds to me like a load of horse manure,and I think he was trying to avoid crawling underneath and getting a faceful of bitumen.

Am I right? or is the man correct?  I welcome any input.

The vast majority of boats aren't blacked on the bottom.

There is truth in what the man says but if blacking the bottom was as easy as doing the sides then I suspect it would be routinely done. It's better if you can do it but not a major issue if you can't.

JP

Link to post
Share on other sites
36 minutes ago, Furness said:

Had my boat blacked recently,but not the bottom,because the man said it would soon be scraped off and anyway the bottom won't rust because of lack of oxygen under the boat. This sounds to me like a load of horse manure,and I think he was trying to avoid crawling underneath and getting a faceful of bitumen.

Am I right? or is the man correct?  I welcome any input.

Has been discussed recently:

 

Tim

Link to post
Share on other sites
24 minutes ago, Tony Brooks said:

and if there is any electrical corrosion it will be  concentrated on the un-blacked strips.

Thanks folks.Had a look at brassedoff' thread and this and other replies have covered the subject nicely.

This Grasshopper has much to learn and this forum is wonderful for bringing enlightenment and illumination.:rolleyes:

Link to post
Share on other sites
7 minutes ago, David Schweizer said:

Our old boat was 39 years old when it had it's last survey, and the worst pitting the surveyor could find was 0.5mm on a 10mm bottom plate. and it had never been blacked.

We always black the bottom of Fulbourne, it is 81 years old and still has it’s original bottom!

Tim

Link to post
Share on other sites
8 minutes ago, Tim Lewis said:

We always black the bottom of Fulbourne, it is 81 years old and still has it’s original bottom!

Tim

What you will never know is would it have survived as well without blacking, I doubt that the bottom even got looked at during it's first 25 years or so, with the GUCCC and BW.  I suspect that one of the reasons why so many older boats still bave bottom plates in good condition is patrtially due to the quality of steel, and the absence of 240v electrics.

  • Happy 1
Link to post
Share on other sites
1 hour ago, Tim Lewis said:

We always black the bottom of Fulbourne, it is 81 years old and still has it’s original bottom!

Tim

I'm getting on for that age, and I still have a peachy bottom, the same one I wuz born with.

Link to post
Share on other sites
2 hours ago, Furness said:

This sounds to me like a load of horse manure,and I think he was trying to avoid crawling underneath and getting a faceful of bitumen.

 

Perhaps, but then in doing so he also turned away money making business as you would have had to reward him handsomely!

I think there's some truth in what he says and, with the usual 6mm sides and 10mm baseplate, you do have an extra 4mm of steel to substitute for blacking! ;)

Link to post
Share on other sites
2 hours ago, Bee said:

Iron, steel or any other ferric alloy + water + oxygen = corrosion. Paint everything that will get all three  

Fixed that for you. 

Edited by WotEver
Pedants ;)
Link to post
Share on other sites
On 01/03/2018 at 19:00, TheBiscuits said:

Cast iron would be OK then?

Apart from being very brittle cast iron can become porous. Seen quite a few big old gas mains with gas microbubbles emerging when sprayed with water/soap.

Bits of the alloy can corrode leaving just a leaking matrix.

 

Edited by mark99
Link to post
Share on other sites
On 01/03/2018 at 10:57, David Schweizer said:

What you will never know is would it have survived as well without blacking, I doubt that the bottom even got looked at during it's first 25 years or so, with the GUCCC and BW.  I suspect that one of the reasons why so many older boats still bave bottom plates in good condition is patrtially due to the quality of steel, and the absence of 240v electrics.

If mains electrical systems on boats are properly isolated then having 240v onboard shouldn't be a reason for corrosion. Are there really many steel boats still sitting in marinas hooked to shore power without any form of isolation?

Edit: Actually I knew a bloke in the marina at Brentford whose form of isolation was deliberately not to bond his mains earth to his steel hull! But that's a whole "nuther" can of worms. 

Edited by blackrose
Link to post
Share on other sites
3 minutes ago, blackrose said:

If mains electrical systems on boats are properly isolated then having 240v onboard shouldn't be a reason for corrosion. Are there really many steel boats still sitting in marinas hooked to shore power without any form of isolation?

Less than there used to be ...

  • Haha 1
Link to post
Share on other sites

I spoke to a bloke years ago when I had a lumpy water boat and fitting new anodes as they were nearly all gone and he said he paints his and they last for years, I just told him to carry on if you think saving a few quid on anodes outweighs new stern gear, still don't think he got it.

Neil

Link to post
Share on other sites
  • 2 weeks later...

Funny one really  I always epoxy everything under the waterline. I have just spent the morning rotoblasting and epoxying the baseplate of our new  second hand widebeam.  Given that it is 10 years old and doesn't appear to have ever been blacked "down there"  I am quite surprised at how shallow the pits are.  Most of the corrosion is galvanic (electricity corrosion) which isn't surprising as it seems to have been fitted with every type of gizmo available (still not sure if a full size freezer is actually necessary) my first narrowboat (a lovely old dartline) had no worse pitting despite being 25 at the time.  But the most sophisticated gizmo on that boat was a gas hob.

I suppose the answer is  paint it unless you want to spend a Sunday in the year 2028 waving a grinder around near to your face whilst laying on your back in a puddle.

Link to post
Share on other sites

This was the bottom of Harnser when I was in Middlewich dry dock last autumn, I put the camera under the boat not my head. The boat was blacked underneath by Fox's on the ML back in April 2012 and they only use long handle rollers to do it. The interesting point is I have anodes half way down the sides of the hull and they line up where the bostock is and you can see a difference in the bottom in that area. You can also see how much of that black has been scraped off in five and a half years.

DSCF9650small.jpg

DSCF9649small.jpg

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.