Couple of questions: counter and weed hatch.

[Ricco1]

My boat is 10mm bottom, 6mm sides. The counter plate is 6mm. Leads to my first question: is it normal to build the counter plate from the thinner steel rather than the same as the bottom?

 

Now my weed hatch: it's built from 3mm steel, or it could be 4. This seems ridiculously thin to me. The bottom part of it is submerged so why isn't it made from at least 6mm steel? Feeling inside the hatch it's quite badly pitted, below the waterline. I guess there's only 1 or 2mm of good steel left so at some stage it will need to be repaired.

 

Regarding the repair: I think it might be possible to do the work without removing the boat from the water. Sections of steel could possibly be welded to the counter, outside the weed hatch rather than in the water, effectively overplating the existing hatch. Then, if the existing weed hatch does rot through there's a brand new one ready to receive the water.

 

Would the above be good practice?

 

Many thanks for any replies.

[Bloomsberry]

Trouble is , once the original hatch has rotted through and you're relying on the new hatch, the original hatch will prevent you from treating the new hatch surface (if that makes sense).

 

I assume the boat will be coming out of the water at some stage in the future, couldn't you plan to replace the hatch metal then ?

[Ricco1]

Fair point. My thinking was that if I used 6mm steel for the overplate hatch it would have a very long lifespan, even if not treated. Hell, it's such a small amount of metal that even 10mm would only be a few quid.

[Bloomsberry]

I don't know much about welding but I would have thought the weld would be the weakest and thinest part of the structure as it can only be done from one side and would be inconsistent ?

 

To weld the foot of the new hatch would mean the metal to be welded to would be the counter and have canal water on the other side of it which would reduce how hot the metal surface could get and may compromise the weld ? But like I say I know little about welding so may be talking rubbish. And I've had a drink tonight. Hick !

Edited June 4, 2016 by Bloomsberry

[Claude]

By overplating the hatch on the wrong side (underplating), you're effectively creating a corrosion point between the two plates that you can do nothing about when the thin one on the water side eventually rots through.

 

Ideally a counter or uxter plate should be made of the same thickness of steel as the baseplate, but mine isn't. The baseplate is 10mm and the uxter is only 6mm. Then again 6mm used to be the standard thickness for baseplates. So assuming it's in reasonable condition and as long as you keep it painted it shouldn't be a problem.

Edited June 4, 2016 by Claude

[RubyTuesday]

I don't know much about welding but I would have thought the weld would be the weakest and thinest part of the structure as it can only be done from one side and would be inconsistent ?

 

To weld the foot of the new hatch would mean the metal to be welded to would be the counter and have canal water on the other side of it which would reduce how hot the metal surface could get and may compromise the weld ? But like I say I know little about welding so may be talking rubbish. And I've had a drink tonight. Hick !

It's all down to how good the person welding is, theory goes a wed with 100% penetration should be as strong as the metal. The problem is that that sort of quality weld rarely happens. You can all make your own minds up as to why.

 

3mm steel is strong. And as a hatch it isn't doing anything at 20cm below water level.

The thinner plate at the counter will be because it will help balance against the weight of the engine (a bit) as the heaviest object in the boat is in the area with least displacement. (Unless you have a nice environmentally friendly, quiet and light weight electric motor!)

 

If you want steel to last, get it blasted and coated in Zinga and then the relevant modern paints and you won't have to do any major re-blacking or over plating in the future. The up front cost is higher but the protection will last longer than us.

[Claude]

I prefer to grit blast and use Jotamastic 87 two-part epoxy rather than Zinga, but again it's an expensive job.

Edited June 4, 2016 by Claude

[David Mack]

Can you move enough ballast from the stern to the bows to get the uxter plate a couple of inches above water level? Then you could cut out the old weedhatch trunk and weld in a new one (and paint it) in the dry.

[RubyTuesday]

I prefer to grit blast and use Jotamastic 87 two-part epoxy rather than Zinga, but again it's an expensive job.

I must point out that plain epoxy on to bare metal is not even slightly similar to the Zinga followed by PU or (after a primer) Epoxy finish.

They lifespan can't even be compared. Epoxy is cheap by square meter comparison to Zinga. I believe epoxy to be 7/8 times cheaper at £15/L and 5sqM/L so £3/sqM for epoxy and £25/sqM for Zinga. With that coating of Zinga you are looking at over 80 years of steel protection.

 

Anyway, best is to take the boat out of the water get it replaced by a good metalworker then when the new steel is in get it prepared and coated as best budget will allow. If you can do the entire boats external hull! Then think of the saving and hassle of future, blacking and over plating ect!

Edited June 4, 2016 by RubyTuesday

[Claude]

I must point out that plain epoxy on to bare metal is not even slightly similar to the Zinga followed by PU or (after a primer) Epoxy finish.

They lifespan can't even be compared. Epoxy is cheap by square meter comparison to Zinga. I believe epoxy to be 7/8 times cheaper at £15/L and 5sqM/L so £3/sqM for epoxy and £25/sqM for Zinga. With that coating of Zinga you are looking at over 80 years of steel protection.

 

I must point out that as a product Zinga has only been around for about 8-10 years so hasn't been proven to last 80 years as you claim. In fact it's not a proven product at all.

 

Correctly applied Jotamastic 87 can last 10 years - what's "plain epoxy" anyway? Jotamastic 87 comes in several varieties including with aluminium for greater corrosion resistance and with glass for greater abrasion resistance. It's widely regarded in industry as the best paint for underwater structures.

 

Anyway, it all comes down to personal choice. As I said I wouldn't use Zinga but each to their own. Most people still choose bitumen.

Edited June 5, 2016 by Claude

[Mike Jordan]

As you say it would be normal (in my opinion) to arrange to build on a keel plate that is long enough to allow you to burn round the completed swim plates and lift up the remaining section of keel plate to form the uxter plate. It's nice and economical since it's already nearly the right shape and it is certainly better made in 10mm plate.

With regard to your existing weed hatch, I think it would be better to get a new one made slightly larger than the existing thin job. When the boat is docked to would be easy to burn round the outer edge of the rusty hatch and then weld the new one on to the uxter both inside and out of the bottom edge. A 6 or 8mm thick hatch would solve the problem long term without the trouble, expense, and repaired look, you would get with over plating. The job begs to be be done properly!

As to why anyone would make a thin hatch in the first place, it may be that the yards equipment wasn't up to folding anything thicker.

I can't see any real saving having been made on either the hatch or uxter plate?

Best of luck with the project.

Mike.

[Claude]

As to why anyone would make a thin hatch in the first place, it may be that the yards equipment wasn't up to folding anything thicker.

I can't see any real saving having been made on either the hatch or uxter plate?

Best of luck with the project.

Mike.

Liverpool boats and others made thousands of boats with 10mm baseplates and 6mm uxter plates. They definitely didn't lack the equipment so obviously did it for a reason. I assume over the thousands of boats they built it resulted in huge cost savings. As you say, a 10mm uxter is better than a 6mm uxter plate, however 6mm is not "thin plate"!

 

As I said earlier, there are lots of older boats from respected builders with 6mm baseplates and 6mm uxter plates so it's not a major issue unless you don't keep it painted.

 

I never really looked at the thickness of Liverpool boats weed hatches, but they aren't folded, they're welded. I guess if the uxter and sides are 6mm then the hatch must be 6mm too. I've seen lots of them over 10 years old which are still 6mm with no pitting, so again not an issue unless you neglect them.

Edited June 5, 2016 by Claude

[RubyTuesday]

I must point out that as a product Zinga has only been around for about 8-10 years so hasn't been proven to last 80 years as you claim. In fact it's not a proven product at all.

Correctly applied Jotamastic 87 can last 10 years - what's "plain epoxy" anyway? Jotamastic 87 comes in several varieties including with aluminium for greater corrosion resistance and with glass for greater abrasion resistance. It's widely regarded in industry as the best paint for underwater structures.

Anyway, it all comes down to personal choice. As I said I wouldn't use Zinga but each to their own. Most people still choose bitumen.

Actually Zinga has been around for over 40 years! Lifespan prediction is quite possible to test and calculate in a lab now.

Yes some people still use bitumen but that doesn't make it the best option. By "Plain epoxy" I mean a single type epoxy coat rather than a set of composite layers such as Primer, Undercoat and topcoat or Zinga, Primer and topcoat.

 

Zinga has been used extensively in some very serious civil and marine engineering products, it's superiority as a means of protecting steel cannot be denied. It is on par with hot dip galvanising but a practical option for boat owners and large projects. It is also ideal for canal boats because of the way it deals with scratches and how it protect the steel even when exposed.

 

It comes down to personal choice as to what someone puts on their boat, but it is not personal choice that dictates which is actually the better option. Seeing how many boats have to be overplayed and repaired due to rust, Zinga is an easy choice if you want to care for your boat long term.

 

There is nothing wrong structurally with steel down to 3mm on a boat hull. Look at Springer Boats for example. Why use 6mm steel in an area that is not liable to mechanical stress? There you can use 3mm steel plate and save money and metal.

[raymondh]

Just checked our build and yes its 10mm counter as bottom plate and 6mm weed hatch as sides, weed hatch lid is 10mm

 

Edited June 5, 2016 by raymondh