Advice Sought - Removing / Grinding Horiztontal Deck Welds

[PaulRainbow]

Looking at the photos ,it would appear that the rail is not solid but probably a U section. I am guessing this by the holes drilled in the top of the rails.
Hope for your sake that this is the case, as it will make the job a lot easier.

Surprisingly no one has suggested hiring a hefty angle grinder , at least a 150 mm wheel size. which will be big enough for the job and relatively easy to handle. Firstly I would cut vertically down the cross section of the rails to divide them into sections, about 400 long and then cut along the bottom of the outside face,as close to the deck as practical. Then cut along the back face but not all the way through, you might then be able to lever each length off ,(saves a lot of work.)
Then swap your cutting disc for a coarse grinding disc, and clean up the remaining welds, finish off with a finer disc .
Be very aware of safety ,, don't take chances wear proper gear .
Get plenty discs from the hire place, normally they will only charge you for what you use.
I have done this type of work very often ... don't envy you!


Awaiting incoming.

Well done for actually reading the OP

 

[Blue Seas]

Paddys milestone is a viable method. But there is a lot of awkward corners there for someone not familiar with hefty grinders so lots of opportunity for kick-back and accidents. Personally I would cut down vertically as Paddy says and then get someone decent with a gas torch (Oxy acetylene)) to run along the bottom (assuming you can get access to the deckhead below for a fire-watcher). Couple of hours tops and a big saving on discs / effort. Remove all flam stuff and use wet blankets to limit spread.

 

[MisterBaxter]

I would definitely try and get 110/240v tools to the job not cordless. I echo everything that's been said re fire risk, and I would really emphasise the physical discomfort of a job like this - you need big knee pads, tough overalls, long, thick leather gloves (welder's gloves are good) serious eye protection with no gaps down the sides (ie goggles not safety glasses) and proper ear protection. I'd wear earplugs inside ear defenders myself. And a really good mask, not just a casual paper mask but a chunky filter cartridge one. And some kind of hat to protect your hair too.
I think you'll end up kneeling on the deck with the tool braced against a knee, rather than just waving it about at arm's length - you can control it much better that way, especially if you go bigger in terms of disc size.

 

[thinwater]

Looking at the photos ,it would appear that the rail is not solid but probably a U section. I am guessing this by the holes drilled in the top of the rails.
Hope for your sake that this is the case, as it will make the job a lot easier.

Surprisingly no one has suggested hiring a hefty angle grinder , at least a 150 mm wheel size. which will be big enough for the job and relatively easy to handle. Firstly I would cut vertically down the cross section of the rails to divide them into sections, about 400 long and then cut along the bottom of the outside face,as close to the deck as practical. Then cut along the back face but not all the way through, you might then be able to lever each length off ,(saves a lot of work.)
Then swap your cutting disc for a coarse grinding disc, and clean up the remaining welds, finish off with a finer disc .
Be very aware of safety ,, don't take chances wear proper gear .
Get plenty discs from the hire place, normally they will only charge you for what you use.
I have done this type of work very often ... don't envy you!


Awaiting incoming.

Yes, all of that^^. But with the amount of grinding, cup brushing, and flap disk sanding this boat will need, I'd go larger, maybe 7" (180 mm). Not cordless, and I would buy it. A good one is only $150. Also a good corded 4.5-5" grinder for many, many smaller things. You're going to live with these. Metabo, Makita, Bosch, DeWalt, or equivalent.

I've spent a good many hours with a 9" grinder, but that is probably more than you need and they can be hard to handle. You wouldn't use it often enough to warrant.

 

[Paddys milestone]

Another couple of points, looking at the photo, it might be that the rails have been tack welded? Difficult to confirm from the image. If so this would make the job easier.
Also it it was gas welded rather than Arc welded,(or Migged or tigged ) the weld will be much softer and easier to grind.

Just a thought?

 

[DownWest]

Are we looking at a section with wood decking up against it? Is it welded under the wood? If so, complicates matters.
I would also go with a smallish grinder. 125mm and thin discs. Far easier to control in awkward places.

 

[MisterBaxter]

Honestly you wouldn't regret having two grinders for this job, a big one for blasting through the straightforward bits with easy access, and a little one for the fiddly bits. In my experience a non-cordless angle grinder is one of the power tools that it's safe enough to get secondhand, they're so simple in terms of the mechanicals there isn't much to go wrong, so you could grab a couple of decent quality ones on eBay for the price of one new one.

 

[Wansworth]

With your boat you will need a whole range of good tools and safety equipment ,my four inch angle grinder is still going…..25 years later!

 

[Rum Run]

Just to reiterate the fire risk - I have set far more stuff on fire with a grinder than by welding, mainly my own overalls or trousers . Don't keep a lighter in your pocket either, unless you really like hospital food (not me, H&S pamphlet from the early 80's). Having a spotter is good, though that did not stop a chap I once worked for setting fire to a quarry conveyor while they were 30' up over a loading bay.
Have fun!