Ergonomically friendly scraping method

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Paulus
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Ergonomically friendly scraping method

Post by Paulus »

Just completed scraping the bottom of Guillemot. I watched others do theirs; hired hands do pay-jobs and it seems each has their own preferred ways.

The fastest and dirtiest method I saw was a hired hand dressed in a hazmat suit and professional breathing filter, take it all off with a rotating disc sander, as I saw the painting team use on my house exterior shingles last year. It took off the paint superfast but filled the area with copious amounts of dust and left deep swirls on the boat bottom.

Saw the majority of folks using scrapers - from cheap paint supply scrapers to special order giant double grip monsters - with varying measures of success.

The biggest issue seemed to be fatigue - especially when the scraping needed to be done upside down or near to it, i.e. anything higher than the vertical surfaces on the keel. It is just a bear to apply the pressure needed by pushing up, to get the scraper to work.

It also became clear to me that the weight of the scraper, or lack thereof, definitely was a variant in it's effectiveness - a light scraper would stop when it bumped against a ridge, or change in surface, while a heavier one would have a little more inertia and continue on a while further.

Based on my observations - for what it's worth, I decided on using a heavy chisel - sometimes referred to as a "Boat Slick"

Image

Took the handle off and stuck an even longer handle in the tapered receiver as is shown in the pick above (believe it or not - the ones in the picture are small baseball bat size). The cutting edge of the chisel is as wide as the blade of a good size scraper; the new handle (I stuck the chisel on the 5' handle of a garden ho) and the chisel combined had a nice weight to it which helped me to push through multiple layers of old bottom paint.

Then to assist in the upside down scraping, I added a second stick with a flat top to it, on which I rested the center (lenght) of the chisel-stick - close to mid point or elsewhere, depending on where I was scraping and what kind of angle/leverage I was seeking - thus creating a see-saw and allowing me to stand next to the boat, pushing down on the end and move the contraption back and forth thus pushing the cutting edge of the chisel up against the paint at almost zero angle. This worked very well, even on surfaces close to vertical (if you put the hinge point stick on a 45 degree angle away from the vertical surface, the see-saw action will still apply pressure on the chisel while you move (with your whole body) the entire assembly back and forth to scrape off the paint). The surface under the bottom paint proved hard enough to stop the chisel from digging into glass - except for maybe 15 or so small gauges that were taken out - less than 1/8th" deep.

I found that, being able to stand most of the time, rather than having to position myself either kneeling or crouching near or even under the boat… and pushing down on a stick with considerable leverage (varying based on where the hinge-point was selected) I was able to do the entire surface in less than two whole days work…. With the added benefit that my face (think air intake, dust in eyes, ears, nose, etc.) was further away from the surface being scraped that it would have been, had I used the popular hand scraper.

I used the same method when I sanded the boat afterwards – coarse sandpaper on a ceiling pad on a stick with the additional leverage stick as described above.

Of course, YMMV, but, hey, it worked for me….
Last edited by Paulus on Thu Dec 09, 2010 5:31 pm, edited 1 time in total.
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Rachel
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Re: Ergonomically friendly scraping method

Post by Rachel »

That sounds really interesting, not to mention ingenious. I'm almost visualizing it, but I have a couple of questions:

1) You mention "baseball-sized," but which part is that referring to? The width of the chisel blade? (that would be something like 4-1/2"?)

2) I'm not quite picturing how you used the second stick. Could you explain/draw/show a photo?

Thanks,
Rachel
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Chris Campbell
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Re: Ergonomically friendly scraping method

Post by Chris Campbell »

Excellent idea, and well worth remembering for anyone that has to do it (which is all of us, eventually). I've used the carbide-blade scrapers from Lee Valley, which are great scrapers, but a lot more work than getting a pair of levers working for you, for sure.

I'll second Rachel's call for photos, mostly to ensure that this method of removing bottom paint gets to be used by many and known as the Paulus technique!
Quetzalsailor
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Re: Ergonomically friendly scraping method

Post by Quetzalsailor »

I'm not gonna' second Rachel's and Chris' call for photos. I want a video!

I suspect that you're not really scraping but peeling, no? And your secondary push stick gives you more force to keep the blade against the glass? Have you arrived at an opinion about how sharp the chisel edge needs to be? I suspect that well shy of sharp is important to reduce digging. I'd also imagine that the edge should be slightly arc-ed so that the corners are less a problem; sloppy sharpening would help that.

I had to solve much the same problem when peeling the veneer off the outside of the FD. Too sharp would cut, a little less and splitting the (failed) glue line was easier. Interestingly, a 'froe' has a fairly dull edge. A froe is the tool used to split shingles and bevel siding.
Hirilondë
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Re: Ergonomically friendly scraping method

Post by Hirilondë »

I will start by saying that your "boat sticks" Paulus, are the refinement of the chisel I used on my boat bottom the first winter of work. I found pushing much more back friendly, less tiring and more efficient than pulling normal scrapers. Good stuff!
Quetzalsailor wrote: Have you arrived at an opinion about how sharp the chisel edge needs to be? I suspect that well shy of sharp is important to reduce digging. I'd also imagine that the edge should be slightly arc-ed so that the corners are less a problem; sloppy sharpening would help that.
I found that I liked them sharper than you might imagine, but certainly not as sharp as I would make my wood chisels for the very reason of avoiding digging. And yes, slightly arced helped significantly. More like rounded at the corners than an even arc, but the same idea and reasoning. I would sharpen my bottom scraping chisel on the same slow wet wheel as my wood chisels. Rather than going to my 1000 grit Chinese wet stone for a finish honing I would then take it to the wire wheel. I would carefully run it across the wire wheel perpendicular to it and just lightly against it for a few seconds. This would just barely take the edge off without blunting it. It still took a little care and technique to avoid digs, but was just right for getting under the old paint. Like any hand tooling work even bottom scraping takes practice and attention to develop the skills to do it well and fast. Ok, fast is a relative word. No matter how fast you scrape your bottom it won't be fast enough.

As satisfying as developing my sharpening technique and improving my scraping/chiseling methods were I will be more than happy to never do it again!!!!! I highly recommend to anyone facing this project to try and emulate the tools and methods Paulus outlines in this thread.
Dave Finnegan
builder of Spindrift 9N #521 'Wingë'
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Paulus
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Re: Ergonomically friendly scraping method

Post by Paulus »

Rachel wrote:That sounds really interesting, not to mention ingenious. I'm almost visualizing it, but I have a couple of questions:

1) You mention "baseball-sized," but which part is that referring to? The width of the chisel blade? (that would be something like 4-1/2"?)

2) I'm not quite picturing how you used the second stick. Could you explain/draw/show a photo?

Thanks,
Rachel
... baseball BAT - size of a small baseball bat (sorry)

I don't have pictures, but this is a simplistic drawing showing the principle for the sanding portion.

Image

The chisel (blade approx 2 - 2.5" wide) would sit as an extension to the stick scraping at almost zero angle - basically just knocking the paint off...
Paulus
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Re: Ergonomically friendly scraping method

Post by Paulus »

Quetzalsailor wrote: Have you arrived at an opinion about how sharp the chisel edge needs to be? I suspect that well shy of sharp is important to reduce digging. I'd also imagine that the edge should be slightly arc-ed so that the corners are less a problem; sloppy sharpening would help that..
The chisel, when I initially mounted it on the end of the stick, had not been sharpened for quite a while and had been uses for all sorts of non-chisel use.. heh, heh.. The corners were pretty 'rounded' and in general, the chisel was fairly dull.

As I progressed, however, the scraping would further dull the chisel and it became harder and harder to get it to move the paint... but, I too thought that it would be better to keep it dull (and with rounded corners) in order to avoid digging.

To my surprise, however, when it became too dull and I brought the edge to a razor sharp edge,(thinking it would dull fast enough once I started using it) it did the job with even less effort, and it still didn't gouge or dig as would seem intuitive. From then on, I used a honing stone about every 5 minutes or so, to keep the blade super sharp...

Even the perfect (sharp, pointy) corners were great to get hard to move paint off - especially near the waterline, where the PO had applied many extra layers. With the chisel razor sharp, I could actually just walk the chisel/stick the lenght of the boat and continue past the entire waterline - taking off about a half inch of paint at a time - the rest of the chisel running over already clean surface without digging.

Mind you, my paint was in really bad shape and it did pop off almost effortlessly. Then again, when I used the "system" on other people's boat (when they asked me to, to see how it would work for them), it still did a remarkable job there too.

By the way, I estimate I removed three five gallon buckets of paint chips and dust when all was said and done... the total weight easily exeeded 300lbs - about 100lbs each bucket (upon emptying the tarp into the bucket)

In the end, it was a pretty clean bottom with minimal chips or gouges.

Image
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Rachel
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Re: Ergonomically friendly scraping method

Post by Rachel »

Thanks for extrapolating; the drawing really helped. Looks practically leisurely from way back there ;)
One Way David
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Re: Ergonomically friendly scraping method

Post by One Way David »

Also called a timber slick for timber framing. The handle fits like the conical wiid chisles handles but are more on the size of a base ball bat handle. As they appear in the pictures. Sad but it is re-purposing of a very old traditional craftsman tool. They can be found in farm sales in the midwest or about any Amish areas. Often they have been used as root cutters for tree stumps and cold chisles. I never really thought of using one for bottom scraping, though.

Dave.
Never finish all your projects or you'll be bored.
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