Making a Case for Sodablasting Your Hull

Posted by Darrell Nicholson at 11:50AM - Comments: (20)

Quick. What’s your least favorite boat maintenance project? Cleaning the bilge? Changing the engine oil?  ... How about stripping off several years worth of bottom paint?

One of the first things my wife, Theresa, and I did with our cruising boat was to strip 10 (20? 30?) years of bottom paint off of the old wooden ketch using an 8-inch electric sander. It probably shaved 10 (20? 30?) years off of my life. I wince just thinking about that summer.

A couple of seasons ago, PS Technical Editor Ralph Naranjo and contributor Frank Lanier took a different approach: chemical strippers. These reduced the amount of sanding involved, sparing some backbreaking work, but that was about it.

After that experience, Ralph decided to look into sodablasting, featured in the October 2011 issue of Practical Sailor. One of the chief complaints you hear about any for-hire boat work is the exorbitant price charged, but once you start to do the math—and start thinking about your health—a $1,500 fore-hire sodablasting job doesn’t seem so indulgent. 

One of the biggest mistakes an owner makes when estimating how much time it takes to strip a hull is to peck away at one of the easy spots where the paint is peeling and then assume the rest of the coating will come off just as easily. Ralph gives a more realistic formula for estimating the amount of time a stripping project will take. First, you estimate the wetted surface area (WSA) using the formula: waterline length (Lwl) x (beam waterline (Bwl) + draft (T)). Multiply this number by .75 for a medium-displacement boat or by .5 for a light-displacement boat. This gives you a very crude estimate of surface area, but it’s fine for estimating paint removal (or painting).

Now that you’ve got your total area, you can figure out the amount of actual time it will take you to do the job. Start your stopwatch and attack one square-foot of an “easy” section. Do the same to a patch where the paint is well adhered. Now estimate how much of your hull will be “easy” to strip and how much will be hard. No cheating! It will only bite you in the end. Once you’ve estimated the percentage of hard and easy sections, you can apply your timed results to the total area of the hull.

Here’s an example: Your boat has a 30-foot waterline, a 6-foot draft, a waterline beam of 10 feet, and is a medium-displacement vessel. Our fuzzy math for a medium-displacement sailboat  

WSA = Lwl x (Bwl + T)

says you’ve got 360 square feet of paint to strip: 30 x (10 + 6) (.75) = 360.

Next comes the all-important apportionment of “easy” versus difficult paint removal. In this case, 85 percent of the hull is tough stuff, taking four minutes per square foot to strip: 0.85 x 360 x 4 = 1,224 minutes of backbreaking work. Add in the 15 percent of easy scraping area that takes only 30 seconds per square foot to strip: 0.15 x 360 x 0.5 = 27 minutes. The result is 1,251 minutes, or just under 21 hours of serious scraping. That’s 21 hours of serious work, not including coffee breaks, admiring sisterships hauled out in the same yard, or gazing numbly at the water wishing you were sailing.

Now, how much is your time worth? And don’t forget the money you’ll be spending on scrapers, chemical strippers (if you use them), sand paper, etc. As much as I like to do my own boat work, this is one for-hire job that is worth considering.

Comments (19)

My boat had a ultrtasonic Barnacle Zapper installed. The boat has not been out of the water in Florida since 2005. The bottom is still relatively clean.

Posted by: Sailor Jerome | March 23, 2017 4:03 PM    Report this comment

My boat had a ultrtasonic Barnacle Zapper installed. The boat has not been out of the water in Florida since 2005. The bottom is still relatively clean.

Posted by: Sailor Jerome | March 23, 2017 4:03 PM    Report this comment

EcoQuip2 from Graco is the quickest, least mess, high pressure water vapor with recycled glass beads, virtually dustless. Great for bottom paint, car restoration, etc.
See: graco abrasive-blasting

We learned about and observed the process from Painter George Custom Coatings in Northport, FL. (See Facebook)

Posted by: 630 | March 17, 2017 4:54 PM    Report this comment

I'm with Piberman, bottom paint is for racers...

I "cruise" a small lake where DIY dry docks are not available. Every July I jump in the water with a plastic ice scraper. One afternoon, then I'm back to sailing...

Posted by: Poco Loco | March 17, 2017 12:51 PM    Report this comment

My CCA era 28 footer (8.5' beam) was done 6 years ago. From beginning to end my bottom got a complete re-do in one running week.

Day 1: Sodablasting contractor came onsite and did the entire job in one morning. That afternoon I spot-sanded the few areas with paint vestiges remaining. Wiped hull clean.

Day 2: Careful exam on the bottom and prep and fill several pinholes, gouges and similar irregularities with epoxy fairing compound.

Day 3: Sanded epoxy repairs and second pass of fairing repairs followed by final sanding. The result was a bottom a racer would not be happy with, but for a daysailor / cruiser, it was fine.

Day 4: 3 coats of Pettit's barrier coat epoxy, alternating gray and white so coverage was obvious. Very easy to apply.

Day 5: 3 more coats of barrier coat epoxy plus first coat of red bottom paint, Pettit Hydrocoat, (while final epoxy was still tacky).

Day 6: Second red coat of bottom paint, then a third coat of black Hydrocoat.

I've had five New England seasons since and now each spring's bottom prep is maybe an hour spot-rolling where black has worn off and is showing tinges of red. Very easy.

I totally endorse the results and value from sodablasting.

Posted by: Hriehl1 | March 17, 2017 9:17 AM    Report this comment

Very good article, the term soda blasting tends to cover several different methods. I chose the Farrow system (and contracted w/Dale at Atlantic Green Pro in New Jersey) on my previous boat. I
I was thrilled with the results and the price was VERY reasonable. If I ever needed... for my current boat would not hesitate to use him or this system again. It is very low pressure (only about 40-50 psi) and uses a recycled glass blast media w/hot water. So there is no dust and another advantage is there's no prep sanding involved afterwards because there's tooth put into the surface... it's essentially ready for paint.

Posted by: CaptainKornchex | March 16, 2017 3:50 PM    Report this comment

I did my 42ft sailing cat a few years ago. I had a few very minor blister areas and wanted to get all the years of paint off. I used a soda blaster from the Chesapeake and was very happy with the work. One thing that should be noted is that after you strip it all the way down you have to do some sort of barrier coat. Interlux and Algrip and many other make good two part epoxy barriers. They are not cheap and you have to have time to do at least a few coats. I believe we did 3 on mine. Those paints are not cheap and need to be factored in. My soda blast cost me around 3000, but the boat is 24' wide. They also came to where the boat was hauled. I was glad I did it, but it was all in a very expensive project even though I did the barrier coat and the bottom paint. Worth doing maybe once every 10-12 years.

Posted by: hwturn | March 16, 2017 3:49 PM    Report this comment

For 4 centuries during the age of sail tens of thousands of vessels cruised the globe with only an occasional scrubbing. For offshore cruising in the tropics an occasional scrub is all that's needed. Bottom repainting really belongs to the racing crowd seeking medals and for power boats where clean bottoms actually save big dollars. For most cruisers better spend time and monies on other projects. If speed is essential then fly by airplane.

Posted by: Piberman | March 16, 2017 3:37 PM    Report this comment

Someone please explain the process "soda blast".

Posted by: Hoverlover | March 16, 2017 3:33 PM    Report this comment

I have stripped 4 cruising boats from 34 to 45 ft in the last 25 years and I am amazed that even PS (which is usually a great source for accurate advice) ignores the best way to strip a bottom. Sanding and chemicals are dirty, toxic, and expensive. My method is to use 4 high quality wood chisels (2', 1 1/2", 1" & 1/2") and a sharpening stone. You start with the 2" blade on the loose areas with the blade bevel out and at a very oblique angle. In one swipe (2 sec) I can take off a 2" by 18" strip (1/3rd sq ft).. When the 2" blade stalls on a tough spot I drop to the 1 1/2' and then the 1" and then the 1/2 inch. You sharpen the chisels frequently! It takes some practice to not gouge the gel coat but this gets 90% of paint off down to bare glass. which comes off in chips (not toxic dust or glop) and is easy to collect on a tarp. The last 10% (turn of the bilge, round of the keel etc.) I use stripper and or sanding. It took me and a helper less that 16 hrs to do my Bristol 45.5 (approx 2,400 sq ft per the PS formula). The sandblasting quote was $4,000! It is tough on the shoulder muscles but good exercise. I was 59 when I did the Bristol 6 yeras ago.

Posted by: KENT B | October 1, 2011 2:41 AM    Report this comment

While on the topic of sensible ways of removing antifouling from FRG hulls, has anyone any experience with removal by dry ice blasting? The aviation world has used dry ice blasting to successfully remove paint from aluminum fuselage skins, without the many environmental concerns associated with chemical strippers, and the somewhat delicate surface is not damaged.
I'd be interested in cost comparisons...

Posted by: WM | September 29, 2011 11:44 AM    Report this comment

My 42 foot sailboat with wing keel is $2k. At an estimated 20 hours to chem strip and $700 of peal away, my per hour wages to strip would be $10 per hour plus the $700 stripper. Lets not talk about the lost time. Guess I am soda blasting

Posted by: Catalina 42 | September 28, 2011 6:37 PM    Report this comment

Hope you have more spare time than I do. Considering removal of old hard paint (many years) on a 28 footer and some blister repair 3 coats of barier 3 coats of epoxy and 4 coats of anti-foul it only cost me one summer. PS

Posted by: PHIL S | September 28, 2011 4:50 PM    Report this comment

And we wonder why our five year old is struggling with math:
Here is Ralph's original formula:

WSA = Lwl x (Bwl + T)

For more info on soda-blasting check out the article or call the folks at Chesapeake Blasting Services.

Posted by: sailordn | September 28, 2011 3:26 PM    Report this comment

Something else to consider...
Any bottom paint that is above the waterline will be hard as rocks and careful scraping along the boot stripe is very tedious. This adds huge chunks of time not to mention moving the stands or cradle, scraping those areas, under the keel etc.

Posted by: Jay K | September 28, 2011 3:23 PM    Report this comment

I've had a couple of older boats that I've attempted to strip physically and chemically, using several different methods of the latter. I guess it all depends on how much you value your time, knuckles, weekends, and nights out (without falling into your plate). That's why I had my last boat soda blasted. It was worth every darn nickel.

Posted by: Ed White | September 28, 2011 2:42 PM    Report this comment

OK article but something is amiss with the formula. In the body of the article you state: multiple LWL x Bwl x draft. But when you do the calculation for the example you have added BWL plus draft then multiplied by LWL and then applied the .75 factor.

With the curve of the boat I'm not sure how the formula was arrived at but I'm guessing that 360 is closer then 1,350 (30x10x6=1800x.75=1350). Which is it?


Posted by: Frank B | September 28, 2011 2:31 PM    Report this comment

You sold me on not sanding and scraping so... any more information on the soda blasting option?

Posted by: ANDREW N | September 28, 2011 2:20 PM    Report this comment

When we purchased our 33' sailboat boat in 1987 she already had 13 years of accumulated bottom paint. We chemically stripped the bottom paint over the course of a couple spring weekends, and repainted with an ablative paint.
More recently during the spring of 2009 I decided I wanted to strip the bottom, apply a barrier and repaint. After making a calculation similar to the one in the article I chose to have the bottom soda blasted. I'm glad I made that decision.
The work of barrier coating and painting was more than enough for that spring.

Posted by: Guy J | September 28, 2011 2:19 PM    Report this comment

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