Blasting the hull below the waterline

[Summerfun]

I am considering having the bottom paint stripped to the original fiberglass and have a couple of questions.
1. The bottom has never been stripped it is a 1986 is it worth the trouble?
2. Some people say to have it soda blasted others sand blasted and others water/glass bead blasted. What one is the best?
3. Bottom paint afterwards any recommendations?

 

[oscarvan]

My previous boat was soda blasted, after which I applied a barrier coat (three layers), primer (two coats) and anti fouling (three coats, first red, the "signal coat" then two more in black). After that every year I coated where the red came through, and a total coat. (I did put a lot of miles on it)

Yes, it's worth it, especially if what you find after blasting is in good shape, and you then protect it.

Of course you could also find some things you don't like, and then you would have to address those.

 

[Boatsb]

Depending on what paint is on it you may need to blast more aggressively. Strip it to the glass or barrier coat then add barrier coat and ablative paint. I use micron 66. It's the best for this area by far.

 

[brico]

I am considering having the bottom paint stripped to the original fiberglass and have a couple of questions.
1. The bottom has never been stripped it is a 1986 is it worth the trouble?
2. Some people say to have it soda blasted others sand blasted and others water/glass bead blasted. What one is the best?
3. Bottom paint afterwards any recommendations?

Unless your underwater hull is rough due to many, many flaked off sections and subsequent buildup making it look like surface of the moon then i do not see any need to do it. These are not racing sailboats and even 15 coats of dried out paint on them only add a little more weight which is insignificant in comparison with the overall weight of the boat.

It is the slime and barnacles that slow you down most which has nothing to do with the thickness of old dried out and non active paint that does not prevent the weed and barnacles to grow on it. Just power wash it every year, and apply new coat of anti fouling every two or three years, dependent on when the paint stops working. For a power boat i'd prefer hard instead of ablative. During cruising season scrub regularly as much as you can especially areas that are exposed to sunlight where growth is biggest and enjoy extra mileage you can do with it for the money you would spend on stripping the old paint and applying (what one of the responders said) another 8 coats before he put it back in the water.

It is only worth doing if you notice many, many blisters and potential osmosis but that is another can of worms i do not want to think of....

 

[SEVEN]

Well stated MV.

 

[Boatsb]

Unless your underwater hull is rough due to many, many flaked off sections and subsequent buildup making it look like surface of the moon then i do not see any need to do it. These are not racing sailboats and even 15 coats of dried out paint on them only add a little more weight which is insignificant in comparison with the overall weight of the boat.

It is the slime and barnacles that slow you down most which has nothing to do with the thickness of old dried out and non active paint that does not prevent the weed and barnacles to grow on it. Just power wash it every year, and apply new coat of anti fouling every two or three years, dependent on when the paint stops working. For a power boat i'd prefer hard instead of ablative. During cruising season scrub regularly as much as you can especially areas that are exposed to sunlight where growth is biggest and enjoy extra mileage you can do with it for the money you would spend on stripping the old paint and applying (what one of the responders said) another 8 coats before he put it back in the water.

It is only worth doing if you notice many, many blisters and potential osmosis but that is another can of worms i do not want to think of....

Just a few questions on your theory.

1) How would you explain gaining 1 to 2 knots after a smooth bottom job? Removing 1/4" of paint and creating a smooth surface makes difference in drag.

2) How would you assess the barrier coat that's not visable? Unless you put it on you don't know what shape it's in or if it's doing its job. Especially in warm waters where it's most necessary.

3) why add more build up and weight? Even the best hard paints do not work as well as modern ablative paints that don't add to the problem


These old boats are not speed demons but the ability to plane 200 rpms lower or even plane at all could be the difference of a smooth bottom.

 

[tomrealest]

Scott, have you ever tried the Sea Hawk paints?

 

[rmatt]

I have an 1986 36 Sedan that probably had 28 years of accumulated bottom paint on her.
When fresh paint was applied with a roller it took off some of the old paint.
I had the bottom blasted with walnut media which did a great job and and a bonus of no blisters.
Did I gain any speed, don't know as I was playing with props. Do I care, no as painting the bottom now is a
pleasure compared to years past.

 

[Boatsb]

Scott, have you ever tried the Sea Hawk paints?

Yes. They re a local company ( Tampa area) but we use Micron 66 on almost anything ( except hard paint) for a good reason. It outperforms everything else here.

FWIW we go through about 10 gals of bottom paint a month. Sometimes more. Had 2 paint failures in 5 years that interlux replaced the paint and then some to make up for it. Ive also gotten 4+ years on a heavily coated bottom ( 4 coats ) with almost no growth. 5 and I started to foul.

 

[rwappleton]

When we bought our boat we glass beaded to factory Gel coat, repaired the blisters, barrier coated with 2000E and 2 coats of CSC (three on side and stern).

We are on year three (Charleston to Panama City cruising area) and it still looks good.

Our plan is next winter haul, pressure wash, inspect for more blisters, repair and re barrier coat if needed and two more coats.

My opinion is drag is drag is drag. weight you don't need, rough bottom, Bimini that acts like a sail at 5 knots they are all the same. I removed antennas that were not being used! I get 1.7 NMPG at hull speed and I can do 24KTS when the bottom is clean.

 

[oscarvan]

Agreed, moonscape is bad, but smooth surface is OK regardless of number of layers. (Within reason).

And don't forget to go down there with a brush and a scraper. I have an air bottle with 60' of hose and a regulator. Especially keeping props, shafts, struts and rudder clean. Cuts down on possible vibration related wear too. And, lets you keep an eye on your zincs in case there's a "hot" boat around.

 

[brico]

Just a few questions on your theory.

1) How would you explain gaining 1 to 2 knots after a smooth bottom job? Removing 1/4" of paint and creating a smooth surface makes difference in drag.

2) How would you assess the barrier coat that's not visable? Unless you put it on you don't know what shape it's in or if it's doing its job. Especially in warm waters where it's most necessary.

3) why add more build up and weight? Even the best hard paints do not work as well as modern ablative paints that don't add to the problem


These old boats are not speed demons but the ability to plane 200 rpms lower or even plane at all could be the difference of a smooth bottom.

1.) Well, every time you haulout and power wash removing slime, weed and barnacles you gain the speed irrespective of whether you apply new coat of paint or not.

2. why bother unless you observe blisters but that is another can of worms as previously stated.

3. Ablatives are good but you cannot scrub them much otherwise you have nothing left to protect against growth. Hard core sailboat racers are using hard paint and not the ablative one.

 

[Boatsb]

Scrub?

How abut a light wipe. 4+ years with no growth in a high fouling area. By the way the serious sailboat and powerboat racers use waxed hulls and no bottom paint.

A smooth bottom and the loss of 500 lbs of old paint makes the boat go through the water easier. With 10 years coming up since I bought the boat I just did my second bottom job this past June. It has been painted with micron 66 since I bought it. 4 years + from the po's paint job. 5 from my first.

I took the po's paint to the end of life where I was starting to see primer through the paint. After putting 4 coats on I got almost 5 years of clean bottom. Wore that to the primer, lightly blasted, 2 coats barrier coat, 4 new coats ...

Why would I consider hard paint?

 

[oscarvan]

When I put ablative paint over the primer I make the first color different than the last two or three..... It's called a signal coat and tells you you're down to one coat as it wears off. Better than getting down to primer as it has no anti fouling capability whatsoever.

 

[Avenger]

Time to break out the classic pictures again.

Mine had 30+ years of paint on it that was rough and coming off in large chunks.

The yard I use had a guy come in and sand blast it. Sand worked well for me since it opened up all the blisters and craters. If the OP has a newer hull it may be from a time after Hatteras started using better resins on their mat layer. So it may not be anything like this.

Also, using sand requires a skilled operator. I had already seen the guy's work before I okayed them using it on my boat.

This mess required a long time to fill in the rash with epoxy. After that it was barrier coat, two coats of hard paint, then two seasons later when it was time to paint again we started using ablative. The hard paint was recommended as a better interface between the barrier coat than going straight to ablative. Other than that, after the effort to remove years of built up hard paint I can't see any reason to put it back.

And in it goes. Nice and smooth. The yard said they weighed the paint they collected and it was a couple of hundred pounds. I'll take that with a grain of salt, because I'd have to guess there were some grains of sand in it as well. However, there was a slight, but measurable performance improvement when the job was done. I don't know if it was significant enough to warrant the investment for that alone, but "investment" and "boat" really should be used in the same sentence anyway.

 

[oscarvan]

it may be from a time after Hatteras started using better resins on their mat layer

Is there consensus on the time this started happening?

 

[Boatsb]

I run through the signal coat as the last year of paint. When its starting to show primer I repaint. I have the hull dusted to remove anything loose and bring it down to barrier coat. Then the paint. I had 2 blisters last time after 5 years and 6 months in Florida waters. Yes I should have done it at the 5 year mark but I was busy. When I hauled I had not wiped the bottom in a year and usually dont) but sat for a while for some engine work. Less than 10% was fouled with soft or hard growth.

 

[motoryacht lover]

I had my 54 Vikings hull sand blasted. I didn't really notice a performance improvement. Also I was told in the right hands sand blasting is ok.