Blasting the hull with walnut shells

[McZube]

My boat is a Hunter 31 with an 11' beam. Any idea how many hours it will take to blast the bottom using walnut shells and how many pounds of shells I will need? Also, how many CFM compressor will I need?

The boat has an external iron shoal keel that I might actually blast with sand. We can either leave that out of the estimate or make a separate estimate for it.

Thanks.

 

[patrickfarley]

Are you doing it yourself or having it done?
I was shocked when I checked prices for my keel. The shops around me use diesel engines to run their blasters and since the Government changed the diesel formulation it has become more expensive than gasoline which translates into expensive blasting. I ended up purchasing a blaster from Harbor Freight and using soda to take of the bottom paint and then using black diamond from Northern Tools for the keel.
I used the Portable Abrasive Blaster Kit from Harbor Freight and it worked great. My only problem was my 3hp compressor. It would work better if I would work a small area and then let it catch up. Since I worked with a small compressor I could not give you an accurate time frame. I can say that you will be much happier with a good respirator and a nice hood.
I did not try walnut shells. The soda took off the paint and left the gel coat. The Black Diamond cleaned right down to the metal.
My boat is only a 25 and it took several days. A real blaster is probably much faster.

 

[Tim R.]

I did my Ericson 35 a few years ago. 300lbs of shells. You can run them through about 3 times so make sure you tarp the ground to collect them. I rented a diesel compressor and blaster from the local rental company. I used a ceramic tip. The whole job took about 4 hours and cost roughly $500.

A few others have done this over at ericsonyachts.org

 

[McZube]

Patrick, my compressor is a 6hp. Do you think that would allow me to work continuously, or not?

Tim, i was planning on doing exactly what you did with the tarp.

Thanks both of you.

 

[Charlie Jones s/v Tehani]

HP is not the only part involved. I have a 4 hp, with a 20 gallon tank that wouldn't keep up. I also have a 6 HP, but it has a 60 gallon tank - IT will do nicely.

I usually run my blaster at 100 - 120 PSI.

 

[Ray Bowles]

The main concern when media blasting is air pressure and a high volumn of air at that pressure. I have found a 60 tp 90 gal air tank is a must with an 80 gal working very well. A dual stage air compressor is also a must. You would be nicely served to rent an industrial diesel powered air compressor with hose and ceramic tipped blaster. Tim R. wrote a well thought out reply to your question. I would follow his advice.
Ray

 

[finding41]

Squirrels.

 

[Sumner]

.. A dual stage air compressor is also a must. You would be nicely served to rent an industrial diesel powered air compressor with hose and ceramic tipped blaster..Ray

Yep, the key word there is 'dual stage/2stage'. Don't mix that up with a 2 cylinder single stage compressor. A larger tank just means it will take a few more minutes to run out if the compressor isn't big enough. Blasting takes a lot of air. I've done a fair amount with a 220 volt 5 and 6 hp 2 cylinder and it wasn't fun. Now I have a 220 volt 2 stage at home and it keeps up, but just barely.

We paid about $1200 to have the 37 foot Endeavour taken down to the gel coat via blasting by a guy that does it for a living. He did a great job and was about 1/2 the price of the quote we got to have it sanded down to the gel coat,

Sum

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