The miracles of silicone oil

Discussion in 'Materials' started by CDK, Sep 18, 2007.

  1. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    The following is an excerpt from Wikipedia's text about silicone oil:

    "Polydimethylsiloxane (PDMS) is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. It is optically clear, and is generally considered to be inert, non-toxic and non-flammable. It is one of several types of silicone oil (polymerized siloxane)."

    I started using silicone oil to impregnate the boat's hood after applications of several specialty products on pieces of a similar fabric didn't bring the desired effect. The once perfectly watertight material had lost its color and water repelling properties after several meditteranean summers, but after a good spray of silicone oil in April it looked like new and behaved likeaccordingly.
    That was 5 sonny months ago: I checked today after an extensive rainshower: not a drop of water in the cockpit!

    Because the can wasn't empty I used it to lubricate hinges, restore the dull appearance of my car's plastic parts before I traded it for a new one and applied it on that as well to protect it from UV. I also used it as cutting oil when drilling in stainless steel and found it to be much more effective than the "real" cutting oil.
    Next I applied a coat to the lower half of a strip of galvanized steel plate and hung that from the pier in front of my house in the Adriatic sea. The oil did not wash away in the waves but very slowly crept up on the untreated part and finally stopped.
    The untreated part showed the first signs of marine growth, the "siliconized" surface remained exactly as it was. I checked it regularly for a couple of months and saw no deposits whatsoever in the treated surface while the sea snails, algea and clams took posession of the rest.

    Last week I wanted to take it out to photograph the test, but some #$*& had taken it away. I just prepared a new sample; the tourist season is over, so maybe it will be left in place now.
    Of course my not so scientific experiment does not prove that silicone oil is the ultimate antifouling, but it looks very promising. In fact it did much better than the copper based coating on my boat, that has been out of service this summer and looks like a submerged vegetable garden. It may be very useful on a sterndrive also, because it reaches the smallest corners.

    Another quote from Wikipedia:

    "PDMS is viscoelastic, meaning that at long flow times (or high temperatures), it acts like a viscous liquid, similar to honey. However at short flow times (or low temperatures) it acts like an elastic solid, similar to rubber. In other words, if you leave some PDMS on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface imperfections. However if you roll the same PDMS into a sphere and throw it onto the same surface (short flow time), it will bounce like a rubber ball."

    This suggests that on a hull at planing speed the coat of oil will remain where you want it to be, at least for quite some time. Not bad for a product that costs just a fraction of commercial antifouling and can be applied as easily as suntan lotion from a spray can. Silicone oil when used as a lubricant is very, very slippery. I do not know what the friction coefficient is when submerged but would be disappointed if it wasn't equally low. So it may even improve mileage or top speed.

    And there is more. In the "inboards" forum I presented my plans for an oil filled stern tube with ball bearings and neoprene seals, which weren't very ethousiastically received, the danger of a leaking outer seal being the main issue.
    I did some -again- unscientific testing with a piece of shaft, a tube, a purposely damaged neoprene seal and my oldest Makita power drill. The shaft was wetted with silicone oil, the seal's lip cut with a Stanley knife in 4 places and I was sitting with my legs in the water and the tube between them until both me the battery were exhausted. The seal was 1-2 ft deep in the water, yet not a trace of the salty liquid entered the tube. So there's my answer against the dangers of seawater destroying the bearings.

    Of course there are drawbacks. My tools remain slippery, a part of the boat's deck was very dangerous to walk on for many weeks and something coated with silicone oil is extremely hard -maybe impossible- to paint. I use acetone to remove it where it was spilled, but somehow traces still seem to be there......And not all materials are happy with an acetone bath.
  2. wannasail53
    Joined: Jul 2008
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    Location: P.V. Mexico

    wannasail53 Junior Member

    CDK thanks for the post, is very interesting and i will do some experiments on my own, What was the brand name of the product you used and where can it be found? is it a product sold for use on dodgers? thanks for the idea.
  3. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Tried once to use it as a release agent in a canoe mold but didn't succeed to spread the gelcoat over it :p my bad..

  4. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    I've used several brands, there isn't much difference, at least for my applications. One Italian brand that promised the oil doesn't creep, contained the same product, but with a fragrance added. And of course it crept like all silicone oils do.
    The fabrics I sprayed over a year ago are still waterproof, but they do not look as shiny, so it is about time for a new spray job.
    Where I used it as anti-fouling, it did the job for 1 summer season, so it is a good solution for trailered boats, not for boats that stay in the water all year.
    The prop shafts that rely on silicone oil to keep the water out are submerged for half a year and seem in perfect order, just as I expected.
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