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Old 24-10-2013, 03:24   #1
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fairing block

boat was hauled for winter and i'm writing the list of projects.
Since moving the boat to a different location the fairing block for the depth sounder has severely rotted (???) and needs to be replaced.
I think i'd like to remake it in epoxy but i don't know much about epoxys.
looking for some guidance on epoxy and what material to bed it against the hull with.
can cured epoxy be shaped with woodworking tools?
Thanks
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Old 24-10-2013, 05:43   #2
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Re: fairing block

Had a similar problem with the fairing block on Bluestocking. Removed it carefully, placed it, heavily waxed, on a piece of glass, and gave it 3 chopped strand layers. Popped the mold off the glass, and filled it in 3 pours of polyester resin, m/balloons, and some chopped up fibre. Sealed with epoxy, 5200 to hull and redrilled. No problems in 15 yrs.
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Old 24-10-2013, 05:57   #3
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Re: fairing block

Most everything you might like to know about epoxy as it relates to boatbuilding can be found here in this excellent resource from the Gougeon brothers. As an architect you might enjoy reading it just for fun.

http://www.westsystem.com/ss/assets/...k%20061205.pdf

Can you carve cured epoxy? One of the things that makes epoxy so handy to the ability to modify its physical properties through the use of various fillers. For example a high density filler(usually marble dust) or a low density filler(glass or phenolic micro-balloons) can affect the strength of the finished product significantly.
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Old 24-10-2013, 13:20   #4
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Re: fairing block

thanks for the replies.
the Gougeon reference is exactly what i was looking for.
all 412 pages ;!
always good to learn about other materials.
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Old 24-10-2013, 13:41   #5
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Re: fairing block

Epoxy is very useful stuff, however it is a strong skin sensitizer and if you read the MSDS you might notice it tests positive for invitro mutagenicity. The vapor pressure is low so you mainly need to watch out for skin contact, always wear gloves! Barrier creams are great too. If you get it on you, best to use a waterless hand cleaner to remove it and avoid taking a solvent bath at all costs.

Supposedly the resin itself is fairly benign, the hardener is what you have to watch out for. I know someone who is sensitized and gets a rash even when exposed to cured dust from sanding, not fun.

Generally the higher the ratio of hardener to resin the less hazardous it is. 1:2 for Systems Three vs 1:5 WEST System for example. Sadly, the lower ratio systems like WEST tend to have better mechanical properties.

All of part A plus all of part B equals all of part C so don't try to get creative, try to be as precise in measuring and as thorough in mixing as possible. Volume varies by temperature but pumps are good for most purposes, use a scale if your are a perfectionist.

Take the time to plan your work flow before you start mixing. Stay safe and have fun!

Epoxy fun fact: Epoxy is commonly used for potting electronic components. Turn off that LED light and inspect the "bulb", it's a stack of gem chips potted in epoxy!
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Old 24-10-2013, 13:53   #6
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Re: fairing block

Roger on MSDS
I'll read the reference material: but i've one more question: does the size of the casting matter in terms of composition or setting/curing properties?
Have to measure it but for this conversation i imagine a 6" diameter cylinder 3" or so high. a 2" hole for the transducer and after cure shaped for the deadrise of the hull.
Thanks again
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Old 24-10-2013, 13:56   #7
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Re: fairing block

The chemical reaction is exothermic, meaning it produces heat. If you mix up a batch and let it sit, it will gain heat at a compounding rate which is usually referred to as "cooking off in the pot".

The take away here is that it is not suitable for casting in large volumes. Mix and pour in smaller quantities. If you re-coat inside of the "green window" you can achieve a chemical bond. If you wait for more than partial cure, you will have to wait longer for a full cure, remove the amine blush if it occurs, then abrade the surface to provide for a mechanical bond.

Filler is cheap compared to resin, for a non structural application like this I think low density or microlight would be good. Add filler to achieve a peanut butter consistency, apply with plastic spatula. Wear dust protection when using fillers.
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Old 24-10-2013, 14:20   #8
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Re: fairing block

For casting larger volumes where the adhesive properties of epoxy are not essential you can check out this product called Seacast. I know a couple people who have used it to replace rotted-out mast steps. Polyester resin based. Cheaper than epoxy.

www.transomrepair.net - The Home of Seacast™ - www.transomrepair.net - The Home of Seacast™
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Old 24-10-2013, 19:55   #9
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Re: fairing block

I've fit about a million of these. Never had a failure. They are pretty bomber, right off the shelf. Lots of newer 'ducers are designed for these. No possibility of rotation.
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Old 24-10-2013, 19:57   #10
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Re: fairing block

Quote:
Originally Posted by Delancey View Post
For casting larger volumes where the adhesive properties of epoxy are not essential you can check out this product called Seacast. I know a couple people who have used it to replace rotted-out mast steps. Polyester resin based. Cheaper than epoxy.

www.transomrepair.net - The Home of Seacast™ - www.transomrepair.net - The Home of Seacast™



Casting resin, while common, is brittle and totally inappropriate for this use. If I was to cast a fairing block (which I wouldn't), I would only consider Chockfast Orange.
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Old 24-10-2013, 20:00   #11
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Re: fairing block

Just make sure to set your bevel gauge correctly-and don't cut it backwards! In my shop, I'm the only one allowed to cut these anymore. Even our most experienced guys cut them backwards sometimes, it's just challenging to visualize correct under bevel/over bevel. Check thrice, cut once!
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Old 24-10-2013, 20:08   #12
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Re: fairing block

Quote:
Originally Posted by Delancey View Post
Epoxy is very useful stuff, however it is a strong skin sensitizer and if you read the MSDS you might notice it tests positive for invitro mutagenicity. The vapor pressure is low so you mainly need to watch out for skin contact, always wear gloves! Barrier creams are great too. If you get it on you, best to use a waterless hand cleaner to remove it and avoid taking a solvent bath at all costs.

Supposedly the resin itself is fairly benign, the hardener is what you have to watch out for. I know someone who is sensitized and gets a rash even when exposed to cured dust from sanding, not fun.

Generally the higher the ratio of hardener to resin the less hazardous it is. 1:2 for Systems Three vs 1:5 WEST System for example. Sadly, the lower ratio systems like WEST tend to have better mechanical properties.

All of part A plus all of part B equals all of part C so don't try to get creative, try to be as precise in measuring and as thorough in mixing as possible. Volume varies by temperature but pumps are good for most purposes, use a scale if your are a perfectionist.

Take the time to plan your work flow before you start mixing. Stay safe and have fun!

Epoxy fun fact: Epoxy is commonly used for potting electronic components. Turn off that LED light and inspect the "bulb", it's a stack of gem chips potted in epoxy!


Hardener ratios generally vary with type of hardener, not just brand to brand. WEST has numerous products in both 3:1 and 5:1. Proset for instance is mostly 3:1.

Amines in the hardener are what contribute most to toxicity and sensitization. This means cleaning amine blush with a solvent (common) is dangerous. Skin sensitization is ugly, and I have seen careers end because of it. But respiratory sensitization is much much worse. I know guys who can't come within 100 yards of wet epoxy without breaking out in hives all over. Several of them.
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Old 24-10-2013, 20:10   #13
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Re: fairing block

Yes the more I look at this project the more I think epoxy is too brittle in this application.
I may be wrong but where I'm sailing these days (Hudson River and extended environs) there's lots of heavy floating debris. Last year I came upon an entire oak tree....and yes I hit it.

My point: as much as I like the properties of epoxy to resist attack from organisms, I don't believe it has the ductile strength to resist impact.
It would shatter like glass.

Back to wood. It lasted for 40 years.....it'll last for another 40.

And then it will be time for someone else to take care of Voyager. :!
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Old 24-10-2013, 20:11   #14
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Re: fairing block

Quote:
Originally Posted by Delancey View Post
Most everything you might like to know about epoxy as it relates to boatbuilding can be found here in this excellent resource from the Gougeon brothers. As an architect you might enjoy reading it just for fun.

http://www.westsystem.com/ss/assets/...k%20061205.pdf

Can you carve cured epoxy? One of the things that makes epoxy so handy to the ability to modify its physical properties through the use of various fillers. For example a high density filler(usually marble dust) or a low density filler(glass or phenolic micro-balloons) can affect the strength of the finished product significantly.


Epoxy green trims OK. Not as nice as poly, but if you catch it at just the right moment in the cure cycle it carves oK. I often do thirty minutes worth of sanding in thirty seconds with a Shur-Form (the Japanese kind) at trim stage. Always very satisfying.
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Old 24-10-2013, 20:14   #15
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Re: fairing block

Quote:
Originally Posted by smaarch View Post
Yes the more I look at this project the more I think epoxy is too brittle in this application.
I may be wrong but where I'm sailing these days (Hudson River and extended environs) there's lots of heavy floating debris. Last year I came upon an entire oak tree....and yes I hit it.

My point: as much as I like the properties of epoxy to resist attack from organisms, I don't believe it has the ductile strength to resist impact.
It would shatter like glass.

Back to wood. It lasted for 40 years.....it'll last for another 40.

And then it will be time for someone else to take care of Voyager. :!



Maybe. The off the shelf option will last forever, be about as cheap as a big chunk of hardwood plus the time to make it, and is superior in design as well. Probably cost a little more, but much better result.
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