graphite+epoxy+saltwater

[double trouble]

I am nearing the finishing line for the boat I have been building. It will be fished mainly in the bay and ocean. I was planning on coating the bottom with an epoxy graphite mix, but lately have heard that is not such a good idea due to graphite being a conductor, and the increased electrolysis that may take place. I plan on taking the boat out of the water nearly everyday. The most I would leave the boat in the water is 3-4 days. Is there a problem with graphite bottoms used in saltwater? Am I making a mistake by putting a graphite bottom on my boat that will be used mainly in saltwater?

thanks for the advise

[Dutch Rub]

Why would you want graphite on your boats bottom?

Have you ever tried to sand graphite and epoxy mix? Its a bit like sanding concrete and Id like to see how youre going to get it on there perfectly smooth and avoid having to sand it fair.

[double trouble]

I want graphite on the bottom of my boat exactly because it does not sand well. The graphite epoxy mix is used on boat bottoms so the bottom will slide over rocks and up on to sand beaches with little wear. This is a fishing boat not a yacht. If the fish see brush stokes on the bottom of my boat so be it.

[gary porter]

Well actually you can sand it if you want. Sanded graphite is theoretically the slickest and is used in competition surfaces in other applications. I use it on the bottom because its tough, and very slick so it makes for a great surface on a planing hull. I don't bother sanding it as that takes the gloss off of it. A mix of 25% will flow out nicely. I roll it on and then tip it if needed with a foam brush.
Gary

[gary porter]

Sorry, I forgot the original question,,,, I don't think there is a real problem when mixed at the levels you would use with epoxy. 25% max , theres not much in the way of any sort of conductivity.
I don't really know anyone that has such a bottom and has left it in the water all year but I would still say, no problem.
Gary

[double trouble]

Thanks for the infor Gary Porter.

[Dutch Rub]

Help yourself- its your elbows, but I seriously doubt shell be " gliding " over the rocks because you have a thin layer of graphite on her.

[TomRobb]

I've noticed that some drift boat guys put UHMW plastic on the bottom of their river dorys. Slicker-n-buttered poop and there for the reasons you cited. Electrolysis on a boat that's out of the water more than she's in may not be a huge problem.

[gary porter]

Originally posted by Dutch Rub:
Help yourself- its your elbows, but I seriously doubt shell be " gliding " over the rocks because you have a thin layer of graphite on her.Right , not much of anything will glide over the rocks but sand and gravel it will. There is actually or should be several building coats. I use about three or so untill the bottom becomes very black. After three years its still glossy.
No sanding needed and no bottom paint.
Gary

[Mike Keers]

This question comes up once in a while--to myself a while back in fact. I contacted WEST (Gougeon) about electrolysis concerns, and they said no problema at the levels we're talking--25% or so.

The epoxy acts as an insulator between all the little graphite particles suspended in it, or so sez they. Same story for aluminum, which is what I ended up adding rather than graphite--different purpose-I was after UV protection for the upturned hull during construction, and a bit of additional hardness as a secondary benefit for trailering.

[paul oman]

If you are concerned about the graphite, or don't want the black color, you can use powdered teflon instead.

The most common industrial approach is aluminium oxide in the epoxy (can use more available quarz sand instead - but ground garden dolomite (soft) might also be a good additive into the epoxy). Epoxy is basically a hard plastic, adding 'stone' makes it 'rock' hard. Adding graphite or teflon makes it 'slippery'

graphite and teflon, in small amounts is available at
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

paul

[WOODZOWL]

D.T.
This method is reccommended by some designers. I have used it on a few boats. There are at least two that I can document .both are power boats, one has spent the last 14 summers in the water without a failure, the other 4 full seasons in. Both had bottom paint applied, don't know if that makes a diff? I would say looking at the bottom of both boats, that I would use it again!

[PugetSound]

Previous replies about the graphite being OK because it will be insulated by the epoxy is basically correct. What you want to understand about graphite, however, is that it's danger with regard to corrosion (electrolysis) is not that it is a conductor (which it is, but so is the salt water) but that it ranks right up there at the very tip top of the noble 'metals' on the galvanic series (Zirconium, gold, and platinum are more noble; titanium is right below graphite).

It probably would be a good idea to put a non-graphite finish coat on the hull and any metal to be painted and then do the graphite routine.

[Tom Lathrop]

I have two experiences that both shed some light and shadow on the subject.

The telephone and many power cables that you see used on poles and underground in all kinds of environments use graphite. The graphite is mixed with the plastic sheathing to give it proof against deterioration from the sun. The electrical resistance across this sheath is essentially infinite even when measuring a length of thousands of feet.

In the second case, I have painted a couple of boat bottoms with Copperpoxy which is minute copper flakes mixed in epoxy. I have never been able to measure any electrical conductivity in this material, either freshly mixed or set up. On the other hand if one of these boats is left in salt water for a long time, a distinct greenish tint will occur in some places. This indicates that the copper is making contact with the water and oxidizing. I expect this is a sufface effect only with exposed copper particles.

Graphite is a poorer conductor than copper though. I've never heard of problems from graphite paint on boat bottoms from a number of people who have used it.

Me, I don't know.