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Graphite Added to Epoxy Based Coatings to Reduce Drag?


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Anyone have any experience or data surrounding this? Obviously graphite reduces friction in numerous applications, but after looking online, I've mainly found refences to graphite added to bottoms of work skiffs to reduce damage when landing on rocks and sandy beaches. Could an epoxy bottom with graphite added (and faired) carry a noticeable difference through water versus the same bottom without graphite added? 

What would be the influence of adding graphite to an awlgrip or durapox type of coating?

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48 minutes ago, Tubes said:

Anyone have any experience or data surrounding this? Obviously graphite reduces friction in numerous applications, but after looking online, I've mainly found refences to graphite added to bottoms of work skiffs to reduce damage when landing on rocks and sandy beaches. Could an epoxy bottom with graphite added (and faired) carry a noticeable difference through water versus the same bottom without graphite added? 

What would be the influence of adding graphite to an awlgrip or durapox type of coating?

You could spend some money in the effort to screw up the paint. Throw in some sand and gravel while you're at it. YMMV.

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Back in about 1975 - 76 some Kiwi sailors had grahite bottoms on their Lasers.  The poms (Rodney Pattinson et al) had been using a product (called Graphspeed IIRC) on their Flying Dutchman, but that product was no longer available.

After the NZ Laser Champs in Wellington I travelled to Nelson in the South Island to learn how to make this coating, and I then used it on my Laser in Darwin.  I don't know if it was faster, but it certainly fucked with my competitors' heads.

Adding graphite to epoxy wouldn't have the effect you are seeking - the epoxy would "hang on" to the grahite, whereas releasing the graphite is what is supposed to modify the boundary layer and reduce drag. 

I have a feeling that the practice was banned - offshore boats had taken to drilling holes in the hull and attaching tubes through which they released polymers into the boundary laywer to reduce drag - that was banned and I think the wording of the ban captured the graphite system also.

It was also a pain the the ass to maintain and required frequent replenishment.  It's dead, let it stay that way. ;)

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53 SKIN FRICTION A boat shall not eject or release a substance, such as a polymer, or have specially textured surfaces that could improve the character of the flow of water inside the boundary layer.

There are a few paints out there that claim to be lower friction, but i its unlikely any would make a measurable difference without falling fowl of rule 53.  As it operates outside the auspices of would sailing, the America's Cup teams back in the early IACC days used to chase this holy grail quite a bit until from memory they ended up writing a list of allowed paints into the rule. Oracle was also also rumored to have played with releasing compounds during the lead up to the DOG match.

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17 hours ago, SCARECROW said:

53 SKIN FRICTION A boat shall not eject or release a substance, such as a polymer, or have specially textured surfaces that could improve the character of the flow of water inside the boundary layer.

There are a few paints out there that claim to be lower friction, but i its unlikely any would make a measurable difference without falling fowl of rule 53.  As it operates outside the auspices of would sailing, the America's Cup teams back in the early IACC days used to chase this holy grail quite a bit until from memory they ended up writing a list of allowed paints into the rule. Oracle was also also rumored to have played with releasing compounds during the lead up to the DOG match.

if a boundary layer exists between the paint and moving water, how could anything in the paint make the boat go faster?

that's why I don't understand how those ptfe, wax, or teflon  coatings can make a difference...

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27 minutes ago, Grande Mastere Dreade said:

if a boundary layer exists between the paint and moving water, how could anything in the paint make the boat go faster?

that's why I don't understand how those ptfe, wax, or teflon  coatings can make a difference...

Easy, there is no boundary layer in marketing.  Also worth noting that the concept of a boundary layer assumes constant flow, not something that really exists in around a sailing boat operating in waves.

Most of the coatings above are about stopping stuff growing on / sticking to the hull which would then cause drag.

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Long time ago, I did an epoxy/graphite coating on a Lightning centerboard. It was a mild steel plate, not stainless, and the idea was to reduce friction in the case more than fluid friction / drag.

It takes a LOT of graphite. The mix should should be very stiff, a putty rather than a paint. I ground  the steel surface and did a very light coating of epoxy with no graphite then laid on the filled mix. Getting it uniform and fair was a bitch though.

It worked very well, especially after I did a similar coating on the inside of the trunk.

As for drag, having the board at max thickness and slightly better-shaped than a chamfered steel plate was almost certainly far more benefit than drag reduction.

FB- Doug

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17 hours ago, SCARECROW said:

Also worth noting that the concept of a boundary layer assumes constant flow, not something that really exists in around a sailing boat operating in waves.

It's probably better to think of the simplified mathematical models for boundary layers breaking down than the concept itself failing.   Anytime the hull is moving relative to the water there's some sort of boundary layer present, but in complex conditions they don't necessarily behave the way the simple equations in textbooks suggest.  These equations are mostly derived for extremely idealized scenarios (e.g. steady flows over infinite flat plates).

On 4/5/2021 at 12:59 PM, SCARECROW said:

53 SKIN FRICTION A boat shall not eject or release a substance, such as a polymer, or have specially textured surfaces that could improve the character of the flow of water inside the boundary layer.

Does anyone know why textured surfaces were banned?  I can see why releasing polymers is environmentally unfriendly and race committee's might want to discourage it.

I think the big BMW/Oracle trimaran used a polymer release system, but they ultimately decided that the weight of the system was too high to be worth it.

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3 hours ago, MFH125 said:

It's probably better to think of the simplified mathematical models for boundary layers breaking down than the concept itself failing.   Anytime the hull is moving relative to the water there's some sort of boundary layer present, but in complex conditions they don't necessarily behave the way the simple equations in textbooks suggest.  These equations are mostly derived for extremely idealized scenarios (e.g. steady flows over infinite flat plates).

Does anyone know why textured surfaces were banned?  I can see why releasing polymers is environmentally unfriendly and race committee's might want to discourage it.

I think the big BMW/Oracle trimaran used a polymer release system, but they ultimately decided that the weight of the system was too high to be worth it.

Didn't that go back to one of Connor's S&S with a 3M textured film on the bottom? Memory may fail...

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Various ships have. Need a fair bit of power to run the compressor to make sufficient bubbles to matter. I don't think it's practical on a sailboat.

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  • 2 weeks later...
On 4/13/2021 at 11:01 AM, Zonker said:

I don't think it's practical on a sailboat.

Didn't the Route 66 have some sort of forced air system to try to break it out on plane? Not sure if it worked. 

http://www.yachtroute66.com/

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They did I recall. But I think they were just vents to the deck above to promote planing aft (maybe they had a step or little venturis to suck air down?)

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