Skin friction

[Dull Spark]

One for the naval architects.

The only thing that grows on my coppercoat (or copper something) is fine green slime. It's far more slippery than the coppercoat itself, so why do I bother to remove it?

 

[AntarcticPilot]

One for the naval architects.

The only thing that grows on my coppercoat (or copper something) is fine green slime. It's far more slippery than the coppercoat itself, so why do I bother to remove it?

It increases the wetted area substantially, and that would be expected to increase drag. However, it isn't certain - some textured surfaces are actually MORE efficient than the equivalent smooth surface. For example, shark's skin has denticles that improve the hydrodynamic properties, and the mucus on cetaceans also improves their hydrodynamic efficiency, though bubble formation has a lot to do with it, too.

Perhaps you should carry out some experiments, motoring at fixed revs and measuring the speed through the water at various intervals after cleaning the hull? My gut reaction would be that you'll find that it does slow the boat down, but I'd be very interested to know! FWIW, I left Capricious in the water for 4 years after applying coppercoat; she came out with a fair bit of slime on her, but no large weeds or barnacles, except in a few areas. I was beginning to feel that she was slowing down a little, but not vastly so.

 

[[70521]]

One for the naval architects.

The only thing that grows on my coppercoat (or copper something) is fine green slime. It's far more slippery than the coppercoat itself, so why do I bother to remove it?

Because some new life form may develop in the primeval soup.

 

[earlybird]

Isn't it all bound up with boundary layers, as with golf ball dimples?

 

[Buck Turgidson]

If your surface roughness is such that it penetrates the theoretical smooth surface boundary layer it will add drag. The boundary layer thickness grows along the length of the hull and reduces with velocity. So if you just clean the first 1/4 of the hull you will probably have the same drag as if you cleaned it all but the length you need clean increases with velocity.

 

[Joker]

Ah, golf ball dimples are associated with the Magnus effect

 

[lw395]

Because some new life form may develop in the primeval soup.

In one.
Also the slime corrodes the copper unevenly, wiping it over keeps it smoother in the long run, although no doubt losing more copper?

 

[Hydrozoan]

Because some new life form may develop in the primeval soup.

Well yes, surely the argument for removing it - hydrodynamic issues aside - is that doing so hinders the natural succession of fouling organisms from getting going?

 

[[163233]]

Wipe it off on one side only and see which way the boat turns..

 

[Dull Spark]

Thanks to all of you. I can see I have a winter project ahead. I need to put some shark skin on the first 1/4 of the hull and some golf ball dimples on the rest. (Would osmosis have the same effect?)

Then, I need to cover the whole lot in a thicker boundary layer. Can I buy one from ASAP?

��

 

[Skipper_Christoph]

Then, I need to cover the whole lot in a thicker boundary layer. Can I buy one from ASAP?

��

No! As boundary and border are quite synonymous you just have to wait for the Brexit

 

[savageseadog]

Slime is a feature of Liverpool Marina. I can assure the OP that Liverpool Marina slime slows the boat, badly.