Bjorn,

  Clearly, the smoother the finish, the faster the boat is going to be.

  But for the sake of discussion:

    - How necessary is that 20-micron finish?  A 1.5% reduction in speed might not be that bad.

    - More to the point, unless you dry-sail the boat, how often will you really have a 20-micron finish?  Even if you scrub the boat before a race, the finish isn't likely going to be 600-grit quality over the full hull.  Chances are, fouling is going to be more of an issue than the paint.

    - The copper/epoxy could easily be burnished by anyone who purchases the boat.  Unlike an ablative bottom paint, it's a sturdy finish.

    - Have you ever tried a product like sea slide?  It claims to be able to create that smooth boundary layer without going crazy with the finish.

        http://www.fasterwithseaslide.com/

      The 17% reduction in drag at 20 knots as tested in Lake Hopatcong, and the 8% to 14% reduction in drag with the tank tests at the University of Rhode Island, would both outweigh the penalty of a less-than-perfect finish.

  We've used this on a power dinghy with a noticeable decrease in time to get the boat on plane, so we know it works, but we don't know how well it works or for how long.  I've been planning for years to do a test with two torpedoes being dragged while connected to a load cell, both right after coating and then after having been in the water for two months.

---

  You could always burnish the surface and then add sea slide, but I probably wouldn't put in that kind of labor.  Tactics, boat design, and fouling are probably going to be much more significant than getting the copper/epoxy smoother than it already is.

        - Mike

Björn bjornmail@gmail.com [harryproa] wrote on 9/4/2016 3:10 PM:

 

Nice to see progress.

How much drag will this not perfect paint finish add to the hull? I thought it would be neglible, but then I read this article which shows how much drag an uneven surface adds. At 15 knots a less than 20 microns finish is necessary.

On Aug 12, 2016 04:01, "Rob Denney harryproa@gmail.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:

 

Fun times. 4 x 15-16 hour days, just like when i was young and gung ho.  Except I spent yesterday in bed recovering.  ;-)

Got the mast step towed in place, the bottom glassed and faired.    It was pretty rough but a couple of swipes with a straight edge got it feeling good fore and aft, but there is a definite kink sideways due to the extra piece I added to fix the stuff up.  

Shaped and added the ends, glassed the deck join,  rough faired the deck (still haven't decided what, if anything,  to do about the V in the deck) and painted everything.  Pics will be on the web page soon. I didn't take any of the processes as they are just conventional building.  I spent most of the time muttering "this would not be necessary with Intelligent Infusion".  The rest  was painting and antifouling.   

The cheap copper/epoxy is a bear to put on and runs like crazy, but is self levelling on flat surfaces so I did the sides separately to the bottom.    A light sand to expose the copper and knock off the few runs and it will be good.  

The waterline is drawn (easy with a flat bottom) at 150mm/6" draft, which is what it will draw when flying a hull, with the bow knuckle just submerged.   At anchor, about half as much. 

Paint looks ok from 3m/10', but only has to keep the sun off, so will be fine.  Once I know it all works, I may be inspired to get out the longboard and tart it up.  

Things to do before sailing?

Build mast and beams.  Peter has a couple of urgent jobs to wind, then the beams and mast. He says within a month. 

The beams have to be fitted into the sockets in the lee hull and aligned.

Rudder mounts on the beams.

Truck hull, beams and mast from Adelaide to here.

Assemble it and install the ww hull beam sockets.

Finish the rudders. The carbon ones are built, need gluing together.  I am trying to source some helicopter blades to use instead.  

Laminate the battens.  The mould is set up for this, the first one looks good, but was slow to build as I wet the tow by hand.  A wet out bath is the next job. I will also see how much difference adding a core makes to the weight/stiffness.

Paint mast, boom, rudders, beams, tillers and extensions.  

Tie on the tramp.  Bit of experimenting required as I want it to stay on the beams and tighten it with a single or perhaps 2 lines.

Set up the mast and boom so the sail can be made.

Go sailing and see what works and what doesn't.

Latest on the sail is I have some slightly soiled cloth for $20 per sqm instead of $80.  Marginally heavier than an optimal "string" sail, but recutting it will not be a problem, so we will start with this and see what happens.