How to get a sharp edge on channels?

[SDSG]

Looking for some guidance on getting a sharp edge on channels. I’ve read a few suggestions here on Swaylocks, but didn’t find a detailed thread on the various ways to do it and pros, cons, effort, etc. The board is a 4 channel twin fin, photos attached.

Before lamination, I rounded the edges of the channels a bit. The lam in one layer 6 oz. Using polyester resin. I have completed the hot coat on the deck, and now ready to do the hot coat on bottom. I’ve read about using tape dams for getting the channel edges sharp, cheater coats before hot coat, double hot coats for the edge of the channel, etc. Here’s some thoughts and questions going through my head.

• Lam resin or sanding resin? I’m hesitant to do anything along the lines of cheater coat with lam resin as I don’t really want to end up trying to sand lam resin in/around the channels if it doesn’t go according to plan.

• Tape dams: See pic. Is this how one would do it? I’d have to tilt the board to get the resin to flow into the void created by the tape dam, meaning I’d have to do it twice, one for each side. If I did this would I do it before the regular hot coat, or after the regular hot coat.

• Is it ideal to make the edge sharp along the entire channel or only where the channel is deep enough that it’s side wall approaches vertical. Seems it would be difficult to do in the entry part of the channel where the channel is not very deep and the side of the channel is far from vertical.

• Is the sharp edge really necessary? Pros and cons from a performance standpoint.

Any and all advice, methods, and tricks would be welcome. The more detail the better since I’m still fairly new to this craft. This is board #5 for me, and only one of my previous boards required a sharp trailing edge, so not much experience with tape dams. Thanks in advance to all with an opinion

[OSS1]

That last photo looks fine to me. Hotcoat it and hand sand. A hard block with sandpaper wrapped around it will harden/sharpen the edge.

[stoneburner]

For my Coanda Channel, a hard edge (90 degree walls) is critical for proper hydrodynamics, especially related turbulence affecting the boundary layer. As a shaper referred to it during a discussion we had, the hard 90 degree at the edge of the cliff — where my channel wall meets the bottom surface of the SB.

I developed this technique for hand lamming my channel (I used epoxy for this one). Since I have been using XLPE and CNC for prototyping my current BB/Paipo projects, I haven’t used it (No glassing required). However, I am one prototype away from using it now. (BTW I built my own channel shaping tool using large dimension square dowel with sandpaper on one side).
Follow link.

Stoneburner's assist build 48 1/2" body board

My glassing skills with epoxy are mediocre.  The biggest challenge for me on this channel was a clean glass job on the channel’s 90 degree edges and inner bottom angles.  I figured Charlie could do it without problems. While Charlie was working on this build, I was trying to come up with a good way to hand laminate the channel.  The standard recommendation from several members has been to use spray adhesive to tack the dry cloth to the channel walls.  The biggest drawback to that method is find…

[SDSG]

Thanks OSS1. That sounds a lot simpler than I expected. And thank you Stoneburner as well. I’ve actually read that thread about your channel cartridge before, which is very cool. Having been raised by a physicist, your work resonates with me. You were one of the people I had seen a post from about this before, in which you said “Tape inside channels like a Hot Coat, Cheater them,pull the tape and Hot Coat as normal.”