I posted this over on GuillemotKayaks - doing the same here to cast a wider net...here goes:

I'm about to sand the 'final' coat of varnish off an S&G Petrel for the fourth time due to a dissatisfying finish. I'm giving it one more try, and will then call it and take this vessel for a paddle, no matter the results. I'm sharing issues encountered and application methods used, with hope that folks on this forum have suggestions I can use towards better results.

On the first four (base) coats of varnish, I masked off the hull, varnished the deck, let this cure, then did the same on the hull. This worked well using 2" foam brushes as an applicator, inasmuch as the coats were smooth and even. However, a raised seam at the meeting place of hull and deck coats required sanding, so I switched things up to apply the final coat.

I hung the boat for my "first" final coat, the notion being that I'd work 6-12" sections around the boat and do the whole thing at once. Using 2" foam brushes again, I found that by the time I got around the boat, the previous section had set up to the point of creating permanent brush marks. In other words, I wasn't able to move fast enough. This was particularly true around the cockpit - where the beam is greatest (i.e. the most surface area to cover), and where there are many details to address while applying varnish.

I tried a 3/16" x 4" mohair roller as the applicator on my "second" final coat. The roller covers surface area faster, but despite vigorously rolling it over tape before starting, too many fibers we deposited into the varnish. I was again left with permanent brush marks around the cockpit, too.

For my third and fourth final coats, I tried a 4" foam roller, smoothing off with a badger hair brush. I switched up the process additionally by first doing the deck and immediately afterwards doing the hull, rather than working in full vertical sections.

Foam rollers leave bubbles in the varnish (more so than other applicators I've used) and hold too much varnish, creating perfect conditions for runs. On the last coat I was extra mindful about lightly applying the roller (i.e. to avoid squeezing out excess varnish) but still, runs. 

In addition to previous issues, just enough varnish pushes over the shear seam in places to create a noticeable extra build up. This has happened even though I have been careful about applying and spreading varnish evenly. Hence, varnishing the entire boat in one go may not be the ticket.

One final note about working conditions -- my "shop" is in an unheated basement. I have the shop area insulated in a manner, and get temps to ~65 degrees with a single, radiant space heater. The application specs on the product I'm using (Interlux Schooner 96) indicate nothing contrary for this as a working temp.
 
So here I am, contemplating a TENTH coat of varnish (but really, the fifth-ish), unsure of how to improve the outcome...

I've considered masking again, but only the deck. In this revised scenario I'd mask off and varnish the deck, sand smooth the seam at the mask line, and varnish the hull, varnishing right over the smooth seam. I'd use foam brushes as applicators, since these have provided the best results to date. 

This approach seems to leave a lot to chance, with no real mitigation against aforementioned issues, and I'm not convinced I'd get a smooth deck-to-hull transition.

Any additional ideas from the crew on this forum is greatly appreciated. Mainly, feedback focused on how to get a good, final coat over the entire boat surface is what I'm after. That said, open questions that I have:

- Would thinning the varnish help (1) with the speed of application and (2) mitigation against runs?
- Would getting the shop warmer do anything other than decrease the cure time? 

Thanks in advance...