Hi Andy.
I've been giving some thought to the problems that you mentioned earlier, re the varnishing.
I can't offer any explanation as to the reason for short drying times that you are experiencing with the varnish, as I am getting at least 20/25 mins. before the brush starts to drag. Maybe, the original recipe has been tweaked somewhat by the German new owners, they have owned the company for about a year now and yours is, "fresh" stock. I will certainly be very disappointed if that proves to be the case.
The Classic that I am using if old stock and that may explain the difference. Fortunate for me if that is the case.
Re. brush marks. Quick drying times will definitely not allow the varnish time to level,only reduced temps. will extend it. Also, "tipping off", could help in this respect.
Forgive me if you already know all this, but the brush angle is very important when tipping off. I don't know your varnishing sequence but just for an example, let's say, bottom and sides first and then top and transom last. When tipping off always hold the brush at an high angle and use the tip only and not loaded with varnish.
In the example, do the bottom, thin coats always, tip off, then varnish one or both side, tip off, then tip off the bottom again, tip off the now varnished sides, tip off the sides again before doing the top etc. Varnish the top and transom, tip off, wait a few minutes, check for runs and sages, tip off to correct. Finally tip off the top etc.
After a minute or two check all over for any faults and you should have enough time to correct.
Sounds complicated but worth the effort to achieve your desired finish. Hope that helps.
Mike.