As a former varnish-aholic and if you have extensive teak, I dont think you want to screw around with varnish, oil, Cetol, and all the other complicated coating systems that ultimately and relatively quickly fail, etc.
The following pic is a
TEN year old "Honey Teak" (
www.signature finish.com) job. HT for the Chesapeake only requires an every two year 'maintenance' clear coat - 'scratch' the surface with a 3M purple pad and 'flow on' a catalyzed acrylic-urethane clear coat. Since its a part acylic base you can powerbuff every other year (when you powerbuff your gelcoat).
HT is
expensive but when you amortize over the years it turns out to be the long term cheapest in both cost and labor. Its a 2 part base using ferrous oxide as the UV protectant and a 2 part clear top coat. Its applied THICK for best UV protection (the bane of ALL other coatings). It goes on 'brownish' but quickly fades to be equivalent to an amber/honey oil based varnish finish. Only problem with HT is if you apply the base coats too thin the surface wood cells will be UV damaged and you will get lifting; apply 'extra - thick' and you can have the base last to ~12+years.
Best of all its easily repairable. It requires a
HIGH learning curve, can be applied wet-on-wet with brief waiting time to allow it to 'kick'. Best applied in cool/cold weather for best 'flow out' with resistant quality foam brushes .... or sprayed with a PreVal self contained sprayer (self-loadable aerosol bottle) for the finish coat. Horizontal surfaces can be laid down very thick, but vertical surfaces may require 'many' coats to build up the 'thickness' ... its quite flexible yet the surface is hard. Like all other finishes, it should NOT be applied at near the end of the day or in humid weather.
For the Ches (and further south) I recommend to apply the base coat 50% thicker than the mfg. recommended for longer life in the sun.
If youre a fanatic ... like all finishes, you really have to 'finish it' ... either by wet flat-sanding with 1500-2000 grit (wet) and then hand-rubbing with rottenstone and water or by powerbuffing with a foam knobbypad and 3M "Perfect-it" ... if you want a Hinckley type ultra-gloss finish as is found on large mega-yachts or private jet aircraft. I even 'finish' after spraying (with PreVal). Most just apply the last coat with a brush and leave it --- if you already have a well developed 'varnish/brush technique'
I also use HT clear to coat the mirror-polished bronze - portlights, hawse holes, binnacle, etc. ... again THICK coated with 'clear'.
Dont use HT on Iroko or other 'soft woods' such as found on Pearsons, etc.
Ive gone through just about every damn combination and method: epoxy - oil base - urethane - topped with Interthane/Perfection clear; resinated oils; epoxy encapsulation + Varnish, butt-ugly Cetol, Bristol, etc. etc. etc. and now use HT almost exclusively on teak.
Signature Finish recently had a fire and the site was totally destroyed. They are back in business but orders, etc. are a bit slow.