Normally wood is bleached lighter with oxalic acid, available at at some paint and hardware stores. It is also in many of the teak cleaning products available in marine stores. I can't imagine why anyone would stain teak as it looks great the way it is. I've always picked wood for its looks without stain rather than trying to make it look different or like another wood. If you can remove the varnish totally it shouldn't be a problem. The teak should look great with plain varnish or oil as it is a beautiful wood.

 

TeKa A & B...

 

If I read your thread correctly you're referring to the interior teak, not the cockpit. If that's the case be careful what product you use as some of them are rather toxic. TEKA A-B is one them. Oxcylic acid to a lesser extent. BTW household bleach mixed with water at a 1:3 ration cleans teak but not sure it would lighten it consistently. Good luck.

 

I've had good luck with sanding with an orbital sander.

 

On surfaces where the veneer is 1/16" or less sanding can be a mistake if you're not very careful.

 

why would some one have to refinish a ten yr old boat on the inside? since you don't know who did this see if you can track down the owner who did this and find out if he used a water based stain. you should be able to get it off with water and soap and scotch-brite pad/sponges. if it is oil based leave it alone because the out come will never be right enough to restain to original.

 

If you can get down to bare wood, I have had very good luck with a two part system called "Snappy Teak-Nu". URL here: Snappy Teak-Nu: 2-part teak cleaning system

Read instructions well and be careful not to let product get on other painted or sensitive surfaces, as there is a mild varnish remover in it that will lift paint.

 

depending on the location (ie interior/exterior) ive found the typical PO has been lazy in many cases and simply stained over what needed actual TLC. If in the cockpit, or the top of the stern rail i would seriously consider sanding until ive found good wood.... that stinkin mildew finds every crevice (except the those in our pants i hope) and needs to be eraditcated..... then finish as desired.