I assume that your teak is BARE untreated teak - no oil finish, no
varnish, nuthin; but teak.

If so, get some *paraformalyehyde crystals* (MildewGaz®, etc.) -
available from West Marine, etc. Cover and seal the teak with Saran or
other plastic and add the crystals between the wood and the plastic.
The crystals will turn to gas and that will kill the mildew but will
take days or even weeks. Paraformaldehyde is a noxious toxicant so
keep the boat well ventilated when using. When the mildew is dead
(good and dead) scrub the wood with a dry brush (IMPORTANT**** wear a
respirator to prevent breathing the potentially very toxic mildew
spores).

If you haave a major mildew contamation close the boat tight, load up
on paraformaldehyde and kill ALL the hidden mildew ... or you will
continually reinfect every time the boat gets damp. Then get into all
the hidden places and scrub with caustic soaps to dissolve alll the
dead mildew. Be **sure** to wear a respirator and other body
protection when cleaning mildew

Otherwise, plan on sanding, bleaching, etc. Any 'soap' that you use
on bare teak will dissolve some of the wood cells and will/may turn the
area darker (can be lightened again by using successive very dilute
'washes' with oxalic acid).

Nothing beats a

;-)