Card says if your hull value is 4 or less receive a stress. My opponent said it wouldn't work on a firespray. I said not until I get your hull value to 4. He said no my hull value is 6. Is Hull value static? It seems to me that it should change as you damage the ship? Clarification please.
Flechette torpedo question.
Hull Value is a static number. It does not change when damage is dealt. Referencing the core rulebook, page 13:
"When the number of Damage cards dealt to a ship
equals or exceeds its hull value (yellow number), that
ship is destroyed (see “Destroying Ships” on page 16)."
The yellow printed number does not change. Currently I believe the only way to alter a Hull Value is to equip a ship with Hull Upgrade, which increases the number by one.
Hull value is the base value. It does not degrade as you take damage.
If you look at the rules for destruction, a ship is destroyed when it has damage cards equal or greater the hull value... Which would be bad if hull decreased 
A lot of people use a shorthand of "I have X hull left" but the value does not technically change.
BREAKING NEWS: This situation is directly addressed in the brand-new FAQ:
"When determining whether the defender receives a
stress token from Flechette Torpedoes, the defender’s
starting hull value (including any equipped Hull Upgrade
card) is used, not the defender’s remaining hull points."
Very clear and concise. Thanks for the clarification!