A lot of these are Royal Navy designations of vessels, which existed through the steam age and up to the 1950's.
Maritime Explaination of Designations:
Gun Whale- The largest row boat or launch carried by a warship, usually a Frigate. It is the only one that is armed. In Nelson's time with a 3 or 6 Pounder cannon, in the 20th century with a machine gun. Used by boarding parties to intimidate and surpress an enemy, land marines, etc.
In SFB / SFC terms, any Multi-Role Shuttle (MRS).
(Motor) Torpedo Boat- Short ranged wooden hulled coastal attack vessel. Armed with a limited number of torpedoes.
(Motor) Gunboat- Small short ranged wooden hulled coastal attack and escort vessel. In SFB / SFC terms the Klingon G1 Gunboat.
(Motor) Clipper- Small fast short voyage coastal escort vessel. Larger than a Motor Gunboat and usually metal hulled. Armament similar to a Gunboat. Used to defend against Torpedo Boat and Gunboat attacks.
(Motor) Skiff- Small short ranged slow coastal patrol vessel. Armament similar to a Clipper. Operates around harbours and local waters guarding minefields, etc. Acts as a local scout for shore based defences. Able to engage ships no larger than a Corsair on equal terms. Skiffs are never at sea for more than a day.
Corsair- Similar to a Clipper except totally offensive in role. Generally an opportunist, raiding and harrying vessel. Weaponry tending to be light but in quanity. In SFB / SFC terms the Orion Light Raider.
Corvette- A small to medium sized escort vessel. Smaller than a Sloop, Frigate or Destroyer. In WW2 the most numerous class of warship was the Flower Class Corvette with 167 in total. Always based on small to medium sized rugged civilian hulls and utilising civilian shipyards, components, propulsion, etc. The Flower Class was based on an artic whaler design, others were based around similar vessels. These are never conversions (see Caravelles) but new designs founded on a good civilian vessel. Despite being described as "one hit wonders" Corvettes carry more technology, electronics, ECM and ECCM than any other naval vessel. Defensive armament is usually token. In SFB / SFC terms were talking 1 x Ph2, 1 x Ph3 / PhG. Offensive armament is extremely specialised towards destroying submarines. In SFB / SFC terms replace hedgehog launchers with multiple transporters and depth charges / hedgehog missiles with transporter bombs. Replace submarine with any cloaked enemy warship, most likely Romulan.
Sloop- Frigate sized warship with reduced armament. Operates in coastal waters for patrol and escort duties.Cannot undertake long voyage durations. Relies heavily on visiting ports to resupply. Also used to transport personnel and materials between locations and bases. Most common duty is carrying the mail.
If you removed the Photons and nose Phaser from the F-FF and replaced them with cargo then you'd have a Sloop.
Mine Sweeper- A Sloop equiped to lay mines and remove mines.
Mine Hunter- A Sloop that can only remove mines.
Flak Ship- Sometimes refered to as a Point Defence Ship in the US Navy. A Sloop equiped completely as an anti-aircraft platform. Deployed in numbers by the German Kreigsmarine during WW2.
Frigate- A small well armed warship that carries a complement of marines and this is what defines a frigate. Capable of long extended voyages and shore based incursions. Does not carry torpedoes.
Destroyer- Originally intended to destroy motor torpedo boats and motor gunboats in WW1. Later used to escort convoys and screen battlefleet against submarine attack. Can sometimes have exactly the same hull and shape as a frigate. Carries torpedoes.
Fleet Battle Tender- Unique to the US Navy in WW 2. Created from gutted out 1920's destroyers. Carries and supplies spare parts, aircraft and ammunition to battlefleets enabling them to stay at sea for longer. Able to move at fleet speeds. Has limited point defence armament only.
Caravelle- A merchant vessel converted into an ad hoc frigate. Unique to Spain and South American nations.
I hope that this explains the smaller boats used by some navies.