Internet description of the 2018 Yellowfin 21 Bay.

Hull and construction

The hull is arguably the most important part of the 21 Bay.

Yellowfin based it on the company's 21 Hybrid high-performance hull, rather than designing a conventional, relatively heavy bay-boat hull. The hull uses a stepped configuration, which is a major reason the boat can combine shallow-water capability with unusually high speed. 

The 15° transom deadrise is a good compromise. It isn't as deep-V as a dedicated offshore center console, but it's considerably more substantial than a very shallow flats skiff.

That gives you:

• Excellent shallow-water access
• Good stability at rest
• Very quick acceleration
• Good efficiency at cruise
• A surprisingly good ride for a 21-foot bay boat
• The ability to make occasional offshore/nearshore runs

The hull also has a relatively high bow and flared sides. That helps keep spray down and gives the boat more capability when you're running through chop rather than merely fishing protected flats.

One of the more impressive characteristics reported during testing was how the hull behaved in 1–2-foot chop. The tester found that the boat actually became smoother as speed increased, with the hull skimming across the tops of the waves when properly trimmed.

Shallow-water capability

This is one of the 21 Bay's strongest attributes.

With the engine trimmed up, the boat could operate in roughly a foot of water during the Sport Fishing test. The published draft is around 13 inches.

It also came with a hydraulic jack plate, which is particularly useful on a boat like this.

The jack plate lets you raise and lower the outboard vertically without changing the engine's trim angle. That is valuable when:

• Getting on plane in very shallow water
• Crossing shallow grass flats
• Running through skinny channels
• Getting the propeller higher when fishing extremely shallow
• Optimizing engine height for performance

So although the boat is capable of running fast, it's still very much designed around skinny-water fishing.