It's really pretty simple.
To answer the second question first. A flat keel, typically tapered from about the last third of the length of the hull to the stern, is a delta pad.
The "what it does" is basically vertical lift. You would either have wide flats on the strakes or a delta bottom. It would be rare to have both.
The delta pad offers a couple different advantages over a rounded keel.
The first advantage is the ability to plane at a lower hull speed. As a side benefit, quicker planing times from dead stop to plane.
The second benefit is a higher riding attitude at speed. It mimics a lower "x" dimension. This creates bow lift and a higher attainable top speed with moderate hp.
It also makes the boat more stable up to certain speeds. Unfortunately, once that speed is exceeded, makes it unstable, it can "step off" and create a dangerous hook to either direction.
Another drawback is they can sometimes cause odd intake flows on a jet. Necessitating creative "spoons" and shoes to keep the pump loaded properly.
It's not until the lower 70 mph ranges that any of this comes into play in my experience.
They also don't turn nearly as well as a rounded keel, I feel it is that "step off" that causes a strange transition entering a turn.
I like delta pad hulls for the family ride that occasionally gets flogged on the weekend.
Up to about 75mph I don't think the negatives can be realized. The positives are far more beneficial for the average schmoe.
They also very seldom experience a porpoise problem and the hooks on these hulls are typically very slight.
GT
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