Originally Posted by Locozodiac
If I got the idea correct: the anchor is no good because cannot secure itself properly or well burried on sandy bottoms, or even securing properly will free itself easily ? Would it be a matter of adding extra weight to the anchor or maybe larger & thicker chain, etc.
No, an anchor works by a combination of anchor weight (ensures that the anchor penetrates the substrate), fluke (or other equivalent displacement object) design such that it a) orients itself to set, and b) tends to bury itself deeper with greater pull. The chain is there to make sure the anchor line pull stays in a relatively horizontal direction at the anchor (also helps avoid chafe, but that's a different matter.)
The problems with the grapnels is that a) it's not heavy enough at the flukes to penetrate the bottom very well, and b) the flukes are relatively tall and thin (not to mention sitting in the bottom at 45 degree angles), and offer very little resistance in soft bottom compositions.
Compare that to, say, a Danforth, where the anchor weight as it sets is brought to bear on the two fluke tips, which helps it penetrate. Then once it's buried, the entire flat surface of the flukes offers resistance to pullout.
Grapnels work well on irregular hard bottoms (make sure you have a trip line rigged), but are useless on smoothish hard bottoms or just about any soft bottom.