Can a knife really substitute for a hatchet?

 Can a knife really substitute for a hatchet (Even a small hatchet)?

Shown above: Halfbreed Blades Large Bush Knife LBK-01 GEN-2 in Böhler K340 ISODUR

Well the answer to that question really depends upon several things not the least being the skill of the person holding that knife. and what it is they want to chop apart.

But let's try and answer it seriously. it is not just a question of having a big knife, say for example with a blade over 7" and thinking this knife will substitute for a hatchet. What does a hatchet 

Long handle with centre of gravity located some distance from the user's hands.

have that a regular knife does not have, even say for example a knife with a 9" blade? Well, the hatchet has an entirely different centre of gravity to most knives. How does it achieve this? By way of a relatively long handle compared to any knife. All of the mass is at the head of the axe unlike most knife designs. This means it is easier to swing and achieve the greatest impact force possible with the least amount of effort.

Yes, it is also possible to achieve the same impact force by swinging a knife however in order to do this one must exert more "swinging force" to begin with. Can this be changed? Well possibly by tying a heavy knife on to a stick is one way. Maybe?

An example of a "heavy knife" almost 500grm (495grams) knife only! The "Centre of gravity" is  central to the knife. design.

Of course this could only be done for a knife where it is safe to do so, (as seen for an example knife above, possessing multiple anchoring points to lash a pole to).

There is no doubt about it that a heavy knife will (all things being equal) remove more wood per chop for the same amount of initial velocity than a lighter knife with the same geometry (of course no such comparison exists.) 

                                Halfbreed blades Large Bush knife GEN 2

that knife would need to be made pretty much similar in shape but with material removed to decrease its weight. The momentum would be different.

Since a knife can not be a hatchet (by design), is it possible to come close to what I would call a "lightweight hatchet" but still a knife? The design, for example, of FKMD's Parus comes a little close but it is still physically a knife!

Despite the FKMD Parus acting like a "small/mini hatchet" it's centre of gravity is still at the hilt! Although for swinging, the tip being furthest away from the handle, is much heavier than the portion of steel directly behind the tip.

Swinging a heavy knife should not be done in such a way as to mimic the swing of a hatchet. Instead the weight of the knife should be capitalised upon because one can not achieve the same swinging arc as that for a hatchet with a knife because of the knife's much shorter handle. It is also not possible to stiffen the arm to mimic the handle of a hatchet without incurring an injury to your arm (especially the elbow joint).

So in effect, the technique is to let the momentum of the heavy knife do the work 

                                 Halfbreed blades Large Bush knife GEN 2

just like one allows the momentum of the moving axe head do the work. and be satisfied that the mechanical advantage between axe and heavy/big knife will always be different. I have demonstrated this technique countless times for example in the many videos I've released on the channel @BushCampingTools showing how to "et the weight of the knife do the work" After all one must ask themselves "what's the hurry?" Are you late for some appointment? No, then don't rush such things because haste makes waste and incurring an accident in the bush you can become a serious liability!

So to return to the title question,:

Can a knife really substitute for a  (lightweight) hatchet?

I believe the answer to this is: "sort of yes" if the wood you are trying to chop is not seasoned and not of some crazy diameter! But big knives 

Lionsteel M7

will not replace the hatchet by no means.

Halfbreed blades Large Bush knife GEN 2