"The problem with the undercut in any of these variations is that it allows the tree (or lead) to bend down due to the compression side of the cut collapsing on itself. This puts more strain on the tension (top) side resulting in earlier tear out and less successful clean separation. If you guys are making an undercut then it isn't a Coos Bay."
What Brian said is spot on.
Undercuts just increase the pressure and tension forces in the stem. The idea of the Coos Bay is to work around those forces and circumvent the potential consequences they present.
The Coos Bay is accomplished in 3 cuts. Side cut, side cut, top cut.
Triangular cut? Hold on to that thought.
First, always remember this... when attempting to cut a heavy limb, spare or tree, no matter what method you use, there's strong potential of rip roaring consequences and TOTAL LOSS OF CONTROL. It's the nature of the beast. Cutting any heavy stems is serious business.
Using the Coos bay there's no need for an undercut. Not at all.
Instead place a side cut into the stem a quarter to third of the way in, either the right or left side. Why you might chose right or left side depends if there is any side favor in the work. Side favor, in excess, can cause the work to twist off the cut instead of popping off clean. Foiling any cut.
In lesser cases I always place the first side cut on the side of any favor. I have learned that saves on stuck saw scenarios.
So go ahead, place the first side cut square... up to a third of the way into the stem. and while making the cut observe the stem for any movement. Generally speaking, if the stem is sound and balanced it will not move appreciably. Up to half of the way in!
Next, place another side cut into the stem, opposite the first, about a third of the way in also.
If nothing unexpected or bad has happened at this point consider yourself a savvy sawyer.
I declare, up to two thirds of the wood fiber in the stem of a heavy limb, spar or tree can be severed without any rip roaring consequences.
No conventional cut can sever as much wood fiber in a heavy limb, spar or tree without some consequence. Once again it is the beauty of the Coos Bay cut.
At which point, with proper warnings to all around, execute the Coos Bay by severing the tension wood.
A savvy sawyer can expect 80 to 90 percent success rates using the Coos Bay cut.
Success rates are equivalent to ones skill and knowledge of predicted outcomes.
I'm here to tell, cutting heavy limbs, spars and trees is the Treeman's nemesis. Be aware. Stepping into any such scenario holds sure and certain risks.
If you don't feel sure or certain about the situation don't be a fool, use an approach you know will guarantee the results you seek. Good decisions in this work have far less consequences.
The Coos Bay is just one one method of many in the Treeman's tool box.
Be wise, be smart, be safe and prosper.
