I have not run these comments by Harald, but I feel reasonably confident that he will be in agreement with most or all of what I am saying. And if not, I am happy to hear the corrections.
I learned something last year that is actually quite obvious so it's not surprising that it took me 9 years of skiing to figure it. When skiing 3-D snow (powder, fresh snow and soft crud) the skis need to come up enough out of the snow so that they can release and so that the skier can tip the skis on edge to initiate the next turn (release, transfer and engage). The relationship between float and velocity is an important one. Most intermediate skiers that try to ski in powder on skinny skis find it very challenging. Many advanced/expert skiers don't find it very difficult at all. The reason why is speed or velocity. At a high enough speed, even the skinniest of skis will plane enough to allow release and transfer and re-engagement onto the other set of edges. Having said that, if you are on thinner skis and you feel uncomfortable with skiing at a faster speed, then it is likely that you will not plane high enough to make RT and E free and easy and the skis will get caught up in the snow. Now add to this some other potential issues that intermediates may bring with them into 3-D conditions (like poor fore-aft balance, or rotating the upper body, not releasing the stance ski causing a stem) and without enough speed on thinner skis it can get ugly fast.
In PMTS the goal is to get the bullet proof short radius turn bullet proof enough so that the skier can ski at terminal velocity and continue to make short radius turns. Terminal Velocity is a term Harald uses. It is the speed one arrives at doing SRT’s. It is also the speed at which one stays at as long as the rhythm and pace of the SRT’s stays the same (hence a terminal speed that does not increase). This is the goal for any PMTS skier in steep difficult off piste conditions. In steep terrain the speed may seem high at first but if the skier stays diligent with SRT’s that speed will not increase. If you watch HH and Diana ski pow this is how they do it. Max has mastered this as well. I can do it on dark blue terrain for 15 turns but not always on black terrain. So again from the PMTS perspective, the goal is to ski at terminal velocity using the bullet proof short radius turn. And this is a lofty goal for any skier. It took Max years and I am still working to get there.
So when looking at the issue of equipment when one is focusing on skiing this way, it is very simple. Sidecut and TR actually become more important than float!! I will say it again, when skiing at terminal velocity with BPSRT's sidecut is actually more important than float. The float is coming from the speed and at terminal velocity, almost anyone at any weight will have enough speed to plane high enough to RTand E all the way down the hill. No one is ever going to claim that this is easy, but it is the goal. And anyone that gets there (even if it is only for 15 turns at a time) will tell you that it is an amazing experience.
So it absolutely follows that if you can't or don't want to ski at terminal velocity then you will need more float than the skier who is skiing at TV. This is why wide skis got popular in the first place. Speed will eliminate many issues that 3-D snow will throw at a skier. Without the speed we need more float. Add to this the issue of size and weight and 6 4" 220lb guys that don't want to go fast need a lot more float to be able to plane high enough in the snow to RTand E.
So there is no doubt that skiing on fatter skis can makes things easier in 3-D snow especially for the skier that wants to ski at slower speeds. You can ski at a slower more leisurely pace and not need to work as hard to get the skis to plane high enough to make turns. But it is important to remember that in PMTS, that is not the goal. The goal is to ski at terminal velocity using slalom turns in Pow and Crud to control one’s speed.
It is also true that generally the longer and wider that you go, the wider the TR of the skis goes. What you gain in float you are losing in edging ability. So if you are on a 192cm ski that is 120mm underfoot and the TR is 36m, you have great float but you are also skiing on a plank and the natural TR is that of a super G ski. In PMTS we are trying to ski slalom turns in steeps in 3-d conditions (again at terminal velocity). This is very simply why Harald Harb has hated fat skis for so many years. He is giving up so much in TR and because he can ski fast he doesn't need the float. That's why he'd most times rather ski steep pow on his IM 78's than on a 30m TR ski. Can he ski it on the wide TR ski, of course, but he actually has to work harder because he can't use the sidecut of the ski to help him turn the skis.
Rockered skis: Does rocker give more float? Yes. So this makes it easier to ski at slower speeds and still be able to RT and E. But from a PMTS perspective rocker (especially rockered tails) come with another set of issues that complicates it for PMTS technique. Rockered tails make it incredibly easy to slip, pivot and steer the tails, so easy that this often becomes the default move for many skiers that are on them. This is very important factor. Rockered skis and especially rockered tails respond better to pivoting that to tipping. In PMTS our first and primary movement to initiate any turn is to tip first and ask questions later. On some rockered skis it is almost impossible to tip without the tails sliding out because they respond so quickly to any lateral pressure. So on skis of this nature the skier will start to adapt to the natural pivoting that is occurring in each edge change and the skier is now watching and listening to how the ski pivots and no longer to how much the skis are tipping.
Something that I haven't mentioned is the necessary component of counteracting forces and counter balancing forces in good PMTS skiing. When skiing SRT's at terminal velocity, there is no steering. There is only flexing to release and the CA and CB forces naturally move the skis to their new edge. This is the only way that a skier can actually do slalom turns or BPSRT's at speed. Everything needs to be lined up with upper and lower body separation. It is hard or impossible to steer skis into turns at these speeds. Rockered skis (again especially tail rockered skis) are designed to be pivoted, smeared, steered and slarved). So when a skier skis on a ski that not only does not require proper CA and CB forces to initiate the edge change, but actually requires some modest amount of rotational force (that is what steering, pivoting, slithering, slarving and skarving require) this is why we will say again that rockered skis do not promote good PMTS technique and in fact promote the opposite. Again there is more than enough float available for any skier that wants a ski without rocker (at least at this point in time), but what attracts people to rocker is the amazing float and the ease with which the skis will pivot, smear, steer, slither, slarve and skarve, (all of which we try to avoid in good PMTS skiing)
The great news is that there are excellent 3-d skis available that do support PMTS technique. PMTS skiers that want to learn how to ski at TV should be choosing skis that support this, with no rocker and tighter turn radii. The skis that come to mind are the Icelantic Shaman and the Movement Pariah and Jam. The Head Peak 78 and Peak 85 also fit into this discussion. (Ski Logik makes quite a few skis with tighter turn radii but I have yet to try them. Perhaps I can try them and get Harald on them this season.). My goal is to be able to ski any condition on any ski (within reason as I don’t want to take my ISL RD slalom skis into a steep powder ridge and ski it. It may be possible but it will never be fun!). Perfecting the BPSRT is what it is all about and getting there happens on skinny skis as it is harder to do them correctly on wider skis.
So it’s pretty simple: if you want to ski better in steep powder and more difficult off piste conditions and maintain quality PMTS technique, stay off of tail rockered skis. Stay on skis that support tipping as the first and primary movement and use these skis to perfect the BPSRT. If you want to ski at speeds slower than terminal velocity, get a wide ski that has no tail rocker and has a tight turn radius and a god flex pattern like the skis mentioned above.
And as always and most importantly, do the drills and truly master the bullet proof part of SRT’s!!