Help w/ DIY Swallow Tail

[nowinski02]

So long story short, I'm looking for some help with my DIY swallow tail design.


Long story: I've been intrigued by the newer swallow tail skis recently (specifically the Line Pescado/Sakana and Season Forma). I've been watching to pick up a pair either on sale new or used with not much luck. Then I realized I have some older, unmounted skis sitting around that I want to try and make into a swallow tail.


The skis in question are Black Diamond Amperage in essentially new old stock unmounted condition. Ski specs:
185 length

143-115-124 sidecut

2140 grams per



Consequentially, I'm much more happy with both the sidecut profile and flex of the Amperage than that of the Pescado or Sakana I've checked out. Anyways I plan to cut into the tails to make the swallow tail and then seal with epoxy. The details of the tail are what I would like some help with. Note, I will be using these for snowmobile access backcountry, and some touring, and I am 5'10", 170lbs, and obviously the best skier on the mountain...


I'm trying to decide my overall ski length, swallow shape, swallow rocker, and mount position.


Overall ski length: Since I'll be using this ski for some touring, a shorter length would be better, however I don't mind a little extra weight going up for the benefit of the length on downhill. Secondarily, Line suggests to get one size smaller than usual (10cm) in the swallow tail skis because of the effective edge and effect of the tail. The ski length is also a big factor of swallow tail rocker.


Swallow shape: I've been doing lots of research and analyzing many swallow tail skis and the only thing that's conclusive is that everyone does it differently. Line Pescado and Sakana, Season Forma, Moment Comi, Folsom Pow Fish, Volkl Sanouk, etc all have a different swallow tail design in shape and length. I truly have no idea which style to go with because I can't find any info on why companies shape them the way they have.


Swallow rocker: Tail rocker plays a big part in the overall length as I mentioned earlier. It seems most, if not all, of the swallow tail skis on the market now and in the past had at least a little rocker on the tails. The tail of the ski has about 25cm until hitting the rear camber point. I'm leaning towards having about 1cm of tail rocker so that I'll have both the slashability associated with tail rocker and reducing the length of the ski slightly.


Mount position: Lots of factory recommended mount positions are about -8cm from center. I plan to go with about there for now and I can remount as needed to play with it.


I'm still learning about specific ski design components and their corresponding effect on performance, so I'm more than open to input from more knowledgeable people that understand inner workings more than I. Thanks in advance for any help!

[riff]

As I understand it, swallowtails are a way to preserve effective edge length and thus stability, while reducing surface area of the tail and allowing it to sink more easily in pow. This theoretically allows better tip floatation all else being equal.
I’m not sure that swallowing these would mean you want to change the mount. If you’re happy with how they initiate turns, I’d keep the mount the same. Mount point has to do with taper length relative to the narrowest part of the shape; that won’t change when you swallow it.

I’d ponder two things- is the ski unsatisfactory as is/ have you skied it yet?
What is driving the urge to swallow? Thats a reasonably modern pow ski, removing surface area in the tail will perhaps increase tip float, but at what coat to longevity….

Not trying to talk you out of it! I’ve wanted to try pescados for some time.


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[DarthMarkus]

I've entertained the same idea in the past. All the skis I considered had a flat tail for the same reasons stated above though. Correct me if I'm wrong, but I believe the amperage has a bit of a turned up tail. It would likely achieve no noticable effect unless you lopped all the rocker off before you carved the swallow tail in.

Skis that come to mind where I think a swallow tail might achieve something would be something like a Nordica Girish, newer katanas (older katanas had their own version of a swallowtail), sender squads, or dynastar pro riders.

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[nowinski02]

As I understand it, swallowtails are a way to preserve effective edge length and thus stability, while reducing surface area of the tail and allowing it to sink more easily in pow. This theoretically allows better tip floatation all else being equal.
I’m not sure that swallowing these would mean you want to change the mount. If you’re happy with how they initiate turns, I’d keep the mount the same. Mount point has to do with taper length relative to the narrowest part of the shape; that won’t change when you swallow it.

I’d ponder two things- is the ski unsatisfactory as is/ have you skied it yet?
What is driving the urge to swallow? Thats a reasonably modern pow ski, removing surface area in the tail will perhaps increase tip float, but at what coat to longevity….

Not trying to talk you out of it! I’ve wanted to try pescados for some time.

The reason I question the mount is because I'm really changing the functionality of the ski. Lots of people had the most fun on the Amperage at a center mount or just ahead. Being that the Pescados are so far back there must be something to the reason they did that. And I do agree with your understanding of the swallowtail dynamics.

To answer your question of why, it's mostly just because I can. Like I said these are unmounted and never skied, so I don't know how they ski normal. I do have a pre-ARV JJ as my dedicated pow ski so I'm just wanting to fool around with the swallow tail idea for cheaper than buying one. Worst case if they blow apart on my first outing, I'm only out the $100 I bought them for and had a fun tim. I'll learn something either way.

[nowinski02]

I've entertained the same idea in the past. All the skis I considered had a flat tail for the same reasons stated above though. Correct me if I'm wrong, but I believe the amperage has a bit of a turned up tail. It would likely achieve no noticable effect unless you lopped all the rocker off before you carved the swallow tail in.

Skis that come to mind where I think a swallow tail might achieve something would be something like a Nordica Girish, newer katanas (older katanas had their own version of a swallowtail), sender squads, or dynastar pro riders.

The Amperage do indeed have a tall tail at about 3.8cm (decambered). The Sakana, Forma, and Pescado have 1.8cm, 2cm, and 2.2cm of tail splay respectively. Line's ski construction may not be trustworthy, but I trust their engineering and robust design testing. I'm leaning toward 2cm of tail splay as it's in between the Pescado and Sakana. To get that 2cm of splay the ski would be cut down to 176cm. And if I went to the flat tail like you mentioned, the ski would be about 160cm. Shorter length would definitely be beneficial for touring and wouldn't affect the downhill performance due to the swallowtail. I agree with you that if I swallowed the current tail, there would be little to no effect.

[utagonian]

Pollard claimed to have spent 10 years getting the Pescado sorted out. Might be marketing rap but the results of a one-off test might be deceiving. I'd also ski those same skis at least once so you know the change from the single variable change. For science.

I've got quite a bit of time on the Pescado I think I understand the design on that one. The cut out tail is to give a longer side-cut length in the tail on packed/groomed snow while still letting it sink and be loose in powder. The Amperage uses a lot of tail taper to get that loose/sinky tail in powder already, it might be more loose with the cut out, but on groomers the tail would still be tapered and, if you were digging trenches deep enough (or were far enough into survival mode) to access that last foot of tail, it would have less torsional strength than before.

I don't know if you know but soothski has the Pescado & Sakana data. If you can find a ski with similar shape to the Aprerage to compare it might help you.

The Line skis' effective edge and side-cut length are very long for their length and category and they have only a little tail taper and rocker.

[nowinski02]

Pollard claimed to have spent 10 years getting the Pescado sorted out. Might be marketing rap but the results of a one-off test might be deceiving. I'd also ski those same skis at least once so you know the change from the single variable change. For science.

I've got quite a bit of time on the Pescado I think I understand the design on that one. The cut out tail is to give a longer side-cut length in the tail on packed/groomed snow while still letting it sink and be loose in powder. The Amperage uses a lot of tail taper to get that loose/sinky tail in powder already, it might be more loose with the cut out, but on groomers the tail would still be tapered and, if you were digging trenches deep enough (or were far enough into survival mode) to access that last foot of tail, it would have less torsional strength than before.

I don't know if you know but soothski has the Pescado & Sakana data. If you can find a ski with similar shape to the Aprerage to compare it might help you.

The Line skis' effective edge and side-cut length are very long for their length and category and they have only a little tail taper and rocker.

You do bring up a really good point about the Line ski contact length and effective edge. I couldn't find numbers for the Pescado, but the Forma has a 130cm contact length and 148cm effective edge, where I measured the Amperage to be 118cm and 123cm respectively. This, as you mentioned, is due to the large tail rocker and especially large tip rocker. But I'm curious if the effective edge shouldn't be much of a problem for me because I wouldn't ever be using them on groomers or similar hardpack? Is there a comonent to effective edge when on loose/pow snow?

As for the groomer or hardpack issues like torsional strength, I'm not worried at all. I would only be using these skis in the BC on good snow days. I don't plan to ride resort much if any and I don't need to put them through the ringer in hardpack BC conditions.

I have considered trying to locate a few skis that would be better suited for the swallow (longer effective edge and less entry and exit rocker), but I don't see it going great financially. I'm into these skis for 100 bucks and I doubt I could find my exactly ideal ski without 3 mounts for double that. But, I could very well be wrong.

I have mostly decided on a few design characteristics for whatever ski I end up cutting. I'll keep the decambered tail splay at about 2cm and cut the tails to a depth right at the rear contact point. These two designs seem about the same across most swallowtails, so I'm going to trust the designers there. The width and specific tail cut, I have yet to determine my path.

[utagonian]

If you are not worried about firm snow skiing, what are you trying to accomplish with the swallow tail in powder?

[nowinski02]

Because I've wanted a pair of Pescados or Sakana for a while, but they're not readily for sale used and usually aren't cheap when they are. Mostly because why not. This way once I ruin these skis and outright buy a swallowtail I'll have used more money and time than I needed to...

Also thank you so much for the soothski plug. I had no idea they existed and I've been looking for something like that for a while. Up until now I've been relying on Blister review measurements.