C-Forum

There are several threads from way back where the Necky Zip is recommended as a conversion. I'm doing one right now. I'm going to have to widen the rim (a LOT) to get my knees into the chines, and this means that I'm having to raise the rim first so that the rim can ride over the gap. I'm doing this by jacking on a board under a sheet of plywood that fills the cockpit hole. I'm applying heat with a Harbor Freight heat gun, playing it on the sides or the groove just outside of the rim.

It's going ok, but I'm still not applying enough heat to the right areas, so everything springs back a lot when I let it cool and release the jack. How much more heat does this need, and where do I apply it. I just don't want to melt through or heat it too much in the wrong place.

Let me help.
First thing to do is bump up your fire coverage if you're going to use a harbor freight heat gun.. I watched one spontaneously combust while turned off on a benchtop. Those tools are JUNK!

Hard to say and unless you have a DR. Heatgun present (SqueakyKnee or Rockstar) you have to play it by ear.

I was told by "them" to take into account air temp (cooling), plastic type (necky verse riot, etc.) and amount of change.

So here is my $.01 (any you get what you pay for):
o Heat till shape can be changed but don't over do it. If it looks like things are going south on you... they are!
o Take your time - with the heating and the overall shape changing (cooling sessions) - Heat and shape then let cool then come back to do it again. Leaving shaping structure in place over time.
o Take into account other changes in the boat shape as the "squash" / modification is being executed. There might be something that is pulling it back into shape ( you might have to be heating more than one area to get the shape needed).

That said I had a red Zwo that took 2 sessions to modify the cockpit to get it where I liked it. Now I have a yellow Zwo and its just not holding its shape - so more time is required. I'm assuming that this is due to the Red Zwo also being "squashed" (volume taken out of it and tip and tail being modified to get more rocker) while the Yellow one I've just been focusing on widening the cockpit area.

Hope this helps and let us know how it goes.

Nothing like persistence, then. Didn't want to overdo things, and it sounds like I just need to keep going until all the areas with stress have moved.

This might be a good time for a new gun. I've been using my plastic welder in order to localize the heat, but it is a little weak.