Looks like your blades are dull. The blades are ripping the foam as oppossed to cutting it.
A few things.
1. There are two different marks on the foam. Some from a sureform. Some from a dull hand plane. When I shaped my first EPS board I got so frustrated by those marks that I stopped using my handplane and only used the sureform. I then read a thread on sways in which a technique is described to sharpen planer blades using a sheet of glass. After sharpening the blades it was a world of difference. A dull blade will always cause problems. It should cut you when you look at it.
2. The handplane needs to be held at an angle to the stringer somewhere between 30 and 45 degrees. That will allow the blade to slice instead of plow. But nothing will work if the blades are dull.
3. take down the stringer first then the foam to stringer level. Back and fort, stringer then foam, stringer then foam until you have it at the proper thickness.
4. All this will be made tons easier if you just went and bought a power planer and mowed the foam to thickness with that and then turned the rails by hand using the sureform. Better yet use the planer for all of it. I was resistant at first to use the planer but after using it on a few board I dont know what I ever did without it.
5. ALL BLADES NEED TO BE SHARP !!!!!
http://www2.swaylocks.com/forums/perfect-razor-edge-hand-planes-4-5
make sure your tools are sharp, a dull tool is a useless tool thats why you are having problems with the plane. and my .02 that looks at least 3" thick, bring it down some more.
Sorry heres the pic
Hi Zman,
Too thick is kind of subjective, but I bet some will give advice. You didn’t give the thickness. Did you mean too wide?
If your foam is polyurethane take most of the thickness off the bottom. You can use the block plane to cut down the stringer then use a long sanding block to take the foam down to the stringer. Repeat until you get it where you want it. I try to use long strokes when sanding and I try to avoid ‘scrubbing.’ Mike