if your intention is to increase the fillet size anyway, just lay the new material down on the old without sanding and fill in the low spots to get an even level.

You can guarantee smooth fillets that need no sanding by brushing the freshly-laid fillet with a 1" chip brush dipped in unthickened epoxy. This also feathers the fillet edges so there's no ridge to sand. It works for new fillets and cosmetic fillets-on-fillets, too.

Have fun,

Laszlo

   Thanks Lazlo,  that sounds way too easy so will for sure give it a try.  I'm also having trouble making even fillets because the width of the boat and reach of my arm don't seem particularly compatible. 

If you're not blessed with arms so long that you have to wear high heels to keep your knuckles from dragging on the ground and don't have a trained gibbon handy, you could try something like I did with my Brand X dinghy.

Obviously this won't work for a boat that's just wired, but it should be fine for a boat that's tacked and waiting for its final fillets.

Laszlo

I find the loose hairs from chip brushes extremely frustrating.  I just glove up and use my fingers to smooth the fillets.  My "tack welds" are 3/4" radius and my final fillets are 1" radius.  I don't use the pastry bag method, I just use my filleting tool to grab some mix out of the solo cup and use a spatula to clean it up.  After smoothing, very little sanding in required.