Hi Andrew,
Sorry to hear about your numbness. It really sucks when it stops you enjoying your brand new boat.
The heel wedge can work but if you read back thru these posts you'll notice its a combination of factors that solves the problem, its seldom a 1 wonder fix. In your case, the wedge is reducing the stretch in your calves and hamstrings, which in turn is reducing the pressure on the sciatic nerve. Logically the same result can be achieved by increasing the flexibility of your pelvis, gluts, hamis and calves.
Surf ski season here has tailed off so I have moved back in to k1's and k2's and the numbness problem has reared its head again. I have put my multi factor theory to test and I have managed to eradicate the problem completely very quickly.
First, stretch, stretch, stretch. Every day, before and after paddling. Then get your boat set up correctly in terms of pedal angle and knee bend. I then spend a lot of time working on the seat, getting it padded in the right areas to relieve pressure on the sciatic nerve.
For me that means 1 thick pad with a raised section in the middle like a bicycle saddle. Then I cut out 2 large sections of the pad under each sit bone. The result is the pad has an exaggerated egg timer shape when viewed from above. The raised central section and the lack of padding laterally, removes most of the pressure from the piriformis muscle and the sciatic nerve. As long as the raised central section is kept to a minimum this set up is quite comfortable, a lot more comfortable than the alternative.
Check out
www.tukscanoe.co.za/tips.asp for some deeper insight.