After getting thru the 90 degree turn, it got much easier to break the ice. The problem with Issuma in breaking this type of ice is that the bobstay (the pipe structure in front of the boat is called the bowsprit, the wire that supports the bowsprit from the bottom is called the bobstay) is low enough that it sometimes cuts the ice, instead of the hull riding up on the ice and then using its weight to break the ice. The bobstay supports the masts via the jibstay, so, even though I wasn't using much power (to reduce strains), it is not that good for the bobstay to be cutting ice.

Issuma is loaded heavily, and floats lower than it would in seawater (because freshwater is less buoyant), so the bobstay hits the ice more than it might otherwise. I think the solution is to remove the bowsprit (not a simple thing to do, it involves moving the jibstay back and shortening the jibstay and the jib and probably needing to compensate the sail area change forward by removing the roach from mainsail).