Garmin makes a download of Winni. I got one 3 years ago. $10. Works great. Of course I have the Garmin 541s GPS/Fish Finder.
They surveyed the lake last year so an updated version might be out this year.
https://buy.garmin.com/en-US/US/maps...prod36400.html
Unfortunately I did not find your Lowrance.
Lowrance does make a map set for the NE US and they say Winnipesaukee is included. The premium version is $197.35, ouch,
http://lr.factoryoutletstore.com/det...-lowrance.html