Alright... after much number grinding and batch image processing, I've built my own maemo mapper repository for narragansett bay in Rhode Island using the rasterized ENC images from NOAA. After this weekend I'll hopefully come up with a automated way to bring in NOAA charts at various zoom levels -- always preferring the highest detailed map at a point (hopefully). At this point, the Naragansett Bay overview chart is available only at the zoom level of 6 (in maemo mapper terms, zoom level 15 in OSM terms).

I'm going to try this with GPS on the boat tomorrow! To take a look at the map create a new repository with the address:
http://www.robgfx.com/noaa/%0d/%d/%d.png
Download Zoom steps 2/4
View Zoom Steps 1/4, next able
Downloadable Zooms: Min 4, Max 20

These are basically the default settings. Note.. the map will only show up at zoom levels 1-6 (native zoom level is 6).

Hopefully this weekend I'll write a how to explaining what I did, then start a batch process to incorporate more maps.

By the way -- for those who don't know the area, just go to this lat/lon to see the maps: Newport, RI is at 41.48051,-71.30823