I am curious how often you use them, especially on inland northern lakes.
None. Northern Lake trips involve portages and its a PITA to get a big pack out from under a cover. Especially the snappy ones that don't come off easily. Covers are more for rain and splash resistance and anything bigger than a partial is a entrapment possibility.
If you are on northern rivers and its cold a spray cover is a help in keeping you warm, It aids in making you more aerodynamic but I don't know how much
I have a slightly different spray cover take than Yellowcanoe. I do not portage much anymore, so that is not an issue. My usual big open water is oft windy coastal stuff, but even so most of our covers are partials covering just the bow and stern. Not much entrapment hazard, but without a full skirt they do little to keep us warm.
I have seldom been in waves that were breaking over the covers, except some too steep haystacks in a short section of whitewater. Since my usual covers are bow and stern partials with an open center area those haystack bow waves just rode across the bow cover, deflected off the raised drip baffle and hit me square in the chest. I was soaked worse than no covers at all. It was a frigid New Years Day trip. Nuff said.
Covers probably do help some with eliminating wind catch in quartering breezes, how minor that is I do not know. My canoe is near gunwales full of gear when tripping, and if there is room left I will stuff a short float bag in the stems, so there is not much open hull inside the canoe for the wind to catch.
But waves and splash and wind catch are a minor part of why I use spraycovers on some trips. Aside from a torrential downpour I track a rainy mornings worth water inside the hull on wet foot entries. I have a sponge, and a bailer, and know how to use them.
It is the other cover advantages that are most functional for my uses.
Shade for the food barrel or cooler. And, early in the warm weather season, shade for my winter pale legs and feet. Coolness in summer under a hot sun, the shade under the covers combined with the ambient water temperature on the hull is noticable. My Snickers Bars do not melt and if I am using stem flotation bags the float bags do not
Shes gonna blow swell and need pressure relief as often.
But, mostly, I like having a bow cover for the paddles plural spare blade pocket and lash strips for the shafts. And for a horizontal place to lay out and secure the map case in close enough readable orientation, and for providing a splash guard up front to catch paddle drips. Enough that I often use only the bow partial, leaving the less multifunctional stern cover off entirely, which makes for easier midday lunch stop gear accessibility and half a canoe unloading at camp.
I think I can achieve most of those advantageous fabric deck functions, drip barrier, center shade, map case held readably flat, and paddle grip restraints, with the blade stuffed under a gear webbing strap across the now open and easier unloading gear storage in the bow. All via a simple hull width piece of waterproof cloth front of midships, using snap rivets positioned under the outwale on each side.
