How to Select the Right Boat Cover
BoatTEST once received this question: "Would you please ask Capt. Steve to discuss the use of canvas covers in trailering boats. Will covers improve air dynamics going down the highway at speed or is it better to go without? If so, how do you keep stuff like seat cushions and other things that you must have from blowing out? Any other boat canvas advice would be gratefully received."
Capt. Steve Responds —
First off, if you're looking at air dynamics for improving your gas mileage, forget it. Any cover will have a minimal effect on improving your mileage against the loss of economy that the boat and trailer itself generates, so let's focus on keeping your gear in the boat instead.
Station Wagon Effect
The station wagon effect will certainly cause you to lose any loose and light items in your boat. Keep everything stowed if you plan to trailer without a cover. It won't be much worse than what will blow out while your boat is cruising on the water, so this shouldn't be too much of a problem.
If you live within a couple of miles from your ramp and are going a short distance then a cover is certainly not necessary. You'll have to just uncover it to wash it down when you get the boat home (you do wash it down as soon as you get home, right?).
If you plan on going for a longer distance while towing, and certainly if getting up to highway speed, then a cover is much more of a necessity. Now, without a cover, heavier items such as seat covers and the like can and will be blown out and onto the highway.
Specialized Covers
As for what sort of cover to get, let’s first discuss what not to get: a mooring cover. These are covers that go over your whole boat, but around the perimeter is typically just elastic cord that you stretch over the gunwale to hold it in place and protect your boat while it sits on the mooring. They're not able to withstand high winds. It's usually understood that if a storm is coming, your boat will be hauled or protected in some way and the mooring cover will not be the first line of defense to protect your boat.
For the same reason, towing at any speed will likely blow this cover right off the boat and into the windshield of the car behind you.
Made for Towing
A full canvas cover that is appropriate for towing will have tie downs or straps that attach to the trailer at multiple places. This keeps it secure in high winds generated at highway speeds. It will also have vents so that the interior of the boat can breathe. There are poles to support the centers against water pooling and weighing down the center and stretching it to a useless state.
One step down from this version is a cover that has snaps all the way around to secure it to the perimeter of the boat. This is the most common scenario, as it is nearly as effective at protecting the boat and its contents plus it's easier to use. The downside is that you have snaps drilled into your boat and sometimes they get pulled out and have to be replaced.
At the lower end of the spectrum is a cover that will have a line running through the circumference so that it can be drawn up tight around the entire boat. That usually will hold but make sure it's pulled good and tight and that it comes down to the bottom of the boat. If you have to worry about the line breaking, then you need to replace that line. Tie a new one on the old one and pull it through the whole canvas.
The bottom line is that you need a cover that gets secured and held in place. Not just stretched over the boat.
— Capt. Steve