Driving hazards that are normally only an annoyance to an automobile - potholes, uneven pavement, sharp curves, etc.—can be scary when you’re towing a trailer, especially if the weight is not distributed correctly. Five to 10 percent of the total weight of the boat, motor, trailer, and gear should be on the trailer ball when the coupler is parallel to the ground.
Too much weight on the ball and the car will be difficult to steer (and good luck retrieving your boat at a steep launch ramp, especially if your car has front-wheel drive). You can also wreck the car’s suspension system. Too little weight on the ball and the trailer is prone to fishtailing - excessive swaying from side to side. (Fishtailing can also occur when tires are too soft or the trailer and the boat are too heavy for the car.)
Techniques for redistributing weight at the coupler include shifting gear inside the boat, emptying water and fuel tanks, and adjusting the boat’s position on the trailer. If all else fails, you can remedy the problem by moving the trailer's axle - a much larger job that usually requires a pro.
Positioning the Boat
Many boats spend the better part of their lives atop a trailer. To reduce the chances of sagging or oil-canning (flexing) that could permanently disfigure or even weaken the boat’s hull, the boat should always be level and supported evenly, with rollers or padded bunks concentrated in critical areas such as the engine and chine. On boats with outboard or I/O’s, transoms must be well supported. Poly rollers, incidentally, last considerably longer than their rubber counterparts, which deteriorate in sunlight.
Securing the Boat
Keep in mind that when you’re barreling down the highway at speeds of 65 mph or more, the boat will be buffeted by near hurricane force winds.
Anything loose on the deck or in the cockpit, including things like Bimini tops, will probably be blown away. Either stow them below or make sure they are secured. Better yet, wrap the boat in a snug-fitting cover, which protects the upholstery from sunlight and road grit, as well as reduces fuel consumption.
A heavy strap should always be used to anchor the boat's stern to the trailer. If a strap isn't used, the boat will bounce against (or off) the trailer. Don't rely solely on the winch cable to tie down the bow. Use a separate line from the bow eye down to the trailer. When you're traveling, check the straps and the bow eye itself whenever you stop.
Always use a safety chain, criss-crossed between
the car and the trailer coupling. Should the hitch fail, heaven forbid, the chain will keep the trailer from flying off the road. Crossing the chain prevents the trailer coupler from separating completely from the car. Leave enough slack in the chain to allow for proper turning, but not so much that it drags. Using a shackle/pin is far more secure than relying on the standard S-hooks, which have been known to jiggle loose.