I used to cartop a (fiberglass) Force 5 Sail boat, weighing 250 lbs.,
and 13 ft. long. Loading was easiest with 2 people, one in front and
one at the back of the boat, lift it up to roofrack height, and slide
it sideways, to center of car.

But there is an easier way. I attached a 2 x 4 frame to my roofrack. On
both sides I attached 2 ring screws (woodscrew with one end looped
around to form a ring, don't know the technical term for it). The screw
location was at the very front (approx. over the front door hinges),
and the other set of screws was screwed in on both sides at the very
end of the wooden frame (roughly at the rear end of the back door). It
was a 4 door full size car.

You then take two 8ft lenghts of 2 x 4 and screw in a hook on ONE end
of each of the 8ft lenght.

To make single handed loading possible, I hook the end of the two 8 ft
sections, into the ring (which stick out on the side of the roof rack,
one in the front and one in the back (on the same side of the car).

I then take the boat, and lean it with the open (top side of the boat)
side against these two poles, which basically form a 30 degree ramp, up
to the height of the roof rack.

It is then easy for one person, to stand between the 8 ft section, and
push the boat onto the roof.

I had padded the roof rack with indoor-outdoor carpet, to prevent
scratching. You can do the same with the ramp.

When tying down the boat, make sure you tie one set of straps to the
roof rack which holds the 2x4 frame, and another completely seperate
set of straps directly to the car (bypassing the roof rack), just in
case the roof rack comes loose, you then still have the whole assembly
anchored to the car, (i.e. front and reach bumpers).

For single handed unloading, the same in reverse. That's when its handy
to have the hooks on both sides of the car, gives you a choice on which
side you are going to load/unload the boat.

The two 8 ft sections of 2x4, the mast (which came apart into 3
sections), the dagger board, and the rudder, were slid under the boat,
into its own slots, which I made under the wooden frame/ between the
metal roof rack and the wooden boat rack.

Unless you really know how to tie knots, use ratchet straps. Faster,
easier, safer, and much more secure.

Depending on what kind of car you are driving, make sure, the gross
vehicle weight is not exceeded, and of course, with so much weight on
the top of the car, slow down, escpecially in corners :-)

Hope this helps.
B19