Hi all!
The number of sources of trailer instability seems endless, so when using a marginal tow vehicle, it sure will help to eliminate as many of them as possible.
One source not mentioned in this thread that is fairly specific to the Mac is the importance of having the bow eye winched tight, and securely engaged with the rubber V on the trailer. Not doing this is inviting sway.
The aluminum I beams are very flexible and, as I have noted in other threads, the hull of the boat forms part of the structure of the trailer. If they are not suitably fastened to each other the trailer becomes springy which will contribute to trailer sway.
Also of importance is not only the total weight, and the portion of it on the tongue, but also often overlooked is the distribution of the weight fore and aft relative to the wheels.
For example; two 300# weights located 8’ on either side of the trailer wheel centerline (front and back) will give you a more likely scenario for sway than if the same weights were placed 2’ on either side of the trailer wheel centerline.
In both cases, the tongue weight will be measured as being the same- but the moment of inertia is the important factor, not simply the weight. (For those buying snow skiis, this is referred to as the “swing weight” of the ski, and is more significant to performance than the total weight of the ski).
This illustrates the shortcoming of simply using a bathroom scale and calculating 10% on the tongue. It really is just measuring an artifact of the centre of balance of the trailer+ boat. It is indirect, but it is an easy way to do it.
Of course, it would also be important to keep the weight centered, and low, on the longitudinal axis (side to side, or port to starboard) as well.
Whether or not the trailer is level is more a function of the proper hitch being used, than what the actual vehicle is- looks like you have the right hitch receiver offset to keep yours level, Crikey.
Note that as you gain speed on the highway, your tongue weight will somewhat decrease from aerodynamic drag, and will tend to lift the front of the boat.
Also be aware that all of the factors that affect a sailboat in the water, also affect the boat while on the trailer. The location of the daggerboard equals the location of the trailer wheels for the centre of lateral resistance, and center of area of the high-freeboard hull becomes the centre of lateral pressure when the sails are down.
So the weather helm you experience on the water is also experienced in a crosswind as “weathercocking” when the boat is on the trailer. Except that when on the trailer, in order to be stable, the bow needs to be pushed away from the wind instead of into the wind. This to push the rear of the tow vehicle downwind, and steer the front of the vehicle into the wind, which is what you want to happen for stability and safety.
Good luck Crikey – I’m still putting off buying a tow vehicle too. My car is good for short slow trips, but I borrow my sister’s SUV for highway use. It’s a catch 22 if you only have one vehicle – a vehicle that’s good as a tow vehicle, is not as good as a non-tow vehicle when it’s not towing something! So you end up driving a vehicle that’s inappropriate 90% of the time, just so you can use it to tow something the other 10% of the time. Sheesh!
- Brian.
. That being said, I find myself looking into sway control solutions to take away some of the craziness on the highway during truck passing's, and high winds.
watch the Birdie 
