Agprice22;
As a former dealer who pulled a lot of boats, designed sailboat trailers, use to teach trailer safety and so on, I will pipe in.
First the gross vehicle weight include that of the trailer, boat and gear. If you are ever pulled over by State Police or DOT and weighed, you in many cases if over GVWR will not be able to move that trailer unless to get it off the interstate or on secondary routes pulled to a "safe" area. Although you are private pulling, they will fine you and those fines are enourmous. Therefore, I would not go over the gross vehicle rating.
I have seen the aftermath of over weighted trailers and the damage. One time I came to my dealership and and found blocking the entrance to my dealership a MacGregor 22 trailer loaded with a 4000 lb boat that nearly collapsed. It cost that owner a lot to move the boat and to bring in another trailer which I refused to load onto due to GVWR being way over. He was bent bound and determined bringing in a crane onto my dealership after hours when we were gone, loading up that boat. Well, 10 miles down the road, he lost the entire rig and his truck. No one was hurt but had to pay damages and a lot of fines. I refused to help in the future.
When trailers are designed, there should be a 10% safety margin built into the load. What I mean is the total weight of trailer, boat, gear and so on should not exceed the GVWR of 90% leaving a 10% safety margin. The idea of the boat being lower on a trailer is good when you are lowering the Center of Gravity. For high keel boats, the CG is greater, thus lower speeds and SAFETY IN CURVES AND BRAKING have to be considered more vs. swing keel boats sitting much lower on trailers.
You can beef up any trailer adding additional weight but there are two primary considerations. Believe it or not, axles and tires are rated to carry just so much. That is a major factor when designing trailers. Then from there, placement of bunk style supports or boat stands. When putting a cradle on, securing a boat to the cradle as well as the cradle to the trailer is a must.
When you load any boat onto a trailer, some think you need to place it so the axles are carrying equal weight. That is totally unsafe as that trailer will sway on you regardless. This is why when loading that the industry norm is 10% of the total GVWR should be on the trailer tongue.
Strapping keel style sailboats onto trailers without the bow resting on a bow chock attached to a winch stand is another issue. I have always suggested strapping down with four straps. One should be from the bow going backwards with another from the stern going forwards. Strapping over the boats side to side does not cut it with me. As a former investigator and sailboat dealer, I can tell you sailboats of any size will move for example when the idiot lane changer cuts in front of you and you have to apply your brakes suddenly. The two added straps will greatly enhance that from happennning. Fired an employee who did not follow my rules as he nearly lost a Catalina 309 on a tandem axle trailer. NO damage to the boat, but extensive repairs to the trailer not to mention a new transmission.
I could go on but if bent bound and determined, first look at your trailer axles and tires and see what the capacity ratings are. Jackdaw is correct in many cases insurance will not cover if the owner uses unwise judgement. In Virginia as in many states, homebuilt trailers have to be inspected before you get a title to a home built trailer. In some cases, states require any modifications to be inspected but that is state by state. Some states require annual inspections with two axles, any brakes on a trailer, and so on but again this is a state by state issue as there are no uniform laws across the state lines.
