Dave Ritter;
I am a retired dealer for Hunter and top dealer for the 23 wing keel. The center of gravity was very high and the first trailers without brakes was a very big issue with me. Brakes at first were an option but standard on my 23 wind keel trailers and that alone is one major reason why maintenance on trailer brakes are important particularly when braking. Adding a second axle to that would improve the stability of the trailer some but again the most important requirements I stressed to my customers to maintain the brakes on the single axle and do not go over 50-55 when towing. Now you ask if a tandem axle is necessary but that decision will be yours but let me first point out a few things.
When the center of gravity is substantially lowered, the sideways stability is greatly enhanced vs. a standard keel boat as it is much higher particularly when turning. Thus a single axle with brakes may do the job alone for a swing keel sailboat as the center of gravity is lower.
The total weight of the boat with gear and motor to also include the trailer will determine whether or not a single or tandem axle is warranted. First check the load weights of the tires to see if they will carry the entire load. Secondly, make sure you have 20% additional load carrying capacity on the entire load when configuring total weight as a safety factor. For example two tires rated total weight load capacity at 100 lbs. with the boat, trailer and gear weighing 80 lbs... If the total weight exceeds the total carrying capacity load with a safety margin built in, then you would have to go to a tandem axle trailer.
In some states, once your load reaches a total load weight carrying capacity, then you will be required to have brakes. If trailering a lot and putting into the water, I suggest surge vs. electric brakes. There are no issues with surge brakes when on a personal trailer vs. commercial trailer. Examples first include NC and VA state anything over 3000 lbs. require brakes on one axle whereas PA specifies that on tandem axles, both axles require brakes. So you will have to check on the state requirements where the trailer is registered and titled. In some states to include TN and SC which does not require titling and registration, other states do recognize that and accept that but make sure that the tow vehicle for example TN and SC has those plates on.
I hope this will help you sir.
crazy dave condon