Trailer capacity is the specification buyers most often get wrong, usually because they compare the trailer's rating against the boat's advertised dry weight. Dry weight is the boat and nothing else. What you actually tow is the boat, the outboard, a full fuel tank, batteries, water, and every piece of gear you leave aboard — and that number is routinely 30% higher.
Here is how to size a trailer properly.
The three ratings that matter
- GVWR (Gross Vehicle Weight Rating) — the maximum total weight the loaded trailer is rated for, including the trailer's own weight.
- GAWR (Gross Axle Weight Rating) — the maximum each axle can carry. On a tandem-axle trailer, the combined figure is the sum of both.
- Payload — GVWR minus the trailer's dry weight. This is what you can actually put on it.
Our 25 ft tandem-axle trailer is a useful worked example: 5,200 lb GAWR per axle, so 10,400 lb combined; 1,673 lb trailer weight; 7,716 lb maximum payload; roughly 9,390 lb GVWR. Note that the payload figure is the one that answers “will my boat fit” — not the axle rating.
The 85% rule
Do not buy to the limit. The widely used guideline is that the loaded boat should come to no more than 85% of the trailer's rated capacity. A trailer running at its ceiling has no margin for wet gear, a second fuel tank, or the slow accumulation of equipment that happens to every boat over a few seasons — and it will wear bearings, tires and springs noticeably faster.
On a 7,716 lb payload, 85% means planning around 6,550 lb of boat, motor, fuel and gear.
Calculating your real number
- Start with the boat's dry hull weight from the manufacturer.
- Add the outboard — a mid-size four-stroke runs 350–550 lb.
- Add fuel at 6.1 lb per gallon. A 60-gallon tank is 366 lb.
- Add batteries at roughly 50 lb each, plus water, and 200–400 lb of gear if you are honest about it.
- Divide by 0.85. That is the minimum payload rating to shop for.
If you cannot find reliable numbers, take the loaded rig to a certified scale. Most truck stops have one, it costs a few dollars, and it settles the question permanently.
Single axle or tandem
Single-axle trailers are lighter, cheaper, easier to maneuver by hand, and simpler to maintain. They make sense up to roughly 3,000 lb of load.
Tandem axles buy you three things. They track straighter and are far less prone to fishtailing at highway speed. They spread load across four tires, so a blowout is an inconvenience rather than an emergency. And they carry substantially more — tandem trailers handle boats up to around 7,500 lb, which is roughly where you begin considering a triple axle.
If you tow long distances, at highway speed, or with a boat over about 3,500 lb, buy the tandem. The handling difference alone justifies it.
Tongue weight: the number that causes sway
Tongue weight should sit between 10% and 15% of the total loaded boat-and-trailer weight. Too little and the trailer sways — the oscillation that builds at speed and is genuinely dangerous. Too much and you unload the tow vehicle's front axle, which degrades steering and braking.
Tongue weight is adjusted by moving the boat forward or back on the bunks. If your rig sways, this is the first thing to check, before you buy a sway-control hitch.
Torsion or leaf springs
Leaf springs are cheap and field-repairable — a real advantage in a remote area. Torsion axles, which our trailers use, mount independently, ride noticeably smoother, sit lower for easier loading, and have no shackles or bushings to corrode and seize. For saltwater or heavily salted winter roads, torsion is the better long-term buy.
Length and bunk support
The trailer should support the hull along its full running surface, with the transom fully supported at the rear. A boat overhanging its bunks develops hook in the hull over time — a permanent deformation that costs you speed and fuel economy and cannot be undone.
Err slightly long rather than slightly short. A 25 ft trailer under a 22 ft boat is fine; the reverse is not.
Before you buy
- Confirm the certified capacity label on the trailer itself, not the brochure.
- Check your state's requirements for trailer brakes — most mandate them above a threshold, commonly 3,000 lb.
- Verify your tow vehicle's rating with passengers and cargo accounted for.
- Confirm coupler size matches your ball — 2 in and 2-5/16 in are not interchangeable.
Tell us the boat's length, dry weight and outboard, and we will tell you the payload rating you need — and whether the trailer you are already looking at is enough.
