Why a Boat Trailer Fishtails, and How to Stop It

Boat trailers sway for the same underlying reason every trailer does - not enough weight on the ball - but they get there by a route no other trailer takes. The load is not bolted down. It sits on bunks or rollers and it can end up anywhere along them, which means a boat trailer's tongue weight changes every time the boat is loaded.

On a bunk trailer the boat should be winched forward until the bow eye is snug against the bow stop. It is common for a boat to end up an inch or several inches short of that, especially when the ramp is steep or the current is pushing. Every inch rearward moves load off the tongue and toward the axle, and a trailer whose load sits at or behind the axle will yaw at speed no matter what hardware is on the hitch.

Gear makes it worse in the same direction. Fuel in a rear tank, a kicker motor, batteries in the stern, coolers and anchors in the back of the cockpit all sit well behind the axle. Two people loading the same boat the same way can produce completely different tongue weights depending on where the heavy items went.

1. 1Bow eye against the bow stop. The simplest and most common fix. Re-winch it and look along the trailer from the side: the boat should sit square on the bunks, not hanging back.
2. 2Tongue weight, measured. 10 to 15 percent of the loaded trailer weight. The measuring methods all work on a boat trailer, and the bathroom-scale lever method is enough to tell you whether you are near 5 percent or near 12.
3. 3Where the heavy gear is. Fuel, batteries, kicker, anchor. Move what you can forward of the axle.
4. 4Trailer tire pressure. Cold, to the sidewall figure, on both sides. A soft tire on one side introduces a steering input the trailer did not ask for, and boat trailer tires sit unused for months at a time.
5. 5Towing attitude. A trailer towed nose-high shifts load rearward all over again. Measure the coupler height with the trailer level and buy the mount drop from the difference.
6. 6Bunk and roller condition. A collapsed bunk or a seized roller lets the hull sit in a position it was never meant to.

The standard answer to sway on a travel trailer is a weight distribution hitch with integrated sway control. On a boat trailer that advice has to be qualified twice.

• Many boat trailer makers prohibit weight distribution hitches. The spring bar brackets clamp to an A-frame that was not designed for that load. Check the trailer manufacturer's instruction before you consider one, and treat a prohibition as final.
• Surge brake couplers complicate a friction sway bar. A friction bar runs between the trailer A-frame and the ball mount, and a surge actuator needs to slide. Confirm the sway bar's own instructions allow fitting to a surge coupler before buying one.
• Immersion is hard on friction hardware. Friction faces want to be clean and dry, which is not the life a boat trailer leads. Expect to clean and inspect them more often than a travel trailer owner would.

That is not a reason to rule hardware out, but it is a reason to fix the loading first. On a boat trailer the loading fix is free, it is usually the whole problem, and it takes five minutes at the ramp.

Quick picks

Tap any row to jump to the full write-up. How these are chosen - and what we do and do not claim to know - is published in full on our research methodology page.

#	Product	Best for	Our read	Price
1	Sherline Trailer Tongue Weight Scale Check this first	Measuring tongue weight at home	Tells you whether the boat is too far back	Check price on Amazon→ #ad Affiliate link - we publish no price; Amazon shows the current one
2	CURT Adjustable Channel Mount with Dual Ball (2 in shank, 6 in drop) If it tows nose-high	Garages with several trailers	Two ball sizes and 6 in of drop to get level	Check price on Amazon→ #ad Affiliate link - we publish no price; Amazon shows the current one
3	CURT Sway Control Kit If it still wanders	Light trailers that wander	Adjustable friction bar, 14 lb, bolt-on	Check price on Amazon→ #ad Affiliate link - we publish no price; Amazon shows the current one

1. Check this first

Sherline Trailer Tongue Weight Scale

Sherline · Best for measuring tongue weight at home

A dedicated scale you sit under the coupler to read tongue weight directly, with no arithmetic and no trip to a weighbridge. It is the one tool on this site that turns the single most important towing number from a guess into a measurement.

We have not sourced a full specification table for this model from the manufacturer’s own site at a stable address. Rather than repeat figures we cannot cite, the assessment above is limited to what the design and the maker’s published description genuinely establish.

What works

• +Direct reading, with no bathroom-scale-and-lever arithmetic
• +Repeatable, so you can see what moving the load actually does
• +Mechanical gauge with no batteries to be flat when you need it

What does not

• −Must be used on level ground with the coupler at towing height
• −Single-purpose tool that spends most of its life in a cupboard

Skip it if

Unnecessary if your hitch already has a built-in gauge, or if you have a public scale nearby and are happy to use it.

Check price on Amazon→

#ad Affiliate link - we publish no price; Amazon shows the current one

Raw specifications: Sherline’s own page. We earn nothing on that link.

2. If it tows nose-high

CURT Adjustable Channel Mount with Dual Ball (2 in shank, 6 in drop)

CURT · Best for garages with several trailers

One mount that covers two ball sizes and a range of heights, which is the answer when the garage contains a boat trailer, a utility trailer and a camper that all sit at different heights. Capacity drops to the lower-rated ball you are actually using.

Published specifications

Gross trailer weight

14,000 lb source

Ball capacities

2 in ball to 10,000 lb; 2-5/16 in ball to 14,000 lb source

Adjustment range

6 in maximum drop, 5-1/4 in maximum rise source

Receiver size

2 in source

What works

• +Two ball sizes and a height range in a single mount
• +Flipping it gives rise as well as drop
• +Rated to 14,000 lb on the larger ball

What does not

• −Heavy, and more joints means more places for rattle to start
• −The pins and bolts need checking for torque, unlike a one-piece mount

Skip it if

Pointless if you own one trailer and tow it with one truck - a fixed mount at the right height is lighter, quieter and cheaper.

Check price on Amazon→

#ad Affiliate link - we publish no price; Amazon shows the current one

Raw specifications: CURT’s own page. We earn nothing on that link.

3. If it still wanders

CURT Sway Control Kit

CURT · Best for light trailers that wander

A single friction bar between the trailer tongue and the ball mount, with adjustable tension. It damps yaw; it does not transfer load. On a light trailer that wanders a little it is the cheapest honest fix, and on a heavy one it is not enough on its own.

Published specifications

Finish

Carbide black powder coat source

Shipping weight

14 lb source

What works

• +Simple, serviceable and easy to fit to an existing ball mount
• +Tension is adjustable, so you can match it to the trailer
• +Takes minutes to add to a setup you already own

What does not

• −Must be disconnected before backing up tightly or in icy conditions
• −Damps sway but does nothing about a tow vehicle that is squatting

Skip it if

The wrong answer if your truck sags at the back when the trailer is on - that is a load-distribution problem and a friction bar will not touch it.

Check price on Amazon→

#ad Affiliate link - we publish no price; Amazon shows the current one

Raw specifications: CURT’s own page. We earn nothing on that link.

An unloaded boat trailer is light, stiffly sprung and has almost nothing on the tongue, which is a recipe for wandering at highway speed. That is normal behavior for an empty trailer rather than a fault, and the reasons an empty trailer sways more are worth reading if the outbound trip is the part that unsettles you. Lower speed is the practical answer; there is not much weight to redistribute.

If the sway persists with the boat correctly positioned, measured tongue weight in the 10 to 15 percent band and tires at pressure, then it is worth looking at the broader causes - the three real causes of trailer sway covers axle position, trailer length and tow vehicle wheelbase, all of which apply to boats too.