Once you have your classic Boston Whaler boat on the proper trailer, with good tires and a proper hitch, you are ready for towing down the road. There are more things to consider before you get on the highway.


Lights are required for any highway movement of the trailer. Connecting trailer lighting circuits to car lighting circuits has become more complicated. The electrical wiring of modern cars is complex, with more circuits and smaller size wiring than in the past. This may require additional attention when connecting your trailer's relatively simple lamp circuits to your car's electrical system.

Most all trailers are wired with three lighting circuits: running lights, left-turn light, and right-turn light. When the brake is applied, all the lights come on. For years, most cars were wired this same way. Connecting the car and trailer was straightforward and simple. Then automakers began using "Euro-style" tail lights on their cars, which separated the turn signal indicator lamp from the brake indicator lamp. Cars equipped with these style lights have four circuits: running lights, brake lights, left turn light, right turn light. Connecting four circuits of the car lighting to three circuits on the trailer requires use of a convertor.

There is not much inside the convertor in most cases. It usually consists of some diodes or transistors to steer the brake lighting circuit of the car into the left-turn/right-turn circuits of the trailer, but to not mix them together for the turn signal function. Often the convertor is integrated with an adaptor plug/connector to make the installation a simple plug in-line arrangement in which no car wiring has to be spliced.

A second problem with modern cars is the reduction in capacity of their lighting circuits. Because modern cars contain much more electrical wiring than ever before, there has been a trend to reduce the size of the wiring used to the minimum. This reduces the size of the wiring bundles, and also reduces the cost. But is also reduces the current carrying capacity of the wire and in some cases, it may mean that connecting a large trailer lighting load to the car's wiring may overload it. To work around this, it will be necessary to obtain an additional convertor device, which takes the power for the trailer lighting load directly from the battery via a separate heavy gauge wire and uses the lighting circuits from the car only as triggers to determine when lamps in the trailer should be illuminated.


Trailer axles are usually submerged during the launching process. This places special demands on the bearings and their lubrication. You should pay special attention to the bearings if you want to avoid highway problems.

The most common approach to bearing lubrication protection is the Bearing Buddy and its imitators. These act to prevent water ingress into the bearing by providing a slight pressure on the grease against the rear seal. Unfortunately, this pressure will also tend to push the grease past the seals while towing, as the bearing heats up slightly, lowering the viscosity of the grease a little and letting some get past the rear seal. To guard against this, the makers of Bearing Buddy also sell a line of special rear seals. Unfortunately, these are much harder to find than the Bearing Buddy, so they are often omitted with the result that grease is allowed to escape.

You can tell if your bearing seals are throwing grease because it will land on the wheels, the fenders, and just about anywhere else under the trailer in the vicinity of the axle.

Also part of the Bearing Buddy system is the inclusion of a grease fitting on the bearing cap to permit more grease to be easily added. Add just enough grease to move the spring loaded diaphragm from rest into a slight compression. If you pack the bearing with tons of grease under pressure, it will eventually find its way out past the rear seal.

Some specialized axles contain their own lubricating channels and fill fittings for adding grease. These route the grease through the center of the axle and introduce it between the inner and outer bearings. This is opposed to the conventional fill fitting which justs adds grease outside the outer bearing and relies on pressure and circulation to move the grease to the inner bearing. Typically the axle that came with your trailer will not have this feature; you must replace the axle to get this style of bearing lubrication.


Up to about 1,500 pounds towed weight, you can legally operate a trailer without brakes in most states. Above 1,500 pounds many states' laws require that the trailer have brakes. It is not only a legal issue, but a good idea for your safety.

There are two main styles of brakes: drum and disk. There are proponents of each type as better for use on trailers. That debate will not be settled here. But it is important to consider the special environment the brakes must operate in. They will often be driven long distances, heated quite hot from the friction of use, then completely submerged in cold water. To add a little extra fun, make that completely submerged in cold salt water. Then they will be left for weeks or months without use. The potential for corrosion and rust is very high in this type of use.

Because their use and environment is so prone to rust, many trailer brakes are now fabricated from stainless steel and aluminum components. This raises their cost much higher than equivalent car brakes, but the reduction in failure-rate is probably worth the extra expense. When you really need the trailer brakes you will want them to operate and not be a rusted, stuck, mess of non-working metal.

Trailer brakes must be actuated by some mechanism, and again there are two main styles, surge and electrical. The most common is the surge brake actuator.

Surge brake actuators rely on two principals for their operation: that you are moving forward and want to stop, and that the trailer has momentum. Without these, there is no braking action.

The surge brake actuator is coupled to a moveable joint at the trailer hitch/tow vehicle connection. When the tow vehicle slows down, momentum pushes the trailer against the hitch, providing pressure on a hydralic cylinder which in turn applies pressure to the brakes. If the tow vehicle releases its brakes, the pressure on the actuator is removed, and the trailer releases its brakes, too. Thus the two independent brake systems are operated in synchronism by a simple mechanism.

There are two flaws in the surge brake actuator concept. The first is evident when you back the trailer on level ground or up an incline. The surge actuator cannot differentiate between the compression it gets when decellerating for highway braking and the pressure it gets when you want to back up in your drive way. It applies the brakes in both situations. In the latter case, brakes are not required, but are, in fact, decidedly unwelcome. A little electricity to the rescue.

When backing up, one thing is different in most cars: the back-up lights come on! Some of the current from this lighting circuit can be borrowed and routed to an electrical solenoid which will operate to defeat the braking action of the surge coupler. Is the problem solved?

Consider the case where we want to back a large trailer and boat down a steep launching ramp. As described elsewhere, the descent of the ramp will add significant pull into the water, which must be resisted by the brakes. So now there is a situation where extra braking power from the trailer's brakes would be welcomed, but, unfortunately, they are disabled by the reverse solenoid.

Although surge actuated brakes suffer from these flaws, they are the most common. Their construction and installation has been refined by many years of experience, and in general they provide a well-engineered solution to the problem of trailer braking.

An alternative to surge-brake actuators is an electrical brake actuator. A simple sensor, typically a rheostat, is linked to the brake pedal of the tow vehicle and provides a signal of brake actuation. The electrical signal is amplified and used to apply braking action. The advantage to his approach is the brakes work when you want them, even backing uphill or downhill. The can also be adjusted to balance the breaking action so that the trailer brakes come on harder than the tow vehicle brakes, which is useful in correcting fish-tailing problems in the trailer. The disadvantage is the inherent problem of keeping electrical apparatus in working condition when it is constantly being submerged in water.

Thus electrically operated braking systems are not commonly used on boat trailers because of their in-water environment. Systems may be available and used on other large trailers, but they were probably not designed to be capable of reliable operation after repeated dunkings at the launch ramp.

Tongue Wheel

Very light weight trailers often rest the tongue directly on the ground when not coupled, but once the tongue weight is above about 50 pounds, you will find you may prefer to add a wheeled jack.

DISCLAIMER: This information is believed to be accurate but there is no guarantee. We do our best!

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Copyright © 2000 by James W. Hebert. Unauthorized reproduction prohibited!

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Author: James W. Hebert with important contributions from others with attribution in the text.
This article first appeared July 4, 2000.