$60,000 boat on a $200 Trailer – Part I – by Bill Nalle

This article was first published in the Southwester Newsletter, editor Craig Stanfield, of the Southwest Chapter of ACBS.  Bill Nalle was awarded the 2017 ACBS-Hagerty Safety Award for the best published article on boating safety.  It will be shared with you this week in three segments.

Last year’s Keels and Wheels found me admiring the quality of entrants with fellow member and good friend Jacob Deegan. One thing led to another, as they usually do, and we started noticing the number of $60,000 boats arriving on $200 trailers. Gorgeous boats arriving on little more than a wing and a prayer. 

First, a little about myself. By day, I am a Professional Engineer specializing in accident reconstruction. In that capacity I have had numerous cases involving trailers with deadly results. In addition, I have designed and built custom trailers for both my wife’s and my wooden boats, Natte and Dawn Treader. Her Natte is 28 feet and 8,000 pounds while Dawn Treader is 38 feet and 6,500 pounds. Dawn Treader’s custom trailer was recently completed by Lagoon Trailers in Port O’Conner, TX. It is a welded aluminum, “I” beam trailer with torsion axles, electric over hydraulic disc brakes and all LED lights. John Stapp, owner of Lagoon, is a master at dealing with the special needs of our wood boats and getting the details done correctly…..down to the blue accent lights inside the “I” beams that light up under the boat. I thought it was time to share some insight on this complicated topic of trailers.

Most of the accident cases I see generally fall into one of the following categories:

  1. Worn out, junk trailers
  2. Improperly sized trailers
  3. Too small a tow vehicle for the trailers
  4. Unbalanced trailers
  5. Uncoupled trailers
  6. Poorly lit trailers

Nearly every trailer accident I see involving one of these problems could have been prevented had someone taken a bit of time, identified the problem and sought a solution. To that end, I want to look at the various parts of a trailer pulling operation, identify potential problems and offer solutions. In Part I of this article, I will cover a discussion of the number of axles, types of axles and suspension, brakes, couplers, safety chains, and winch peculiarities. In Part II, I will cover the tow vehicles, axles weights, tongue weights, and balance of the trailers.

How Many Axles:

How many axles do you really want to have? Here are some things to consider. 
First of all a single axle trailer is good for only the very smallest of boats. One simple way to look at it is if your boat is big enough to tow a skier or boarder you really should have four tires on the ground. A single axle trailer is very critical on balance. A few loaded ice chests, empty or full fuel load or some sloshing water can change the balance greatly. Also, consider the control of your trailer when a tire or wheel fails. Something as simple as a blow out or tread failure on one tire leaves a grossly unbalanced situation.

A dual axle trailer does solve a lot of problems. On a light duty trailer most people will put brakes on the front axle and leave the rear axle as a “tag axle” to carry weight and provide stability. Considering the wide range of axle capacities available, the dual axle trailer is the solution for most recreational boaters. On a heavier duty dual axle trailer you will want brakes on both axles. We will talk about brakes later.


When do you want or need a triple axle trailer? First consider that triples are hard on tires when maneuvering in close spaces. It is possible to literally shear a tire off the rim when making slow, tight turns. On the positive side, a triple is very stable on the highway and can carry a lot of boat. A single tire failure on a triple is for the most part a non issue. Some people do not even carry a spare with a triple. If a tire or bearing fails, just take off the wheel, chain the axle up and move on down the road.

Take a careful look at axle ratings. It is not as simple as one might think. You can’t just look at the boat weight and call it a day. First you need to look at the full gross weight, that is … the loaded boat plus the empty weight of the trailer. Then consider the overload on the front axle when coming over the break point on a boat ramp. Most people never think about this seemingly minor point. Some ramps transition quickly from the down slope into the water to the flatter part at the top. This “break” causes what can be a severe overload on the front axle. I recommend at least a 50 % factor of safety on axle specifications. If your boat and trailer weigh in at 7,000 pounds, I would look at two 5,000 or 6,000 pound axles under it. For the most part the only price paid for extra heavy axle ratings is a slightly stiffer ride. Axles that are too light for the duty are prone to failures of the axle, wheels, bearings, suspension and tires. Be safe. Be over spec with the axle ratings. In conclusion, my thoughts about the number of axles are these. A small boat, say less than 2,000 pounds can live on a single axle trailer. I draw the line between dual and triples somewhere in the 6,000 to 7,000 pound boat range. For example, we built a triple for my wife’s boat, Natte, which weighs in around 8,000 pounds. Dawn Treader, at just over 6,000 pounds, is on the brand new dual axle trailer we discussed earlier.

Types of Axles / Suspension:

There are two basic types of axles in wide use today, the conventional spring axle and the internal torsion axle. As with almost everything else in the trailer world one costs more than the other. The old standby is the spring axle. It comes in almost any size one might desire and is quite durable. The main draw back is that it is going to rust…. fresh or salt water, it is going to rust. The spring hangers and bolts are subject to wear and problems in the long run. For infrequent use and an owner willing to keep up with maintenance, there is nothing wrong with a conventional spring trailer. These axles are less expensive and have been around a long time.

There are several manufacturers who make internal torsion axles. There are no leaf springs to rub and rust. The attachment to the trailer frame is hard bolted with no moving parts. The axle tube is a square steel tube, either straight or with a dropped middle section bolted to the bottom of the trailer frame rails. The wheel assembly shaft has a solid square rod that goes inside the axle tube and is mounted at a 45 degree angle. Between the solid square rod and the hollow axle tube are four rubber “rods” and the whole thing is thermally assembled. Although sizes will vary according to the loads to be carried, some typical dimensions might be a 3 inch ID axle tube, a 1.5 inch solid square rod with the four rubber “rods” about 1 inch in diameter. Again the length of the square rod and the four rubber “rods” will vary according to the capacity of the axle.

The tire and brake are mounted on an arm about 12 inches long. As the wheel moves up and down over bumps the solid square rod rotates only a few degrees inside the axle shaft and energy is absorbed by the four rubber “rods”. By the very nature of a conventional spring axle, that trailer will stand a bit higher than the internal torsion axle units. With the torsion axles the arms can be set at different angles thus allowing some latitude in overall trailer height, so if you have a clearance problem getting into the garage the torsion axles might be the answer. Lower trailers tend to be more stable on the highway and easier to launch on shallow angle ramps. However, the lower you are to the ground the more you will drag, especially on long trailers that have a lot of rear overhang.  Drop axles can offer you a bit lower keel height which might be nice on a deep V boat. One must be careful not to get too low and do possible damage to the running gear. A good trailer builder will design a “must have” protection cage for your props and shafts. On more flat bottom boats a straight axle will make the build easier and not cost anything on height.

The information from Bill Nalle’s article will continue on Wednesday of this week.  Wednesday’s post will focus on Brakes.  Friday’s post will be about Couplers, Chains and Winch/Bow Support.



  1. Thanks for the great article! The point about overloading the front axle when going over the break point of a ramp is very interesting. The ramp we use all the time with our new dual-axle trailer is steep enough that the rear tires lift up off the ground – leaving the front axle on its own to support the weight of the boat. I’ll be checking the stated axle rating in the paperwork when I get home tonight.

  2. You leave out one factor for spring axles. Dual and triple spring axles can be rigged in either of two forms – “equalized” or “unequalized”. Although it is common for boat trailers to have “unequalized” axles. With “equalized” axles the load is transferred between the axles, reducing, and often eliminating, the issue overloading one axle as trailer crosses a break in slope. But get flat tire and you must chain the axle up to keep the load on the good axle – or repair the flat before the trailer can be moved. With “unequalized” axles you often can simply remove the wheel with the flat tire (particularly with triple axles) and continue on to a more convenient place to repair the flat. The limited travel of the spring keeping the brake and hub off the ground.
    Torsion axles only come as “unequalized”.
    Note also, the axle weight rating is for dynamic conditions – that 70 MPH+ trip up the Interstate to get the boat to the lake, and has a large safety factor built in. Unless the trailer is grossly overloaded to start with, the axles – and tires – have plenty of reserve strength to handle the short low speed trip up or down the launch ramp.

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