View Full Version : Correct Boat Trailer Axle position

09-25-2012, 12:45 AM
Hi All.

I am in need of some good advice please.

I have a 17ft bowrider which wants to sway badly at any speeds over 60mph.

The weight on the hitch also seems to be low.

I have told that both are due to the axle being placed too far forward on the trailer.

I have attached a picture of the trailer for reference purposes.

I am hoping someone can tell me how to determine the correct position for the axle placement as I would like to correct this as part of the trailer refurbishment.


09-25-2012, 02:49 AM
Hi kimcrwbr1. I haven't weighed it exactly but I can lift it easily with one hand. It becomes a lot easier a few inches above the hitch, but it's a lot lighter than my previous boat. Is there an ideal weight it should be? The trailer is beautifully in the centre of the vehicle when towed.
I am towing it with a Nissan X-trail and the trailer is in a "level" position during towing. Tyre pressure on the vehicle is as specified for "loaded" conditions and trailer pressure on the trailer is 250 KPI with trailer tyres. The picture doesn't show it but I replaced the rims with proper trailer rims, which widened the track a few inches and gives proper clearance in the wheel well. The fuel tank is removable and according to local laws down here if it's removable I can't tow the boat with it in place. I do however put my tool box which is a few pounds in the nose along with anything heave I can think of. The suspension is made up of 3 leaf springs, with no shocks and the shocks on the vehicle are good. Should I look to fit shocks for more stability? My dad restores old cars so the welding and setting up would be straight when changed, but I want to avoid moving it and then having to move it again because it's not right. Thanks for the help.

09-25-2012, 08:09 AM
your tongue weight should be 10-15% of the gross trailer weight....do you have room to move the boat winch assy forward on the trailer?....this will move the boat weight forward and have the same effect as moving the axle...six inches will make a big difference.....and watch for scalloping on the trailer tires....i am surprised you dont have that now with the boat too far back...

09-26-2012, 12:53 PM
I always heard tongue weight was to be no more than 10% and no less than 8% of total boat and trailer weight combined. Another cause of sway is that the tires on your tow vehicle are too low or too soft.

09-26-2012, 04:01 PM
What papyson said in post #7...your axle won't move so adjust the boat on the trailer is the only approach left.

Take the boat and trailer to a local gravel yard or transport company to weight it. measure the weight on the tongue with a bathroom scale, with the tongue at "towing height".

From what i see you have a real light boat with a heavy engine way out back. the closer the engine is to your axle, the less impact it will have to varying the tongue weight (with height of the tongue).

And do NOT put this off...worst case is one day the boat will sway until it leaves the trailer and the whole outfit becomes scrap

09-30-2012, 06:00 PM
i was just taking the easy approach...its only 4 bolts on most of the small trailers and all you have to do is loosen them and maybe a little tap or two with a maul and tighten them back down...thats if he has the room....that 10-15% is the book recommended distribution.....8% is probably ok....adding trim tabs is where most people get into trouble...they add the tabs and then move the boat position where the tabs wont hit the trailer when loading...on aluminum boats its common for trim tabs to be welded even with the bottom on the transom....in that case its best to cut the runners on the trailer and recarpet them...btw....moving the winch assy 6 inches make a big difference...

12-05-2012, 09:00 PM
G'day all,

What you are describing as to the swaying motion is caused by too much weight behind the axle

Firstly, there should be a minimum of around 50 Lbs weight bearing down on the tow ball with a single-axle trailer.

Secondly, tyre pressures on the towing vehicle MUST be set at the maximum pressure for the vehicle as most cars have radials these days, and there is nothing worse than low pressures, allowing the towing vehicle to be able to move side to side in a swaying motion. I would be recommending 40 PSI for the vehicle, and 35 for the trailer, but that also depends on the type of tyres used.

Thirdly, the trailer tyres should be of the Cross-ply variety, as this also limits the sideways movement. Combine the both vehicles with soft radials, and low tongue weight, then you are looking for trouble.

Fourthly, make sure that the trailer draw bar isn't flexing.

I have never heard of a law that prevents fuel tanks being carried in a towed boat, as most tanks are retained within the vessel by some means, as you don't want them moving around whilst on the water.


01-14-2013, 09:07 PM
coming from someone who has built trailers for for 20yrs.....axle too far forward...buy a welder or rent one. you are wasting your time any other way...

01-14-2013, 10:22 PM
Thanks for the reply kbcave. It's currently my summer and i didn't want the trailer in pieces when i could be using the boat. I have a plan to have the trailer redone in winter, about 4 months from now. I will be moving the axle as part of this process. In the mean time what I did was move the bow stop on the trailer forward 4 inches and that cured my sway problem nicely. Can you give me the correct method to calculate how far back the axle should be?

01-15-2013, 02:58 AM
Papyson is right with the 10% for the the tongue weight. If you move the axle though, be sure and get it square.

01-15-2013, 08:08 AM
I've had the same problem, and did a huge amount of research to solve it. Here is the solution: The easiest way to fix the problem is simply move the winch bar forward if possible so that the center of gravity is forward of the axel, and the tongue weight is approximately 10% (+/- 2%) of total weight (boat & trailer.) If moving the winch bar is not an option, the the axel must go back to meet the same specs - center of gravity forward of axel and tongue weight 10% of total. Those specs are from the experts at Trailering Magazine.

Once done, if you still get sway, you can beef up your tow vehicle suspension. Often, your tow vehicle will have very soft-sided tires which contributes to the problem. If you are taking a short trip, over inflate the tires. (On my F-150, I over inflate to 55 lbs compared to the normal 36 lbs.) For longer hauls, I use a Reese anti-sway distribution hitch, and switch by rear tires on the truck to Continental E-rated tires with 80 lbs. PSI. This allows me to trailer a 6000 lb boat 300 miles each way to Cape Hatteras safely and comfortably, except for a lousy gas mileage.

02-07-2013, 10:07 PM
Make sure you have the same size tires on it. That will make one sway bad. The same goes with air pressure. Never exceed the max tire psi rating. Make sure your wheel bearings are good. A bad wheel bearing will change the tire line. The same with the suspension. One side worn will cause problems. Usually swaying is from misalignment of the tires from the above issues.

As a former truck driver and well versed on balancing loads with sliding axles...18 wheelers are ~100 lbs an inch. You are probably looking around 20-30 lbs an inch. I would move the axles back about 8 inches. You should have roughly a 150 lb tongue weight which is about what most boats I've owned that size had.

You can always go to a truck stop and use their scales to see what you are working with. Just put the boat on the scales and push the button and the person will weigh you. Then you go inside to the fuel desk and usually it's around $9 for a scale ticket. If they ain't busy which weekends are best, drop the trailer on the scales for a split weight. Then you know exactly what your tongue weight is. Pull off the scales prior to going in or the truck drivers will get mad. :)

My brother uses a sway bar on his RV and it fixed his sway problem. The longer the wheel base the better they pull because they are more forgiving.