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boat sways when towing

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  • boat sways when towing

    i have a 2002 suburban and tow a 24ft four winns..it sways alittle when i go about 60 mph what should i do to adjust weight?


  • #2
    Re: boat sways when towing

    Hi,Use a bathroom scale and place under trailer hook (use some piece of wood or similar so you reach up). About 70-75 kg (155-165 lbs) is usually OK force on the trailer hook. You want some force on the hook, but not to much, and not to little. You want good balance on the trailer wheels.Make sure you have correct airpressure on trailer tyres - too low pressure and trailer will tend to lurch and if too much pressure it tend do bounce. High centre of gravity on the trailer will make trailer more instable also.I have a trailer (two wheel, not boogie) with 70 kg force on the trailer hook and it is fine balance. I can trailer 80 km/h=50 mph (max allowed speed in my country with trailer that has brakes) without any problem at all. My boat weight is 1050 kg (2315 lbs) with outboard, fuel etc. I have actually tried 100 km/h=62 mph without problem.This is how my trailer look:

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    • #3
      Re: boat sways when towing

      tim10034,Basically, two things will cause boat trailer sway.1. Too little tongue weight. Resolve by moving the boat forward or the axle back.2. Mismatched tires and/or uneven tire inflation pressures.

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      • #4
        Re: boat sways when towing

        Tim; If your trailer is swaying at highway speeds, your tounge weight is too light.You need to either move the axles rearward or the boat forward to get the tounge weight 5 to 7 percent of the total gross weight of the boat and trailer.If your 24 foot boat weighs in the neighborhood of 4500 lbs. add another 1500 for a galvanized steel trailer and your up to 6000 lbs.7 percent of that would put your tounge weight at 420 lbs.

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        • #5
          Re: boat sways when towing

          Tim,Make sure that you didn't load all your weekend things in the back of the boat shifting the load to the back. Was gas and water full etc... If the boat is left on the trailer for a prolonged period the tires can develop a flat spot, this usually goes away when they warm up. Was the boat loaded straight on the trailer?Tire inflation is also important.If everything is in order than you will need to move the trailer axles back slightly. This is a trial and error deal. You want 10-15% of your gross trailer weight on the tongue. Assuming you are around 6000lbs that would be roughly 600-650lbs. This should be enough weight. Loosen the U bolts and use your boat winch to work them backwards. Maybe 1 to 1.5 inches at a time. This is not a hard job at all. You shouldn't have any problem trailering at speeds 70+ mph. This is not recommended but entirely possible. Do not trailer with the canvas up!! Bad on canvas, and creates undue windage.

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          • #6
            Re: boat sways when towing

            thanks guys....my tires all match and inflation is at 48psi....i think i will try to move the boat alittle forward on the trailer it sways when i go over bumbs in the road....funny how this is happening...it has it's orininal trailer on there

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            • #7
              Re: boat sways when towing

              Tim,Is this a roller or bunk trailer? Be very careful moving the winch stand if it is a bunk. It would be better to move the axle if so.

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              • #8
                Re: boat sways when towing

                Radial tires will cause sway too, especially if running near max tire load. That's why most trailer tires are not radial ply.

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                • #9
                  Re: boat sways when towing

                  tire pressure makes a big difference. i never thought so until my last trip when i pulled my boat for the season. turns out i had the tires real low. trip went great with little sway.as for weight, you simply need more on the tongue. if you can move the boat fwd, even a few inches, it may help. i put my spare trailer tire in the bow of the boat- that even helps.good luck-
                  2002 Wellcraft 290 Coastal
                  Twin 2002 Yamaha F225s

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                  • #10
                    Re: boat sways when towing

                    Now for a really dumb question. I know about the 10% forward weight stuff, but why does it work? It reduces load on the steering (front) wheels of the car which reduces steering control and concentrates weight at the tow ball which is a fulchrum point about which both the trailer and car can pivot. This would suggest that the weight of the trailer would be more likely to jacknife the car on braking and that any sway would be harder to correct because there's less steering grip at the front of the car.On the other hand too little weight on the tongue would lift the rear of the car and make it plough (nose down) and lose steering control in a different way as it is pushed by the trailer, while any sway would have a similar effect.The 10% tongue weight mightn't be more than the weight of a full load in the boot (trunk), but a car with a full boot is going to behave differently to one with half a ton to a ton of free weight behind it as well.This is just one of those things that I can't understand how it works when I think about it although I see it working all around me, like there's no sense to a bicycle staying up when someone is riding it and turning it (and it's a fact that if the front forks on a bike are reversed it becomes unrideable).

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                    • #11
                      Re: boat sways when towing

                      I found this out on the web and I am still working through the computations to see if I can verify if this is real world usable:Repeat: Not my Work.lets see if I can explain this calculation - this message may be a tad long though. I placed (assumed) the transom at the back of the trailer. Denoting the length of the trailer as X3, the distance from the transom to the center of the wheels as X1, the distance from the center of gravity to the transom as X2, the total weight of the boat/motor/trailer/et.al as Lt, the weight of the boat/motor as Lb and the hitch load as Lh.Now, the bending moment at the transom (back of the trailer) must be zero by definition. Then, writing the summation of moments about the transom (defining clockwise as positive) gives:X3(Lt) + (Lt - Lh)X1 - Lb(X2) = 0and the same basic equation for the modified configuration - same loads but different distances as:Y3(Lt) + (Lt - Lh)Y1 - Lb(Y2) = 0Notice the load on the wheels is written as (Lt- Lh). Now, from the transom, the bending moment of the boat/engine will not change - or namely, Lb(X2) = Lb(Y2)- so strictly speaking, we don't require the location of the center of gravity of the boat/engine. Remember that everything is referenced to the transom.Solving each of the above equations for Lb(X2) or Lb(Y2) - remember, these are the same - and equating those equations gives:LbX2 = X3Lh + X1(Lt - Lh)andLbY2 = Y3Lh + Y1(Lt - Lh)and equating these equations gives:X3Lh + X1(Lt - Lh) = Y3Lh + Y1(Lt - Lh)and solving for Y1 (the distance from the transom to the centerline of the wheels) in the modified configuration gives:Y1 = [X3Lt + (Lt-Lh)X1 - Y3Lh]/ (Lt - Lh)which, when rearranged gives:Y1 = [Lt(X3-Y3) + (Lt-Lh)X1] / (Lt - Lh)and with X3 = 300, Lt = 4700, Lh = 300, X1 = 58, Y3 = 285 i.e. (300-15 : from moving the boat forward 15 inches) gives:Y1 = 59 inches. Which is the distance from the transom to the centerline of the tandem axles in the modified configuration.Note, the original distance from the transom to the centerline of the tandem axles was 58 inches (300 - 242). Therefore, the tandem axle should be placed 59 inches forward of the transom - or in other words, moving the boat forward 15 inches should be accompanied by moving the centerline of the axles 16 inches forward.The above calc considers the transom at the end of the trailer - a few inches one way or the other will not make much difference.Calculating the center of gravity of the boat/engine/et.al can be obtained by solving one of the initial equations, or:fromX3Lt + (Lt-Lh)X1 - LbX2 = 0and solve for X2 as:X2 = [X3Lt + (Lt-Lh)X1] / Lbwhich gives: X2 = 98.63 so the boat/engine center of gravity is 98.63 inches forward of the transom.Everyone should, as desired, check the above calculations. Should you have questions, let me know. I have, rounded some number off - for example, the above 59 inches is actually calculated as 59.024 inches.Now, regarding some of the wags/guesses etc, remember that the boat is the controlling component at 3500 pounds of the total 4700 - so if I were NOT making calculations, I would move the axles the same distance as I wanted to move the boat.

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                      • #12
                        Re: boat sways when towing

                        Ohhh! My head hurts.

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                        • #13
                          Re: boat sways when towing

                          I worked out the calculations, Then I moved my gas tanks and battery forward once the boat was loaded on the trailer and made sure that the plug was removed to let any water out that might have splashed in and resulted in extra weight in the rear.Then used the paper I had worked out the calculations on to start a campfire at my destination. Cheers

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                          • #14
                            Re: boat sways when towing

                            Mathimagician I'm Not,But,I Am a Mechanic, with a Doctorate from the College of Common Sense..... Move the Boat Forward on the Trailer,Or,The Axles Rearward,And Your Problems will Go Away........10% to 15%, Tongue Weight Is the Ticket
                            Any Grease is Better,..... Than No Grease at All.......

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                            • #15
                              Re: boat sways when towing

                              I am a mechanical engineer and I didn't even wanna read all those equations. :-) Like everyone said , you have too little tounge weight. Move trailer stand forward or axles back. The new boat has nothing to do with, I have seen several brand new boat/trailer combos that were all messed up. If your tow vehicle will allow it (and it should), too much is way better than not enough. If you have a decent size boat 10% weight is more than an average bathroom scale can measure and not get harmed. However, you can use statics to use a standard scale though. Get a stiff board, like a 4x4 about 36 inches long and a couple round things about 1 inch dimeter , like wooden dowels. Brace the 4x4 between the scale and a support of the same height as the scale like a bridge. At 1/3 of the distance across the 4x4 put the jack of the trailer. You get a 2 to 1 reduction in force at the scale. Measurement between trailer jack and the bathroom scale dowel center / measurement of the trailer jack to the to the support dowel. That ratio is the force reduction to save you bathroom scale. Think of a skinny kid equalling out a fat kid on a seasaw on the playground. If a 2:1 ratio is not enough for your scale adjust it accordingly. Hope this helps. If my verbal explaination is confusing, post an email address and I will send you a diagram, I dunno how to post stuff like that here.

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