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Author Topic:   Adjusting Trailer Tongue Weight

kamie posted 08-16-2007 07:07 PM ET (US)
Now that I have added a heavier engine and taken off the t-top the tongue weight is way too light. I don't want to change the position of the boat on the trailer so I was thinking that if I moved the axle back that would put more boat forward of the axle and increase the tongue weight?
Yes I have read the reference article, just confirming if my theory is correct.
ConB posted 08-16-2007 09:10 PM ET (US)
Yes, and the engineer types should be able to say how much to move the axle.
Con
Casco Bay Outrage posted 08-16-2007 09:41 PM ET (US)
Kamie -
Do you have a spare tire mounted on the trailer tongue? If not, consider adding it. This might get you the weight plus adds the redundancy.
Regards,
CBO
Alex K posted 08-17-2007 07:38 AM ET (US)
Kamie,
I just switched from a 60HP to a 75HP E-TEC on my Alert 15 and had the same problem. I couldn't move the hull forward as the winch stand is already as close to the end of the trailer tongue as possible. So I moved the axle backwards about 12cm.
It was just a guess but proved to be OK. I have an EZ Loader trailer and it was done in an hour. No big deal.
Alex
Tom W Clark posted 08-17-2007 08:34 AM ET (US)
Yes Kamie, you're theory is correct. Move the axle back a couple inches and see what the tongue weight is then.
Jerry Townsend posted 08-17-2007 01:58 PM ET (US)
Kamie - you are correct - moving the axle back will increase your hitch load. But a little movement goes a long way - try an inch or two instead of six inches.
The reference section contains a computer program that you can use to determine what change is necessary. ---- Jerry/Idaho
Whale1 posted 08-17-2007 03:08 PM ET (US)
Jerry Townsend's excellent reference article takes the guesswork out of the move.
By moving the axle rearward, you are changing the geometry and will also realize a possibly unanticipated benefit in the longer distance between the axle and the hitch ball. You will basically have a longer trailer which should make backing somewhat easier.
Happy trailering:-)

ONH2O
kamie posted 08-18-2007 08:01 AM ET (US)
Thanks all,
As I said I have the caculator but it requires you know exact tongue weight of center of gravity neither I was confident in my numbers. I used it two years ago to adjust the trailer. I moved the axle back about 6 inches and now I can go 55 to 60 without any fishtailing. With the boat on the trailer I will measure tounge weight to see where the center of gravity is now. My guess is that it is slightly behind the axle. If that is the case, I may move the axle back 6 more inches which will be exacly where the axle was when I purchased the boat.
Thanks again
Jerry Townsend posted 08-18-2007 03:37 PM ET (US)
kamie - you can use the program for an iterative process as discussed in the program operation discussion to determine the location of the CG of the boat. The CG location is referenced to the transom and will not change as you make other calculations.
The tongue load is well within the capability of bathroom scales - just be as accurate as possible, have the load reasonably close to the center of the load table, and if you have several scales (borrowed from relatives or neighbors) available - then average those readings that are reasonably close to the others. Reject any reading that is obviously different from others. -------- Jerry/Idaho
lordswork2007 posted 08-19-2007 01:07 PM ET (US)
The interesting issue is, it is not tongue weight per se, but location of the center of drag in relation to the center of mass. The tongue weight is a rough approximation.
There are two kinds of drag: rolling drag and aerodynamic drag. The center of drag for rolling drag is the tire contact patch. Aero drag is much more complicated and would require a wind tunnel to measure accurately. It is probably centered well forward of the tires. Aero drag increases as the square of the speed. Rolling drag increases linearly with speed. Trailers stable at lower speeds may become unstable as the center of drag moves forward due to increased aero drag.
The tow vehicle is considered to exert its force on the trailer/boat system at the center of mass for the system. If that center of mass is behind the combined center of drag, the trailer is unstable. Instability means small perterbations will increase, because the a counter restorative force occurs. Stable trailers generate a restorative force to cancel small movements. It is the same principle as pulling rolling luggage. If you try to push it, it is unstable.
Tongue weight is used because it measures in a way the amount of difference between the center of mass and the tire contact patches. It ignores aero drag. For dual axle trailers it is not as reliable either. But short of just trying things (testing), tongue weight is a convenient metric. There is nothing absolute about the 10% figure often quoted, however.
lordswork2007 posted 08-19-2007 01:08 PM ET (US)
Sorry perturbations not perterbations.
kamie posted 08-19-2007 02:47 PM ET (US)
Thanks Jerry,
To get tongue weight you need the boat on the trailer but I needed to make adjustments before that. Thew adjustments I made let me do two things, first drive the boat to the dealer without being run over by guys in big trucks, and second measure the current tongue weight. Now that I have that, I can use the program to input the desired tongue weight given the weight of the total rig, also now known. Looks like I need to move the axle back 6 more inches.
HAPPYJIM posted 08-19-2007 03:13 PM ET (US)
If your tow vehicle is heavy, adjust the axle until you have 10% of the boat/trailer/equipment/fuel on the tongue(use a bathroom scale). If pulling with a car, that will be too much for most early model cars.
A little extra tongue weight is better than not enough as long as the tow vehicle can handle it.
HAPPYJIM posted 08-19-2007 03:23 PM ET (US)
As far as drag is concerned, I recommend not trailering the boat when winds are above 80 knots indicated with 90 degree crosswinds. You could increase that to 100 knots with no crosswind. If in doubt, run the rig up to NASA Cleveland. They have a wind tunnel to beat all. They would be pleased to run it through. I'll just bet they never had a Classic Whaler tested.
lordswork2007 posted 08-19-2007 04:36 PM ET (US)
Mr. High and Dry, please be more precise.
All wind surface measurements in the US are by anemometer, which measures true, not indicated wind speed because it is velocity, not dynamic pressure, sensitive.
The correct terminology for crosswind metric is "crosswind component" not "x degree crosswinds."
Actually, very little is done to improve the aerodynamics of towed boats. Yet much lucre is spent on gas dragging boats through the air. I wonder if anyone has come up with an "aero kit" that improves the coefficient of drag of the tow.
An idea, that.
lordswork2007 posted 08-19-2007 04:37 PM ET (US)
Sorry I meant Mr. Happy Jim.
Binkie posted 08-19-2007 05:03 PM ET (US)
If no one responds, maybe it will go away.

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Author	Topic: Adjusting Trailer Tongue Weight
kamie	posted 08-16-2007 07:07 PM ET (US) Now that I have added a heavier engine and taken off the t-top the tongue weight is way too light. I don't want to change the position of the boat on the trailer so I was thinking that if I moved the axle back that would put more boat forward of the axle and increase the tongue weight? Yes I have read the reference article, just confirming if my theory is correct.
ConB	posted 08-16-2007 09:10 PM ET (US) Yes, and the engineer types should be able to say how much to move the axle. Con
Casco Bay Outrage	posted 08-16-2007 09:41 PM ET (US) Kamie - Do you have a spare tire mounted on the trailer tongue? If not, consider adding it. This might get you the weight plus adds the redundancy. Regards, CBO
Alex K	posted 08-17-2007 07:38 AM ET (US) Kamie, I just switched from a 60HP to a 75HP E-TEC on my Alert 15 and had the same problem. I couldn't move the hull forward as the winch stand is already as close to the end of the trailer tongue as possible. So I moved the axle backwards about 12cm. It was just a guess but proved to be OK. I have an EZ Loader trailer and it was done in an hour. No big deal. Alex
Tom W Clark	posted 08-17-2007 08:34 AM ET (US) Yes Kamie, you're theory is correct. Move the axle back a couple inches and see what the tongue weight is then.
Jerry Townsend	posted 08-17-2007 01:58 PM ET (US) Kamie - you are correct - moving the axle back will increase your hitch load. But a little movement goes a long way - try an inch or two instead of six inches. The reference section contains a computer program that you can use to determine what change is necessary. ---- Jerry/Idaho
Whale1	posted 08-17-2007 03:08 PM ET (US) Jerry Townsend's excellent reference article takes the guesswork out of the move. By moving the axle rearward, you are changing the geometry and will also realize a possibly unanticipated benefit in the longer distance between the axle and the hitch ball. You will basically have a longer trailer which should make backing somewhat easier. Happy trailering:-) ONH2O
kamie	posted 08-18-2007 08:01 AM ET (US) Thanks all, As I said I have the caculator but it requires you know exact tongue weight of center of gravity neither I was confident in my numbers. I used it two years ago to adjust the trailer. I moved the axle back about 6 inches and now I can go 55 to 60 without any fishtailing. With the boat on the trailer I will measure tounge weight to see where the center of gravity is now. My guess is that it is slightly behind the axle. If that is the case, I may move the axle back 6 more inches which will be exacly where the axle was when I purchased the boat. Thanks again
Jerry Townsend	posted 08-18-2007 03:37 PM ET (US) kamie - you can use the program for an iterative process as discussed in the program operation discussion to determine the location of the CG of the boat. The CG location is referenced to the transom and will not change as you make other calculations. The tongue load is well within the capability of bathroom scales - just be as accurate as possible, have the load reasonably close to the center of the load table, and if you have several scales (borrowed from relatives or neighbors) available - then average those readings that are reasonably close to the others. Reject any reading that is obviously different from others. -------- Jerry/Idaho
lordswork2007	posted 08-19-2007 01:07 PM ET (US) The interesting issue is, it is not tongue weight per se, but location of the center of drag in relation to the center of mass. The tongue weight is a rough approximation. There are two kinds of drag: rolling drag and aerodynamic drag. The center of drag for rolling drag is the tire contact patch. Aero drag is much more complicated and would require a wind tunnel to measure accurately. It is probably centered well forward of the tires. Aero drag increases as the square of the speed. Rolling drag increases linearly with speed. Trailers stable at lower speeds may become unstable as the center of drag moves forward due to increased aero drag. The tow vehicle is considered to exert its force on the trailer/boat system at the center of mass for the system. If that center of mass is behind the combined center of drag, the trailer is unstable. Instability means small perterbations will increase, because the a counter restorative force occurs. Stable trailers generate a restorative force to cancel small movements. It is the same principle as pulling rolling luggage. If you try to push it, it is unstable. Tongue weight is used because it measures in a way the amount of difference between the center of mass and the tire contact patches. It ignores aero drag. For dual axle trailers it is not as reliable either. But short of just trying things (testing), tongue weight is a convenient metric. There is nothing absolute about the 10% figure often quoted, however.
lordswork2007	posted 08-19-2007 01:08 PM ET (US) Sorry perturbations not perterbations.
kamie	posted 08-19-2007 02:47 PM ET (US) Thanks Jerry, To get tongue weight you need the boat on the trailer but I needed to make adjustments before that. Thew adjustments I made let me do two things, first drive the boat to the dealer without being run over by guys in big trucks, and second measure the current tongue weight. Now that I have that, I can use the program to input the desired tongue weight given the weight of the total rig, also now known. Looks like I need to move the axle back 6 more inches.
HAPPYJIM	posted 08-19-2007 03:13 PM ET (US) If your tow vehicle is heavy, adjust the axle until you have 10% of the boat/trailer/equipment/fuel on the tongue(use a bathroom scale). If pulling with a car, that will be too much for most early model cars. A little extra tongue weight is better than not enough as long as the tow vehicle can handle it.
HAPPYJIM	posted 08-19-2007 03:23 PM ET (US) As far as drag is concerned, I recommend not trailering the boat when winds are above 80 knots indicated with 90 degree crosswinds. You could increase that to 100 knots with no crosswind. If in doubt, run the rig up to NASA Cleveland. They have a wind tunnel to beat all. They would be pleased to run it through. I'll just bet they never had a Classic Whaler tested.
lordswork2007	posted 08-19-2007 04:36 PM ET (US) Mr. High and Dry, please be more precise. All wind surface measurements in the US are by anemometer, which measures true, not indicated wind speed because it is velocity, not dynamic pressure, sensitive. The correct terminology for crosswind metric is "crosswind component" not "x degree crosswinds." Actually, very little is done to improve the aerodynamics of towed boats. Yet much lucre is spent on gas dragging boats through the air. I wonder if anyone has come up with an "aero kit" that improves the coefficient of drag of the tow. An idea, that.
lordswork2007	posted 08-19-2007 04:37 PM ET (US) Sorry I meant Mr. Happy Jim.
Binkie	posted 08-19-2007 05:03 PM ET (US) If no one responds, maybe it will go away.