What Causes Fishtailing?

[escavader]

I do agree lack of tounge weight is the primary cause,however ive found rapid acceleration[on ramp of expressway] has made my trailer take off before.Must of been a weight transfer thing
ALAN

 

[Skyco]

Boat trailers are especially bad about fishtailing because the majority of a boat's weight is in the rear.

On the plus side, at least on my two boat trailers, the suspension can be relatively easily moved fore/aft to help adjust the weight distribution...

I have only had 1 boat trailer of the 10 or more that I have owned that the axles were movable. Moving the boat forward as little as 4" can make all the difference in the world. This is accomplished by moving the bow stop forward or aft to get the desired balance.

As for swaying its as others stated and loaded to tail heavy. Also, short wheel based tow vehicles are much worse than a longer based one.

Chris

Odd...I've owned 5 boats and 4 of the trailers had adjustable position axles...only one that didn't was for a small lightweight jon boat.

One thing to watch is don't let the boat hang over the bunks in the rear...that can put a "hook" in the hull over time.

 

[texasjohn]

Hmmmm... excellent thread...I'll have to keep it to point to next time there is a discussion of bumper hitch vs gooseneck trailers. Y'all have well described the problems that can and do occur with bumper hitch trailers. They can be safe, but are FAR less forgiving than a gooseneck.

 

[Diamondpilot]

Odd...I've owned 5 boats and 4 of the trailers had adjustable position axles...only one that didn't was for a small lightweight jon boat.

One thing to watch is don't let the boat hang over the bunks in the rear...that can put a "hook" in the hull over time.

Yes, very true. You need a minimum of 2" overhang with the bunks. Like you said, it can cause a hook or lip and can also crack the transom over time from the bouncing of the outdrive or outboard over time with trailering.

Adjustable axle trailers are usually found on single axle on-size fits all type trailers. Most of the stuff I deal with is tandem and tri-axle. They have trailers that are custom built for the boat they are hauling.

Talking about a boat not being right on the trailer. I was at the ramp 4-5 years ago and saw a guy in a 3/4 ton Gas Ram smoking all 4 tires trying to get up the ramp pulling a 9,500# 27' Rinker Cruiser. I hooked up a tow strap and got him to the top of the ramp with my F-350. He was cussing the tires on his truck but that was not the issue. Anyway we started talking and I was looking over his boat. It was hanging a good 6" beyond the bunks. This was a new boat, not more than a year old on a custom tri-axle trailer. It was obvious to me it was too far aft and did not have enough tongue weight. I helped him make a few adjustments and we put it back in the water and got it right. I am now good friends with Rick and his family and he has had no issues since. He could not believe how moving it 6" made so much difference.

Chris

 

[mbrule]

I do agree lack of tounge weight is the primary cause,however ive found rapid acceleration[on ramp of expressway] has made my trailer take off before.Must of been a weight transfer thing
ALAN

Interesting..... Acceleration is one way to pull a trailer out of a sway, assuming that one can afford to speed up slightly. If the trailer has brakes sway can be stopped immediately by applying the trailer brakes (and only the trailer brakes).

Agree with the others it is load balance, too much weight on the rear, = not enough on the front, = a light tongue.

When you rebuild the trailer possibly consider shifting the axes back a bit?

just my .02. It is based on some experience, I tow a good size camper that is a swaying machine, it has a light tongue despite my load balancing attempts. I once spin out a rented car trailer (no trailer brakes, improperly damaged load, short tow vehicle with a soft rear tire). I didn't realize the tire was soft until after the incident. Was a freshly painted K5 blazer, jackknifed and wrecked the rear quarter!!!! Lost the chains and the axle of the car shifted off the back of the trailer. Broke the ***-a-long when loading initially, had to reload with lever chain binders and inch at a time. Made it home SLOWLY after that!

Now I know better, always balance the load and have trailer brakes OR DO NOT TOW IT! And I have a much more suitable tow vehicle.

Matt

 

[jwstewar]

A few years ago I borrowed my F-I-L's 5x10 single 3500# axle trailer - no brakes. Went to town and got a ton of sand for something. Problem was, I didn't get a ton of sand. I think they gave me about 3000 - 3500 lbs of it - it rained the night before so it was wet, so was probably only a "ton" of dry sand. Anyway, they loaded and they loaded it to the rear of that little trailer, unfortunately I didn't notice it - until I got on the highway. I hit 50 MPH and that trailer started jerking my 1500 ECSB 4x4 Silverado all over the road. I went from berm to berm across all 3 lanes to catch that trailer. Fortunately nobody was around me. My daughter in the backseat was yelling at me to "Stop doing that Dad!" I'm thinking only if I could!!! Finally got it slowed up and got the swaying stopped. About that time a Highway Patrolman came up behind me. He had to see everything. Don't know why he didn't pull me over, but glad he didn't - maybe he was in amazement that we did what we did and didn't lose it completely. I vowed that was the last time I was using an inadequate trailer. Went a couple of months later and bought my 16+2 utility trailer with brakes on both 3500# axles.

 

[slowzuki]

Electric brakes can help, you touch the manual override on the controller and the trailer will pull all the slack out of the hitch system and usually calm down.

The going faster works by the same principle, but you better hope you have a hill to go up to slow down on, because you can't accelerate forever!

 

[Iplayfarmer]

Electric brakes can help, you touch the manual override on the controller and the trailer will pull all the slack out of the hitch system and usually calm down.

The going faster works by the same principle, but you better hope you have a hill to go up to slow down on, because you can't accelerate forever!

I know the brakes trick. That's one of the reasons I need to re-build this POS. I currently don't have brakes. Everything went fine. I just had to go slower than I wanted. I've learned to be aware of how my load is hauling, and I was only about a mile down the road when I felt the swaying. I never really fishtailed good. Someone following me may have never even noticed. The seat of my pants sure noticed, though.

I did find that I could go a little faster when going uphill, but I made a point to slow down before I crested the hill and started downhill faster than I wanted to go with a swaying trailer and no trailer brakes.

I had a brother tear up the side of a Chevy Avalanche a few years back when he was hauling a skid steer. He doesn't tow as often, and the whole rig was jacknifed in the ditch with the trailer smashed into the side of the truck before he could think his way out of the situation. If I remember right, he didn't want to overload the suspension on his truck, so he loaded the skid steer further back to keep more of the weight on the (rented) trailer's suspension.

 

[beppington]

What Causes Fishtailing??! ... The fish's body, that's what ... That's how they swim.

 

[Iplayfarmer]

What Causes Fishtailing??! ... The fish's body, that's what ... That's how they swim.

Man, I felt like I was swimming that day. Not only was my trailer loaded wrong and slowing me down, but we had a killer April snow storm. Snow flakes the size of my head were falling so heavy that the slush couldn't run off the road fast enough. I guess it's good that the horses have something to eat now.

 

[woodsmith]

I've only fishtailed a trailer twice.

First time I had a SWB Land Rover with a twin axle car transporter carrying a VW bug. The hitch on the Land Rover was too high and not adjustable. Hiched up the trailer front axle was off the ground. That fish tailed at about 55mph but with an old Land Rover there wasn't anything left to accelerate out with so I held out as best I could and let it slow down to below 50.

The second time I took my car and box trailer to pick up some concrete paving slabs locally. When I got there and opened the trailer doors I realised that my last load, a huge settee, was still in the trailer. As it was raining I left it in there and put the slabs behind it knowing it would be tail heavy. However, what the heck, it was only a mile or so down the road.:thumbsup:

That set up was fish tailing all over the place and I only got home crawing at 5mph and stopping everytime it went sideways.
When I went to unload I opened the back doors and placed my foot on the trailer bed to help lift the first slab and the back wheels of the car left the ground!:confused2: :laughing:

No wonder it was fish tailing so bad. Definately a nose/tongue weight issue.:laughing:

 

[PILOON]

I had a 3/4 ton PU and 5 x 9 trailer and a contractor friend offered to 'fill me up' for like $20. with nice garden soil.
OK, but he REALLY filled me up, even packed it down with his excavator bucket!
Plenty of power to pull OK -BUT when I headed towards the traffic lights I just plain ran out of brakes, down shifted (1st not syncro) as best as I could, prayed for the stop light to change all while looking where I might do the least damage should the light not change in time.
Lady luck was with me! The light changed in time.
Tell you the ride home was real slow.
A wire to the electric brakes was cut. (not that I was overloaded- much)
Lesson learned, but I had no sway!-, no wonder, springs were just about bottomed out.

 

[slowzuki]

a) need a better controller that tells you if the brake circuit is cut. Prodigy is a good fair priced model.
b) always do a brake check when leaving loaded, this is when you adjust your braking gain on the controller.

I had a 3/4 ton PU and 5 x 9 trailer and a contractor friend offered to 'fill me up' for like $20. with nice garden soil.
OK, but he REALLY filled me up, even packed it down with his excavator bucket!
Plenty of power to pull OK -BUT when I headed towards the traffic lights I just plain ran out of brakes, down shifted (1st not syncro) as best as I could, prayed for the stop light to change all while looking where I might do the least damage should the light not change in time.
Lady luck was with me! The light changed in time.
Tell you the ride home was real slow.
A wire to the electric brakes was cut. (not that I was overloaded- much)
Lesson learned, but I had no sway!-, no wonder, springs were just about bottomed out.

 

[77bronco]

I'm planning a full rebuild on this trailer including new axles, new wheel wells, and a new tongue in the very near future, so I haven't been the most diligent about maintenance of the current axles, tires, etc.

Sometimes it's cheaper to buy a new trailer than try to rebuild one. Depends on how much work the trailer needs.

 

[Diamondpilot]

Sometimes it's cheaper to buy a new trailer than try to rebuild one. Depends on how much work the trailer needs.

I agree.

Its even cheaper to buy a trailer then build one.

Back in 2003 I needed a new trailer to replace the monster 25+5 25,000 GN. Though my connections I got a 18x82 tandem trailer for under $1,000

Axles, 4 tires, springs, steel, and nothing else cost over that. I still needed paint, wood for the deck, lights and electrical, ect. I don't know how they can do it.

Chris

 

[Iplayfarmer]

Sometimes it's cheaper to buy a new trailer than try to rebuild one. Depends on how much work the trailer needs.

I agree.

Its even cheaper to buy a trailer then build one.

Back in 2003 I needed a new trailer to replace the monster 25+5 25,000 GN. Though my connections I got a 18x82 tandem trailer for under $1,000

Axles, 4 tires, springs, steel, and nothing else cost over that. I still needed paint, wood for the deck, lights and electrical, ect. I don't know how they can do it.

Chris

I already have the brake axles and coupler (I got them pretty cheap through a friend), and there are some things I really like about this trailer. I like that it's narrow, and I like that it's a tilt deck. I thought about selling this one and building a new one with the axles I have, but it would cost me more to buy the steel than I could get out of this one. The only real unkown at this point is the fenders. The new brake axles have a little more drop to them, and I'm afraid my wheels will be uncomfortably close to the tops of the fenders.

 

[Reg]

For some reason, my trailer decided that today was fishtailing day. I've had it loaded before with a similar load (2 tons of hay), but this time it would start to sway back and forth if I went any faster than 50 mph. In the extra 15 minutes that it took me to get home I found myself wondering why that happens. I know I've heard it before, but I've never really understood. Why do trailers fishtail?

The following may appear to be contradictory;
Assuming it is a tandem axle trailer;
a) You want the Center of Gravity AHEAD of the front axle.
b) You want slightly more load on the REAR axle.

Don't shoot it down yet (-:

Ball height will get you b) after you have a)
A tow vehicle that squats under hitch load allows the front weight bias to become a front axle load bias.
(CAREFUL use of the words "weight" and "load")
This explains why the same trailer with the same load sometimes behaves differently behind different tow vehicles, i.e. the li'l SUV squats a lot more than the hefty farm truck - resulting in lower ball height and the load transfer from rear to front axle - greater sway tendency.
When that happens you can think of it as being like a teeter totter that is closer to being balanced.
With a bit if side wind, bumps, road seams, etc. it pivots around backwards/forwards and is unstable.

 

[Iplayfarmer]

The following may appear to be contradictory;
Assuming it is a tandem axle trailer;
a) You want the Center of Gravity AHEAD of the front axle.
b) You want slightly more load on the REAR axle.

Don't shoot it down yet (-:

Ball height will get you b) after you have a)
A tow vehicle that squats under hitch load allows the front weight bias to become a front axle load bias.
(CAREFUL use of the words "weight" and "load")
This explains why the same trailer with the same load sometimes behaves differently behind different tow vehicles, i.e. the li'l SUV squats a lot more than the hefty farm truck - resulting in lower ball height and the load transfer from rear to front axle - greater sway tendency.
When that happens you can think of it as being like a teeter totter that is closer to being balanced.
With a bit if side wind, bumps, road seams, etc. it pivots around backwards/forwards and is unstable.

That explains the uphill phenomenon.

 

[art]

Those big square bales are what got you! At least the one on the rear!!! You can bring a flat bed trailer to it's max capacity with big square bales! And yet you could take a drop deck trailer of small squares and still not max the load out!

You had to much weight on the rear of the trailer is all the problem you had and your lucky you realized there was a problem before there was more of one!

Good driving!!!

Through the years I've had the pleasure of towing many things with trucks that were inbalanced. Disc harrows, and then with tines added to the rear, cultimulchers, that could only be towed at 20 or less and they would wip like crazy at that!! At 17 years I hit both sides of a bridge with a cultimulcher at 20mph!!! That was less then 1/4 mile from starting point! Found I could lift the back of the truck off the ground while I was thinking about the thirty miles I had to go!

 

[mbrule]

The following may appear to be contradictory;
Assuming it is a tandem axle trailer;
a) You want the Center of Gravity AHEAD of the front axle.
b) You want slightly more load on the REAR axle.

Don't shoot it down yet (-:

Ball height will get you b) after you have a)
A tow vehicle that squats under hitch load allows the front weight bias to become a front axle load bias.
(CAREFUL use of the words "weight" and "load")
This explains why the same trailer with the same load sometimes behaves differently behind different tow vehicles, i.e. the li'l SUV squats a lot more than the hefty farm truck - resulting in lower ball height and the load transfer from rear to front axle - greater sway tendency.
When that happens you can think of it as being like a teeter totter that is closer to being balanced.
With a bit if side wind, bumps, road seams, etc. it pivots around backwards/forwards and is unstable.

Very Interesting.....

I think that perspective helps explain my swaying camper, due to the placement of the axles on the camper there is only about 400 lbs tongue weight (7k trailer), which is nothing for my 3/4 ton pickup. So, I cannot get a and b at the same time....

Sorry did not mean to hi-jack, but I like your explanation, simple and makes sense!