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.