The dreaded trailer snake

The most fun you can have is to look in your mirrors and watch 3 lanes of traffic all backing off to a respectable distance whilst you wrestle your way back out of the swervy zone, avoiding all the while, the temptation to brake.
 
landlockedpirate said:
I would take the towing advice from the CC with a pinch of salt, according to their 'rules' the heaviest load anyone should tow would be around 2000kg.
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There is only one 'Learned Institution' which have investigated trailer towing stability AFAIK, that's the Department of Mechanical Engineering, University of Bath. These investigations have been going on for about 20 years, jointly sponsored by a caravan manufacturer and The Caravan Club, so I would respectfully suggest the they are very well qualified to offer towing advice. :rolleyes:

Try searching for 'towing stability studies' in the search engine of your choice.
 
claymore said:
The most fun you can have is to look in your mirrors ....
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whilst towing a cat and being able to see only one hull .... verra nasty

Or, seeing the bike that was last seen attached to your roof rack, doing 70mph behind you. The gent whose bike it was could only mutter "It was securely fastened".
 
My boat and trailer weigh 2300 kgs. 230Kgs on my tow hitch? I don't think so.

I would have thought nose weight is far more relevant to single axle trailers. With twin axle whilst a reasonable noise weight is needed, with a twin axle trailer the noise weight will change depending on the relative height of ball and socket and as the trailer pitches, I think height of hitch is very important.

I have a removable hitch, does anyone know if Westfalia do aremovable hitches with different drop heights? I haven't looked yet.
 
The air suspension on the Discovery is self leveling so the adjustment will need to be made elsewhere.

The factory fitted towball system only has two positions and its on the highest one already; there's no adjustment other than to unbolt it and move to the lower position.

The trailer is twin axle and the boat balances on its bilge keels which were midway between the axles, the trailer was level and lined up pretty damn close to the towball height. There's possibly 6inch further forward the boat could rest on the trailer but its very difficulty to measure or estimate the effect: its virtually impossible to slide the boat on the trailer once its out of the water and no way to measure the nose weight while its still in the water or on the slipway ramp.

I'll certainly look into a damper; 50-55mph is more than enough for me so if I can reduce the effects when 7.5 tonners come barreling past or on long downhills or merging into faster traffic when speed creeps up a bit higher I'll be a much happier bunny.
 
The Axles are too far foward. Move the axles back 6". Talking about "snaking" at the age of 18 I was asked to tow a 24ft Mobile Home from Wilmslow to Liverpool. It was an American one with Big Wheels. I was towing with an Austin Champ. Doing 50 down hill it started "snaking" I knew I could not brake so I accelerated and the snaking stopped, I then very slowly slowed down and I carried on at 30mph. I can remember it now 52 years later.
 
The axle positions are fixed attached to two main crossbeams that form the chassis of the trailer for the maximum load bearing directly under the bilge keels, so moving the axles is not practical.

I just had another thought though: the four wheels each have a drum brake with a rod and wire linkage mechanism to the tow hitch - its very unlikley that all the wheels brake perfectly evenly given the crudeness of this arrangement. When it starts to snake perhaps the resulting alternate pulls on the tow hitch actuate the brakes slightly more on one side than the other and hence reduce or increase the snake depending on the direction involved ?

The research above that talks about aerodynamics lift on aircraft and race cars pointing to critical speeds around 50-60mph is fascinating. Clearly no matter how well balanced a rig is there will be some critical speed above which the effects of aerodynamics takes over and this must also be affected by hull shape and height above the road as well as character of the turbulence from the towing vehicle and others nearby as well as the wind direction. Most comments here and elsewhere talk about difficulties around these speeds too - perhaps this is the critical air speed zone.

Thinking back to Friday morning when we towed the boat down it was pretty gusty which will undoubtedly made things worse.
 
One thing no-one has mentioned is the distribution of weight within the boat itself. Shifting moveable masses like outboards, dinghy and sail bags towards the axles will moderate the tendency to fishtail.

I towed a double horsebox with a Rover 75. Swapped it for a Rav4 and suddenly everything was much calmer and easier. It's because the tow ball is much closer to the rear wheels of the towing vehicle. From memory, the current Landy's have quite an overhang at the back.
 
winsbury said:
The air suspension on the Discovery is self leveling so the adjustment will need to be made elsewhere.

The factory fitted towball system only has two positions and its on the highest one already; there's no adjustment other than to unbolt it and move to the lower position.

The trailer is twin axle and the boat balances on its bilge keels which were midway between the axles, the trailer was level and lined up pretty damn close to the towball height. There's possibly 6inch further forward the boat could rest on the trailer but its very difficulty to measure or estimate the effect: its virtually impossible to slide the boat on the trailer once its out of the water and no way to measure the nose weight while its still in the water or on the slipway ramp.

I'll certainly look into a damper; 50-55mph is more than enough for me so if I can reduce the effects when 7.5 tonners come barreling past or on long downhills or merging into faster traffic when speed creeps up a bit higher I'll be a much happier bunny.
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Really, you want to end up with the hitch a fair bit lower than the towball so that you can get the noseweight (that's really the only way on a 4-wheel trailer). I wouldn't under-estimate the effect of moving the boat forward 6" either - that could make all the difference! When we used to tow our Leisure 17, I could move it forward on the trailer by putting a ratchet strap round the trailer and round the back of each bilge keel, then ratcheting it forward and sliding the boat along a few inches on each side. For "fine tuning" you could try running the front pair of trailer tyres a few PSI softer than the rears - again to drop the hitch a bit harder on to the towball. Those anti-snake devices aren't that expensive though, and they work very well.
 
Trailer snaking

I have had problems with the trailer snaking when towing 1.7 tons of boat and trailer with a 2 wheel trailer. The towing vehicle was a Landrover Defender, short wheel base fitted with heavy duty springs.
The snaking was noticeable at less than 30mph. Moving as much weight forward as possible did improve things- allowing safe progress at 30mph. Later taking the outboard out of its well and carrying it in the LR allowed travel at 45mph. I am interested in fitting a anti-snaking device but which type? - with friction pads or a gas strut?

When I enquired at a caravan shop they were uncertain that a anti-snake device would help. They also said that they had 2 towing vehicles- same make and model. One towed nicely and one had snaking problems. They cured the problem by changing the make of tyres on the snaking one to the same make of tyre used on the stable towing vehicle.
The factors that I think may contribute to snaking include:

Boat (load) aerodynamics
Towing vehicle wind shadow / disturbance
Centre of gravity of load/boat
The spread of weight towards the ends of the load
The tow hitch (its adjustable with some play on its height adjusting slide)
Nose weight
Trailer tyres and pressures
Trailer springs
Tow vehicle tyres and pressures
Tow vehicle springs / shock absorbers
Use of a anti-snaking device
Road surface
Wind from passing vehicles / weather conditions- would a cockpit cover smooth the air flow?

When I first trailed the empty trailer there was terrible vibration (resonance) at 50mph. The wheels are large- Land rover wheels and I had them balanced which stopped the vibration when towing empty

My previous boat and trailer (slightly smaller and lighter, outboard on transom) towed beautifully (60mph) behind the same LR but it still had standard springs then.
Thanks for any helpful suggestions.
 
I've had great success with one of the cheapo friction pad ones - like a big leaf spring with a circular friction pad. I've had it for 20 years or so now and have used it on a variety of both towing vehicles and trailers. In every case it has solved the problem completely.
 
I have a friend who tows a 26 ft steam boat with a SWB Series 2 landy. He uses an ancient friction damper that sound similar to yours. If he forgets to clip it on he can tell within a couple of hundred yards.

Egbod seems to have a a good list of possible problem areas. The truth is any variations can upset the stability. My trials car on it's trailer has varied between rock-solid and nervous. Probably tyre pressure and a slight problem with a suspension unit moving towards negative camber.
 
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Only one thing to say, I hate towing anything. I've had a couple of snakes happen to me and they live on, burnt into my memory even though I recovered from them. I've seen a caravan and car combo snake its way into oblivion on a motorway, I was right behind as it happened. Anyone who wants to tow a caravan around for a holiday needs to be certified in my opinion.
 
savageseadog said:
Only one thing to say, I hate towing anything. I've had a couple of snakes happen to me and they live on, burnt into my memory even though I recovered from them. I've seen a caravan and car combo snake its way into oblivion on a motorway, I was right behind as it happened. Anyone who wants to tow a caravan around for a holiday needs to be certified in my opinion.
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I have one and tow one, 1.8 tonnes of it. As big as I am allowed to to tow. Started by accident, long story. Anyway it is the perfect companion for a sailing boat. When the weather is iffy for sailing we can tow it in land and go to places we would not normally visit. Do not knock it until you have tried it.

Snakes are not the nicest things, quite alarming when you do not expect them... Get the balance right and you should be good as others say your towbar weight should be in the region of 100kg+ Think of 100kg as 1 large person and it is not that much weight in the boot of a disco...

On our caravan I cannot lift the towbar in fact unless its on the smoothest ground, sod it even then it we want to move it we hook it up...
 
I towed my boat home last month (Poole to Farnham) 1.5 ton on a single axle trailer with a TD5, the trailer tyres were well under rated for the load, odd sized and couldn't get any others fast enough. 1st time use of the trailer.

I measured and fitted blocks before hand to the trailer so the boat could only be fitted on dead centre, with the main load directly over the axles.

The tyres were my main concern as I had to seriously over inflate to get them to look any where near the shape they should have been. 38max psi I had to put 50 psi in :eek:

Stuck to 50mph, it was a lovely tow, no snaking! not even the run going down hill through the new forest on the M27.

I have had two trailers snake in the past, both times I would say it was loading issues and speed.

Trailing can be a very stressful. I have no intention of doing it too often, stuff that!

Good Luck

Gareth
 
tjanna said:
I towed my boat home last month (Poole to Farnham) 1.5 ton on a single axle trailer with a TD5, the trailer tyres were well under rated for the load, odd sized and couldn't get any others fast enough. 1st time use of the trailer.

I measured and fitted blocks before hand to the trailer so the boat could only be fitted on dead centre, with the main load directly over the axles.

The tyres were my main concern as I had to seriously over inflate to get them to look any where near the shape they should have been. 38max psi I had to put 50 psi in :eek:

Stuck to 50mph, it was a lovely tow, no snaking! not even the run going down hill through the new forest on the M27.

I have had two trailers snake in the past, both times I would say it was loading issues and speed.

Trailing can be a very stressful. I have no intention of doing it too often, stuff that!

Good Luck

Gareth
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Do get some new tyres of the correct rating before you tow it again. Over inflated tyres could end up in a blow out.
 
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