Setting up a boat trailer

[Deefor]

Tongue weight, that's the one . http://www.shorelandr.com/pages/pf_trstep3.htm

 

[fisherman]

Beware, I had a 1250kg triple axle trailer with a 1050kg car on it, behind my 1450kg Volvo. My hitch was too low, so I had the car forward on the trailer just to give say 25kg noseweight. All fine, til I went up a steep hill. The car on the trailer rocked back on it's suspension (in your case the fuel sloshes back) and lifted the back wheels of the Volvo, I was cwrapping myself, if I stopped I would have had the whole lot hanging on the Volvo brakes, 3.75 tons, no trailer brakes in reverse.

I also had a 750kg box trailer, the old car had a drop plate on the hitch, the new one didn't. Trailer on the new car was lethal just through the nose up attitude, put the drop plate on and all fine, so I would say small adjustments make a big difference.

 

[Pete54]

You have had most of the advice you need - just spread across a couple of threads.

Tongue or nose weight is very necessary to balance the load and the tow vehicle. The various 'rules of thumb' and the data for the tow vehicle will often contradict - use the vehicle manual.

With a twin or triple axle trailer the hitch height adds a further complication. To get the required nose weight it will often be necessary to adjust the hitch height - otherwise the nose weight will be altered by shifting the attitude of the trailer.

I used to tow a 25 foot yacht and getting that right took a bit of fiddling with the hitch height and the boat position.

You do not say how long the trailer is - but I suspect that moving the axles 8.5 inches is likely to cause the nose weight to substantially increase. The obvious answer is not to fill the fuel tank. Equally you can increase the nose weight with a higher hitch height.

A well balanced twin axle trailer will sit roughly level - so the hitch height is more critical with twins and triples. Either way putting more weight into the ends of the boat is the worst possible thing to do - if the trailer becomes unstable is just gives it more energy to snake......

 

[Avocet]

From that link:

Q: Can I use a riser plate to increase the towball height ?

A: NO.

Oops.

So what IS one supposed to do when the trailer has a tow hitch height of 550mm, well outside the "normal" range.

I'll stick to my riser plate, I know it works.

There's a lot of misinformation about type approval legislation and I'm not sure I agree with all the Q&As on the Witter website.

First of all, the Directive is poorly drafted in that respect. The UK Vehicle Certification Agency issues "Technical Interpretations" when a Directive is ambiguous and it has decided on the car being loaded to the manufacturer's Maximum Permitted Mass AND with the distribution of that weight as specified by the manufacturer.

Secondly, "Off-road" vehicles are exempt from this tow ball height requirement in the Directive anyway. Most 4x4s that would be used for towing a bigg-ish boat would therefore be exempt.

Thirdly, the type approval legislation applies to the MANUFACTURER AT THE POINT OF SALE. Which means the car manufacturer and the tow bar / towing equipment manufacturer need to comply. After the point of sale, the user can do what he likes to the setup (which in the UK would then be governed by the Construction and Use Regs). These don't have much in them specific to modification of towbars, but the most likely outcome would be that nobody would take a scrap of notice unless there was a big accident and then you might get done for "insecure load" or something like that. What it WOULD mean, however, is that by undertaking a modification (like fitting a drop plate or spring assisters, etc), you'd give the manufacturers their "get-out-of-jail-free card" because they could walk away saying "that's not how it was approved by us".

 

[Deefor]

As the OP's boat transom is sitting roughly where it should be in relation to the last trailer hull support (roller/bunk), then at least the stern of boat is being supported, thereby reducing possible flex in the hull especially with the heavy engine and full tank at the back.

I used to have a single axle trailer and setting the nose weight was relatively simple. Then along came my twin axle SBS trailer and things became a little more difficult. Having spent many hours looking at articles on the net, this is what I came up with:

1) Get the boat supported correctly on the trailer which the OP has done.

2) To achieve correct nose weight, then move the axle/s on the chassis either forward or backwards. Don't move the boat as you'll lose the support on the transom.

3) When trying to get the "correct" nose weight with a twin axle, you need to break some of the physical "moments" involved. This entails having the trailer on level ground, handbrake off. Then, using the jockey wheel, lower the trailer hitch as low as it will go, then raise it as high as it will go. Repeat this two or three times and then measure the trailer nose weight at a height that is roughly equal to the height of your car's tow ball.

When I first set my nose weight, I got 100kg. A week later, a checked it and went off the scale at 150kg. If you don't break the moments, you can end up with spurious nose weight readings. In my case, I was getting a deviation of +/- 40kg . By doing 3) above, I can get readings of no more than +/- 2kg.

Another thing to watch out for is the max nose weight allowable on the tow ball itself. There should be a plate on the tow ball stating what the max is. Likewise, there should be a similar plate on the trailer that gives the max tow hitch capacity. In my case, I have a Jeep Grand Cherokee which in theory, will pulll 3500lg. However, the max nose weight that the tow bar brackets will carry is 150kg, the tow ball itself is rated at 120kg and the trailer hitch is also rated at 120kg.

With my boat, the water 120lt water tank is in the bow. With a full tank (120kg), my nose weight comes in at around 95kg and the rig has proved to have perfect handling under all road conditions. However, if at the end of a cruise when recovering the boat, I'm concious that nose weight will have changed as the water in the bow is now less, sometimes maybe 60kg, other times zero. I then have to compensate for this by fixing the spare wheel to the trailer and strapping 2 x 25lt water containers near the trailer hitch. As there are many factors which can change after you've been out on the boat (less fuel, less water, less beer and wine etc.), all your careful nose weight set up can go out the window.

You can get too anal over all of this but as has been said already, some nose weight is better than none at all.

 

[viago]

what about putting lower profile tyres on the front axle and lowering tow ball height accordingly?

or stick a couple of 56lb weights in your chain locker.

or move both axles back 4 inches. should be enough slack in the brake cables.

car recovery guys stick any size/shape cars on their trailers, strap them down and drive off. never seen one worry about nose weight.

4-7% of trailer weight + min 25 kg used to be the recomendation when i had a caravan.

 

[Avocet]

I have a twin axle trailer and find that I can make fairly significant adjustments to the nose weight simply by altering the trailer tyre pressures slightly (i.e. front tyres a tad softer than rears to increase nose weight). Just need to be careful of tyre temperature on long runs.

As has been said by many other posters though, nose weight on a twin axle trailer is messy to get right; changes enormously during driving anyway (as the car goes over bumps and dips); and is by no means the only determinant of towing stability anyway (though I agree it helps to have "some")!

 

[ProDave]

The one thing I DON'T agree in some of these posts, is the suggestion of ADDING extra weight to a boat to get the nose weight correct.

I always aim for the minimum weight on the trailer possible. Lets face it, even most "small" boats are a sizeable load to be carried on a trailer.

So I take my OB off and carry it in the car. I don't carry any water or fuel in the boat.

Aim for no water of fuel in the boat, and you have a repeatable situation each time the boat is loaded onto the trailer.

By all means move smallish items like anchors forwards or backwards to fine trim the noseweight but don't just add weight for the sake of it. That shows it's not set up right.

It took me about 3 goes to get it just right with my boat and trailer and I now have confidence that when it's craned out in a few weeks, the boat will sit in exactly the right place on the trailer and it will tow nicely.

 

[davidpbo]

As others have said, my understanding is that when determining whether a vehicle can tow a trailer, maximum permissable gross weight on the plate of the trailer that is the important number.

If you have trailer with an MGW of 2500 kgs with load, a car rated to tow 1250kgs, it is mynunderstanding that it cannot tow that trailer even if empty and weighing say 500kgs legally.

On my trailer I cannot move the axles without drilling, they are bolted to the frame. I had new axles made some years ago and the manufacturer had changed the way they made them resulting in the axles moving one way or the other by a few inches. I think that made a difference ot how the trailer towed.

I wish I had an adjustable tow ball (it is a Westfalia removable one) on my present vehicle. I think tow ball height is critical with a 4 or more wheel trailer. I suppose I could look at lifting the tow hitch on the trailer.

Negative nose weight is an absolute no no IMHO as you are relying on the locking lug of the tow hitch to keep the trailer attached which is effectively pulling the back of the tow vehicle up. The forces involved are I imagine large.

 

[GrahamHR]

I have a twin axle trailer and find that I can make fairly significant adjustments to the nose weight simply by altering the trailer tyre pressures slightly (i.e. front tyres a tad softer than rears to increase nose weight). Just need to be careful of tyre temperature on long runs.

As has been said by many other posters though, nose weight on a twin axle trailer is messy to get right; changes enormously during driving anyway (as the car goes over bumps and dips); and is by no means the only determinant of towing stability anyway (though I agree it helps to have "some")!

I cannot adjust the axles backwards by less than 8.5", If I did I'd not be able to fit the forward mounting U bolts on the rear ones ( they are ALKO axles,with one pair of mounting holes ahead of the axle tube and 4 pairs behind the tube).

I like the idea of adjusting the tyre pressures so the front are lower than the back; they currently are all the same, @ the maximum permissible indicated on the tyre sidewalls. How much difference in pressure makes a difference on your trailer? ; dropping from 60 to 55, or 50 psi perhaps?

I understand why minimising the weight on the trailer is preferred. However, getting the fuel tank, which is under the cockpit floor, completely empty is difficult to do without risking running out of fuel. Might it be better to keep it full, so it's weight is always a constant effect ? The water tank (on the port side, behind the axles) is always empty when the boat is on the trailer, but the twin 110 A/H batteries are on the opposite side, but not further back than the end of the keel/ the last keel roller. There's a lot of weight back there.

 

[lw395]

I have a twin axle trailer and find that I can make fairly significant adjustments to the nose weight simply by altering the trailer tyre pressures slightly (i.e. front tyres a tad softer than rears to increase nose weight). ...!

I think this might be wrong.
The principle behind having nose weight, as I understand it, is that the centre of mass of the trailer should be a bit forward of the vector where the tyres are providing lateral resistance.
By having wrong tyre pressures, you may force the nose weight to be right, but the lateral force from the tyres could be unpredictable.
Nose weight is mainly an indicator that the centre of mass is in the right place, not a goal in itself.

Personally, I find towing very heavy trailers a bit of a worry and would be reluctant not to have it fairly spot on.

 

[viago]

The mass of the trailer should be a bit forward of the vector where the tyres are providing lateral resistance.

surely the vector should be forward of the trailer.

long time since i ve seen one of they old vauxhalls.

 

[colingr]

If you move the axle back and you are getting too much nose weight you can fine tune by moving the winch post back a bit to compensate.

 

[Lakesailor]

I can't see what is wrong with adjusting the weight placement within the boat. It's not a false situation. You are trimming the boat, as you would on the water, to get the correct weight distribution for the trailer as it is set up.
Introducing some extra weight where it's needed would help enormously.
It's hardly likely that the bit of weight needed to trim the trailer would be a large percentage of the the Gross Trailer Weight or take it over the maximum. The extra weight forward would help reduce the "tail-wagging-dog" propensity that a lot of weight at the back of the trailer would induce.

Two plastic bags of aggregate from the builder's merchant in the bow will add 50Kg half way between the axles and the hitch. That will effectively put 25kg on the hitch weight.
For about £5, that's a result.

 

[Avocet]

As others have said, my understanding is that when determining whether a vehicle can tow a trailer, maximum permissable gross weight on the plate of the trailer that is the important number.

If you have trailer with an MGW of 2500 kgs with load, a car rated to tow 1250kgs, it is mynunderstanding that it cannot tow that trailer even if empty and weighing say 500kgs legally.

I've heard this a few times too, but nobody has ever been able to point me at the bit of legislation that says it! To be honest, I'm beginning to think it's one of those motoring myths. Let's face it, just looking at it from a "common sense" point of view, it would be utterly bizarre! It would be like making it illegal to posess a car that was capable of exceeding the speed limit - even though you weren't driving it in excess of the speed limit at the time! What next? Making it illegal to own a car if it isn't capable of carrying all the members in your family and their combned luggage?

 

[lw395]

I've heard this a few times too, but nobody has ever been able to point me at the bit of legislation that says it! To be honest, I'm beginning to think it's one of those motoring myths. Let's face it, just looking at it from a "common sense" point of view, it would be utterly bizarre! It would be like making it illegal to posess a car that was capable of exceeding the speed limit - even though you weren't driving it in excess of the speed limit at the time! What next? Making it illegal to own a car if it isn't capable of carrying all the members in your family and their combned luggage?

Looking at the Directgov website, it does imply that the MAM of the trailer is what matters for driver licencing, so younger drivers who don't have B+E category on their licence could be in trouble. I've not spent any time looking, but haven't found anything else.
I know a copper who tows a RIB, I'll ask him if I see him.

 

[GrahamHR]

It would be like making it illegal to posess a car that was capable of exceeding the speed limit - even though you weren't driving it in excess of the speed limit at the time! What next? Making it illegal to own a car if it isn't capable of carrying all the members in your family and their combned luggage?

Or not homologating the most powerful version of a family car for towing, even though the same V6 engine is fitted to other versions with the same bodyshell, same brakes (and same suspension as on the diesel version of that trim level) !

Strange but true !

 

[Avocet]

I like the idea of adjusting the tyre pressures so the front are lower than the back; they currently are all the same, @ the maximum permissible indicated on the tyre sidewalls. How much difference in pressure makes a difference on your trailer? ; dropping from 60 to 55, or 50 psi perhaps?

OK, this is going to be a long one! It's a dropside, flat bed trailer, so the amount of change in nose weight obtained by altering tyre pressures varies enormously with a number of factors.

The distance between the axle centres is about 600mm. The distance from the front axle to the towing hitch is about 2.3m The suspension units are VERY stiff (virtually seized, in fact!) and the wheels are 10" with 8 ply tyres running at a nominal 45PSI. When empty, the trailer weighs about 450kg. When the trailer is empty, and parked on level ground, and all tyre pressures are at 45PSI, if I wind the jockey wheel up until it lifts off the floor, the tow hitch is about 200mm above the ground. The trailer is visibly nose-down and the front axle is taking most of the weight. If I hitch it up to a car with a tow ball at about 350mm above the ground, there is about 50kg of nose weight. If I drop the front tyre pressures by about 3PSI each in this condition, I can get another 15kg (roughly) of nose weight. Dropping them by about 5PSI seems to make it more like 20kg.

HOWEVER, because the tow ball height moves when I get into the towing vehicle (or fill it with fuel), the trailer nose weight will become less. How much less, I've no idea!

If I put a weight in the trailer, and I were to balance the weight perfectly between the axles, I'd get a bit more nose weight (because the whole trailer would sit uniformly a tiny bit lower). If the weight was a very tall weight, dropping the front tyre pressures would give me a BIGGER change in nose weight than when the trailer is empty, because the centre of gravity of the load would shift forwards a bit as the trailer went nose-down.

This is the problem with trying to relate any figures I get to those that you might get on your trailer. The amount of weight change will depend mainly, on the distance between the axles and the tow hitch. You've probably got more distannce there than me, so your nose weight change is likely to be greater than mine when you vary the pressures. On the other hand, I've got very stiff suspension units so I can more or less neglect the effect of suspension compression, whereas you probably can't.

All I can suggest (and I think someone has already touched on it) is that you measure the height of your tow vehicle's tow ball centre WITH THE TOW VEHICLE LADEN AS IT WOULD BE WHEN TOWING. That means fuel, passengers AND the boat hitched on to it! Then unhitch it, get some bathroom scales, and a stout bit of wood so that you can rest the bit of wood on the bathroom scales, and then rest the trailer tow hitch on top of the wood so that it is exactly the same height above the ground as when it was hitched on to the towing vehicle. Read what the scales say. While it's all set up, you can then alter the tyre pressures in each axle, and see what kind of difference it makes to the reading on the scales. There are a couple of things to bear in mind doing this though. One is that if you have the trailer handbrake on, it might prevent you seeing the full weight change because the handbrake might prevent the suspension from settling to its new attitude. Conversely, if you DON'T have the handbrake on, it will be a rpetty risky exercise to carry out! The second is that as the nose weight increases, it will push the back of the tow car down a bit more on its springs, so unlike the piece of wood on the scales, the towball height will change as you alter the nose weight (unless your tow vehicle self-levels). This means you won't quite get the extra weight in practice that you think you'll get.

All in all, it's such a complex problem (and remember that as soon as you start driving, the nose weight will be constantly changing anyway)! That being the case, I probably wouldn't bother with getting too anal about it. Just make sure you've got "some" nose weight and see how the car and trailer feel. Some of those anti-snake devices are pretty good. We had an Evolution 22 that towed like an absolute PIG. Scared the living daylights out of me a few times! Moving weight backwards and forwards down it made little difference. It was originally on a single axle trailer and I added another axle (still surprisingly little difference)! I tried it with everything from "zero" nose weight to "more-than-I could-lift!" nose weight and that didn't make much difference either. (more nose weight helped but it was still awful). In the end, I bought a cheap anti-snake bar and it cured the problem completely!

 

[sarabande]

no NO NO ! Please do not use the tyre pressures to adjust the nose weight.

Air in the tyres is meant to support a given mass (the tyres will have the maximum load and pressure engraved in the side) If you reduce the tyre pressure, the side walls will flex excessively, overheat, and blow out.

To check what I am saying, lower the pressure in one of your car tyres to half the normal. Drive a mile, slowly, then check the wall temperature. Then pump it back up.

You must get the balance of the load in relation to the axles right.


FWIW, even using my 30ft three axle trailer, I load the boat so that the nose weight is about 50kg (enough for it to be starting to be difficult to lift)

 

[Avocet]

Looking at the Directgov website, it does imply that the MAM of the trailer is what matters for driver licencing, so younger drivers who don't have B+E category on their licence could be in trouble. I've not spent any time looking, but haven't found anything else.
I know a copper who tows a RIB, I'll ask him if I see him.

I'd be interested to hear how you get on. Obviously, driver licensing is one thing, (and I could see the sense in that relating to a theoretical maximum), but when it comes to the "in-use" situation, I think it's utterly barmy!