Setting up a boat trailer

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GrahamHR

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The twin axle trailer that came with my boat, which has sufficient load capacity, has zero noseweight when the boat is on it with a full 246 litre fuel tank. That cast iron V8 at the stern has something to do with it as well ! The winch post is as forward as it can get. If I drop the winch/ snubber so it is well below the forward eye on the bow, I might be able to get the boat forward a few inches, but not a lot. This is how it was set up by the supplying dealer. The people that tow it to North Wales for me are understandably not very comfortable with the zero noseweight. Last time we loaded it up with 25 litre plastic cans full of water; not ideal.

I've moved the spare wheel forward as far as it can go.

It looks like the only option is to move the axles back so they are closer to the mass at the stern. From photos I have seen, they look to be in a "standard" position on the trailer at the moment. The minimum I can move them back is 8.5" ( because of parts of the trailer frame). Does anyone have any idea whether this is enough to affet the noseweight to any extent?
 
246 litres of fuel will weigh about 200kg. Do you need to transport it full of fuel? That would seem the easiest way (depending on where the fuel tanks are) - and a fair bit safer in the even of a road accident!

Calculating nose weight change through moving axles isn't easy on a twin-axle trailer. It also depends on the height of the tow ball on the towing vehicle. If your springs and tyres were completely rigid, altering the height of the tow ball by a tiny amount would have a very big effect on nose weight (because effectively, it would be taking all the weight off the front wheels and putting it on to the back wheels. Unfortunately, as the stiffness of the tyre sidewalls and the suspension units is unknown, it will be hard to guess how much of the weight will be taken by the back axle and how much by the front, for any given movement of towball height. Obviously, that also means that the load condition of the towing vehicle affects the trailer nose weight. As a wild guess, I'd have thought moving both axles backwards 8" would be MORE than enough - probably too much.
 
I would have thought towing with some 250 litres of fuel sloshing about is a bit much. I would certainly talk to the manufacturers before shifting the axles, there are things like brake activation you have to worry about too and ensuring the axles remain correctly aligned
 
You might get some guide of how much to move the axles by taking your set up to a public weighbridge.

Measure the current weight distribution by axle.

This will tell you how much of the weight is on the rear axle and how much on the front.

It would be fair to assume your current centre of gravity is still in between the axles or your boat would be tipping off backwards!

You then can take the ratio of axle weights and the distance between front and back wheels to define where the cog of your current set up.

Move the axles a corresponding amount and get the cog dead between axles. Put as much chain and anchor in the bow as you want for noseweight....

Makes it much easier to manoevre when unhitched as you dont end up with too much noseweight on your jockey wheel

Simples
 
I thought moving the axles was fairly standard, at least on smaller trailers.
To work out how much it is going to increase the nose weight, you need to know the all-up weight, take off a bit for the axles, then it should be accurate enough to treat the trailer as a simple lever, taking the pivot as the mid point between the two axles.
This should work, assuming the two axles are sharing the weight reasonably well, which basically comes down to having the tow hitch at the right height. It should be accurate enough to estimate the amount you need to move the axles.
Is the fuel tank behind both axles? If not, emptying it is not going to help much.
Probably better that it's full than half full in terms of sloshing effects.

Obviously, the brake cables will require adjustment, and you don't want to move outside the design range of the trailer.
So, how long is it, what's the all up weight and what nose weight do you want?
 
Thanks for all the advice. As to the desired noseweight, I don't know ! I was told some nose weight is better than none !

With no boat on the trailer and hitched up, the rear wheels are off the ground. I've never measured the nose weight in that configuration, but there is actual noseweight; it tows really nicely ( I tow it to and from Anglesey empty, it's too heavy for my car to tow with the boat on it) . I understand now the danger is that if I move the axles back, then when unladen the nose weight may becore too high. So, I don't think I'll risk doing it.

When the boat is on the trailer, the rear wheels are I'm sure taking more lof the load, as the sidewalls of the (8 ply) tyres bulge out slightly more than the front ones.

The fuel tank is just ahead of the engine; 2/3 of it sits pretty much above the axles, but the back 1/3 is behind the rear axle. There's no petrol at the marina, so the boat tank is filled from jerrycans. That's why I fill it up when it's at home for the winter. I'll try getting it as empty as I can, maybe losing 150 kg or so, before it's towed back to see if it makes a noticeable difference; partially filled, the fuel is going to move around a lot more than it does in a completely full tank though, isn't it ?
 
this is EXACTLY the problem I had with my own boat trailer when I bought the boat. In fact it was even worse I had negative noseweight. I had to stand on the tow hitch to force it down to the level of the car. and it towed dreadfully.

I solved it by moving the axles back 6 inches. On my trailer, the axle frame, and the spine member are two completely separate things. So just loosening the bolts enabled me to move the spine forwards / axles back 6 inches.

Any adjustable rollers may need re adjusting next time the boat is loaded on.

Also, check the tow vehicles tow ball height. When my boat trailer was sitting level, the tow hitch was still higher than that on the car (Subaru Forrester) so I solved that issue with an "upside down" drop plate to give me a second, higher up towball on the car.


EDIT:
reading the above "With no boat on the trailer and hitched up, the rear wheels are off the ground"

Your towball is DEFINITELY too low on your car, so do as I did and use a "drop" plate to raise the towball height on the towcar. That on it's own may solve the issue, as you are forcing the towball too low, and trying to lift the back wheels off the ground, hence the negative nose weight.
 
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It may be wrong, but I have been told it's illegal to tow a trailer which would be too heavy for your car fully loaded, even if it's unloaded.

I think it's worth getting the nose weight about right.
 
It was the case that the towing vehicle had to have a plated towing weight greater than the trailer plated GTW whether loaded or not.
I am not sure but that may have changed. Need to check

Tyce is quite right. With a close-coupled trailer the hitch height is very important.

You need to hitch it (loaded) to the towing vehicle (which is not your own I understand). Measure the ground to hitch height.
Disconnect the tow vehicle. Put bathroom scales beneath the tow hitch. Put a jack on the scales. Zero scales. Jack up tow-hitch until it is the height you measured.
See what the scales tell you the nose weight is.

Messing about with the axles or loading are a waste of time until you have done this.
The nose weight for a close-coupled trailer doesn't need to be anything like as high as for a two-wheeled trailer. It is much more important to have the hitch height on the tow vehicle right. When loaded the weight needs to be pretty equally spread between the two axles. The hitch then needs to be at the right height to maintain that stance.
 
The vehicle used to tow the trailer + boat has an adjustable towbar height; a plate which can be locked in at various heights. With the tank full and the front of the trailer on the jockey wheel/ the trailer members parallel to the ground, I can lift the jockey wheel off the ground with virtually no effort. It's close to not needing the jockey wheel to support the front of the trailer. I'll move as much weight as I can forwards ( spare wheel, bolt on steps - which are now behind the axles)

The tow hitch on my car is not adjustable. The car does have self levelling rear suspension. With only 2 wheels on the ground when unladen/ attached to my car, isn't it then just going to behave like a 2 wheel trailer ? The total weight then is only ca 600 kg, well within the load limit for a single one of the axles/ pair of tyres.
 
Do you need much nose weight on a twin axle? Can you raise the towbar on the car a bit? Or lower the tow hitch on the trailer?
I'd be more concerned if it was a single axle, most twin axles I've seen seem to be balanced.
 
Re the towbar, it's a removeable one, I'll check if the supplier can supply one with a longer "neck" to take the ball higher up,

I really don't know whether the twin axle trailer needs a certain noseweight like a singe axle one does ( it tows very nicely as a single axle one !)
 
Just to firm up what's been said.

With a twin axle trailer, see what the tow hitch height of the trailer is when loaded and the trailer NOT coupled to the car.

then ensure your car's tow ball is HIGHER than that static trailer height.

If you can't raise the car's towball (I hate those swan neck ones for that reason) then the only solution is to modify the trailer, or move the weight forward. But be careful about overloading the front axle. Ideally the spine of the trailer should be level. If it's nose down, chances are you are forcing too much weight onto the front axle.
 
I know this link applies to caravans but some interesting reading, especially the bit about EU towball heights. http://www.witter-towbars.co.uk/faq/faq_category.aspx?id=448

Just out of interest, what type of trailer is it? Bunks & keel rollers, swing beam rollers or a combination? Where does the transom of the boat sit realtive to the last roller or the rearmost of the last bunk?
 
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Deefor said:
I know this link applies to caravans but some interesting reading, especially the bit about EU towball heights. http://www.witter-towbars.co.uk/faq/faq_category.aspx?id=448
Click to expand...

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.
 
GrahamHR said:
Re the towbar, it's a removeable one, I'll check if the supplier can supply one with a longer "neck" to take the ball higher up,

I really don't know whether the twin axle trailer needs a certain noseweight like a singe axle one does ( it tows very nicely as a single axle one !)
Click to expand...

The tow vehicle needs nose weight to remain stable, zero or negative noseweight will tend to make the tow vehicle unstable, I used to find even 50% of the recomended weight with my caravan made the car handling sort of woosey.

The tow vehicle will have a max recommended nosewieght and uaually works best close to that
 
ProDave said:
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.
Click to expand...

But is that 550mm ball height with a laden tow vehicle? Now here's the stupidity of EU tow ball heights..........

I have two tow cars, a 2010 Volvo V70 with a so called factory fitted towbar (it's not as it's a Witter fitted by a Volvo dealer's contractor before I collected the brand new car :mad:) and a 2004 Grand Cherokee Jeep with an aftermarket towbar.

The Jeep's ball height is within the EU range, regardless of whether the car's just got me in it or 5 people and fully laden. The V70 has a ball height of 570mm with just me in it and 420mm when it's fully laden (very soft suspension). So the EU idiots are telling me to load the V70 to the max every time I want to tow :rolleyes:.

There's a very good American website that describes how to set the nose weight on a twin axle trailer but I can't find it. If only I could remember what the Yanks call "nose weight" then all would be revealed.
 
Deefor said:
I know this link applies to caravans but some interesting reading, especially the bit about EU towball heights. http://www.witter-towbars.co.uk/faq/faq_category.aspx?id=448

Just out of interest, what type of trailer is it? Bunks & keel rollers, swing beam rollers or a combination? Where does the transom of the boat sit realtive to the last roller or the rearmost of the last bunk?
Click to expand...

It's a bunk trailer, with keel rollers. The transom "proper" sits about 2" beyond the rear roller with the engine ahead of it. However, there are "sponsons"; hull extensions, further back, plus the outdrive and swim platform. Close to 150 kg beyond the last keel roller I guess.
 
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Draw bar weight

The draw bar weight on the towing vehicle should be in the range 10 to15% of total mass. Now that i definitely so for single axle and I think also so for twin or even triple axle trailers. The load will be very unstable and unsafe at any speed especially going down hills.
Only a close assessment of the trailer will indicate if moving the axles back or the winch and post forward or combination of both will get the desired end effect.
Regarding height of towing hitch. I would imagine that if the trailer is close to balanced now then measure the height of the hitch with towing vehicle not attached. This will then obviously have equal weight on each axle. Which I would expect is the desired outcome. I guess however that if you move the boat or axles to get the necessary draw bar weight then that will depress the tow bar so putting more load on the front axle.
Incidentally for checking draw bar weight on a smaller trailer boat combination. Stand on the tow hitch yourself and get someone to measure the amount the back of the car goes down. Assuming you are 100kg then that is good amount for a 1 tonne trailer. So measure the depression with the trailer on. Bigger trailers use 2 people on the tow bar.
Just reiterating. Draw bar load is vital for safety. olewill
 
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