Weight calc for ratchet load straps

[Little Star]

Hi

Am looking at ratchet load straps on the internet to secure my boat to the trailer whilst trailing. Boat is 1100kg so what strength rating do I need...was looking at either 5000 kg or 8000 kg...is that overkill or do I need more?

Thanks

 

[sarabande]

the strap 'load' is usually quoted as the Safe Working Load, with a failure factor of x3 at least. If they are EU compliant, a cloth tab giving the SWL and BS will be sewn in to one end. 5K working load is enough.

FWIW I secure my 2.4 tonne boat on the trailer with two lateral straps to hold theboat on to the tralier and keep her upright, and one each fore and aft to prevent movement under breaking and acceleration. Be careful to ensure that the ratchet 'steps' are sharp and not rounded, otherwise if you really pile on the pressure the ratchet jumps back free.

 

[Little Star]

Thanks Sarabande......straps I was looking at states "strength ratings are minimum breaking strength" .....do you think that's the same as SWL? Also says they are made to EN 12195-2:2001

 

[Tintin]

The ones with roughly 2 inch wide webbing are commonplace and used by many lorries for very heavy loads. Am sure you will be OK with either option.

 

[simon barefoot]

If you look at the strap you will see rows of stitching running along it. APPARENTLY each row indicates 1000kg strength. 3 parallel rows=3tons...etc. But that's not something I know for sure, as I said, I've been told that's the case...

 

[Daydream believer]

A lot depends on how the trailer supports the boat
ie a flatbed trailer gives little lateral support to a load
A trailer with lots supports in a "V" shape will possibly provide more lateral support
When tying on there is also the fore & aft movement to consider as well as just strapping down. A good rope around the keel with a couple of tonnes breaking load & will /should stop the load slipping aft. This tendancy to slip aft will be increased if the trailer consists of lots of rollers & will need a stronger restraint
Height of the C of g of the boat will have a rolling effect on the trailer
Reserve carrying capacity of a trailer will help resist rolling stress, ie lots of reserve gives a stiffer ( normally) load
A single axle trailer is not normally as good as a good twin
Swinging axle close coupled trailers are better in some situations than rigid units
So the whole thing depends on more than just " how big is the load"
Also - how do you intend to drive. at a steady pace or at 100mph round lanes

 

[Avocet]

If you look at the strap you will see rows of stitching running along it. APPARENTLY each row indicates 1000kg strength. 3 parallel rows=3tons...etc. But that's not something I know for sure, as I said, I've been told that's the case...

I've heard that before as well! 5 rows of black stitching = 5 tons min breaking strength.

Back to the OP's question though, as other have said, it's impossible without knowing how the boat sits on the trailer. If it is well supported, you won't need anything LIKE 5 tons (never mind 8) - it's only to stop it bouncing out! Perhaps it's worth looking at the problem the other way round? In other words. would you damage your boat if you applied 5 tons across the gunwhales (or cleats or winches or wherever the straps sit?

 

[William_H]

Wow I have towed my trailer sailer over many trips some quite long over 34 years plus one trip 3300kms on the trailer on the back of a truck and never felt the need to tie it down to the trailer. It has a post at the bow with a vee to stop it rolling forward and a winch cable and safety chain to stop it rolling backwards.
The trailer itself is a bed of rollers in a slight vee shaft in mid sections to match the hull and stop sideways movement. The trailer is single axle and the boat about 950kgs.
With lifting keel and no stub keel it does sit fairly low on the trailer and so road.
If straps are to hold the boat upright then perhaps they need lots of strength. I doubt you can get very much static load on those rachet straps anyway. But be it necessary or not it is your peace of mind that matters so do what you have to do. good luck olewill

 

[knuterikt]

Hi

Am looking at ratchet load straps on the internet to secure my boat to the trailer whilst trailing. Boat is 1100kg so what strength rating do I need...was looking at either 5000 kg or 8000 kg...is that overkill or do I need more?

Thanks

The strap(s) and other support that prevent the load form going forward must be able to carry the full weight, you must also take the angle of load into the calculation (the strapping preventing it from sliding forward while breaking)
Assuming that.
- There is no support in front of the load
- An angle of 45° for the strap
- A load of 1100 kg
The strap need a BL of 2200 kg.

The straps preventing sideways and movement aft need to carry 0.5 of the load, again the angle of the straps relative to horizontal must be a part of the calculation.

All the straps should be loaded up to 400 kg tension.

A boat sitting on trailer will have some support from the trailer - so it a SWL of 5000kg should be more than enough.

 

[knuterikt]

Wow I have towed my trailer sailer over many trips some quite long over 34 years plus one trip 3300kms on the trailer on the back of a truck and never felt the need to tie it down to the trailer. It has a post at the bow with a vee to stop it rolling forward and a winch cable and safety chain to stop it rolling backwards.
The trailer itself is a bed of rollers in a slight vee shaft in mid sections to match the hull and stop sideways movement. The trailer is single axle and the boat about 950kgs.
With lifting keel and no stub keel it does sit fairly low on the trailer and so road.
If straps are to hold the boat upright then perhaps they need lots of strength. I doubt you can get very much static load on those rachet straps anyway. But be it necessary or not it is your peace of mind that matters so do what you have to do. good luck olewill

Lucky you (or more correctly the drivers you meet).
It's not the number of years or the miles you have driven that will reveal the need for proper lashing of the load...

My brother was hit by a boat while driving his car once...
He was hit by boat that was only secured on the trailer by the "nose rope", the aft part of the boat slid of it's supports in a bend and hit my brothers car coming in the opposite direction.
The post keeping the roof up at the drivers side and the front and side window broke, it was pure luck that his head was undamaged..

 

[William_H]

Perhaps the secret is not to drive like a lunartic with boat on the back. I would consider 50mph an absolute top for safe towing and that ona very straight good road.
Certainly there are a lot of various trailer boats in our community. I think you will find only a small fraction will strap the back of the boat down and generally only with light weight dinghies. As I said everyone has to do what satisfies his own concerns. I am not aware of any advisories on tieing boats down. I can understand from your brother's experience that you would want to be super cautious. good luck olewill

 

[knuterikt]

Perhaps the secret is not to drive like a lunartic with boat on the back. I would consider 50mph an absolute top for safe towing and that ona very straight good road.
Certainly there are a lot of various trailer boats in our community. I think you will find only a small fraction will strap the back of the boat down and generally only with light weight dinghies. As I said everyone has to do what satisfies his own concerns. I am not aware of any advisories on tieing boats down. I can understand from your brother's experience that you would want to be super cautious. good luck olewill

Maybe the roads in Australia is somewhat different from what you will find other places in the world... we don't have straight roads..
Giving people advice based on your limited experience seems a bad idea..

Here the maximum allowed speed driving with a trailer is 80 km/h = 50 mph so that is not an issue..
Luckily here you would get a fine for not securing the load on a trailer properly

 

[davidpbo]

My

Lucky you (or more correctly the drivers you meet).
It's not the number of years or the miles you have driven that will reveal the need for proper lashing of the load...

+1

My experience of the two trailers I have is that if it can work loose it will.

Far too much risk of the boat moving in an abrupt manoeuvre or emergency stop.

I am interested to see what the consensus is as to appropriate strength of strap.

 

[Tintin]

......
Giving people advice based on your limited experience seems a bad idea..

.......

But many indulge in it

 

[GHA]

The strap(s) and other support that prevent the load form going forward must be able to carry the full weight, you must also take the angle of load into the calculation (the strapping preventing it from sliding forward while breaking)
Assuming that.
- There is no support in front of the load
- An angle of 45° for the strap
- A load of 1100 kg
The strap need a SWL of 2200 kg.

The straps preventing sideways and movement aft need to carry 0.5 of the load, again the angle of the straps relative to horizontal must be a part of the calculation.

All the straps should be loaded up to 400 kg tension.

A boat sitting on trailer will have some support from the trailer - so it a SWL of 5000kg should be more than enough.

Where did those figures come from?

A decent 50mm strap usually has a mbl (max breaking load) of 5t so you'll need one nearly a foot wide. Also straps aren't designed for suspended loads so finding one with a rated swl with be very unlikely.

And cranking a strap up to 400kg by hand will be near to impossible.

I'd go for a few 50mm polyester not just for the strength but they stretch less and more surface area means they dig in less.

 

[Avocet]

The fore-aft one, I can sort of see the logic behind, (although with no support under the load and neglecting friction, it barely covers you for an emergency stop, never mind any kind of crash) but the pre-tension of 400kg is beyond me. That said, why would they need to be a foot wide? IF a 50mm one can carry 5 tons, and the calculations suggest 2.2tons, the 50mm ones will be fine!

 

[knuterikt]

The strap(s) and other support that prevent the load form going forward must be able to carry the full weight, you must also take the angle of load into the calculation (the strapping preventing it from sliding forward while breaking)
Assuming that.
- There is no support in front of the load
- An angle of 45° for the strap
- A load of 1100 kg
The strap need a SWL of 2200 kg.

The straps preventing sideways and movement aft need to carry 0.5 of the load, again the angle of the straps relative to horizontal must be a part of the calculation.

All the straps should be loaded up to 400 kg tension.

A boat sitting on trailer will have some support from the trailer - so it a SWL of 5000kg should be more than enough.

Where did those figures come from?

A decent 50mm strap usually has a mbl (max breaking load) of 5t so you'll need one nearly a foot wide. Also straps aren't designed for suspended loads so finding one with a rated swl with be very unlikely.

And cranking a strap up to 400kg by hand will be near to impossible.

I'd go for a few 50mm polyester not just for the strength but they stretch less and more surface area means they dig in less.

Thanks for spotting the my error.

There is an error/typo in my original post, when sizing strops for lashings the breaking load (BL) is used not the SWL. I will correct that in my post.

The numbers come from the guidelines for securing load on road transport used here in Norway and is based on friction coefficient of 0.2( µ-static)

That make a 50mm strop with a BL of 5t = 5000kg sufficient to carry the whole load in all directions, a strop with BL = 2200 kg would also be enough to stop the load from sliding forward

On a boat trailer the support in the front combined with the winch will probably be strong enough to prevent the boat from moving fore & aft-.

Sideways movement need to be restricted with a strop with BL of 550 kg, could even be less as there are some sideways support on the trailer but it's better to err on the safe side.

I have never measured the tension created by a normal loading ratchet strap - I checked the number in the guide and 400 kg is what it says for 4000kg = 4t BL on the straps.

 

[knuterikt]

But many indulge in it

The spirit of a forum like this is to discuss and share knowledge and ideas.
But a statement like this

Wow I have towed my trailer sailer over many trips some quite long over 34 years plus one trip 3300kms on the trailer on the back of a truck and never felt the need to tie it down to the trailer.

Fall into the same category as
- I have sailed for 34 years and never needed a life jacket - don''t wast money on that.
- I have been driving for 34 years and never needed a seatbelt...

 

[ProDave]

A picture of the boat and / or trailer might help an informed discussion.

For the record on my lifting keel boat, which is probably of a very similar size and weight to the one being discussed, the boat is held into the vee snubber at the bow by the trailers winch, and the boat is then strapped down to the trailer with two 50mm wide webbing straps with ratchet tie down things, one at the front and one at the back.

Don't rate a ratchet tie down strap by it's width alone. The two I use came with the boat and trailer when I bought it and seem adequate. But by comparison I hired a flat bed truck last weekend to shift some scaffold, and the tie down straps that came with it, while still 50mm wide, were at least 4 times as thick as my own and clearly designed for a much much greater load.

 

[knuterikt]

A picture of the boat and / or trailer might help an informed discussion.

For the record on my lifting keel boat, which is probably of a very similar size and weight to the one being discussed, the boat is held into the vee snubber at the bow by the trailers winch, and the boat is then strapped down to the trailer with two 50mm wide webbing straps with ratchet tie down things, one at the front and one at the back.

Don't rate a ratchet tie down strap by it's width alone. The two I use came with the boat and trailer when I bought it and seem adequate. But by comparison I hired a flat bed truck last weekend to shift some scaffold, and the tie down straps that came with it, while still 50mm wide, were at least 4 times as thick as my own and clearly designed for a much much greater load.

The straps should have a label with strength stamped attached.