Trailer rigs - The do's and don'ts of trailer drilling rigs.

I first started building trailer mounted drilling rigs In - After the mining industry basically collapsed under me. At that time, I was building blast hole rigs and mainly rigs mounted on trucks. I actually did not have a choice when i took on the job to design and build a trailer drilling rig - My first was hopelessly overweight and was more a truck rig moved onto two axles than a proper trailer rig. So why do people want a trailer rig and is there a market that depend on them or is it just the perceived "Cheaper Option".  

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The world is changing around us - People are moving from low density areas to high density areas at an increasing speed. That also means that people who want to drill a borehole has most likely already build their house - and in such a way that you need to break down structures to get in with a Truck mounted drilling rig. 

This is where trailer rigs start to shine. 

But it is also here that the basic disadvantages of the trailer rig become glaringly obvious. It is too light duty to drill into hard rock or if it can it can only do so for a shallow hole and the rock drilling has to be a much smaller size than what is used when drilling with a truck rig. Other are so big to compensate for the lighter duty ones that just getting them to the pin is a fear inspiring ordeal.

So when you are looking at a trailer rig what would be the ideal rig to have?

It will not be too heavy. The largest mechanical braked trailer that can be legally towed on a public road has a weight limit of Kg. So, let's say it must weigh less than Kg

You would like to drill the same diameter as a truck rig if at all possible. So what size is that - In my experience that is a 6.5 Inch hole with a 177 mm steel casing in the loose formation. And if you drill 6.5 inch - you will be using a 6-inch hammer - That 6-inch hammer can accommodate an 8.5-inch drill bit - so in reality you will be drilling an 8.5-inch hole with a 6-inch hammer with the ideal trailer rig.

How deep do you need to be able to drill with this ideal rig? Most hand pump wells are less than 60 meters deep as a hand pump has a lifting capacity of about 60 meters. But you would like to drill deeper than that because water tables are receding especially in urban areas. Here i decided that 200 meters is a reasonable limit for a rig that does not weigh 3.5 tons- Cannot expect miracles, can you?

Rotational torque of rigs that generally drill that depth and diameter has been about - Nm torque if you consider a very popular drive motor for truck rig - the HBM80 Staffa - It has a maximum torque of 19.9 Nm / bar of pressure - As most of the truck rigs run a Gear pump their continuous pressure is about 180 Bar - So the formula is 19.9Nm X 180 Bar = Nm Torque. So, my ideal trailer rig will have a torque of Nm or More

So, to lift a drill string and hammer and bit out of a 200-meter borehole how much lifting power do you need. It can be easily calculated by adding the adding the weight of each of the items in the borehole. Drill rod (Here we want to at least work with a 3-meter drill rod and at least 89mm diameter - preferably a 114mm drill rod) So on 89 mm one 3-meter sch 40 drill rod weights 47 Kg - For every 100 meters you will need 1.6 ton od drill rods at minimum. So, 200 meters = 3.2 ton. Then the hammer and bit add another 150 Kg approximate - And a stabilizer another 250 Kg. So, lets add up what is in the borehole - 3.2 Ton of drill rods and 150 Kg hammer and bit and 250 Kg stabilizer and another 50 Kg for adapters and whatever you fancy. That give a grand total of 3.650 Ton. So, the Ideal trailer will have more pullback than 3.650 Ton. You would actually want a bit extra just for a little leeway in case you get stuck.

So, what type of power do you need to drive this? You can actually work it out mathematically. Big word but Hydraulic Kw is (flow in Litre / min X Pressure in Bar) /60 - So let's take some of what we determined before - Rotation = Nm and Kg lift. We need to bring these to Kw and for that we need speed. Rotation will be determined by the smallest drill bit you will be using and the most RPM intensive process - If all else fails have a look at a DTH truck rig - They rarely go over 90 Rpm and that is only while doing mud rotary at lower torque. 6.5 Inch drill bit rotation will be in the order of 20-40 Rpm and 8.5 inch not more than 35 Rpm. But you will use max torque only if you are stuck and that will be at lower rpm - So let us assume that that is 20 RPM. The Staffa HBM80 displaces Litre per Revolution That gives us on 30 rpm a total of 40 Litre per min at 180 Bar = (40*180)/600 = 12 Kw - Next we need to determine the max Kw needed for lifting the drill string - Same variables apply you need pressure and flow - For this we will assume a 1:1 ratio with the hydraulic cylinder Lets work on a 80mm bore cylinder as the main feed cylinder. The barrel side will be used for lifting as it is the bigger side. How do we work out the power of the Cylinder? The formula is surface in Sq cm x pressure in Bar - So The surface of the cylinder piston is 50 cm2 and the pressure of the system is 180 Bar - That gives us Kg force. But the flow at which that can be applied will give you the Kw. So, the slower you lift the less kw you will use. Same reason 30-ton trucks can be lifted by a hydraulic jack - very slow but the pressure does the lifting and the speed makes it possible for n man to lift 30 tons. All said and done if you need to move a drill string at 0.350 Meters per second you will pump 1.75 litters per second or 105 Litre / min to get that speed. - The 180 bar will get you Kg lift. So, what kw do we need (105x180)/600 = 31.5 Kw - If we lift it at 0.175 meters per second you will need 1/2 of the power as you are traveling at 1/2 the speed. And we only need Kg for 200 meters. You can also go slower when you are deep and faster when more of the drill string is out. So, let's work on 15 Kw for the lifting at 175 mm per second. Add that to the 12 Kw for rotation and you are at 27 Kw - But take into account that it will be very rare for you to rotate and pull at full force at the same time. So, let's round it to 25 Kw Hydraulic power - Then add 25 % for mechanical loss and you end up with a power requirement of 31.25 Kw max. So, my ideal rig will have more than 31.25 Kw engine power.

One other item has to be addressed - Size - it should not be wider than a Land Cruiser and it should not be higher than a land cruiser when tower is down. That is my ideal trailer rig size.

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Here is a short list of Ideal rig requirements

1. Less than Kg in weight
2. Capable of drilling to 200 meters 8.5 inch
3. Min Torque Nm
4. Max Rotation Speed 90 Rpm
5. Max Lifting speed 350 mm a second
6. Min Kw engine 31.25
7. Size must not be higher than a Land Cruiser and not wider

I took that as my goal and build the Spider V4 XXL Trailer rig.

It weighs Kg

It is capable of drilling even deeper than 200 Meters but I rate it at 200 meters - having a 9 ton Pull back give you lots of fighting power when you need it.

It has a Max Torque of Nm - The Ideal will be Nm

It can rotate at from 0- Max 90 Rpm and has a separate mud/air box to prevent a leaking seal to damage the gearbox or hydraulic motors.

A tested and reliable air cooled F3L912 engine give me 33 Kw of power to make this powerful trailer rig shine.

This Machine will set you back R680 000 Or $ - You can buy a less expensive rig. But ask yourself this question - Do you want something less?

Contact us for more info or have a look at our other products on www.drill4africa.com ; +27 (0)10 500 ;Cell +27(0)73 092

written by Neels Audie.

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