LBV Performance Characteristics

The LBV sets a standard for high performance small ROV systems. No other small ROV offers the high level of performance matched with the extensive range of features. Small is nice and portable, but without the performance is only a pool cleaner. Very crucial to the usefulness of a small ROV are:

• Powerful Thrusters
• Power to Weight Ratio
• Small Diameter Umbilical
• Drag
• Thrust versus Speed
• Stability
• Maneuverability
• Systems Integration

Each of these are equally important and quite often overlooked. It is very important to consider all aspects when choosing a ROV. Best of all have a demonstration. Lets look at each one.

Powerful Thrusters

The thrusters are the backbone of any ROV. Not enough power and the ROV struggles to operate in average conditions. SeaBotix engineers spent countless hours developing a small thruster with a high Bollard thrust output. Accomplishing this goal the LBV is fitted standard with the HPDC brushless DC thruster with an individual output of 4.5kgf (9.9ft/lbs). With two thrusters in the forward position slightly canted in produce an impressive output of 7kgf (15.4ft/lbs) peak forward thrust.

Each thruster uses the same two blade prop and custom designed Kort nozzle. The Kort nozzle has special fins tostraighten the flow of water reducing torque steer on the LBV.

Power to Weight Ratio

The performance of the thrusters is directly related to the weight of the ROV. There needs to be a balance so the thrusters are able to overcome the inertial weight of the ROV. LBV has an excellent power to weight ratio of 1 to 1.6 standard (7kgf of thrust with a vehicle weight of 11kg).

Small Diameter Umbilical

Just as important as the powerful thrusters is the diameter of the umbilical. This area is often mislead or misunderstood. Umbilical has the most significant impact on drag of any part of the ROV. Roughly calculated at the square of its diameter you can see how the diameter and amount in the water becomes very crucial to the capability of the ROV. Therefore the smallest possible umbilical has the least amount of impact on the ROV.

The LBV has an industry leading umbilical with a diameter of only 8mm (0.3"). This equates to 24% less drag than the closest competitor with an umbilical diameter of 10mm. The umbilical often grows in diameter to provide more power for the thrusters or simply more wires for controls and video. LBV is unique with its twisted pair and shield umbilical and proprietary electronics that eliminate the need for extra pairs. In addition to the reduced drag of the LBV umbilical the nearest competitor has significantly less Bollard thrust (estimated at 70% less).

So you can see more power less drag equals more capability.

Drag

Some will claim that the ROV itself is the contributor to drag. While it does contribute it is far less of an impact than the umbilical. LBV has an approximate forward drag of 2kgf (4.4lbs) at 2 knots where as 30 meters (100ft) of LBV umbilical with a gradual bend has 7.7kg (17lbs) of drag at 2 knots. As an example the nearest competitor to LBV has an estimated ROV drag of .75kgf (1.65lbs) and an umbilical drag of 10.13kgf (22.34lbs). As you can see the competitor has a combined drag of 10.88kgf (23.99lbs) versus the LBV at 9.7kgf (21.38lbs). This wouldn't be as big of an issue, but the competitor has an estimated 70% LESS thrust than LBV.

Thrust versus Speed

Another misconception about ROVs is the speed along the surface versus the Bollard thrust. While speed can be an indicator of performance what it doesn't do is factor in the umbilical. The speed rating is only the ROV. Now that is fine if you are in a ZERO current on the surface situation, but when is that ever the case. The thrust of the ROV must be sufficient to overcome the ROV, umbilical and current.

LBV excels in having a high surface speed of at least 2.75 knots, power to weight ratio sufficient to pull the umbilical or work in a current up to 2 knots. We have had many clients comment on the amount of pulling power with the umbilical in the water.

Stability

A potential drawback to small ROVs can be their stability. Small is nice for deployment, but when operating at depth the ROV must have enough mass to overcome the influence caused by the umbilical. For example if the ROV is too small and the umbilical diameter is too big when the power of the thrusters is let off the ROV will struggle to stay in position. This is referred to as "Tail Wagging the Dog Syndrome".

The LBV has sufficient mass (weight) to enable a stable positioning capability with the umbilical in the water. There is power to overcome the drag and then once released will not move around excessively.

Maneuverability

ROVs are used to inspect objects in various situations. The more maneuverable the easier this task is accomplished. Ideally you would be able to operate the ROV in any direction.

LBV like the larger ROVs is fitted with thrusters providing movement in four (4) axis. You have forward/reverse, rotate left, rotate right, lateral left, lateral right and vertical up and down. Some ROVs lack the lateral movement which greatly complicates some inspections. Imagine trying to survey a ships hull without the lateral movement. You would have to fly at the area then pull away and fly at the next area. Much the same as trying to do a survey with an airplane versus a helicopter.