Archive | BCS Trim Tabs

Overhauling BCS trim tabs on an 85 foot Ferretti

BCS Trim Tab

Trim tabs are an essential component for any yacht. They improve performance, helping to increase speed, reduce pounding and on smaller boats offset prop torque. They help the vessel run more efficiently, reducing fuel consumption and engine laboring and eliminate “squatting.” But more importantly, they increase safety by improving visibility and handling along with reducing wake size and hull stress.

However, years of use and prolonged exposure to salt water can take a toll on their ability to function properly as was the case with an 85’ Ferretti that was hauled at Lauderdale Marine Center.

That is when our hydraulics team was called in to work on the BCS hydraulic trim tabs. Upon close inspection, we found that two of the four trim tab cylinders were corroded beyond repair and needed to be replaced. Because of manufacturer’s long lead time, we decided that we would machine new rods, barrels and re-build the cylinders in-house, using our machine shop, Straight Line Marine.

Corrosion in Barrel

The corrosion we found on the inside of the barrel was caused by salt water intrusion as a result of failed seals. Once the components were machined, we were ready to assemble the new hydraulic trim tab cylinders and re-install in the yacht. Unlike common trim tab cylinders, the BCS model does not use hydraulic hoses to distribute the hydraulic fluid to operate the trim tabs. The fluid is dispersed through a small pin hole in the transom bracket assembly. A clever design that eliminates hose failure external to the transom. However this creates a tricky install.

Pin Hole

The pin has multiple O-rings and requires a special touch to avoid pinching during installation. Great care must be taken in the removal of the old hydraulic trim tab cylinders and the re-installation of the new ones. Damage to the assembly as a result of scratching or scoring the unit would cause them to leak and render the trim tab cylinders useless.

We see these types of nuisances all the time. It takes a team of highly experienced hydraulics technicians to properly diagnosis the problems and take the appropriate actions to correct them.

Rebuilding BCS Trim Tabs for a Smooth Ride

BCS Trim Tab

BCS Trim Tab

One of the more important features on any Super Yacht is the trim tab system for stability, speed and ride comfort in any sea conditions.

The working principle of a trim tab system is simple. By pushing one of the buttons on the control panel, the electro-hydraulic power unit receives an electric impulse which starts the electric motor. In turn, the latter makes the hydraulic pump start, being connected to it by means of a coupling. As the pump starts to turn, it sends an oil flow towards the side of the hydraulic cylinder corresponding to the desired movement (up or down), making the tab raise or go down. By pushing the button on the other side, the cylinder moves in the opposite direction.

As with any marine systems that come in contact with salt water, the trim tab system is subject to pitting and crevice corrosion.

We recently were hired to rebuild the BCS Trim Tabs on a 100 foot Azmit Yacht. The BCS Trim Tabs on this particularly vessel were not retracted in the up position and were left in the extended position too long contributing to significant crevice corrosion and pitting. When the cylinder is extended the rod is sitting in salt water – when retracted it is safely inside the cylinder in hydraulic fluid.

Crevice corrosion and pitting on BCS trim tab shaft

Crevice corrosion and pitting on BCS trim tab shaft

As part of the job, we fabricated new stainless steel rods in our machine shop, Straight Line Marine and rebuilt the BCS cylinders at High Seas Hydraulics.

After final assembly and installation back in the boat, the yacht is good to go for many more years of smooth sailing.