The main engine is fitted on the ship’s hull with the help of holding down bolts and chocks. The floor where the engine is installed is excessively strengthened by heavy flooring and using additional bars and girders. The bedplate which is the base of the engine is attached by means of holding down bolts and chocks arrangement. Chocks are critical to alignment of critical components.

There are mainly three chock types that are used to hold the main engine-

1.    Cast steel Chock

2.   Epoxy resins Chock.

3.   Mechanical Chocks

Chocks onboard or in the industry may be refereed to as chockfast, chockcure, chockfast orange etc. these are brand names for chock products.

What is Chockfast?

Chockfast is an epoxy based, pourable compound that cures at normal temperatures to become an extremely tough and durable solid. Chockfast was specifically developed for chocking marine main propulsion and auxiliary machinery and since its introduction in 1963 has earned the approval of the major classification societies worldwide.
Other shipboard applications include…Sterntube & Strut bearings, Pintle & Rudder Bearings, Pedestal Bearings, Steering Gears, Stern Winches, Engine Room Pumps, Cargo Pumps, Cable Penetrations, Large Ball or Roller Bearings, Bow Thrusters and Anchor Windlasses.

Chockfast is a registered trademark of the epoxy resin made by ITW Philadelphia Resins Corp.

The resin itself can be used in an infinite number of applications but it was developed especially for the chocking of marine diesel engines. Due to the resins physical characteristics the costs gained by the quick, easy and trouble free application have made Chockfast the preferable way to mount diesel engines.

Some of the points raised by the use of Chockfast are:

Installation and chocking of the engine is done within several hours instead of days.
The hardened chock has perfect fit between engine and foundation and therefore spreads the engine forces evenly over the entire bedplate thus eliminating fretting of the contact surfaces.

CHOCKS TYPES

• Support chocks
• Side chocks
• End chocks

PURPOSE OF CHOCKS

Chocks are used to compensate for the natural unevenness of the tank top

And provide engine with flat bed seating as close as to test bed of engine.

Arrangement of holding down bolts and chocks should be:

• Support weight of the engine.
• Secure engine rigidly in all sea conditions.
• Withstand and transmit guide forces and propeller trust.
• Provide enough stiffness to avoid resonance with propeller and engine induced vibrations.
• Maintain alignment of engine.

EFFECTS OF LOOSE HOLDING DOWN BOLTS

• Fretting will occur between chocks bedplate and tank top.
• If re tightened then permanent misalignment.
• Reduce stiffness of holding down bolts.
• Vibrations may be induced.
• Increased load on remaining chocks.
• The same bolt may again loosened.
• Torsional stresses on crankcase due to misalignment.

PROCEDURES TO FIT CHOCKS

• Alignment
• Chocks of 45-50 mm jacked up
• Tapered chocks 1:100
• 80% of contact area
• crankcase deflection

MAINTENANCE

• 1^st check- 500 Hrs
• 2^nd check- 1000 Hrs
• 3^rd check- 2000 Hrs
• 4^th check- 4000 Hrs
• 5^th check- 8000 Hrs
• Subsequently every 8000 Hrs

EPOXY RESIN CHOCKS

Advantages over cast iron chocks

• Approved by all class.
• Better contact without machining the bedplate or tank top.
• Can be operated at 80°c.
• Fuel & L.O. corrosion eliminated.
• No fretting because these gets adhered to the bed plate.
• Reduces noise.
• Fitting is in hours not in days or weeks.
• high physical properties at elevated temperature.

EPOXY TECH

• Removal of grease paint oil mill scale and rust particles.
• Thickness 25mm not restrictions as such
• Below 13 mm and above 44mm is also possible
• Chock area no less than 130cm² for each
• Apply a thin film of inorganic zinc for corrosion resistance
• Quantity required is volume of resin + extra 10%.

CONSIDERATIONS

• Machinery dead weight 7kg/cm²
• No. and dia. of holding down bolts
• Total dead weight includes tensioning of bolts should not exceed 35 kg/cm²
• Effective area of chocking
• Expected temp.
• Holding down bolt torque to be adjusted 2.5 times more than the dead weight.
• No allowance for shrinkage is necessary but we need a allowance of 0.001 *t, for the tightening of holding down bolts.

Below  you can see bulmar services have used chockfast orange on a repair onboard

Chockfast technology applied on engine repair

We performed some complex tasks with Chockfast products on vessels under repair.

On NB801 TSHD Albatros build by MTG Dolphin Yard both stern tubes, two propulsion and one auxiliary reduction gears were mounted as per approved technology with Chockfast Orange and Phillibond Orange as a materials. On NB901 Grab hopper dredger again in MTG Dolphin Yard both stern tubes were fitted on Chockfast Orange. Both projects were submitted to the Yard, Class and Owners without remarks.

Additional one engine Stork 9TM410 and one engine MAN B&W 6S26MC were realigned and new chocks were casted. Both engines were secured on the new chocks with all the bolts tightened as per approved new calculations from the Class and submitted to the owners without remarks and with perfect crankshaft deflection.

below you can see the different chockfast products for various uses