CHOCKFAST is an engineered epoxy chocking material that is used to cast-in-place permanent
machinery supports for all sizes and types of main engines and marine auxiliary equipment. Because it
conforms precisely to any surface profile, CHOCKFAST eliminates the machining of foundation and
mounting surfaces as well as the fitting of the old-style steel chocks.
CHOCKFAST chocks must always be located around one or more machinery hold down bolts. Any
thickness of chock can be cast. For ease of installation, 12mm to 45 mm (1/2” to 1-3/4”) thick chocks
Good chock design requires that all edges and corners of mounting pads and foundations penetrating
the CHOCKFAST be rounded. Also, all grease, oil, mill scale, rust, flaking paint, burs, and welding slag
must be removed. If necessary, a thin coat of inorganic zinc or epoxy primer may be applied to the
machinery base and foundation to prevent rusting.
Selecting the Right Epoxy
There are two grades of CHOCKFAST used to mount marine machinery; CHOCKFAST ORANGE and CHOCKFAST GRAY. Selecting the right grade depends on the machinery’s alignment requirements and the chock’s normal operating temperature.
Precisely Aligned Equipment is equipment that cannot tolerate movement after installation greater than 0.127mm (0.005 inches) under static stresses of up to 3.4 N/mm2 (500 psi). Examples of this class of machinery include main propulsion engines, and reduction gears.
Normal Operating Temperature is the temperature that the chocks will see during typical operating conditions and is usually equal to the temperature of the equipment mounting pads.
Where maintaining precise equipment alignment is required OR when the operating temperatures will typically be over 52oC (125oF), CHOCKFAST ORANGE must be used.
Where alignment does NOT have to be maintained precisely AND the operating temperature is below 52oC (125oF), CHOCKFAST GRAY may be used. Examples of this class of machinery include winches, pumps, skid mounted diesel generators and other self-contained equipment
The following instructions apply to normal CHOCKFAST installations on steel foundations where chock thickness is within the range shown in Table 1. For pours outside of this range, please contact ITW Polymer Technologies or one of its distributors.
Table 1 – Standard Thickness of CHOCKFAST Pours
|CHOCKFAST ORANGE||12 mm – 100 mm||½” – 4”|
|CHOCKFAST GRAY||12 mm – 50 mm||½” – 2”|
Design Calculations – Precisely Aligned Equipment
- The stress on the chocks due to the weight of the machinery is known as Deadweight Loading. Deadweight Loading may be limited by the vessel’s classification society and must be determined prior to designing the chocks. Standard values for Maximum Deadweight Loading are from 0.7 N/mm2 to 0.9 N/mm2 (100 psi to 130 psi).
- When designing precisely aligned chocks, first calculate the Minimum Required Chock Area. This is calculated by dividing the Total Machinery Weight (including water, oil, accessories, etc.) by the Allowed Deadweight Loading. Design the chocks to cover at least this minimum area and follow the General Guidelines for chock design. Remember that this is the MINIMUM area. Keep in mind that you may need to increase this area as you work through the calculations. The Actual Chock Area should be equal or greater than the Minimum Chock Area and be based on what is physically possible.Total Machinery Weight(N or lbs) ÷ Maximum Allowed Deadweight Loading (N/mm2 or lbs/in2) = Minimum Required Chock Area (mm2 or in2)
- Next, find out the Total Static Stress allowed on the chocks by your classification society. Total Allowed Static Stress is the sum of Deadweight Loading Stress and the Bolt Stress caused by the tension on all mounting bolts. Chocks are typically designed to allow a maximum stress of 3.4 N/mm2 (500 psi) on chocks for precisely aligned machinery. However, most classification societies approve a sliding scale
of Static Stress vs. Chock Operating Temperature. For example, a number of societies approve 4.41 N/mm2 (640 psi) at 80°C (176°F).
- The Total Allowable Bolt Stress is what is left over after you subtract the Actual Deadweight Loading
from the Total Allowed Static Stress given by your class society.Maximum Allowable Static Stress (N/mm² or lbs/in²) – Actual Deadweight Loading (N/mm² or lbs/in²) = Total Allowable Bolt Stress (N/mm² or lbs/in²)
- Multiply the Total Allowable Bolt Stress by the Effective Chock Area to get the Maximum Chock Stress Allowed just due to Bolt Tension. This is also known as Total Bolt Tension and is caused by all bolts holding the machinery in place. Then determine the individual Tension per Bolt, divide Total Bolt Tension by the number of bolts.Maximum Bolt Tension (N/mm² or lbs/in²) X Actual Chock Area (mm² or in²) = Total Bolt Tension (N or lbs)Total Bolt Tension (N or lbs) ÷ Number of Bolts = Tension per Bolt (N or lbs)
- To ensure the machine will not move, the Total Bolt Tension must total at least 2.5 times the machinery weight. To ensure the bolts stay tight, the Tension per Bolt divided by the cross sectional area of the bolt must be at least 46.3 N/mm² (6720 psi).
- Finally, calculate the Bolt Torque required that will achieve this Bolt Tension. While there is no absolute relationship between tightening torque and bolt tension, there is a generally accepted formula for calculating bolt torque. Using one of the following formulas calculate the torque required to achieve that tension. As a check, torque and tension must be greater than the minimum values shown in Table 2Torque (N.m) = 0.2 X Tension (N) x Bolt Dia (mm) / 1000Torque (lbf.feet) = 1.2 X Tension (lbf) x Bolt Dia (inches) / 12
Design Calculations – Non-Precisely Aligned Equipment
Chocks for equipment that do not require precise alignment can be made from either CHOCKFAST ORANGE OR CHOCKFAST GRAY.
In designing chocks for non-precisely aligned equipment, Deadweight Loading is not limited and, unless it is significant, need not be considered in the calculations. The primary consideration is the Total Continuous Static Stress on the chocks caused by the Bolt Tension. Bolt Tension is directly related to the Operational Loading of the equipment.
Operational Loading is the force applied to the equipment during its normal operation. For example, the load applied by the line on a capstan, the wire on a winch, the chain on a windlass, or the load on a crane. Operational Loading is classified into 3 groups by how frequently the load is applied: Continuous, Intermittent and Shock. The following table shows the Maximum Static Stress allowed on chocks used under non-precisely aligned machinery and equipment.
Table 3: Maximum Static Stress Allowed N/cm² (psi)
|CHOCKFAST ORANGE||827 (1200)||2452||(3556)||6895 (10000)|
|CHOCKFAST GRAY||552 (800)||2000||(2900)||4000 (5800)|
Static Stress on a chock is the sum of the engine deadweight and the tension on all bolts. The Total Bolt Tension on a piece of equipment may be increased up to a point where the Static Stress reaches either the Maximum Static Stress allowed in Table 3 above or where the Total Bolt Tension is equal to 80% of the Proof Load of the mounting bolt.
If you have any design questions or are in doubt regarding the design limits of the chocks under your equipment, please consult ITW Polymer Technologies or one of its distributors.
Table 2: Minimum Bolt Torque & Tension
Bolt Diameter (inch)
|Minimum Minimum Torque Tension (ft.lbs) (lbs)|
NOTE: Table 2 is the MINIMUM desirable bolt tensions for various size bolts. It is normally advantageous to use more than the minimum shown here. When the bolt material is unknown, a safe Maximum Bolt Tension and Torque is 3 times the value given in this table.
Chock Design Example Calculations
There are six questions that must be answered when designing chocks for precisely aligned marine equipment. They are:
1) What is the Minimum Required Chock required?
2) What is the Tension allowed on each bolt?
4) Is this tension adequate to keep the bolts tight?
5) What torque is required to achieve this tension?
6) How much CHOCKFAST do I need?
The following example shows how these calculations are made for Precisely Aligned Equipment.
Instructions For Installing Chockfast
The following instructions apply to standard CHOCKFAST installations on steel foundations where the chock thickness is within the range specified in Table 1: Standard Thickness of CHOCKFAST Pours. Outside this range, please consult your CHOCKFAST distributor for guidance.
I. Materials Required
The following materials are required to effectively install CHOCKFAST chocks. Assemble all materials prior to starting any work.
- CHOCKFAST: From the Chocking Plan, calculate the amount of CHOCKFAST required based on the following pre-packed units:
Table 4: Unit Sizes
CHOCKFAST ORANGE 3.4 kg (7.5 lbs) 1966 cm3 (120 in3) 6.8 kg (15 lbs) 4261 cm3 (260 in3) CHOCKFAST GRAY 5 kg (11 lbs) 3064 cm3 (187 in3) 21.8 kg (48 lbs) 13372 cm3 (816 in3)
Always have an extra 10% to 15% available for chock thickness variation, waste, accidental loss, etc.
- Damming Materials:
- a) Flexible damming material such as open cell foam.
- b) Metal front dam.
- c) Putty, sealing or caulking compounds.
- d) Contact adhesive for gluing foam sections together.
- ITW Philadelphia Resins Release Agent.
- Non-melt grease.
- Variable –speed, heavy-duty electric hand drill capable of operating at speeds up to 200 rpm.
- Jiffy mixing blade.
- Surface thermometer.
- Safety glasses or face shield.
- Slitting knife
- Hacksaw blade for cutting foam damming material.
- Protective rubber gloves.
- Epoxy solvent for cleanup. IMPAX IXT-59 or equal.
- Plastic sheet or cardboard on which to mix the CHOCKFAST.
- Create a Chocking Plan for your particular piece of machinery. Utilized the machinery manufacturer’s mounting requirements and perform all the necessary calculations related to chock size and hold down bolt torque and tension. Determine exactly where the chocks will be positioned and what size they will be. Assemble all materials required by the plan. If necessary, have the Chocking Plan approved by the governing classification society prior to starting any work.
- If the steel temperature is below 13oC (55oF), have sufficient heaters available to raise it above 15oC (60oF).
- Store the resin and hardener at 20oC to 25oC (68oF to 77oF) for at least 12 hours but preferably 24 hours prior to use. This ensures the best mixing and pouring viscosity and the longest working time.
- Round all corners and edges that may penetrate the CHOCKFAST.
- Align the machinery and pour the CHOCKFAST with the vessel afloat. If alignment is critical, an adjustment should be made in the alignment to compensate for a slight settling that may occur of approximately 0.001cm per 1.0 cm (0.001 inch per 1 inch) of chock height.
- 6) Drill all bolt holes from the equipment bedplate down through the foundation as required by the equipment manufacturer.
- Clean all surfaces that will come in contact with the CHOCKFAST. Surfaces should be free from oil, grease, water, rust, burrs, slag and loose paint. A thin coat of primer is acceptable
The picture sequence below shows the general procedure for damming a mounting foot. Each installation will be different so follow the dimensions shown on the Chocking Plan for your particular machine.
- Trim the foam damming material to the proper height allowing for a 6 mm (1/4 inch) crush on the foam. (A bare hacksaw blade works best for this.) This amount of crush will allow for easy foam installation but still hold the foam firmly in place. When a closed cell foam is used such as neoprene, air vent tubes must be glued intermittently along the top of the foam to allow the air to escape.
- Insert the damming material under the equipment mounting plate and around the hold down bolts and jacking screws as described on your Chocking Plan. The foam damming material must be located on three sides of the chocks.
- Seal the hold down bolts and bolt holes so they do not leak. If you remove the hold down bolts, insert tight-fitting wooden dowels into the holes. If the bolts are left in place, hand-tighten the nuts and wrap the bolt shank with Armaflex tubing. Coat whatever is used to core the hole with a heavycoating of non-melt grease.
- Fitted bolts should be sprayed with ITW Polymer Technologies’ Release Agent then installed.
- With the side dams in place and the bolt holes filled and coated, spray the chock area with Release Agent. See Fig. 3
- Install a front metal dam so that the width and height will be within the limits shown in the drawing below. Install by gluing in place, small pieces of foam to allow the CHOCKFAST to be poured higher than the bottom of the mounting foot. The overpour area is very important as it provides both head pressure to the underside of the mounting foot and a pool of molten CHOCKFAST to feed the chock area if needed. See Fig. 4
- Make sure all potential leak points are well sealed. It is much easier to prevent leaks before the resin is poured in than to stop them afterwards.
- Spray the inside of the front metal dam with Release Agent so that it can easily be removed after the CHOCKFAST hardens. See Fig. 5.
IV Mixing the CHOCKFAST and Pouring
- Ensure that the damming completely surrounds the chock area and that there are no potential leak points.
- Measure the chock thickness of each chock and the temperature of the engine bed and foundation. For CHOCKFAST ORANGE only, determine based on the graph in Fig. 9, how much hardener to use. The amount is based on machinery foundation temperature and the thickness of the chock. See Fig 6
- Bring out the resin and hardener from storage.
- 4) Installing CHOCKFAST is usually a team effort. Assign someone to each of the following jobs:
- a) open the boxes of CHOCKFAST for the mixers,
- b) add the hardener and time the mixing
- c) mix the CHOCKFAST,
- d) pour the CHOCKFAST and inspect for leaks.
- Make sure each member of the team knows their job and have a backup plan if any of the mixing equipment should fail.
- Make sure everyone working with CHOCKFAST puts on gloves and eye protection.
- Add hardener to the resin as needed. Power mix at about 200 RPM (never more than 500 RPM) for 3 minutes using a Jiffy Mixing blade or equal. The mixer should be comfortably seated to hold the can of CHOCKFAST securely between the feet. Keep the blade submerged at all times and traverse the entire can. Make sure the bottom of the can is scoured. See Fig. 7.
Fig.9 Hardener Ratio Guide
V After Pouring
- Pour the resin as soon as possible after mixing. Do not scrape the residue from the can sides or bottom. Always pour from the lowest corner of the chock. Fill from a single point only so that air can escape as you fill. Pour as high above the chock as possible so that there is a thin ribbon of CHOCKFAST going into the chock. This forces any trapped air out of the liquid.
- After Pouring Release the jack screws, alignment wedges or other alignment support devices.
- In order for CHOCKFAST to cure, the temperature must be at least 13°C (55°F). Use heaters if necessary to bring the area up to at least this temperature. Length of cure will depend on
temperature as follows:13°C–18°C (55°F–65°F) 48 hours
19°C–21°C (66°F–70°F) 24 hours Above 21oC (70oF) 18 hours
- When curing is complete, remove heaters and allow the CHOCKFAST to return to ambient temperature.
- Remove the front dams and grind off the sharp edges of the overpour.
- Tighten the hold down bolts to the desired tension.