practice case study

Case study

A yacht that has been hauled out and placed in a bilge cradle needs to have its keel resealed

The boat is a 25yr old 12 metre FRP (fibre reinforced plastic) production boat

It has a moderate depth fin keel butted to a stub with single bolts fore and aft and the rest are doubles
The bolts are silicon bronze the singles are ¾ and the doubles are 1”inch there are 10 bolts in total

The keel to stub joint has been broken approximately half way from the forward end

The joint has been attached with a matrix, several layers of chop strand mat and polyester resin.

Describe the procedure to re-seal the keel

Price the repair using a Gaant chart
To find, the labour cost and the total time taken for the job to be completed
List the materials to be charged to the job

 

How do we put a repair plan into place?

List the problems that might need to be considered that could affect the outcome of the job or the efficiency of the job.

Where is the best place to do the work? Do we need it to be undercover? Is it cost effective to move it from where it is?

Do I need a support structure, a cradle, extra lifts on the travelift, or a crane?

What fittings need to be removed? Should they be crack tested in case they need replacing?

Do I have all the tools and equipment I need to do the job? Do I have all the skills or do I have to subcontract.

What is the construction and laminating schedule? Are the materials I require available immediately or do I have to order in.

How long is the job going to take? Make up a time line by listing all the jobs from prep to finishing and put a labour total of hours beside each job.

Work out a cost based on labour, materials, hardstand, and travel lift fees

 If we consider these options we could make a description for the case study that was as follows

• The Keel is supported by propping with heavy wooden props or acro proping, two on each side  
• Inside the boat keel nuts and washers are removed using a socket and socket wrench
• Care is taken not to damage the exposed bolt threads
• The length is calculated from the top of the bolt head to the lead keel and a hole saw chosen to bore down around the bolts (18mm bolts need at least 4mm clearance)
• Each bolt has a clearance hole made around it by boring down its length to the top of the lead keel with the chosen hole saw
• The hull is separated from the lead keel by lifting with the travelift, the joint may need to be forced apart with the use of steel wedges driven between the lead and the stub
• Once the joint is separated the two equal size blocks are placed between the lead and the stub and the hull rested on the blocks to keep the two surfaces apart. Wash down with fresh water
• Both faces are prepared for re-attaching by using an angle grinder to resurface, and a heat gun to dry
• A stiff epoxy glue mix is prepared and spread over the top of the lead and the stub
• The hull is lowered using the travelift and the keel aligned with the line of the rudder, the line of the mast, using a string line and level. the fore and aft bolts are partially tightened
• The bilge cradle arms are adjusted to support the hull in the correct position and the glue left to dry
• Resin is poured down around each bolt to fill the voids created by the hole saw, this is topped up as it cures
• Keel bolts are re- tightened, filling and fairing completed on the outside
• Undercoat is brushed over the joint area and antifouling applied to the same area and the boat is ready for relaunching