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We were contacted by an owner whose boat did not perform very well at higher speeds. The stern was too low in the water and the boat was carrying almost 285 kg of lead in the bilge.
The concept was to replace the lead bulb of the keel with a heavier bulb with a centre of gravity further forward. The additional weight in the keel would allow removing the lead in the bilge without reducing the righting moment.
We carried out the design of the new bulb completely in 3D which allowed accurate predictions of weights and centres of gravity. The result of the modification was a reduction in boat weight of 165 kg, a centre of gravity that is 100 mm further forward and an increased righting moment compared to the original design. Besides that, the new keel has a much more efficient T shape instead of the old L shape.
The created 3D files were sent straight to the foundry and used to CNC machine the mould pattern with high accuracy.
We are looking forward to learn how the boat performs after the modifications. 


New T - keel bulb


Original L - keel
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Three days after the launch the Bondi 36 went onto a 2-week holiday trip to the Baltic Sea! Everything is working as it should and the performance is outstanding. On a close reach she easily cruises at 8 – 10 knots with only two people on board.

The regular sailing area is the river Elbe in north Germany. The river has a strong tidal current of up to 5 knots. Sailing with the current from behind but against the wind can lead to some very nasty wave conditions. We can report that she passed the test sailing close hauled at up to 30 knots of wind against steep, standing waves.

This weekend she is on the way to Heligoland, a small Island in the North Sea.


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After 5 1/2 years of sweat, blood and tears the KJ Engineering designed Bondi 36 was launched in Hamburg in front of an impressed crowd. Even the sky was mostly an unusual blue colour.

The bondi 36 is probably one of the most sophisticated home building project completed by an amateur. The design is an exciting mix of racing and cruising features to meet the requirements of the owner. Except for the lead bulb, keel fin and engine all major parts are made from carbon to minimise weight. Unusual for a racing yacht is the full interior with proper galley, head, heater, fridge and running water. The owner couple wants to cruise the Baltic and therefore need comfort below when the conditions are unfavorable outside. To make sure a reasonable amount of sails can be carried with only a crew of two, water ballast tanks are located in the aft cabins.

The quality of the work can only be described as exceptional. It will be difficult to find a boat built to this standard anywhere.

Infusion technology was used to laminate the hull and deck. There is plenty of time to place the reinforcements. The infusion process itself only takes a few minutes and is very clean without resin mess everywhere.

We are looking forward to the results of the first sea trials. Speed under engine was 8.5 knots which is very encouraging.

KJ Engineering designed and engineered the hull, keel and rudder structures. Additionally we supported the built process with tips, tricks and detailed instructions.

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The final drawing for the Bondi 36 lead bulb has been issued! The information provided by us included the paths for the CNC mill. As a result, the casting pattern was completed a few days after the files were provided. 

The mass of the lead will be approximately 2.3 t for a total ballast ration of 52%. To achieve such a high ballast ratio, it is important to reduce the mass of other structure. This was accomplished by using carbon fibre composites for the hull, deck, mast, rudder and interior fit out. The only major steel parts are the keel fin and the engine. A high ballast ratio allows to carry larger sails for increased performance. 

We are very much looking forward to the launch and a first test sail.




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The keel fin is the only major steel part of the Bondi 36. For the safety of the boat and crew it is important that this part is reliable over many years. A lead bulb of more than 2 t weight is mounted to the tip of the keel fin to keep the boat upright. Stress ranges are therefore high, especially during tacks, gusts and wave action which can potentially lead to fatigue issues. 

To ensure safety and high fatigue performance a very innovative design was developed by KJ Engineering. The keel consists of a CNC machined top plate to which the load carrying strut is welded. The strut is made from two plates bent into a C - shape. This ensures that all welds on the strut are parallel to the main stress direction and located in the neutral axis to avoid fatigue issues. 

The most critical weld is the connection of the strut to the top plate because of high stress levels. For optimum performance the top plate is shaped in such a way that the weld connection to the strut is a butt weld located away from the stress concentration due to the radius between the top plate and the strut. Butt welds have good fatigue strength compared to other weld types, ensuring maximum fatigue life. Non-destructive testing was carried out after each weld run to ensure this critical weld is crack free.

To complete the aerofoil shape, another C - shaped sheet is welded to the front and two sheets to the back. The inside of the keel was zinc coated after manufacturing to prevent corrosion.




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