Keel Project

The FC Europe has a very low ballast ratio and the keel is in line with its design age, which means higher center of gravity and more wetted area than current designs. While the higher wetted area (from a wider fin) is not all bad for a cruiser, we needed more righting moment.

The keel already had a small bulb and it was obvious that weight should be added there. We wanted as much extra righting moment as reasonable and I did some calculations on the keel bolts with help of the book “Principles of Yacht Design” by Larsson and Eliason. By adding 150 kg. at the bottom of the keel we were increasing the moments at the keel root by 25% and I was not sure if more would be safe and then the rig and the structure also have to handle the extra loads. Another boat Bobsleigh went further. They (former British owner) added approximately 300 kg after having an engineering calculation done. Bobsleigh was racing regularily in the UK SouthWest (now in the North Sea) which is as rough as anything I ever planned to do, so with them having no structural problems feels like a proof with a safety margin.

The description of the Bobsleigh modification was my starting point but it was too crude for my taste, so I made my own design. I wanted the weight as far aft as possible, because the extra weight is basically replacing crew weight which is placed aft of the cg. The boat is mostly cruised wit 2-4 people instead of the racing crew of 8. I wanted sound hydrodynamics as well, which meant using proven NACA models. I went through the NACA profile series recommended by Larsson and Eliason and opted for the 67-series, which had much similarity with the front half of the original profile but carries the volume further aft. This allowed us to design a sleeve that was pushed onto the original bulb from the back and only requiring a moderate amount of fairing to complete the shape forward. The shapes can be compared on the 3-D views which were generated with a CAD tool.

We made a fibreglass female mould of the original bulb (aft half) and built the model on top of that using plywood foam and plaster. This was then used to create the mould for the sleeve in the forgery, which unfortunately destroyed my model in the process. The lead cast (by Postler in Glückstadt) came out beautiful and was a perfect fit. They told me that it weighed 180 kg. which is surprisingly high, because I had calculated the original (150 kg.) in the 3D CAD program (SolidWorks). I could not check the weight myself, so I will never be sure how much it is.

The Sleeve was glued on with epoxy and we had been warned that there was only one try as the tight fitting lead would not come off again. We even forgot to put in the two 10 mm safety bolts and sailed one season without them. Even a full speed grounding on stones, by an unexperienced delivery crew who were too generously keeping clear of traffic in the Kiel channel, left the connection unimpressed.

After almost 10 years and a few more ground contacts, there is still only a hair crack on one side at the joint. This thing will never fall off!

The righting moment was increased further by adding two 250 Ah batteries and 50 meter of anchor chain for about 200 extra kg. in the bilge beneath the cockpit. These items obviously have important functions as well.

With all this Kría is now probably a moderately stiff boat, having been really tender before. As we had to replace the mast (tube), wich had a crack, we went for a heavier profile and meanwhile have also upgraded the weakest part of the rigging to compensate for the increased righting moment when racing with full crew.

I know that Bobsleigh had their rudder redesigned as well for better control. It was done by Hugh Welbourne if I remember correctly. It looks on pictures like the original rudder was just lengthened and got a state of the art shark fin tip. I don’t think this is necessary and I doubt that the shark fin compensates for the drag created by the extra surface.

I am happy with how the boat handles in it’s current configuration. The rudder does not stall so easily and it recovers quickly in most situations. I would say that the FC Europe is a forgiving and well mannered boat, which even a novice can steer on a breesy spinnaker run. This is certainly helped by the amount of reserve buyoancy carried up front, which creates less assymetry of heeled hull shape (immersed) than current IMS style hulls. Those boats certainly need their deeper rudders too keep enough water contact when heeled.

In conclusion, we have a pragmatic compromise which delivers the desired stability but certainly can not be compared performancewise with modern appendice designs.

You can also see pictures of all the modification projects in the galery.