I have started this pond yacht, bread and butter construction with good quality wood that will hopefully look good in a clear varnish finish.

I am looking for help in deciding the size of the keel, I have lead weights for the ballast, and as you can see I would like a long mast on her, to give it a striking look out of the water.

Does anyone have a formula or rule of thumb on the calculation of keel size or balancing mast and keel?

Current dimesions are, L 41cm, B 9cm, D (hull) 6cm

Current mast 70cm, keel 25cm

I found this ut can't really unpick it to understand it….

CSF = Capsize Screening Formula
CSF = Beam / (Disp/64.2)^1/3
The capsize screening formula is a somewhat controversial figure. It came into being after the 1979 Fastnet race in England where a storm shredded the race fleet. The Cruising Club of America (CCA) put together a technical committee that analyzed race boat data. They came up with this formula to compare boats based on readily available data. A lower value is supposed to indicate a boat is less likely to capsize. a value of 2 is taken as a cut off for acceptable to certain race committees. However this is an arbitrary cutoff based on the performance of boats in the '79 Fastnet. The CSF takes no account of hull shape or ballast location. The CCA characterizes the formula as "rough". They go on to say that "While the capsize screening formula places a limit on excess beam, which is important for good stability range, it does not control for another main determinant, ballasting. With only simple data, this is as far as we can go." Naval Architect Robert Perry calls it,"…far too simplistic to be always accurate, but it is one of the currently popular ways of looking at a boat's offshore suitability." (Sailing Magazine, Nov. 2001, p.44). Any two boats will have the same CSF value if their displacement and beam are the same. One could have a light hull with 50% ballast in a bulb at the bottom of an eight foot fin, the other could have a heavy hull with 20% ballast in a 2 foot deep full length keel. The stability characteristics of the two boats will be drastically different despite the identical CSF value.

After some tank trials, I have reduced the keel by about a third, and made the rudder a third the size of the keel and shortened the mast by a third…. see results below.

Unfortunately, due to the small amount of hull above the waterline, when the boat is heeled over 45 degrees or more then water flows into the cockpit. I may have to add a coaming around the edge of the cockpit to help prevent this, and in a future boat I would have a narrower cockpit?

Now to tidy it all up, give it a final sanding and start the varnishing.

That is a great help, thanks for explaining it so clearly, I agree that the keel puts the centre of resistance forward and a cut away front edge would help reduce that, and the bowsprit will allow a bigger foresail to move the centre of effort forward, I can also shorten the boom on the mainsail to reduce the size of the main sail.

Cheers, B

Coaming added, keel reduced, lead bulbs added and rudder reduced.

The tiller uses an elastic band to return it to midships, and I have extended the tiller astern beyond the rudder post, so that a line from the boom connected to this sternmost end will have the effect of pulling the tiller to windward.

I have added a line below the boom to allow easy adjustment in place of sheets made fast to cleats, and the same on the foresail.

Had a go this morning, quite strong winds. No problem with stability, but still heels over and lets water into the cockpit, even with the added coaming. She now seems a little down by the head, perhaps I moved the mast to far forward?

Sailed well, especially when the wind dropped (see pic below), the self steering rig worked pretty well.