Thanks for your reply Mark. I assume I have a shoal draft. It is 1.52m, I have seen data for E35s with deeper keels.
Pointing relative to the apparent wind is good. I.e. Looking at the mast head wind indicator she is where she should be. The real give away is the plot on the chart plotter which shows the excessive amount of leeway that is being made. In tacking she is typically going through 140 degrees. I don’t expect a high performance but this makes up wind sailing time consuming. I have tried most permutations of sail tight and slack as you suggest but it makes little difference.
Any chop, not so much swell can stop it going through the wind. I believe that it is lacking upwind drive which is contributing to the leeway and making it problematic in going through the wind.
I am actively considering replacing the existing yankee/staysail arrangement with a genoa hopefully to increase up wind speed. I have discussed this with a sail maker who says he has made a genoa for an E35 ketch before. Unfortunately I don’t know the reasoning behind the change in that particular case other than making sail handling easier.
Unfortunately she is out of the water now for the winter so I can’t experiment any more.
I would welcome any further comments based on this further information.