Firstly, well done to the many people contributing to this excellent website. As a former Mk 1 owner and current TH 27 owner, I would like to share my opinions on these yachts with other TH owners. Below are some initial thoughts intended to stimulate discussion. I'll follow up in more detail soon.
I'm also very keen to hear from those people who collated the background information on the 27 as I am yet to develop a full spec sheet for my yacht.
Lets start with the Mk 1. To my eye it is the sweetest and most balanced design of all the Top Hats. Yes, they're all gems but the Mk 1 just looks right. The stepped coachroof works well with the low freeboard, generous foredeck and moderate beam and it looks like a 'proper yacht' under sail. By comparison, the 27's broad roof and narrow side decks make the yacht look chunky, unresolved and not at all pretty. It is a much larger yacht in all respects with the wide and long cockpit being the most apparent external feature. Also unlike the Mk 1, the 27 has a very short foredeck due to the extended cabin and sloping forehatch. The wider cabin also means the 10 foot beam of the 27 is not that apparent because of the narrow side decks.
Aesthetics aside, what about performance? I'd have to say the 27 would be my preferred ride. I base this on the additional beam which is carried aft and which provides greater initial stability and stability off the wind. It also retains the upwind performance of the 25 due to its cut away fore foot and 3/4 keel. However, the 27 has that dampening you feel on larger yachts so by comparison it's a much smoother ride upwind and a little drier.
My previous Mk 1 'Georgie Girl' was a reliable, tough and slippery yacht in pretty much any sort of weather Moreton Bay could throw up. Similarly, I don't put my hand up for it, but I've sailed my TH 27 on Moreton Bay in 30-35 knot conditions on a couple of occasions and it lacks none of the heavy weather handling virtues found in the Mk 1. In fact, the extra beam means the 27 does not bury its rale so eagerly and it also seems to be a bit faster than the 25. Some others may have more information on these aspects of the boats.
I've run out of thoughts for now but I look forward to discussion on this - the TH 27 owners club is a pretty small one.
timc
'Tusk'