Part of the reason (I think) was to promote the archive of all the correspondence of the Board of the Longitude, and entrants were encouraged to take inspiration from actual proposals. After poking around, I settled on Samuel Parlour's 1824 "apparatus to render a telescope manageable on shipboard", which was itself a reinvention of Galileo's celatone concept. I bought an antique spyglass and a large chunk of brass off eBay, and started work in late December. The work went pretty fast, making extensive use of my new lathe. I'm comfortable saying it's my best work ever for a piece of this scale.
(Full photoset here.)
And... I just found out it was accepted. Sometime in April I'll be taking it to London, where it will go on display for the rest of the year. Along with, you know, the Harrison Chronometers. In Flamsteed House. On the Prime Meridian. I can't even begin to wrap my head around that. Remind me to keep putting in applications to ridiculous things. It works far more than it should.