Protrim speed indicator

I had one of  those sitting in the garage, just sold it on ebay last week;

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=715 9797234&rd=1&sspagename=STRK%3AMESO%3AIT&rd=1

Slight price difference tho with GPS,  the protrim can also be used for judging tides.  GPS is a little luxurious for improving boat speed.

Rick, did you find it useful at all?

If you enjoy looking at the numbers to know how fast you are going, that's fine. If you want to learn about boat tune, forget it. The numbers change on every wave and in every gust. You need the budget of an AC campaign to be able to tune a boat from instruments.

For example: 1000m beat. A big gain from a tuning change would be a couple of boatlengths, which is something around 10m. That is 1%. Boats go to windward at, very roughly 5 knots, with the speed oscillating +/ 0.2 knots (at least) as you take waves. That's four times your 1% tuning gain, so it is completely lost in the noise.

Take it from someone who has spent thousands of hours helming yachts racing offshore, staring at the 20/20s. You can't tune a boat off instruments: the only thing sensitive enough is another boat to compare to.

That would work.

I've sailed both and the opposite is true. Yachts are heavy and therefore it takes a fair amount to speed them up and slow them down. Dinghies accelerate and declerate quickly by comparison. In most dinghies, you can tack and tack back on a 30 second windshift and gain. If you did the same in a yacht, you'd grind to a halt.  

Well I have tried and it doesn't work for the same reasons tuning on a boatspeed indicator doesn't work. If you turn the damping to something around seconds, the VMG dances all over the place. If you turn the damping to minutes, the breeze is never 100% steady for that long. Not all hand-helds let you change the damping anyway but the units yachts have usually do. The point is changes you get from tuning are very small compared to the changes constantly caused by other factors.

The only way you could make it work is record all the data (breeze speed & direction, speed, VMG, sheet settings, rig settings) and shoreside, feed it into a computer, average it out over weeks of testing and try to make sense of it. That is what the AC teams do but it is completely outside the resources the rest of us have available.

Two-boat tuning is the way to go. That works because, if you do it right, both boats experience the same changes to the breeze etc. and therefore you can make conclusions about the results of tuning changes. Have you noticed that the successfully AC and Volvo campaigns now almost invariably have at least two boats? Allowing two-boat tuning is one major reason for spending all that extra $$$$.