Where are they now?

[Lopez Mike]

Fill me in on this business about GPS inaccuracies. I have been using GPS numbers to calibrate automobile speedometers for several years and have found the data to be far more accurate and repeatable than trying to take times over a measured distance. To be sure, the hand held units commonly available only read out to a tenth of a knot. Not an issue for my application.

A larger issue for us is finding a body of water with no currents and calm wind conditions. Either condition is a far greater variable than any GPS problem I've run into.

I have been surprised how sensitive the boat speeds have been to loading and trim. Leaving unnecessary junk at the dock saves a bunch of fuel!

Another way to measure changes in hull drag is to do some coasting tests. This is covered well in Oceanography and Seamanship by Van Dorn, a volume I recommend as being remarkably free of cant and error.

Mike

[barts]

A GPS will give you quite reasonable speed reading, but you're better off measuring distance made good (w/ GPS or chart) over ten or twenty minutes; if you're dealing with current a run in each direction is called for and the results averaged. If it's windy, forget about measuring speed; the runs cannot be averaged. A GPS fundamentally measures position; differentiating this to produce a speed reading over a short term is always going to induce noise.

Alternatively, a simple pitot tube will provide quite accurate speed estimates, particularly when the difference between the static and dynamic head is measured; this avoid problems with maintaining a correct depth of immersion with the tube..

- Bart

[Lopez Mike]

Boy have we hijacked this thread!!!

I find that the admittedly derived GPS speed readings are way, way more accurate than any conventional speed measuring device. I repair a performance measuring kit for an automotive journalist. It consists of a bicycle wheel that is attached to the rear bumper of a tested automobile. It has a speed sensor that is connected to a laptop which does all the rest. I hadn't heard from him in a while to ask for repairs. They regularly back over the thing!

He called about something else and I asked him how it was working. It turns out that they threw it all away and do it now with an external GPS antenna and a laptop. He said that the data is better and is very repeatable.

GPS altitude is another animal. A low priority algorithm in consumer units. Slow and usually wrong. Fortunately my boat's altitude is usually well known.

By the way, my bicycle speedo tachometer works great. Self powered. Turns itself off after a short time. Water proof. Now to hide the readout unit in an old brass gauge housing so it doesn't look so techie.

Mike

[87gn@tahoe]

I've just returned from an Auckland Steam Engine Society meeting at the workshop of Chris McMullen. I'm pleased to report that progress is being made on the replica Herreshoff steam launch. Chris has for many years been building a replica 34 foot Herreshoff launch, to his usual exacting standards. It is worth noting that while the boat is very similar to Vapor, mentioned earlier, it is NOT a replica of Vapor, but a replica of another Herreshoff launch, so has a different yard number and is indeed a longer vessel.

Chris has built virtually everything himself, engine boiler, hull and fittings. Wes aludes to the crankshaft problem. Chris now knows that his crankshaft was not made from SG iron as originally intended, so fears it may break under load. As the crankshaft is a very complex one to make, it has been rather a problem to chris for quite awhile. he has now decided to get the boat finished and then worry about it, it may end up being ok.

For the first time today we were able to see the Herreshoff launch with the engine and boiler in place at last. Unfortunately I didn't take a camera, but it certainly looks most impressive. Chris also showed us the Marsh pumps he has been building for the boat. For years Chris didn't know what pumps the boat should have on it, as they aren't Herreshoff parts, so aren't on the drawings. When he finally tracked down Vapor, and was able to study it, he found it has Marsh pumps, and was able to measure them up for replicas. Chris hasn't been able to make the valve chest arrangement for the steam shuttle valve, but bought two similar Marsh pumps and is using the shuttle valve chests off these pumps for his ones. Infact he tested one of the ones he'd bought today. The launch carries two pumps, one has an air pump on one side of the steam cylinder, and a feed pump on the other side, while the other is purely a feed pump but has hand operating gear on it too. Chris is well on the way to having the pumps done, then plumbing can commence. he is also finishing off some hull work, and isn't far off being able to finally mount the rudder, allowing the steering to be set up.

This will be a seriously impressive launch when finished, although that may be some way away yet.

Daniel

That's great news. I've been lusting over his work for many years, finding snippets of info and pictures in the Funnel or online. I've exchanged emails with Mr. McMullen before concerning the boat, but have since lost his email.

I'm very glad to hear that progress, albeit a bit slow, is being made.

There ought ot be some sort of punishment for no pictures though

To the OP- sorry to start a speed discussion that hijacked your thread.