Speedometers

[Bob Perkins]

Hi Everyone,

I only have experience with paddlewheel style speedometers..

Does anyone know about the pilot tube style?
How accurate and responsive are they?

I'm instrument shoping and it looks like most of the ones suitable for my application are pilot tube style.

I found the perfect set of instruments (looks/style wise.. There are many that will do the job..) - However, it is an automotive set. The vendor said they could retrofit a marine speedo... etc... but the guy on the phone wasn't crazy about pilot tube..

Just wanted to get the groups thoughs.
Thanks,
Bob

[rbgarr]

FWIW, a cheap, used, handheld GPS will give you speed-over-the-bottom better than any water driven speedometer, but the look of the instruments may be what you're looking for.

[htom]

GPS is probably the most accurate.

Pitot tubes can be very responsive, because they work on the pressure differences, but that leads to problems at very low speeds, especially if there's an electronic interface involved. Some of them use a floating ball which is effective even there, but I doubt that those are what you're interested in.

http://www.grc.nasa.gov/WWW/K-12/airplane/pitot.html

[RonW]

Besides the paddlewheel and the tube, there is also a third one. They are called speed gauges instead of speedometers. They use a transducer instead of the wheel or tube. Basically the same as a transducer used with your depth finder. These gauges measure in tenths, starting with one tenth. Some of the better and higher priced fish finders or depth finders have a optional transducer that will read speed as well and show it on the screen in tenths.
Like rbgarr says, they are much more accurate.
Seems like the way to go if you wanted to do low speed trolling.

[paladin]

actually there's also the fourth type....consisting of a small piece of wood and a tick tock.....cheeeeper too....reliable...seldom needs repairs......

[Nick C]

The GPS speedometer solution is a different measurement of speed. If there is a current it won't give your speed, as you say, over the bottom, but there are reasons to know your boat speed, for instance fuel consumption estimating or trolling speed.

[Dan McCosh]

The pitot tube is prone to clogging. Another old-style system is the Kenyon, which used an arm dragging in the water that activated a hydraulic piston--the instrument showed the pressure on a logrithmic scale. The paddlewheel is pretty foolproof.

[Bob Perkins]

Thanks for the info -

I agree - GPS is the best method for speed over land.

These instruments are for a 40's-50's style mahogany runabout.... So I want *old* looking instruments.

Sounds like the pilot tube will be acceptable though.

Thanks,
Bob

[Paul Scheuer]

Bob: As indicated above the correct spelling for the item you seek is PITOT (pee-toe) tube, in case you're searching. A PILOT tube is a different thing altogether.

[Bob Perkins]

huh...

Thanks for the correction...

I was just on the line with a vendor and she said it that way - which sounded all wrong to me..

Regards,
Bob

[htom]

GPS will measure speed over ground or land equally well. GPS will not measure speed through water (unless the boat is stationary relative to the water.)

[Dan McCosh]

GPS works as an accurate speedometer when the water is stationary relative to the bottom.

[John Bell]

Why have a speedo at all? All I want in a powerboat for instrumentation would be a compass, tach, volts, temp, and oil and water pressure. You can figure speed by the revs the engine is making (calibrated with $90 GPS!). I've never seen a standard speedo that worked across the full range of boat speeds anyway. Either they read 15 mph and above or 15 mph and below, which is tough when 15 mph is about as fast as I ever go on the water!

On my boat I've got it figured like so:

1000 rpm = 3.5 mph
2000 rpm = 6.5 mph
3000 rpm = 13.5 mph
4000 rpm = 19 mph
5000 rpm = 23 mph

If it's critically important that I know my exact speed, Mr. Garmin comes out!

Edited to add: the lower unit on my outboard has a pitot tube to run a speedo on its leading edge. The little hole always seems to have debris stuck in it, usually pine straw.

[ 01-24-2005, 08:48 PM: Message edited by: John Bell ]

[rdapron]

Bob, what company/vendor did you dig up?

rob

[Bob Perkins]

Hi Rob,

I came up with:

http://www.teleflexmarine.com/
http://www.faria-instruments.com/index-new.html

and

http://www.classicinstruments.net/

Classic Instruments has a set called The Vintage Series. I like it the best so far - They make a boat speedo to replace the automotive one..

They are putting together a quote, but it will be more expensive than getting more off the shelf items.

In my application: It's all about looks smile.gif I think the Vintage series is pretty sharp -
It's tough making design choices...

Regards,
Bob

[Donn]

Some very cool stuff at that classic instruments site:

http://www.classicinstruments.net//images/resized/52xhudsonxwaspxdash.jpg

[rdapron]

Bob; let us know what they come up with in terms of price. As I said on Dan’s site, I like the looks of their stuff but I have never have used any of their gauges nor do I know of anyone in the vintage boating crowd using their stuff, so I am curious as to the price and quality of the product. Some time ago when I saw the “Vintage Series” I immediately thought they would look great in a runabout.
rob

[Tom Lathrop]

Depends on what you want. If you want traditional instruments in a classic runabout, the Airguide pitot tube type were used almost universally 50 years ago. Since my latest runabout is from that period, I bought a nice Airguide on ebay where they are usually available.

For speed over the ground, a GPS can't be beat. I have both a GPS and a paddlewheel type on another powerboat and see fairly large differences between them depending on current, wave action and whether I am running a straight course or not. Very often a tachometer will be way off in estimating speed or distance run for the same reasons plus wind and boat load conditions.

[Bob Perkins]

Everyone,

Here is what I did...

I decided to try out the Vintage Series from Classic Instruments.
Vintage Series (http://www.classicinstruments.net/index.phtml?catid=14)

They are really a car Instrument maker. After talking to the sales person - I was able to put together the following:

They make a marine speedometer for the Vintage Series and a tach with an hour meter. This is the only gauge series that they do for marine use.

The issue I was having is they told me up front that the screening of the dial faces for all of the other instruments (volt, water temp, tach, fuel, oil) where done at a different time than the speedo - so the speedo lettering is a slightly lighter brown. They were good enough to tell me up front and not let me find out after spending the $$$$.

I ordered them under the condition I could return them if I was unhappy with the color. She did say that a local (to them) classic boat manufacturer used them all the time and considered it acceptable. So we'll see...

They really are a perfect fit style wise..
http://www.classicinstruments.net//images/resized/1078848322VT60.jpg

I will be getting chrome trim rings since a mahogany runabout is all chrome... My plan is for a mahogany dash panel.

Now to make more design choices...

Regards,
Bob Perkins

My Current project is at:
http://www.imagestation.com/album/?id=4291051329