Speedometer question...

[Reese]

I'm getting a Faria 35 MPH speedometer (no jokes please), will it matter or can it be damaged if the boat is going 70 MPH???

[Techno]

I think the small bellows could be damaged from over pressure.
These pitot tube speedos are nothing more than a pressure gauge with a funny dog leg link to change the ratio for speed.
Bourdon tube? I think thats what the thing is called. It might get bent and not return to zero.

[Reese]

You were right Techno...just got off the phone with faria and they said the gauge would be damaged at higher speeds.

They suggest a shut off valve...but I was thinking of a pressure relieve valve or bypass near the pitot tube with an overflow dumping outboard???

[Boz]

Why a 35 mph speedo for a 70+ mph boat?

[Reese]

because we ski and wakeboard...and if you've ever use an 80 or 100 mph speedo for that purpose you would go blind.

This is much better:

[Boz]

Makes sense

[Techno]

I don't see the prob with a 100mph gauge, your just using the wrong end of the scale when skiing and boarding:p

[Karl817]

I've been looking at speedometers and related such lately. Over at the http://www.hydrostream.org site, there are plans for a flip-up pitot tube. The answer to your situation. ?

Look under the feature articles.




Beerp!

[Reese]

"hey Reese do me a favor...take me up to 32 mph and keep it there" Heeheehee...good luck with this thing.

Karl...the flip up pitot might work but I sure would prefer something more automatic...someday I know I'll forget to flip it up.

[dashrockwell]

Maybe he means it would flip up on its own when you hit 50 or so.
Those cheap plastic pitot tubes will usually flip up around 50mph, your speedo could probably take that pressure without damage.

Just an idea?
good luck


ps. You could always go Digital!

[Reese]

Yes, GPS would be nice but at $400.00 it's too rich for my blood.

[sho305]

You might find something on pneumatic controls, maybe a regulator or a blow off valve out of brass. Problem is most stuff is for higher pressure than that likely is, not sure what pressure they run even. Some of that stuff is for controls, and so it will work at lower pressures or is for gas/propane/etc. Much of it is non corrosive also, to a point. I know you can easily regulate a paint gun pot down to 10lbs for example...you would have to test it as I don't know what flow volume you need to handle at 70mph either.

There also may be a way to shut it off/vent it at a preset pressure level.

[Techno]

Thats the ticket a safety valve. Blows at a preset pressure. Not sure but maybe a hot water tanks might work?
Hook a pressure gauge to the hose and find out the pressure it goes to.

If you want leave off the tie wrap on the hose. Almost an automatic blow off under high pressure.
Once had the thing blow off under the dash, a stream of cold water hosed at your crotch at speed not only is an eye opener but any sudden sense of water in a boat is a panic maker:eek:

[merklebob]

use an electronic paddle wheel. basspro has them for about 75. the speed is a 45 mph. use a mickey mouse circuit to divide by two [ use a 4017 ttl chip email for circuit design] and it becomes a 90 mph speedo. switch back and forth

you dont have to worry about not switching over as it does no harm. you can also run two heads on the paddle wheel on for 45 and 90. the 45 just quit reading

for the high end the paddle location gets tricky but i have had it read to 80 which was 5 mph too high. check the high end with a hand held gps and lable the speedo.