boat speedometers

[kymarlee]

I wanted to get a simple speedometer for a small "minimost" hydroplane I built and find that they require a regular boat battery.

Is there a simple boat speedometer out there which runs on a smaller battery? I really don't want the added weight.

Thanks for your assistance.
John L
Portland OR

[pops67g]

Battery???

Most ordinary boat speedometers operate by having a pickup tube that mounts on the back of the boat using water pressure converted by a gauge to indicate speed. They are strictly mechanical and require no batteries of any sort.

[aojesus]

Most of us use a hand held GPS that we either strap to the life jacket or mount on the dash with a bracket. They will tell you average and maximum speed for each run if you reset it each time. We found the cheap $89 one to be just as accurate as the $229 model.

Here is a link to a Keller pick up tube type speedometer....http://www.portagebaysystems.com/marine/products32.htm

[Tomtall]

Speedometers

John -

You can obtain a complete speedo with pick-up for under $50 for you mini most. No battery required. (other than to make the dash light inside it light up). Check this link below. If you do not like e-bay your local marina can order the one you need. Try and keep the selection for max speed as low as possible when selecting yours. This keeps them more accurate by using the full range of the speedo. Good luck !

http://shop.ebay.com/?_from=R40&_trk...All-Categories

[kymarlee]

Tom L and Russ..thanks for the info. Much appreciated.
John aka Kymarlee

[Raymond]

Now when someone finds one with a highest speed latching feature, let us all know.

[sam]

Its called a check valve. A few racers have been using check valves as highest speed latches for 60+ years (Hill family).

[Raymond]

Ah...I see...very interesting. So with a small parallel bypass with a manual sov one could have the option of capturing top speed or monitoring speed.

Thanks

[sam]

Russ Hill Sr called it his "liar detector" ... he could tell how fast the speedo had seen rather than relying on his sons to report the top speed or guess

[Raymond]

As I research this project I am faced with the question of how much pressure could this system see? Assuming our program grows thougthout the years, what types of pressure will be seen in this circuit at say..80 mph

[ZUL8TR]

system pressure

As I research this project I am faced with the question of how much pressure could this system see? Assuming our program grows thougthout the years, what types of pressure will be seen in this circuit at say..80 mph

At 80 mph the stagnation pressure at the speedo pickup is about 92.6 psi. It would be a little less at the speedo head unit due to the elevation of the unit above the pickup point - each foot head above pickup point reduces the pressure about 0.43 psi.

[Raymond]

Very well then; a 125 to 150 psi check valve and bypass should be just the ticket. I see a couple of plastic units with barbed ends on them in the McMaster Carr catelog to keep weight down.