Speedometer

[jayard78]

Any one know the specifics of a boat speedometor, Im a newb at them. If you buy a guage online, does it contain the actuall mechnism that measures how fast you are going?

 

[ziggy]

Re: Speedometer

don't know the answer to your question, sorry. but....

you don't have a speedo on your boat now?

me either.

a handheld gps fills all the gaps...

that's a h2oc set in the speedo mode. looks like a analog speedo... Velcroed it to the dash..

 

[Silvertip]

Re: Speedometer

Most speedometers will come with the necessary hardware, tubing and the pitot (the pickup). If your engine has a pitot built into the lower unit the tubing can be connected to it. If not, a separate pitot is mounted to the transom and the tube runs from it to the speedometer. A speedometer is not an electronic device. It requires power only for the internal light.

 

[F_R]

Re: Speedometer

Any one know the specifics of a boat speedometor, Im a newb at them. If you buy a guage online, does it contain the actuall mechnism that measures how fast you are going?

Disclaimer: I am about to talk about a conventional boat speedometer, not the kind with a little paddle wheel to dirve it.

A speedometer is nothing more than an ordinary pressure gauge. A forward-pointing tube on your boat's transom, called a pitot tube, supplies the pressure. The faster you go, the more water pressure is rammed up the pitot. The pitot tube and connecting hose comes with a new speedometer.

Boat speedometers are notoriously inaccurate, don't work at less than 10-15mph, and the pitot is always getting fouled. Bottom line they are a nice gimmick, but a total waste of money.

If you want to know how fast you are going, get a gps. Even the cheapest ones will give you your true speed across the face of the earth. Boat speedometers give you your speed across the surface of the water. There can be a considerable difference in a flowing river.

 

[Varago]

Re: Speedometer

If you want to know how fast you are going, get a gps. Even the cheapest ones will give you your true speed across the face of the earth. Boat speedometers give you your speed across the surface of the water. There can be a considerable difference in a flowing river.

Good point. While a speedometer may give the wrong speed its the same wrong speed no matter what direction or body of water your on the GPS does NOT do this. Use a GPS on a river with 3 mph of current while towing a Wakeboater and see how upset they get. Thats 6 mph different up river as down, when doing 18(gps) thats 15-21 mph(water based) based on direction that you have no way to correct for. For this condition a good old fashion speedometer is far better.

GPS is great for a lakes or ocean but just about useless for a river.

Dave


ps: what I find interesting is that the pitot pickup on my VP leg gives a reading that is off the same value as the slip calcs on the prop I am running