I've purchased a new Tahoe 24' pontoon boat. There is no speedometer, and the dealer told me that there is too much turbulence behind the pontoons and therefore speedometers are rarely reliable and don't work. I want to install a speedometer - what could I do to assure that it will work? I have an outboard motor (Mercury) that has a speedometer tube connector I can use. Or I can use an external speedometer tube and mount the "sensor" somewhere. Any suggestions on how best to "make it work reliably?"
Any suggestions on how best to "make it work reliably?"
Yes, use a GPS...
Speedos that use a pitot tube and pressure to measure speed are notoriously falliable and are generally considered to be an approximation of speed at best.
Ditto on the GPS. There are alot of inexpensive handheld units that will do the job. The other option would be the paddlewheel type that many fishfinders use. They are far more accurate and hold up well...
So if I don't want to go GPS, where would the best place be to mount the speedometer sensor on a pontoon boat? On the accessory bracket on the rear of my port side pontoon? Or would it be better to just use the "built in" sensor that I can connect to on my Mercury 115 outboard?
Yes, mount it on the bracket. It will get somewhat cleaner water there. But if you can, get one that uses the paddlewheel. I had one on my last toon and it worked pretty well and you don't have to worry about it clogging up all the time..
Use the pitot tube on the motor. If you want a more accurate reading, buy a fish locator that has a "speed" option. It is less susceptable to the turbulence and the locator will help you see depth, locate fish, tell you the water temp, and speed. You can also buy "electric" speedometers such as those found on tournament ski boats but they are spendy.
Why it is helpful to know your speed on a pontoon (or other) boats...
I've found on my other boats that it's helpful when pulling children on tubes that it's good to get a "consistent" speed for each child's liking. As you know, different kids have different tolerances for different speeds, I therefore try to keep a watch at works best for each kid. The tachometer can be a helpful measure, but, as you know certain RPMs will result in different speeds dependent on water conditions (like wind and waves).
My previous boat had the pitot speedo; I remember one particular instance where I was anchored under the Skyway fishing, due to the tidal current, my speedo was registering over 10MPH at anchor!