Speedometer installation

[eatropefish]

I'm looking to install a speedo on my boat. It has a 45hp Mariner. I see in the service manual the tube for the speedo. How does this work? Will the speedo I order come with a paddle wheel or connect to this tube? Please enlighten this ignorant do-it-yourselfer.

 

[Silvertip]

Re: Speedometer installation

It depends on what type of speedometer you buy. Paddle wheel speedometers are electronic. A pitot speedometer connects to the tube on the engine or to a separate pitot. Electronic speedometers are more expensive. The typical speedometer found on most boats is the pitot type.

 

[ricksrster]

Re: Speedometer installation

you can buy a speedometer either way. Each model of speedometer will specify whether it is a paddle wheel or pitot tube. http://www.iboats.com/mall/?categor..._id=216659&page_number=1&search_type=category

 

[eatropefish]

Re: Speedometer installation

Thanks guys! I did not notice the type from BPS. More than likely it will be pitot(how do you pronounce that?) Could you explain how the pitot type works? Is it vacuum operated? I noticed on the lower unit two holes on either side about where the pitot hose enters. Does this act like a venturi as water passes by?

 

[Silvertip]

Re: Speedometer installation

No - a pitot operates on pressure. The hose is sealed on the speedo end so no water actually flows in the tube. A small hole at the front of the lower unit has water pressure on it -- which compresses the air in the tube, which tries to unwind a capillary tube in the speedo which makes the needle move. Pitot is pronounced <pit - oh>.

 

[eatropefish]

Re: Speedometer installation

Interesting. Once again you are a font of information.

 

[eatropefish]

Re: Speedometer installation

No - a pitot operates on pressure. The hose is sealed on the speedo end so no water actually flows in the tube. A small hole at the front of the lower unit has water pressure on it -- which compresses the air in the tube, which tries to unwind a capillary tube in the speedo which makes the needle move. Pitot is pronounced <pit - oh>.

I see the inlet hole for the pitot hose, however there is a 3/16-1/4" hole directly behind it and a similar one on the right side of the lower unit that are connected. Are these cross-drill holes or casting holes? Should I plug these? It seems the water will just go in and out and not up the pitot. jAlso, what is the proper routing for the pitot hose, thru the shift shaft tube and out the bottom of the cowl?

 

[imported_Jimbo]

Re: Speedometer installation

Hi eatropefish,

If you are looking for a more exact and simpler way of knowing your speed, you may want to buy a cheap water-protected GPS instead, e.g. one of the low-end Garmins! You will get accurate speed (the pitot-speedos are not very accurate), and you do not need to connect any tubing or wires in the boat.

Just an idea...

BR Jimbo

 

[Vlad D Impeller]

Re: Speedometer installation

Yup! i'll second what jimbo said.

 

[eatropefish]

Re: Speedometer installation

Thanks Jimbo and Vlad! My thoughts exactly. I bought a paddle wheel style speed/temp combo from Humminbird that will plug into my current unit. I'm upgrading my old Tracker and have holes for a tach and speedo in my console. While I'm on the subject of tachs, the one I installed was inop after installation. My wire connections are good and correct. The rectifier tested N/G however, my manual doesn't give a spec for the stator. I have about 0.6 ohms(measured with a good DVOM) on the two yellow wires, no short to ground/power on either. Bad rectifier shorting my send signal?

 

[eatropefish]

Re: Speedometer installation

FYI-- I trampled on anothers thread in a different area regarding my tach. Laddie was kind enough to respond anyway. I apologize for my poor etiquette in trying to get an answer by hitting on different threads. Won't happen again.

 

[Mark42]

Re: Speedometer installation

BTW, the paddle wheel speedos are very accurate. They are usually intended for low speed use, like trolling, where a pitot type speedo is not very accurate.

I use a "low range" pitot speedo by Teleflex (sportsman line) that registers from 5 to 40 or so. Teleflex indicates this low range speedo is more accurate in the lower range than their 10 -80 mph speedo.

After a few GPS comparisons, its off by about 1 mph at 20. Close enough for pleasure cruising.