Replacing my speedo/adding a tacho..

[pyro225]

So my speedo is looking dated on my ssv151 / 80hp merc greyband. I have found an awesome orange illuminating one that's the same size - but its for a motorbike. It says its electrical or mechanically fed - would this work?

Also my boat has never had a tacho - the same company make digital tachos do I just connect the green wire somewhere on the ob?

Cheers

 

[H20Rat]

So my speedo is looking dated on my ssv151 / 80hp merc greyband. I have found an awesome orange illuminating one that's the same size - but its for a motorbike. It says its electrical or mechanically fed - would this work?

Also my boat has never had a tacho - the same company make digital tachos do I just connect the green wire somewhere on the ob?

Cheers

1) No, no, and no... Boat speedo's are pressure operated by the water in the pickup pitot. A bike speedo will connect to a wheel sensor or the transmission...

2) yep, but you need a tach that will operate for a 2 stroke with the number of cylinders you have. Not all 2 strokes have the same ignition either, and you need to know if its a wasted spark system or not.

 

[Silvertip]

Very likely this tach will not work. Boat speedometers use either a small paddle wheel device installed at the back of the boat to send a signal to an electronic speedo head, or the speedo requires a pitot that is built into the lower unit on the engine or a separate pitot mounted on the back of the boat. The bike type speedo would very likely be calibrated very different for the boat even if you installed a paddle wheel picklup. There certainly is no way a mechanical (cable operated) installation could be used.

 

[pyro225]

ok in that case is there a reason my speedo would stop working?

 

[Silvertip]

Sure. 1) The tube that runs between the pitot and the speedo is plugged, kinked, or disconnected. 2) The pitot orfice is plugged. 3) the head unit is bad, 4) the pitot is flipped up due to striking an object in the water (separate pitot only).

 

[UncleWillie]

Sure. 1) The tube that runs between the pitot and the speedo is plugged, kinked, or disconnected. 2) The pitot orifice is plugged. 3) the head unit is bad, 4) the pitot is flipped up due to striking an object in the water (separate pitot only).

+1
Disconnecting the hose from the Pitot Tube on the transom, and blowing Hard into it, should indicate ~10mph on the Speedometer.
Disconnecting the hose from the Speedometer and blowing into it should produce Air flow out of the Pitot tube.

 

[pyro225]

Great - thanks for being so helpful

 

[pyro225]

What are these gps speed senders like - save this hassle again!

 

[H20Rat]

What are these gps speed senders like - save this hassle again!

Those aren't replacement gps senders for a normal speedo. They are gps based speedo's that may or may not have an external gps antenna or receiver.

 

[pyro225]

ahh yes are they any good?

 

[Silvertip]

GPS is GPS. "Any good" is rather ambiguous. How accurate do you need to be on a boat? Like all accessories, the features you need/want determines the cost. High cost doesn't make a GPS any better or worse than one that costs less.

 

[UncleWillie]

GPS is GPS. "Any good" is rather ambiguous. How accurate do you need to be on a boat? Like all accessories, the features you need/want determines the cost. High cost doesn't make a GPS any better or worse than one that costs less.

+1
If you just want to know your speed for the sake of curiosity. Any GPS will give the answer.
I added a Water Sports GPS Speedometer. It attaches to my Sonar/Chart-plotter/GPS.
My original Speedometer was a 60mph gage with an exponential scale. Nearly useless below 30mph.
The claim to fame of GPS Speedometers is that they are Linear like the one in your car.
Ii is actually usable below 20mph.

 

[NYBo]

GPS will give you "speed over ground." i.e. how fast you are going over the face of the Earth. This is useful for determining estimated time of arrival, for example. A pitot- or paddlewheel-driven speedometer gives you "speed over water," and as such, will differ from "speed over ground" when you have tidal or other current. Speed over water is useful for evaluation propeller pitch, trim settings, boat loading, etc.


I have both on my boat (the GPS speedometer a feature of my fishfinder/chartplotter). In no-current situations, their readings are very close to each other; depending on the hull configuration and pitot installation, the traditional speedometer may be rather inaccurate.

 

[pyro225]

ok thanks everyone - is there a digital speedo/tacho i can buy for my ob? also how do i retrofit tach on merc 80 as i have no manual :*+(

 

[ssobol]

ok thanks everyone - is there a digital speedo/tacho i can buy for my ob? also how do i retrofit tach on merc 80 as i have no manual :*+(

Check with the engine manufacturer. Using the manufacturer gauges often give additional information than just speed or RPM. Also, for newer engines, the gauges just plug in and the data mostly comes straight from the engine computer. There is no messing about trying to get it to work properly. I've had the digital speedo and tach from Yamaha and the digital tach from Honda on the respective engines. They are very nice, but can be expensive. The digital speedo from Honda can also monitor fuel usage and mpg along with speed. It costs about $950.

 

[pyro225]

Its waaay to old for that merc i4 and i6 1980s