Mobile GPS speed indicator

[Capt Popeye]

Well just slowly cleaning up and putting back into action my latest Boat , and it was (is) fitted with a Speedo , a round Indicator with KpH marked, what is now , a scrupmled up bit of Plastic , mounted on the Stern , that acted , in it good ole days , as a device to measure water pressure or sometng similar to activate the Speedo to show speed through the water : Well it gota be removed soon and replaced by a Speedo based upon a GPS system : All in all very cheap to buy , so will it work well ? Any advice or experience out there , please ?

Thank you , oh cost less than £10 on Ebay

 

[KevinV]

I know of a few custom motorbikes that use them for simplicity of fitting - they're a bit rubbish for that because the speed varies too much - not an issue with a boat. They don't last long in the wet though, and it'll only give SOG of course.

 

[rogerthebodger]

The water pressure speed devices are based on pitot tube and the gauge would measure a differential water pressure.

I have a SIMRAD water speed device that takes a NMEA message and I plan to use a GS mouse and a micro to convert the GPS messahe to a through water message.

Most GPS/s will give the speed over ground so what you feed is a display to indicate the Speed over ground on the display

Water proof GPS speedometers

Waterproof GPS Speedometer - Google Suche

 

[Refueler]

Depends on what you want ... SOG or STW ...

The Pitot tube as you describe gives through water of course and is in my mind a good bit of data as it relates directly to boat performance.

GPS derived as you know is SOG (speed over ground) and is great for time to destination / navigation - but fails to show boat performance ...

Lets say my Progress speedboat .... usual STW is 15kts ....

I go out another day and I only get 13kts ... I know somethings not right ... as the boat moves through water and if water moves - boat moves with it.

But if I was using GPS speed ... I would not know about it ...

 

[Capt Popeye]

Ahoy thank you all for responding to my Question , all with constructive answers , yes wedo sometimes have a , shallwe say , 'discussion' with certain Harbour Staff , about the 6knots speed limit being Through the water or over the river bed ? so guess that the real difference is so so so slight that them H/Staff would not notice it ?

 

[LiftyK]

Not for everyone but there are highly accurate and versatile phone apps. I’m often checking the speed of ferries and trains with mine and used it every day on a canal holiday. Not so useful in an open boat.

 

[sarabande]

Worth buying a little second hand phone and a waterproof case (?) from Facebook or a phone shop in Exeter ? I don't think you need to pay for the app use after its installed.

Lots of GPS speedos on Google Play and IOS. As refueler points out, a boat based speedo can give you a bit of info about tide speed, but a phone gives you so much more.

Round the corner in Plymouth the tidal stream under the Tamar Bridge often goes above 3 kts, so needs to be taken into consideration re harbour speed. What about Teignmouth entrance ?

I'd certainly go for a phone over an impeller driven speedo.

 

[MADRIGAL]

As Refueler says, it depends upon whether you want SOG or STW. Traditional navigation is based on log speed (STW), with corrections made for current and leeway.
If you wanted to know the most efficient course to steer taking the turn of the tide into account, you would need STW. You wouldn't need STW if you were to merely adjust your heading so that boat image on the plotter screen kept pointing towards the destination, but then you would sail extra miles through the water fighting the tide to stay on course on a long passage. On a short passage with a steady or negligible current, SOG would give you the most accurate ETA, as long as you didn't lose the GPS signal.

 

[Capt Popeye]

Worth buying a little second hand phone and a waterproof case (?) from Facebook or a phone shop in Exeter ? I don't think you need to pay for the app use after its installed.

Lots of GPS speedos on Google Play and IOS. As refueler points out, a boat based speedo can give you a bit of info about tide speed, but a phone gives you so much more.

Round the corner in Plymouth the tidal stream under the Tamar Bridge often goes above 3 kts, so needs to be taken into consideration re harbour speed. What about Teignmouth entrance ?

I'd certainly go for a phone over an impeller driven speedo.

Hi thanks sarabande , good ideas : The River Teign has a 6 knot speed limit applied , by the Harbour Authority : in the area of Coombe Cellars , a couple of miles UP river , members of the Ski Club are allowed to exceed that speed , with caution re other boats in the area .

 

[Capt Popeye]

Well thank you for all comments and advice , I feel that I should explain my use of a Mobile GPS Speedo device : I have now embarked on most probably my last (ish) boat ownership adventure , as being into my 80s now : I have a 13ft Outboard driven boat , made from basicaly 2 pieces of moulded Plastic bonded together , with foam between them , so its claimed to be unsinkable ? : there are three fitted lockers , all with locks fitted , so that I can leave Boating Items , on board , but secured , fitted drain holes to self drain , a proper seat for me plus a screen on the console , with a Wheel and remote OB controls , plus (of course) a Dead Engine Switch on a lanyard : So hopefully THIS year I will again enjoy my Boating Calendar : Hopefully {# So with sufficient engine power I hope to be independent of much Tidal , Current , Wind influence , which should mean that if I need to get ashore quickly etc I am able to do so , Flatish vee bottom on the hull means that I can beach her easily and safely : I only need the known speed to not annoy the Harbour Staff often , get ashore quickly if required plus of course to get an ETA of arrival anywhere : I could of replaced the Speed Sensor Tube on the stern , but they are vunerale to beaching etc . Thats my story Thank you