Correcting gear ratio with prop size

[jimmbo]

Yes your boat is goung to go faster as it goes with the current and the gps will show that speed, but your boat is not going faster than what the gps shows!

It will be going faster than what the GPS states when you are going against the current.

 

[QBhoy]

It will be going faster than what the GPS states when you are going against the current.

I need to get me a top speed run in the sea or a river one day…might break the magic 70 once and for all, with the campion. Tell me I haven’t spent all that money on props in the quest..and this is all I had to do, haha. There are 10-15 mph tidal runs not far from me. Might break 80

 

[jimmbo]

I need to get me a top speed run in the sea or a river one day…might break the magic 70 once and for all, with the campion. Tell me I haven’t spent all that money on props in the quest..and this is all I had to do, haha. There are 10-15 mph tidal runs not far from me. Might break 80

You gotta do what ya gotta do

 

[QBhoy]

You gotta do what ya gotta do

Haha. All this bloody money wasted and years spent…

 

[airshot]

It will be going faster than what the GPS states when you are going against the current.

The gps will read the actual speed of that craft no mater current, wind or anything else. It is measuring time and distance between points of reference!!!

 

[jimmbo]

It will report the Speed over the bottom of the river, not the speed in regards to the water, if there any movement of the water. Hence in a current of 5mph, a GPS will report a 10 mph difference in the speed depending which way the boat is going

 

[airshot]

It will report the Speed over the bottom of the river, not the speed in regards to the water, if there any movement of the water. Hence in a current of 5mph, a GPS will report a 10 mph difference in the speed depending which way the boat is going

With all due respect, you are incorrect, not only have I tested this on numerous ocassions, but my nephew is a navigator on a nuclear submarine and is considered an expert on GPS systems. This has been discussed in past seasons and confirmed. A satellite gps system measures the speed of your vehicle by measuring the time between measuring points. You can believe anything you would like, but for the benefit of others reading these posts, your gps is the most accurate way to measure speed and is not affected by wind, current or any other background movement.

 

[jimmbo]

Speed over the top of the water will be different the speed over the Bottom, because the water itself is moving. GPS is measuring what speed is over the Bottom

In the example below, lets assume the water pressure speedo is accurate
Boat speed of 35 mph on a water pressure speedo, going with a 5 mph current, GPS will report 40 mph
Boat speed of 35 mph reported on a water pressure speedo, against a 5mph current, GPS will report 30mph

 

[QBhoy]

To settle an argument . Speed over ground and speed over water, are two different things entirely. That’s why most speed records are either taken over two runs and either ways, or from two points alternatively perhaps. If you want accurate (as reasonably achievable) speed through the water, it’s a calibrated paddle wheel you’re after. If you want speed over ground, it’s gps. I use both to be honest. I’d also add that I mainly find myself in an inland Loch with negligible movement that will affect such things. its gps I mainly use and the paddle wheel is calibrated to that.
But when I’m on the old man’s boat in the sea…here on the west coast of Scotland, there are infamous and staggering tidal flows on occasion. Even whirlpools ! Always blows me away, the difference between speed through the water and gps. There are one or two places here, where the likes of my outboard cuddy, could be just about on the plane, doing 14/15 mph through the water, but absolutely zero or close to it, over the ground on gps. I suppose that’s where such things are most relevant perhaps.

 

[Texasmark]

GPS: GROUND Position Sensor!

 

[QBhoy]

GPS: GROUND Position Sensor!

Haha. Had a wee chuckle to myself there. Here is me thinking it’s Global the g stands for

 

[Texasmark]

Haha. Had a wee chuckle to myself there. Here is me thinking it’s Global the g stands for

Yeah but adding Ground helps one get the idea as to what it actually does, not what it is....grin.

 

[Scott06]

Haha. Had a wee chuckle to myself there. Here is me thinking it’s Global the g stands for

according to the FAA it is global but what do they know …

https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/gps/howitworks#:~:text=Satellite%20Navigation%20is%20based%20on,operated%20by%20the%20United%20States.