Hi all
I have B&G stuff on my boat including a Vulcan 9 in the cabin and a Vulcan 7 on the top of the companion way. I also have 2 Triton 2 displays at the helm. The triton display show a different boat speed than the 7. It's about 1.5 knots out.
Any ideas?
Select to expand quotePatto21 said..
Hi all
I have B&G stuff on my boat including a Vulcan 9 in the cabin and a Vulcan 7 on the top of the companion way. I also have 2 Triton 2 displays at the helm. The triton display show a different boat speed than the 7. It's about 1.5 knots out.
Any ideas?
Are they all displaying the same sentence? ie is one picking up GPS SOG as vs speed from a paddlewheel?
Hi Patto,
Are you instruments both measuring the same thing? If you have a gps and an impeller you have two speed Inputs;
a) speed over ground (GPS) or
b) speed over water (impeller)
The difference is usually current, but if your impeller is not clean the difference in speed will get larger.
Cheers,
SB
I agree with the above. I run two Zeus 3 plotters and three triton 2 displays. There are several inputs to give you a speed. SOG is calculated from the Sat input and SOW will be from the paddle wheel ( DST800 ), normally displayed as "boat Speed" (BSPD on the Triton 2).
Yes I agree with Sydchris and Shaggy, likely reading two different things and the paddlwheel is often different to the gps SOG due to either current or growth on the wheel. Reminds me I must pull mine out and give it a clean, it was way off last time I was out.
Question: when under way, TWS is calculated using AWS, course and boat speed I believe. So if this is the case, is boat speed being taken from the paddlewheel or gps SOG?
Select to expand quoteboty said..
wow way above my pay grade im just happy if the boats going forward
and the breeze in your hair (?)
Select to expand quote2bish said..
Yes I agree with Sydchris and Shaggy, likely reading two different things and the paddlwheel is often different to the gps SOG due to either current or growth on the wheel. Reminds me I must pull mine out and give it a clean, it was way off last time I was out.
Question: when under way, TWS is calculated using AWS, course and boat speed I believe. So if this is the case, is boat speed being taken from the paddlewheel or gps SOG?
That question still catches me every time, as instinctively I'd say SOG, which is incorrect, unless you are lucky enough to sail in zero current or tide. If like the rest of us mere mortals you contend with current or tide, use SoW (impeller) as the input.
The reason being is we sail in a boundary of wind and water, and it moves together. How fast the seafloor is moving under that mass is irrelevant to sailing the boat. Your TWS and TWA, VMG, polars, max speed, all of that is referenced to the boat moving through the water, not the land.
For example, you don't get to claim a new max boat speed of 18 knots because you left Darwin Harbour at the turn of a flood tide!
SoG is good for passage planning or checking your eta, as you are now referencing to fixed points on land. That's logical, as land doesn't move.
Hope that makes sense. Or it probably just helps confuse the issue even more.....
Cheers!
SB
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1.5kn is a big difference even with tide. (Unless you live in Darwin) My guess is the 7 is reading SOG and the display is reading boat speed. The first thing I would be checking is the calibrations, then see how you go. To get the best out of your instruments, you need good calibration of speed, wind and compass
As well as growth on the paddle-wheel I have found that fouling on the hull forward of it can affect the accuracy. Cleaning a couple of feet forward helps (if you're not in the mood for a complete scrub). All to do with laminar vs turbulent flow I guess.
Logs can be calibrated and errors can be there/added/fixed. Some time back dubious boat brokers discovered that they could add a knot onto a boats boat speed indicator so prospective buyers would look and go wow what a fast boat and boost their chance of a sale. Even an app on your phone using GPS is a bit safer if you really want to know the real speed.
I use this one play.google.com/store/apps/details?id=com.VirtualMaze.gpsutils&hl=en_AU its not specifically for boats and probably sends spy information back to Russia, but is free, easy to use and works great
