Craeting a route on a plotter

DoubleEnder

DoubleEnder

Well-Known Member
Joined
27 Apr 2002
Messages
1,563
Location
N Hemisphere
Visit site
My new home berth is at the head of a very very drying creek. At the right state of tide there is enough water for me in the deepest part of the creek, but the margins for error are small, and the consequences of getting it wrong would be embarrassing at best. I was thinking of taking the dinghy and going down the creek at near low water, with some sort of portable device, and creating/recording a route that I could then use on board the boat. I can back this up with transits.
Any good suggestions for a suitable, hopefully inexpensive portable plotter? On board I have an SH180 but I am not really looking for connectability.
Thank you
 
gdallas said:
My new home berth is at the head of a very very drying creek. At the right state of tide there is enough water for me in the deepest part of the creek, but the margins for error are small, and the consequences of getting it wrong would be embarrassing at best. I was thinking of taking the dinghy and going down the creek at near low water, with some sort of portable device, and creating/recording a route that I could then use on board the boat. I can back this up with transits.
Any good suggestions for a suitable, hopefully inexpensive portable plotter? On board I have an SH180 but I am not really looking for connectability.
Thank you
Click to expand...

Though GPS today is very accurate I would not rely on such a track for the kind of tight pilotage you appear to have, a list of transits is probably your best bet.
 
At best I get +/-2m but more usually +/-5m

Mark one eyeball would be my navigation aid of choice on this one.
 
Maybe set up your very own perches - not sure how you could drive them into the seabed though. Alternatively you could maybe buoy it, my old yacht club (LYC) bouyed the Rock channel between the Mersey & the Dee.

Also not certain if you would need any permissions
 
Totally agree that from the way you describe it, GPS (wonderful though it is) might not be accurate enough; it depends on how tight is tight! But remember that quoted accuracies aren't maximum errors; they are standard deviations and you will be outside them 35% of the time, and more than twice outside them 5% of the time (roughly!).

Could you place withies (or even garden canes) from an inflatable dinghy? You could use a long cane as a sounding pole, with the depth you need marked on it. If the mud is soft, you might need to put some sort of shoe on the bottom of the sounding cane to stop the cane penetrating the mud.

I guess they'd need checking after Spring tides or storm surges, but you'll have to do that anyway, whatever method you use.
 
When I had that problem, (I had to go through an 'S' bend that wasn't visible at HW), I used a Garmin Etrex to record my footfall at LW. Never failed me but I did move mooring before it did!

I did discuss putting in some withies/canes/tethered fenders to mark the channel with a fellow moorer but we just didn't get round to it. The tethered fender would have had a cane strapped to it and weighted at the other, think along the lines of a pot marker.

Those days are gone now.. Got a fin keel
 
I have navigated the upper reaches of my local semi-drying river many times in both the dark and bad visibility by following a previous successful track on my SH CP300i plotter. I have never had any problems and found it extremely accurate. I just keep one eye on the plotter and the other on the depth. I had a bilge keeler and frequently navigated with only inches under the keels. Go slowly so if you touch bottom you can easily reverse off and try again.
 
Storyline said:
Also not certain if you would need any permissions
Click to expand...

Unfortunately the last government brought in a system of marine planning permission, explicitly based on the land version, which requires permission for anything left in contact with the seabed.

In practice, because this is a new law that doesn't match what people are used to on the water, the chances are that nobody is going to take exception to some perches or small buoys up a backwater creek.

Pete
 
A physical system of marks is probably best. As an alternative to channel markers and if the distances are small and the surrounding land is rural then maybe you could set up small cairns or even sticks with dayglow paint as transits. This system is used widely on the Scottish west coast. Sometimes the pairs of cairns (whitewashed) are only a metre high and can be seen from quite a distance. If you are dealing with smaller distances then you could get away with a much smaller mark.

Should you decide to go down the electronic route I can recommend the inbuilt GPS in the Motorola Moto G phone. Recently used this with the Antares ultra large scale charts and the accuracy was extraordinary - down to within 2-3 metres or so. Used Memory map charting but the tracks dissappeared after a while.

Also bear in mind that the accuracy of gps can be reduced by solar activity. For example, yesterday the K-index touched 4 and it would be a bummer to arrive back only to find the gps was not reliable.
 
There are some high-tech but expensive solutions to what you require. You could install an IMU (inertial measurement unit) on your boat (very very expensive!). I have one on the survey plane that I fly, and it is accurate to within a couple of cms. Alternatively, you could install a GPS base-station somewhere near the creek. You would need help from a professional surveyor to set it up. Once set up, your boat GPS would be accurate to a few cms too.
 
Storyline said:
As an alternative to channel markers and if the distances are small and the surrounding land is rural then maybe you could set up small cairns or even sticks with dayglow paint as transits.
Click to expand...

I was browsing through the Pilot the other day and it talked about somewhere down west where the local fishermen tie carrier-bags in the bushes as transits!

Pete
 
You must log in or register to reply here.

Share this page

Top