Paddle wheel logs

[Howardnp]

I have currently got my boat out of the water and I'm in the process, amongst other things, of upgrading electronics etc.

The boat has a paddle wheel log (working) and the question is:

If I'm using a chartplotter/gps do I need to leave the log in place (another hole through the hull) or not?

I realise that it's a back up but what are the thoughts on this?

Thanks

 

[Firefly625]

Chartplotter obviously gives speed over ground. Your log gives speed over water, something that I want to know, I think the slower your boat is the more important tidal streams are to help progress as in our case. I guess if you have a fast boat it becomes less important. I seem to remember when this subject was discussed a while back I was in the minority.

 

[wongaero]

It depends. Would you like to know your speed through the water?

Edit - Reason: On reflection my post looked a bit grumpy
It's helpful to have both the paddle log and the gps reading, so as not to break the speed limit, if you have that sort of boat (leaving aside for the moment the increase in general happiness when motorboats stick to hull-speed in confined spaces) .
It is nice to be able to roughly calculate the rate of the tide for comparison with what was expected from the, ahem, detailed passage plan too.

 

[Hurricane]

Not used our paddle wheel for about 6 years (and thousands of miles).
Still connected but the sensor is hanging up in the engine room.

 

[Firefly625]

Not used our paddle wheel for about 6 years (and thousands of miles).
Still connected but the sensor is hanging up in the engine room.

In the med probably not necessary!

 

[Whitelighter]

In the med probably not necessary!

Id like mine to work but its full of gribblies

 

[jrudge]

All my plotters and gauges show gps speed. The plotter will know the paddle wheel speed but I cannot really see any purpose in knowing it. They also get stuck.

I am in the med now but my last boat was in La Rochelle and I never used it then. GPs is reliable and accurate

Just my view

 

[Robin]

All my plotters and gauges show gps speed. The plotter will know the paddle wheel speed but I cannot really see any purpose in knowing it. They also get stuck.

I am in the med now but my last boat was in La Rochelle and I never used it then. GPs is reliable and accurate

Just my view

Yes but does not measure the same thing. GPS gives SOG (speed over ground) paddlewheel gives speed through the water, The two are only the same in zero tidal/current flow. If you do 25kts through the water going upstream against a 5kt current your GPS SOG will read 20kts even though your paddlewheel boatspeed will read 25kts.if you head down river the boatspeed will still be 25kts but SOG will read 30kts. THe difference matters most if navigatiing orpassage plannng in tidal waters, especially with tidal flows that change both in speed(rate) and direction (set). It is more obvious in slower vessels.

 

[oldgit]

Give it a clean and just leave it alone.Its perfectly happy where it is.

 

[Piers]

I have currently got my boat out of the water and I'm in the process, amongst other things, of upgrading electronics etc.

The boat has a paddle wheel log (working) and the question is:

If I'm using a chartplotter/gps do I need to leave the log in place (another hole through the hull) or not? I realise that it's a back up but what are the thoughts on this?

Hi HowardP. The speed from a paddle wheel is of use in one key situtaion if you ever might use your radar's MARPA. If you are travelling slowly (sub-plane), you certainly need the paddle wheel speed through the water for better accuracy for the MARPA calculation. This becomes even more important if the boat is subject to tidal flow and/or windage. To have any where near accurate MARPA information you need boat heading (not COG) and speed through the water (not SOG). This is called being Sea Stabilised in radar terms. Without this, the error for MARPA can be considerable. Instead of using MARPA use your mark 1 eyeball if you can see the vessel to judge if its on a constant relative bearing to your boat from which you'll know if avoiding action needs to be taken. If you can't see the other vessel, use the radar's EBL (and trails if your have them) on your radar which is in effect, the eyeball substitution.

There have been radar assisted accidents when trusting MARPA with GPS inputs. Try Googling for 'Sea Stabilised Radar'.

After attending a Robert Avis radar course, I wrote an article for MBM which I reproduced on my website: http://www.playdeau.com/radar-assisted-collisions-and-marpa/

All the best.

 

[NoviceRod]

I think it is useful, but not essential to have speed through the water from the paddle to compare with speed over ground from the GPS.

However, the paddle does get growth on it, and it becomes slower until it eventually stops until liftout and a clean.

So might as well leave it, and get what use you can from it.

 

[rafiki_]

Ive never been convinced of the accuracy of the paddle wheel, and it is annoying when it stops working due to crud. I hate to have things not working on the boat��

 

[john_morris_uk]

Ive never been convinced of the accuracy of the paddle wheel, and it is annoying when it stops working due to crud. I hate to have things not working on the boat��

Do some measured miles and you might be surprised how accurate logs can be.

Keeping it clean isn't difficult.

 

[Piers]

I've always used a water based anti-foul paint specifically for transducers and logs which I've always bought from:

BT Marine (Electronics)
Unit 11, Falmouth Yacht Marina
North Parade
Falmouth
Cornwall TR11 2TD

t 0800 612 6731 or
0044 1326 312444
sales@sea-kit.co.uk

 

[Firefly625]

Id like mine to work but its full of gribblies

I bet it does, bad enough in the solent, in the med i bet they pack up in a week. I take mine out regularly to give it a clean, but in the Med I would think you would need to leave it out and only put it in when you go out.... however that would be a bit if a faff and in the Med....not so important.

 

[Wavey]

I take mine out regularly to give it a clean.

Mine's packed up too due to growth. Never been brave enough to try and take it our while the boat's afloat though.

Annoying when it's not working. It's only then you realise how much you refer to it. SOG is ok for some things but for others I rely on the log.

 

[Firefly625]

It's a easy job, done it for years. You should have a plug around to screw back in its place, you get a little water in when you first unscrew the log and withdraw it, but there is a flap on the inside of the through hull fitting that flops down to reduce flow of water into the boat quite dramatically. Then you screw in your plug. Give the log a clean and pop it back in. 5 min job and your log works again. When I do it I get in probably 1 sponge full of water, soon cleaned up.

Important thing is don't panic and cross thread the plug or log, take your time, honestly there is nothing to it.

 

[Wavey]

Many thanks. I didn't realise there was anything to restrict the flow of water. I'm feeling much braver about doing it now. Just need to find the plug/cap.

 

[Firefly625]

Just a warning that there is a split second when you withdraw the log and before the restricting flap drops down that seawater will come through the open hole with a spurt, but that is it.

A wooden plug would fill the hole if you can't find correct fitting.

Just a further warning, AFAIK the restriction flap was introduced probably early 90's, so older boats you have to be a bit quicker with plug

 

[aquapower]

Just need to find the plug/cap.

In the factory they would fit plug in clips next to where through hull fitting is.