Speed Log out by around 3 knots - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > Electronics
 Not a Member? 
  #1  
Old 03-30-2012
Dufour 27 Newb
 
Join Date: Dec 2010
Location: Malta
Posts: 108
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 4
jaybeegee is on a distinguished road
Speed Log out by around 3 knots

My Nasa Cruiser speed log is out by around 275%! So when the display shows 2 knots my handheld GPS will show 5! Now I do understand that there is some difference between the speed over water but this is way off! The speed log transducer is of the standard paddle wheel type and fitted through-hull positioned in a correct location and with no obstructions. And whilst there is a calibration facility it is limited to +/- 50%!
Any ideas of what the problem could be?
thanks
J.
Reply With Quote Share with Facebook
  #2  
Old 03-30-2012
svHyLyte's Avatar
Old as Dirt!
 
Join Date: Nov 2008
Location: Tampa Bay Area
Posts: 2,558
Thanks: 11
Thanked 85 Times in 81 Posts
Rep Power: 6
svHyLyte is on a distinguished road
Re: Speed Log out by around 3 knots

Motor at a steady rpm up current for a measured mile--recording your time and the speed displayed on your log, reverse course, without changing your rpm and motor down current over the same distance again recording your time and the speed displayed on your log. Take your average time to determine your actual speed and compare that with the average speed reported by your log which will give your log error which can be adjusted out. Ignor the GPS which is meaningless with respect to speed through the water--particularly if, for example, your making 3 knots through the water into a 5 knot stream. Your GPS will tell you you're making 2 knots in reverse.

Alternately, buy yourself a "KnotStick" with which you can actually measure and calibrate your paddle-wheel knot meter quite accurately.
__________________
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
Reply With Quote Share with Facebook
  #3  
Old 03-30-2012
hellosailor's Avatar
Plausible Deniability
 
Join Date: Apr 2006
Posts: 10,423
Thanks: 1
Thanked 75 Times in 73 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Re: Speed Log out by around 3 knots

"when the display shows 2 knots my handheld GPS will show 5"
In other words, your waterwheel is VERY SLOW.

When is the last time you removed the impeller and cleaned it out? Sometimes you'll find enough growth in there to freeze it up in just a week or two. I'll pull the log whenever the boat is being left at the mooring, and if it has been left in, it gets cleaned (old toothbrush) picked (dental picks) and if there is barnacle crud on it, you may need to soak it in vinegar as well.

Before you decide something needs calibrating--pull it and see if it isn't just crud.
Reply With Quote Share with Facebook
  #4  
Old 03-31-2012
svHyLyte's Avatar
Old as Dirt!
 
Join Date: Nov 2008
Location: Tampa Bay Area
Posts: 2,558
Thanks: 11
Thanked 85 Times in 81 Posts
Rep Power: 6
svHyLyte is on a distinguished road
Re: Speed Log out by around 3 knots

Quote:
Originally Posted by hellosailor View Post
"when the display shows 2 knots my handheld GPS will show 5"
In other words, your waterwheel is VERY SLOW.

When is the last time you removed the impeller and cleaned it out? Sometimes you'll find enough growth in there to freeze it up in just a week or two. I'll pull the log whenever the boat is being left at the mooring, and if it has been left in, it gets cleaned (old toothbrush) picked (dental picks) and if there is barnacle crud on it, you may need to soak it in vinegar as well.

Before you decide something needs calibrating--pull it and see if it isn't just crud.
Amen.

Tho' it may sound odd, I have found that applying Neosporin anti-bacterial ointment to the paddle-wheel and inner faces of the transducer housing significantly extends periods between cleanings.
__________________
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
Reply With Quote Share with Facebook
  #5  
Old 03-31-2012
hellosailor's Avatar
Plausible Deniability
 
Join Date: Apr 2006
Posts: 10,423
Thanks: 1
Thanked 75 Times in 73 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Re: Speed Log out by around 3 knots

Zinc oxide (diaper cream or sunblock) probably would accomplish the same thing, killing critters without breeding antibiotic resistance. FWIW.

Knowing that our antibiotics are going to be useless when we still need them, that's scarier than sea monsters.
Reply With Quote Share with Facebook
  #6  
Old 03-31-2012
svHyLyte's Avatar
Old as Dirt!
 
Join Date: Nov 2008
Location: Tampa Bay Area
Posts: 2,558
Thanks: 11
Thanked 85 Times in 81 Posts
Rep Power: 6
svHyLyte is on a distinguished road
Re: Speed Log out by around 3 knots

Quote:
Originally Posted by hellosailor View Post
Zinc oxide (diaper cream or sunblock) probably would accomplish the same thing, killing critters without breeding antibiotic resistance. FWIW.

Knowing that our antibiotics are going to be useless when we still need them, that's scarier than sea monsters.
__________________
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
Reply With Quote Share with Facebook
  #7  
Old 04-02-2012
Dufour 27 Newb
 
Join Date: Dec 2010
Location: Malta
Posts: 108
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 4
jaybeegee is on a distinguished road
Re: Speed Log out by around 3 knots

Quote:
Originally Posted by hellosailor View Post
"when the display shows 2 knots my handheld GPS will show 5"
In other words, your waterwheel is VERY SLOW.

When is the last time you removed the impeller and cleaned it out? Sometimes you'll find enough growth in there to freeze it up in just a week or two. I'll pull the log whenever the boat is being left at the mooring, and if it has been left in, it gets cleaned (old toothbrush) picked (dental picks) and if there is barnacle crud on it, you may need to soak it in vinegar as well.

Before you decide something needs calibrating--pull it and see if it isn't just crud.
thanks for taking the time to respond. I have never removed the impeller and cleaned it out! But the speed log is easily accessible and I remove it after every trip. So I dont think the problem is dirt! But having said that, I will try and remove the impeller.
Reply With Quote Share with Facebook
  #8  
Old 04-02-2012
hellosailor's Avatar
Plausible Deniability
 
Join Date: Apr 2006
Posts: 10,423
Thanks: 1
Thanked 75 Times in 73 Posts
Rep Power: 10
hellosailor has a spectacular aura about hellosailor has a spectacular aura about
Re: Speed Log out by around 3 knots

If you can clean around the whole "paddlewheel" without temoving it, don't remove it from the "whole plug". But sometimes the wheel is just rotating on a drift pin that easily slides out, making cleaning easier. As long as you don't lose that pin!

No, its not lost, its safely stored in the bilge.
Reply With Quote Share with Facebook
  #9  
Old 04-02-2012
therapy23's Avatar
Back to just the Jon boat
 
Join Date: Jul 2007
Posts: 910
Thanks: 0
Thanked 5 Times in 5 Posts
Rep Power: 7
therapy23 is on a distinguished road
Re: Speed Log out by around 3 knots

I say pull the shaft too.

It doesn't take much growth of anything to slow it down.
Reply With Quote Share with Facebook
  #10  
Old 04-03-2012
Dufour 27 Newb
 
Join Date: Dec 2010
Location: Malta
Posts: 108
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 4
jaybeegee is on a distinguished road
Re: Speed Log out by around 3 knots

thanks for your replies.

please see here: Nasa Paddle Wheel and Spindle - Product Details
It seems that there is a spare part that exists (shaft + paddle wheel) so I guess it would be safe to remove the shaft if i can figure out how!
Reply With Quote Share with Facebook
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
MOB doing 20 knots in 30 knots + recovery AdamLein General Discussion (sailing related) 30 02-11-2012 12:53 AM
New World Speed Record: Macquarie Innovation breaks 50 - hits 54 knots PCP777 General Discussion (sailing related) 2 04-08-2009 04:45 PM
Have I Gone Knots? SEMIJim General Discussion (sailing related) 26 12-31-2008 12:52 PM
Russian VOR broaches at 30 knots boat speed VIDEO LINK Giulietta General Discussion (sailing related) 25 11-24-2008 09:34 AM
Knots bestfriend Seamanship & Navigation 1 06-21-2007 04:18 PM


All times are GMT -4. The time now is 04:21 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.