Speedo Adjustment

[cbavier]

Is there any way to adjust my speedometer to correct it. Mine reads 48 mph while GPS says 54 mph. I'll try to post a picture of the little white spedo pickup. Couldn't get the picture to post so here's the link. Thanks



http://s244.photobucket.com/albums/gg15/cbavier/?action=view&current=BoatTransomeBeforeOWN-IT.jpg

 

[rrhodes]

Re: Speedo Adjustment

I think those are always off. I use mine as a reference but the GPS is the only way to determine speed. Current also comes into play. Turn around and it will say something else.

 

[Bigprairie1]

Re: Speedo Adjustment

I think adjusting it might be doable but difficult.
How does it read in comparison to the GPS at intervals of 10mph? (ie: 10/20/30/40mph?).
If you can get an idea if it is a linear error then you'll know how much you're out always. It looks like you are under reading by about 12%-ish right now. Is it the same error at say...25mph? or ?
If you know that error that might help you adjust the speedo...if it is possible.
Might be a fun project to at least try...but keep track of your original settings in case you mess up.
Good Luck
BP

 

[cbavier]

Re: Speedo Adjustment

It doesn't begin to register until I reach about 10-12 mph. I don't remember at say 25mph. How would you adjust it? Move it up or down? Another question. Do the spedo's with the little paddlewheel seem to be more accurate?

 

[Mischief Managed]

Re: Speedo Adjustment

I heard you can simply enlarge the hole in the pitot to make it read higher. Your's might be partially clogged though, so I'd remove to tubing from the back of the spedometer and force compressed air down it to clear any obstrcutions, before you enlarge the hole.

My pitot speedometer is more accurate than my paddle wheel, according to my GPS.

 

[cbavier]

Re: Speedo Adjustment

I heard you can simply enlarge the hole in the pitot to make it read higher. Your's might be partially clogged though, so I'd remove to tubing from the back of the spedometer and force compressed air down it to clear any obstrcutions, before you enlarge the hole.

My pitot speedometer is more accurate than my paddle wheel, according to my GPS.

Does mine have a hole or does that plastic thing just move up/back from the force of water as the speed is increased? I was wondering if the paddle wheel was more accurate. It's no big deal on accuracy for me but I do wish it registered at the slower speeds. Thanks.

 

[Silvertip]

Re: Speedo Adjustment

The white plastic pitot at the back of the boat has a tiny hole in it that faces forward. Water pressure in that hole compresses air in the tube which tries to uncoil a bourdon tube in the speedometer head. Because pressure is involved, the speedometer will not register until you reach 10 MPH or so. If you look at how the numbers are layed out, some speedometers have them evenly spaced around the dial while others are closer together on the low end and then spread out on the high end. The first type would be a linear speedo and other non linear. Doesn't make any difference though which type you have. If you enlarge the hole in the pitot to correct the top end of the speed range, you screw up the bottom end. There are no adjustments on mechanical speedometers. Paddle wheel speedometers are generally more accurate but that's not always true either. If you have a fish finder, it normally includes a paddle wheel speed capability.

 

[cbavier]

Re: Speedo Adjustment

Ok Thanks Silvertip. I will just leave it alone. I have two fish finders but neither have speed reading capablilty.

 

[Hit It]

Re: Speedo Adjustment

I've been told that the paddle wheel type speedos are more accurate at slower speeds, that's why they're used with fish finders - good for trolling speed. However, I don't think they're as good at faster speeds.

 

[reelfishin]

Re: Speedo Adjustment

If you need an accurate speed reading, you can install one of these, but their a bit pricey.

I've pretty much never worried about my exact speed in a boat, I get the boat up on plane, level it out and cruise, when trolling, the fishing determines what speed I need to be at. I have a paddle wheel type sender on my fish finder, a pitot type sender that came with the boat, (reads about 10 mph high), and a GPS unit that can give me accurate speed.
I rarely look at any of the speed info, just distance traveled, fuel remaining, and location. Knowing my exact speed has never been a high priority to me.