Erratic Speed Reading

M

mawyatt

New Member
Dec 13, 2007
1,001
Clearwater, Fl
Boat Info
2008 Sundancer 38DA
Engines
8.1L Mercruisers
I sometimes get erratic speed readings at low speed. I believe this is due to the speed sensor that's located with the Smartcraft depth transducer. Someone mentioned that the speed sensor can be cleaned? How is this accomplished?

Thanks,
 
Erratic slow speed readings is usually due to slime on the speed sensor. You can go under the boat and clean it, but most are removable from the engine room if you have the plug to go with the transducer mount. In my case, you pull a pin and pull the transducer out then insert the plug and re-pin it. The transducer or speed wheel is easy to clean with a tooth brush, etc from the engine room if you have access.

It can be kind of scary to pull the transducer out.........some let a lot of water in until you insert the plug. If in doubt, wait for your next haul out and do it with the boat in the slings to learn how it all fits together.
 
Frank,

Thanks. I have seen the plug, it is attached to the transducer with some SS wire. I guess I could ask the diver that cleans the bottom to try and clean the sensor. If he can't then I'll have to try and remove the sensor myself.

Now here's an off topic question? Since you live in Tenn an Panama City are you a Vols, Seminole or Gators fan?

Cheers,
 
On my 2005 340, the transducer is held in by a plastic ring that is threaded. Loosen and remove the ring while holding the transducer in. Get the plug ready. Pull the transducer and replace with plug. Screw the retaining ring in loosely. Clean paddle wheel. Then replace the transducer using the same procedure. Just like Frank said.

As a new inboard owner, I did this after owning my boat for just a short period. It's kind of a gutsy move, the first time. You might keep a helper nearby to run and get a tool if you need it while you keep your thumb in the dyke, STS.

On a related note, take this opportunity to re-program your SmartCraft (I assume yours is similar?) to take the speed from the GPS starting at a very low speed (5mph is the minimum on mine). The only draw back to this is that you lose the redundancy of having the speedo on the paddle wheel (SOW - speed over water) and the GPS displaying SOG (speed over ground). The only time the redundant info is worth a dang is when the paddle wheel (and bottom of the boat - turbulence...) is perfectly clean and free spinning. There are times when I miss the paddle wheel readout, but I have never missed having to clean that dang thing all of the time.

I understand that there is a replacement transducer that measures the speed of the molecules going by electronically. That one may be worth having, but I don't know of anyone who has one.
 
Mike,

Spending about equal amounts of time in both TN and on the coast, I have learned not to take sides, or even discuss football. It is suprising how insane otherwise intelligent people can become about both Vol and Gator football.............I figured I'd get one house or the other burned down if I picked sides.

Truthfully, we spend most of our free time on the boat, getting ready to boat, cleaning up from boating, fixing stuff that doesn't work on the boat or needs maintenance on the boat.......add kids and grandkids to the mix and I may have time for one Titans game a year on TV.


John,

Using the SOG output from your GPS does save relying on the speed wheel/transducer but it also introduces some inaccuracy due to winds and currents into the speed input as well as the time lag for the GPS computation.

And, the electronic speed sensor isn't a very good approach. We have B&G electronics on our boat that came with a speed sensor. It never worked satisfactorily and we had it changed to a speed wheel. The problem isn't the technology but that the speed sensor must read thru the hull at a constantly varying surface.......flat smooth, lite chop, lite chop with wind, spray, but suprisingly, it was most accurate in heavy seas. Bottom line, here is if someone will install it for you with a money back guarantee if it doesn't perform, give it a try, but I wouldn't spend the money on a gamble.

I understand the electronics wholesaler for Sea Ray in Florida has about 500 of them on the shelf they had to remove from boats.....bet you can get a steal on one or 100.
 
fwebster said:
Spending about equal amounts of time in both TN and on the coast, I have learned not to take sides, or even discuss football. It is suprising how insane otherwise intelligent people can become about both Vol and Gator football.............I figured I'd get one house or the other burned down if I picked sides.
Click to expand...

Frank I can't believe you said the "G word"..........:smt043
 
fwebster said:
Mike,

John,

I understand the electronics wholesaler for Sea Ray in Florida has about 500 of them on the shelf they had to remove from boats.....bet you can get a steal on one or 100.
Click to expand...

That explains why I don't know anyone that has one. Even with the limitations we both note above, I prefer GPS speed above 5 mph. The lag is almost undetectable, except when accelerating onto plane, and even then it's not bad.

Go Gators!!!!!!!!!!!! Hey, they have my daughter, and my money, and therefore any upgraded boat I may have wanted.
 
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A paddle-wheel sender will not provide accurate SOG when running in a current, which is why I don't see their practical use since the advent of gps. There's two old ones that were on my boat (I believe one is B&G and another Datamarine), but saw no reason to use them as I get more accurate SOG data from the gps.

Am I missing something?
 
tobnpr said:
A paddle-wheel sender will not provide accurate SOG when running in a current, which is why I don't see their practical use since the advent of gps. There's two old ones that were on my boat (I believe one is B&G and another Datamarine), but saw no reason to use them as I get more accurate SOG data from the gps.

Am I missing something?
Click to expand...

Yes. GPS speed is displayed on the GPS display. Paddle wheel is displayed on the Speedo. Let's say they both work well. Speedo says 25 and GPS says 20 - you know you have 5 knots of current. Now, let's say you make your speedo read GPS, which I like, because I hate watching it not work right. You lose the ability to compare one to the other.

So, I'm cruising the ICW and my instruments show me .8 mpg, but I want to be getting .9. If I could compare, I could tell in an instant that the current is 3 knots and that's costing me more than 10% fuel economy. Without the compare, I speed up a little and check, then I slow down a little and check, then I go back to the sweet spot and figure that there must be current of 2 or 3 knots, because I'm getting .8 and not .9.
 
mawyatt said:
I sometimes get erratic speed readings at low speed. I believe this is due to the speed sensor that's located with the Smartcraft depth transducer. Someone mentioned that the speed sensor can be cleaned? How is this accomplished?

Thanks,
Click to expand...

I had a similar issue on our 320 - but it turned out to be a broken wire. While the factory was zip tying all the various bundles to the engines - the speed transducer wires were cut and as they touched I would get a reading - when broke - it was a zero read. Seemed to be a low speed problem as well - but that was more due to general movements while underway. When I spliced and retaped - problem was fixed - this was only temporary as I had it serviced under warranty.
 
Hampton said:
That explains why I don't know anyone that has one. Even with the limitations we both note above, I prefer GPS speed above 5 mph. The lag is almost undetectab le, except when accelerating onto plane, and even then it's not bad.

Go Gators!!!!!!!!!!!! Hey, they have my daughter, and my money, and therefore any upgraded boat I may have wanted.
Click to expand...

Have my youngest daughter (soph) at Florida as well. Went to the pep rally last Sunday, 42,000 showed up. My daughter was in the picture in the paper with Tim Tebow high-5ing students!! They graduated every possible senior on the team, everyone that was a senior graduated...no holdbacks!! I want to go back to school at Florida (hope no Bulls read this I'm a Adjunct teaching engineering grad school at USF (went there many years ago)).

As Tebow said "One more time!!!" Go Gators!!!!
 
mawyatt said:
John,

Maybe only to us Gator fans!!

How much water did get in when you unplugged the sensor?
Click to expand...

it wasn't much fun watching his backside run away...(or the stupid offensive coordinators play calling on the goal line) that's for damn sure.. :smt001


I'm curious about the water inflow as well.. I need to pull a couple of my tranducers and check them.. Does the speed one have the arrow on top of it.. (or maybe that's just for this brand)
 
Hampton said:
That explains why I don't know anyone that has one. Even with the limitations we both note above, I prefer GPS speed above 5 mph. The lag is almost undetectable, except when accelerating onto plane, and even then it's not bad.

Go Gators!!!!!!!!!!!! Hey, they have my daughter, and my money, and therefore any upgraded boat I may have wanted.
Click to expand...


"you keep your thumb in the dyke"

yuck, that just read strange! ;-)
 
found this little gem doing a search on another matter but it sort of answered the question. http://clubsearay.com/forum/showthread.php?t=7923&highlight=ac+water+flow


If I remember correctly, my 380 DA had a flapper on it so when I pulled the plug, it really didn't have much water come out.... I think my 480 DB has a flapper on either the transducer or the paddle wheel... I forget which... The first time I pulled the plug that didn't have a flapper on (480 DB), the water came up so hard it hit me in the face and knocked me backwards on my ass... by the time I got the plug ready (I fumbled it) I had 3-4 inches of water in the bilge... amazing the pressure 4 feet under water... It made me realize that a 2-3 inch hole 3 feet below the water line could sink the boat.

It sorta gave me that feeling when I cracked a keel/hull joint in a sailboat hitting a sandbar and had to beach it to keep it from sinking (many years ago)... I think I need to find a different hobby...

__________________
Gary
 
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Larry&Leisa said:
it wasn't much fun watching his backside run away...(or the stupid offensive coordinators play calling on the goal line) that's for damn sure.. :smt001


I'm curious about the water inflow as well.. I need to pull a couple of my tranducers and check them.. Does the speed one have the arrow on top of it.. (or maybe that's just for this brand)
Click to expand...


I might try it this weekend if I get enough guts to pull the plug!!

BTW, it was one of the best football games I've ever seen pro or college, lot more fun than when the Gators played Ohio State in 2006 (I recall the game was over just after the 1st quarter).
 
mawyatt said:
John,

Maybe only to us Gator fans!!

How much water did get in when you unplugged the sensor?
Click to expand...

I remember something about a flapper, but I don't think this one has one. It's been a while. There was not enough water to worry about. Maybe a quart or two? It depends on how ready you are and how fast you are. If you splash it around, you'll probably get more water in there rinsing it with a hose.
 
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