How many have had GPS errors?

[JR]

I got out of Church Late and decided to try a speed run anyway since the wind was dead calm and all the boats were coming in at the ramp. I left the ramp after dark and found my running lights were not working [they seldom do until I wiggle the bulbs]. Since it was a perfectly clear night and I did not really want to be seen, I kept going.

I then made the several of the fastest passes I have ever made since the tach [which was lit] was turning 7200 and the bow sudenly dropped down and just moving my left leg would throw the boat off balance [I removed the passenger seat].

I had about a 2 mile straight stretch from a 70 MPH start at the Timuquana Bridge [for the Jax Guys] to where the river makes a turn going towards Sandy Landing which was taking about 60 seconds. By the time I made several passes People were out on their docks trying to see what was going on. I beat it back to the ramp and pulled it quickly out of the water before some irate citizen called the Police.

The worst thing imaginable happened. I got a flshlight to read my Garmin 168 sounder's recorded top speed [it was not lit] and the GPS was reading 130.0 MPH [for real].

I was very agrivated to say the least, especially since the Garmin has never messed up before and I was dead sure that I had reached 100 MPH [My boat stays pretty close to 11% slip all the time and the tach was at 7200].

I am charging the batteries on my camera and I'll take a picture of the GPS so you can see it. Hopefully Kevin will let me post it as the fastest GPS reading on a Grandsport [even though it is bogus].

My Brother said it was wound tight when it passed behind his house and somehow knew it was me....


JR

 

[GFinch]

I'm glad you went to church. Whats that saying about, God, fools and dumb animals. Maybe the GPS reading was someone trying to tell you something.:smile

 

[whipper]

Thats very interesting! I was reading about something that might be interesting. I might get this mixs up so bare with me.It all depends on the direction your traveling.If your travelling down river at the exact opposite direction of the earths rotaion you will pick up speed. Kinda like walking in the opposite direction on a merrygoround. The rotation of the marygoround is were your speed is based and even with small steps it will give the elution of traviling farther faster because of the rotation under you.Some land speed guys use this and Nasa for picking the best time to run there equiptment like shuttles and salt flats cars. Most likely not the case but who knows. Thats funny I was just reading about that a few days ago. It can throw your GPS off but in fact acual speed is relevent to the velocity and time traveled over a given distance so how ever it happend may be its real!!?? Try it again and have two GPS on the go down the same stretch and a radar gun at your brothers for good messure. You were never the less at 105 if you were useing your new 32 at 7200 1.85 gears 10% slip!! James

 

[chad202]

My Garmin 162 did that but my Garmin 188 has not yet.

 

[hack02]

I've heard the gov't sends out some strange signals that effect gps around nuc. powerplants sometimes. Something about screwing with prospective terrorists.

 

[JR]

The river I was running was right in the approach to NAS mainside [where Kevin Mac works]. The aircraft on approach are only at about 200' when they pass over. It is quite possible the GPS was being "offset" especially on a crystal clear night like last night.
I am going to try for another night with the right conditions and another bag of lead shot [for balance]. Hopefully I can get a good reading, if not I will give up since, sooner or later, our Neighbors will have the Police waiting for me at the ramp.
The guys who are making A-boat speed runs [with big numbers] during the daytime with boat wakes and wind are a lot more of a "man" than I am. I could hardly keep the boat balanced and ANY steering input would cause the hull to tilt, touching the pad down, and generating wobble. When the nose dropped and the engine began accelerating [around 7K RPM] the hull lifted off and became very quiet on the almost glass-smooth water, losing the jackhammer sound of the pad. The Grandsport hull is too large with too much aerolift to really be easy to drive at high speeds. It felt like trying to do a 100% power landing in a really "light" airplane" for the other pilots out there.
The real secret would be to have a lot of HP to get it up there fast and then get back down before it has a chance to misbehave.
It was definitely a lot fun [but very hard] and I did pray hard before I went out.
BTW I spent all my teenage years [hundreds of hours] running WOT at night down these rivers so it is not as uncomfortable as it would seem...
JR

 

[fishnfireman]

I have had a Garmin and a Humminbird give bad readings but never that much. More than once I have had them read 10 mph high or low..which would be a 20 mph swing. Every time but once it was in rough water so I just figured that had something to do with it. The only other time it was reading fast all day long...I figured the border patrol must have had a drug flight comming in.. and were messing with em...........who knows !!

Jr ....I figure the only reason your still around is cause the good Lord has work for you to do !!! Man you sure do live awful close to the edge!! I can relate to being an adrenaline junkie....but DAUMMM son those floters are hard enough to see in good light.....sure hope the neighbourhood kids don't like to skinny dip after dark as much as I use to !! PLEASEEE be CAREFULL-- I don't think you could live with yourself if it cost a life..

 

[JR]

I was being careful and could have seen a swimmer on top of the water. There are also way too many alligators out there to swim at night. I could see the Crab traps even, but it was hard to dodge them without causing the hull to tilt, so I kind of just picked a line with no obstacles and let it go. Since I had the LASEK surgery on my eyes, my night vision is back to being fantastic.
The last time I drove a new SS2000 at 100 [during the day with wind and boatwakes], it was a walk-in-the-park, along with my Nephew's Mirage. The Grandsport is a whole different story, sort of like using "a screwdriver as a hammer". It would be easier if it did not accelerate so slowly before the nose drops.
I have not been that attentive to the controls since I made my first solo crosswind landing, which is good trianing for driving a grandsport [except the high groundspeed].

 

[Darth VMAX]

GPS's are not entirely accurate all the time. I found this out when my old Tournament partner had a 18'5 ft Cajun with a 150 Force that would run 75 mph on his GPS ! (?)

 

[Jimxb02]

Yes , a GPS can be off by a significant amount !!!!!

Last summer I got a reading of 108.3 on my Garmin when the true speed should have been closer to 98 with the load and prop I was running.

Jim

 

[GotMyAlly]

My old Magellan gave some erratic readings on a few occassions. Last year running down pickwick it was reading something like 118. My new Garmin hasn't thrown out any unrealistic numbers yet though.

 

[whipper]

This is on the other side of the gps reading but they also can read slow if you dont hold the top speed for I think it was 10+ seconds some times. The reason is the time it takes for the signal to bounce back depending on were the sat is sometimes. This is in my instructional booklet. I take it your pleased with the new heads in conjunction with Tonys ACU.:big grin James

 

[Yellowallison]

JR...... I don't do high speed runs or swim in MCGIRTS during the day must less at night for all the floatin log,turds,beer bottles, pieces of docks,etc must less at night..

Yu knwo all that crap out there!!

Go out in the big river and let r eat from tha Fuller Warren to Palatka..in 50 miles yu ought to get'r up to 100..

We test our Drag boats over behind the island underneath the Matthews late in the afternoons.. nobody never messs with us over there... matter of fact quite a few times the MP has eased around the corner and jus watched us..

Be safe and keep us posted if yu make 100:razz :razz

 

[JR]

Scott,
just don't tell anyone that I was the one out there, I don't need the Jax Marine patrol putting out an APB on me. I could not run that fast out there in the wider river [with ya'll], my hull has a real balance issue and a little wind or boat wake will knock it off the pad. I think the 32 pitch prop increases the crab and makes it harder to balance. It wasn't that bad with the 30 at 95 GPS before.
JR

 

[2fast4mom]

My Garmin read 233mph one time as the max speed. I do think the authorities impart an intentional error into the civilian side of the system when they think something is going on, or around bases or nuke plants as has been mentioned.

 

[LAAllison]

So you spent your teenage years running WOT but how fast was WOT 50 years ago?

 

[JR]

You are right, back then it was only half that speed, but we did not have the "hardware" that I have now.
I had removed the 40 HP Gale [an OMC] from my Dad's boat and put it on an aluminum Jon boat that was rated for 4 HP MAX. We never wore lifejackets and were way faster than the Marine patrol [with three people in it to make it balance out with the big motor]. We usually traveled at night on our adventures since the boat had no registration. The fun ended when I hit a boat wake in a blinding rain traveling WOT and split the bow. We had to beach it to keep from sinking and walked home.
This was just another Chapter from "REDNECKS R US".
JR