6,100rpm @ 67mph??? Hmmmm...with a 28p prop

[jayfaro]

I had something happen last weekend and i thought i'd explain the situation to you guys as i have asked a few guys on here privately. My Mom is pretty sick battling lung cancer so Fri was the first time i have had my boat out since last year. Cool air and water temps (60 air/52 water) and a full load of gear and fuel and 2 guys. the holeshot was a bit sluggish than i remember but i thought maybe because it's the first time of the year and i need to clear the fogging and winterzing crap out of the system and the holeshot got better each time i moved. Running down lake, 6,100 rpm and i look down anticipating 80mph. Regardless of the load, i have never not been able to run 80 with these bravos, i was shocked to see 67mph. My buddy who was with me said there was NO way we were only running 67. My RPM said i HAD to be running more than 67, the boat was all the way up on pad and running level. i sortta feel like an ***insert cookie cutter boat owner here *** right now..."I know GPS said 67 but i know was running 80". My motor was running great, no lean sneezes, no stalling, no missing, it ran like it always has. I'm hoping the GPS had a bad signal and that was cause. It got too rough later in the day to run around so i was only able to make 1 WOT pass. If i was losing a cylinder or had a motor problem, i dont think i would have been able to turn 6100. To me, i know what 80 feels like and i know was 67 feels like and i dont think there's any way this wasnt high 70's-80 mph. Ive just never heard of a speed problem from a GPS. LD mentioned possible low voltage to the GPS and i did notice each time i started the big motor, my Lowrance shut off. Any thoughts, ideas, etc? Don from European Marine wasnt too sure what to think. if i had an engine problem, i think the engine would have been running badly, but it was running great. i am ALMOST positive there was a GPS glitch, the boat was all the way up on pad, rooster tail was just at the top of the cowl, and the bow was running up and flat. i just dont get it.

[Gambler Bob]

Sorry to hear about your mother

Sounds like a GPS problem from what you are saying, or a battery problem possibly, you could try cleaning the battery teminals an making sure they are tight, have you checked your hub kit, is your prop nut plenty tight? Honestly i got no idea what might be wrong those are just some of the things that come to mind.

[Table Rock Special]

sorry to hear that Jay.

Luckily my prop guy has a Radar Gun, and all our testing is done with a Gun.
I personally don't trust a puck as far as I can throw it, hell the one on Dad's Z20 wasn't even fastened to the hull, just held there by the wires. Like that was going to read properly.
I think you're on the right track with Bad Battery.

Again, sorry about your Mom.

[low slung cruiser]

sounds like someone switched props with you, and you are running a 26bravo...lol...

[RiverRatMD]

Sad to hear that about your mom

You don't hear of many GPS speed errors, but a low voltage condition can cause strange things in electronics. We have the same boat. I know at 67 mph mine is effortless to drive, but at WOT at 6100 with my 28 Bravo that i'm paying serious attention. I am wondering how it'll go on your next trip out. If you really are only doing 67 gps, then your tach is incorrect. Take another GPS with you to verify your speed. A phone app or car GPS would serve that purpose. Good luck Jay..Prayers for your mom.

[jayfaro]

Thanks for all the well wishes and thoughts guys. i really appreciate it. Depending on what happens at my Mom's Dr's appointment tomorrow, i'll be buying a Sears Diehard Platinum Group34 this week....start with the stuff i know i need to replace and go from there. I still say that there was NO way i was only running 67 but anyone who lives up north where the water gets hard can attest that the first run of the season always feels like the fastest you'll have run all year! if thats the case with my boat, i should be run a wicked 58 mph come August!

[Steve M]

Jay sorry to hear about you mom, I'm going thru the same thing with my mother. She has been doing treatments off and on for 3 years now. Good luck Jay

you know now that someone else has mentioned this, I always thought my GPS was off. Max I have hit has been 72 and it feels like it's a bit faster then that. When I go to Cobby this year I will try the GPS on my phone

[Table Rock Special]

Could have swapped your GPS module with a Rangers

[Gambler Bob]

Could have swapped your GPS module with a Rangers

problem solved.

[Table Rock Special]

Swap it with a Triton's you might Triple Digits with that XB.

[low slung cruiser]

hey steve with the intimidator...
my dad had the exact same boat...
what prop are you running?

[Steve M]

I've run a 25 Tempest, 26 Trophy & a 28 Trophy. So far the 25 Tempest ran the smoothest, no chine at all but 3/4 throttle 70 gps hit the rev limiter. The 26 Trophy gets it to 72 and it gets real swirly. Both are great out of the hole. 28 slower out of the hole and gets swirly at 70

[low slung cruiser]

YOU HAVE SKIPPED THE BEST/FASTEST PROP for that rig...
go try a stock 27 trophy plus....YOU WILL see guaranteed minimum 76.5 GPS @ 5800 RPMS....80 degree water...

[Steve M]

Actually the Tempest is a 26 plus not a 25. I did want a 27 Tempest. For some reason the 3 blade gives the smoothest ride. LD suggested the 3 blade

[t_nipper_74]

I did want a 27 Tempest.

You need a 27 Tempest or a Fury prop. Hitting the limiter on your setup at 70 with a 25p is about where you should be. The best I got with my 25p A45 Tempest was 72 before the limiter. Sounds like the chine walk is putting a damper on your top speed with the other props.

[low slung cruiser]

THE REASON YOU HAVE CHINE WALK IS BECAUSE THE 4 BLADE is actually picking the rear of boat out of water...once you driver through that 3-4mph period it will smooth out and u will see a smooth ride....
TRY THE TROPHY in 27 pitch...TRUST ME...
2nd best is gonna be the 26 fury, but you may need to add some cupping to keep under the REV limit...

[Gambler Bob]

Jayfaro, i took my boat out today and noticed that my GPS is doing something that is very similar to yours, are you sure your GPS is reading in MPH, and not reading in KN. My GPS is not reading in MPH as of right now and but it would read MPH as KNs the best speed i got today was 67.6 KNs, i have no idea what KNs are. I do know that some speeds may be read in kilometers but i dont think that is what it is reading eithers because the abreviation should km for kilometers. My HDS 7 is also reading depth in meters also as of right now, i tried to figure out how to change the settings on the water but could not figure it out. Time for me to start reading the directions. I am sure it was not reading in kilometers because 67.6 kilometers is only like 40 MPH, i was going alot faster than that.

[hispeed]

Knotts

[Gambler Bob]

Knotts

Now i feel stupid, i should have known that.

Thats make alot more sense, 67.6 knotts is about 78 MPH, i could not stay at that speed very long in the chop on Lake Michigan today.