Different Prop slip numbers each time I go out!?!?
 

So I have my new 406 in the boat, runs great, everything is great with it. But my prop slip numbers are not consistent at all. At WOT... one day its 15%, next day 22%, another 18%.... why is this? rpms are pretty much always where they should be at 5200-5300 at wot. MPH is off... of course...

Running a laser 2 25p. Could the blade area be too small? Go to a mirage+ perhaps? I'm getting 65-72 mph with this prop.

Also... when coming on plane, which take longer then I think it should. The rpms will surge up too 4000 and then go back down too 2500.

Any insight or help would be very helpful... I fellow boater in my area said I could try his 23p mirage+ if I put a 300 deposit down for just in case break it you buy it situation.

what are you using to measure the speed? seems like that is the problem.

Using my GPS on my phone...

any big currents or tides that could be affecting the speed? if not i would find something else to measure the speed with, the prop, motor, drive, & rpm are all the same from one run to another and of those only the rpm could vary so i think the phone is the problem. Also assuming your load was similar on each run, unless you had 1/4 tank and you were alone and the next run was full tank and 6 people the numbers should be the same or close.

Are you changing the amount of gear, people, fuel, each time? That makes a big difference especially in a small single

Im on a inland lake... no currents or anything... But I did fill up my tank which is in the bow, so another 180lbs(25 gallon tank). Im going out today to give it another go with my buddys Garmin gps... see what happens. I would still like to try the mirage+ 23p... My cam can spin up too 5900 and Im only getting 5200.

Water in fuel?

Phone GPS (in most cases) are not true GPS. They use tower triangulation not actual GPS. So depending on your cell signal, it could be all over the map. Now with that being said, my iphone was within 1-2 MPH of my real GPS, but I have full solid signal on the Detroit river (where I tested it). Now if I took my boat out to lake Erie, I would bet my iphone GPS would be all over the map because of the limited Cell signal. Get a real GPS and check your numbers.......

In your first post you stated your RPM has been where it should be each time out but your slip numbers have varied by 4-7%. That would equate to a few MPH, right?? So I would lean toward inaccuracy of your "gps" because it is using tower triangulation.

"Also... when coming on plane, which take longer then I think it should. The rpms will surge up too 4000 and then go back down too 2500" Does you prop have a difuser ring? I had a hydromoive prop that did not have the ring. I called hydromotive because I had quite a bit of blow out while planing and was told that is because of the missing difuser ring.

Slight differences in drive trim could cause this

Fuel in a bow tank will have a big impact on speed. With a full tank, your bow will not lift and you will have more wetted hull surface. This will be slower. Mystery solved. Bow fuel tanks are not good in performance boats.