WOT 64mph GPS
WOT 5400rpm
26 pitch 4 blade Think it is a Yamaha prop 13.75'' diam. I know the hub slips! Needs new hub and edges are dinged bad.
6'' jack plate
1 MPG on good day
No rooster tail

I tried moving the motor up and the lower unit was warm to the touch so I moved it back down 1/2'' Now the lower unit is cool after long run. I want to switch to a 3 blade prop. Hoping to get better MPH and MPG. I was told by local prop shop I needed a 27 pitch 14.25'' diam. mercury prop, so I bought the prop from them. The boat fell flat on its face. 40mph and 6000rpm. So a friend let me try his 24p 3 blade 14.25 diam. 46mph and 5700rpm. Then I tried a 23p 3 blade same as the 24p. What should I do. I bought a compression tester and the compression is good on all cylinders 120psi. Any suggestions will be appreciated.

Modified by wvo4dieselfuel at 7:00 PM 2/8/2010

Nothing you described made sense. Nothing....so let's try to get to a starting point and go from there.

"No roostertail" usually means your prop is buried in the water.

A 26 prop spinning 5400 rpms at 60 mph does not have a spun hub, I've never seen a "sorta" spun hub, it either is or it isn't. Then a 27 pitch prop spinning 6,000 rpms with "no" roostertail can't be going 40...Unless you've developed such a tremendous hook in the hull that nothing can save it.

Not having a water pressure gauge isn't helping, but..it's far from your problem here.

That is a skeeter splash hull, and should set up like a skeet, so use that as a basis, then you'll have something to work from.

Go to your prop guy...you want a: 26 Tempest. Known good prop. I assume you have a jack plate, if so, set your prop shaft at 3 1/2" under the pad. (NOTHING hanging off your pad like a transducer or speedo pickup). That should put you *at least* with a 4 second or so hole shot, somewhere around 5,900 rpms at low 70's. Minimum. Roostertail should be about motor cowling height at full trim, should have a good amount of bow lift, should want to walk some, should be fairly light and loose.

If your results are anything but that, come back and let us know what they are, it could be simple, or it could be disastrous.

Pat Goff

Two degrees from center
of nowhere.
Smithwick TX.

Thanks David
The rag heads aren't going to kill anymore Americans with my money.
Make your on diesel fuel for just $0.56 per gallon.

Thanks David
The rag heads aren't going to kill anymore Americans with my money.
Make your on diesel fuel for just $0.56 per gallon.

Thanks David
The rag heads aren't going to kill anymore Americans with my money.
Make your on diesel fuel for just $0.56 per gallon.

Some hub residue happens, doesn't mean the hub is a gonner.

Laser is a turd prop, don't even think about it being equal to a tempest.

Transducer one step up is still able to disrupt water flow, especially on hole shot. Take it off, mount it inside the hull where it belongs.

Here's exactly what you're trying for...rpms in the 5,800 range, any more and the computer is kicking in lowering horsepower. You want the roostertail no higher than cowling. Bow should be high and loose, water straight back, nothing out the sides. Speed should be 70 ish.

Now, I can't help that you've got a jerk prop guy, that certainly doesn't help. But.. a tempest is the deal, you'll have to play with the PVS plugs to dial it in for holeshot. If it's slipping (like you described) then you'll need to cut down the vents, if it's bogging, then open them up.

Motor should be set with prop shaft 3 1/2" under pad, that will be really close, but could be tweaked from there.
Pat Goff

Two degrees from center
of nowhere.
Smithwick TX.

I have the humminbird SI and I was told the through hull wasn't an option. I really appreciate your time and advise on this matter. I have found a tempest on ebay should I stay in the same diameter range or does that matter?

Thanks David
The rag heads aren't going to kill anymore Americans with my money.
Make your on diesel fuel for just $0.56 per gallon.

If that transducer hangs off the bottom, it can and will disrupt water flow, I'd take it off until you can get that rig running right.

Surely there is someone within range that's reading this can take some mercy on you and put an eyeball on your setup. Something just seems horribly wrong, mostly because of the results you're seeing.
Pat Goff

Two degrees from center
of nowhere.
Smithwick TX.

Thanks David

Get on the North Carolina club board and see if anyone is close by that can offer you another set of eyes for some help. It might be worth a try.

Good luck,

Joe

Also I lowered the motor as low as it would go to the ground and tried to measure. On my boat you have the main bottom of the boat at the V and then there is a step up about 1' above that. I put a 4' level off the V on the bottom and held it level. Measured from top of level and it is around 7'' to center of prop. The level was just above the flat plate above the prop. I have the 6'' jack plate and it is almost all the way down I can take it up a bunch.

Thanks David Hiatt

Thanks David