Looking for a bit of advice and guidance before making the trip up to the boat to try and fix it this weekend. I have a 1986 Wellcraft Scarab 1, 21ft. boat. The engine is a 260hp, 5.7L Mercruiser 350 (Carb) with 100hrs on it. The drive is an Alpha 1 that has been recently rebuilt and works great. I recently decided to change my prop from the cheap beat up 19 pitch flow torque prop back to the 21 pitch mirage stainless steel prop (in great shape) that the boat originally came with when I purchased from the previous owner.

I removed the flow torque and stacked the parts that came off if (except the plastic sleeve/hub) next to the boat in the same order they were removed. I removed the Prop, and installed the Mirage prop in the same order and torqued the nut. Everything seemed well and good until I put the boat in the water. When my wife clicked the boat in forward gear to come pick me up from the doc she seemed to idle along as normal. Once I jumped in the boat, she mentioned that the transition from idle to in gear (for lack of a better term) felt a lot less harsh then it used to when she engaged the gear with the old prop.

I switched spots with her to drive the boat to our destination and didn't think much of her comment on the different feel of the gear engagement. Once I went to accelerate from idle the boat revved but didnt move. No forward thrust whatsoever. At first I thought I didn't tighten the prop enough and it fell off the boat. I killed the motor and trimmed the drive all the way up to find that the prop was still attached and tight on the driveshaft. I idled the boat back to the doc and pulled the boat out of the water. Briefly inspected the prop, and the shaft seemed to be turning with the prop when I rotated by hand. I parked the boat and loaded up my things into a buddies boat for the rest of the day.

With my busy schedule I didn't have time to do anything but return the boat to storage and get back to it when I free up. That was 3 weeks ago. The stainless prop that was on the boat when I bought it worked perfect the day I swapped it for the lower pitch (more holeshot) flow torque prop. Stainless Prop has been sitting in my house/garage for the past 3 years until I reinstalled this season. I can't imagine that it would be anything other than the prop since that's the only thing that's changed since I had it out 2 months ago and the boat worked fine then.

Spun hub doesn't make sense since the prop worked perfectly when I first purchased the boat and at the time of removal.

Only thing I can think of is maybe the stainless prop calls for different install parts (washers, retainers, etc..) than the flow torque prop. Or I installed it incorrectly. One thing I forgot to do is bend the tab washer into the little slots on the retaining nut/washer deal. Maybe that's why the prop is slipping? Anyways, I was hoping some of you experts could shed some light on this for me or give me some advice on what to look for or difference in installing stainless vs. flow torque. If I can't figure it out early Saturday morning I will likely change back to the flow torque (which is dinged up but works great still) as I need the boat for this upcoming week on a family vacation. Thanks for the help in advance!

-Heath

Was the thrust washer put back?

Did you try pitting the drive in gear (on trailer) and trying to turn prop to check for hub slip?
You can put a mark on hub and another on prop in line with each other and give it a quick try and verify hub slippage.
Being an amateur, sounds like a hub slipping to me.
Have a great weekend.

The thrust washer was put on. Upon further research, I figured out that the Prop is a Vengeance prop, not a mirage and I also did NOT install the Flo Torq plastic insert hub when installing the stainless prop. Will this cause the Prop to slip?

GLENAMY, thanks for the suggestion, I will try marking and turning the hub to check for slip, that's a great idea! Thoughts on not using the Flo Torq plastic insert hub causing the stainless prop to slip? Does that seem plausible?

Thanks!
Heath

Situational analysis
1) Fri PM
2) Three Day Holiday Weekend
3) Unofficial Opening of Summer
4) FLEET WEEK (Thank all for their Service)
5) "NEED BOATING NOW!" attitude.

My suggestion is take all parts for BOTH props now to local Prop Repair Shop (Somewhere the actually do the work). They can check repair hub in about 15-29 Minutes. My guy charges $ 100 out the door while you wait. They can also make your stacking order is correct for both props.
If none local find one on I-net near launch point and make appt. for tomorrow.
Burn all the gas you can.
Good luck.

Yes, you need a plastic or stainless insert or the propeller will not rotate with the prop shaft.

Brett

THANKS!!!!^^^^^^

This was my suspicion once I went out to the old prop after removal and the plastic hub fell out.. Love having the heads up that this is in fact the problem, I've been thinking about this non-stop since it happened!

Huge thanks to everyone that contributed here!