Prop Size on Alpha Outdrive

[DTM]

I am trying to install the tab on the outdrive of an Alpha outdrive of a just purchased '87 Z-21. When I finally got the right thread size and installed the tab, it interfers with the prop that is installed. The tab is the the smallest size so I am thinking that the prop is "oversized".

I wanted to install the tab becasue at very low speeds (idle and just above) the boat "walks" and I have to be constantly correcting the steering. I was told that not having the tab could casue this issue.

Also at low speeds, the boat is VERY hard to handle (docking etc..). I was told that not have the tab would cause this problem.

Any ideas on what to do / not do regarding these issues.

PS: At higher speeds the boat stays straight and handles well.

[tamburello]

I am sure the smarter heads on the board will fill-in with more info, but here's a start. The torque tab on the bottom of the cavitation plate is designed to counteract the torque of the prop at higher planing speeds not to enhance control at idle speeds. At higher speeds a drive without hydraulic or power steering will tend to turn on its own when you take your hands off the wheel. Obviously, this can lead to some dangerous situations so the torque tab helps keep the drive straight at speed. I have stock Mercruiser power steering on my 1994 Alpha One Gen II and have a flat disc in the cutout for the torque tab. You don't need the tab if you've got power steering.

The wandering you describe at idle speeds is a trait common to shorter deep V hulls. I've heard that dropping trim tabs down at idle speeds can somewhat aleviate this wandering. Ultimately, I guess we just live with the wandering until we trade up to the 38 ZR.

Have fun with that Z-21!

- Jeff

[MOP]

Hi more than likely you have power steering, with power steering you should use the flat zinc no fin. The walking you discribe is inherent to deep V's you can control it pretty darn nice by putting your trim tabs in the full down position at slow speeds. Just don't forget to raise them before you take off.