Changed the water pump yesterday and this part broke while screwing it back on.  What's it's name?

I believe most would refer to that as the "Beaver Tail"

It's a cavitration plate, and it's there to keep air bubbles from reaching your prop.

It's called a "trim" tab or "torque" tab. It's actually part of the sacrificial anode attached to your anti-ventilation plate.

It's called a "trim" tab or "torque" tab. It's actually part of the sacrificial anode attached to your anti-ventilation plate ("fin").

yup and they are magnesium and break real easy.

Oh, that fin, yes, trim tab is mounted underneath the cavitration plate. Sorry.

It's called a "trim" tab or "torque" tab. It's actually part of the sacrificial anode attached to your anti-ventilation plate.

Trim tab!  That's the one.  Thanks.  On the way to the marine store.  I have to get on the water!!

It's called a "trim" tab or "torque" tab. It's actually part of the sacrificial anode attached to your anti-ventilation plate.

Trim tab! That's the one. Thanks. On the way to the marine store. I have to get on the water!!

Don't let it keep you off the water. You can run without it if need be and won't hurt a thing.

Don't let it keep you off the water. You can run without it if need be and won't hurt a thing.

I was wondering about that but wasn't sure.  Got it at lunch time... $8.   

BTW they called it a "zinc anode".    :-/

If the trim tab is not adjusted accurately you'll have a very tough time steering  your boat. It could be dangerously hard to steer.

This Trim tab, should

it be perfectly in line with the lower leg. Mind is offset a little, is this what’s causing my steering to be ‘back and forth’ at slow speeds?

It's supposed to be offset a bit to counteract the torque from the rotating prop.

On 9/13/2022 at 3:14 PM, J Francho said:

It's supposed to be offset a bit to counteract the torque from the rotating prop.

  It’s also works as a sacrificial anode for electrolysis on your boat. It is the weaker of the metals and will corrode first. 

I'm aware. My Merc Racing 2.5 had just a disk, but no fin. My 115 on the Xpress had two rectangular anodes on the sides of the lower unit, and the torque fin was painted black. I assume it was cast aluminum. I didn't bring it all up because it was mentioned already earlier in the thread. 

Most marine anodes are zinc.