Gori Prop makes weird sound on reverse

[downwinder]

Boat was tied up for a couple of months. When the bottom cleaner came he told me he couldn’t open the prop to clean it properly. I get back to the boat and turn on the motor to put the gear in forward/reverse to see if maybe any barnacle growth would clear out. Forward it works fine but when I place it in reverse it makes this random shaking sound. Both gears it moves water. Any advice on what could be the issue. Thanks

[SailingHarmonie]

In reverse this prop relies ONLY on centrifugal force to open the blades. In forward, the force of the water pushes the blades open.

The most likely situation is that there is not enough force in reverse to fully open the blades past the fouling crud. You might want to have the diver back. If he still can't clean it, then it needs to be removed, disassembled and cleaned at the shop. Or get a better diver...

This is also kind of like behavior from a worn blade pivot shaft. That's unlikely if the prop behaved normally the last time it was used. I imagine it is possible that the pivot shaft was bent when you forced the blades open past the crud, but I haven't seen that before.

[Zanshin]

I loved my Gori, but I did need to "exercise" it. The blades need to be opened fully to work, and something is seriously wrong if the diver couldn't do that. I used some nasty underwater grease on the hinged areas; not for lubrication but to keep away growth. Since they blades are all geared together, one big obstruction on one blade stops the others as well. And that imbalance of partially opened blades is what is causing your vibrations.

The blades do need to swing out both ways, that is what the "overdrive" reverse does; keeps the higher incidence angle of reverse gear while moving forward - that's why you need to be moving in reverse when switching to forward for "overdrive".

That having been said, if my current boat hadn't come with a folding prop I'd have gone for another Gori.

[catalystcat]

Your diver should be able to clean it up and get it to fully pivot between the forward and reverse positions.
It just can be a real PIA and takes time and a lot of attention to detail as well as an understanding of how the blades pivot and what that does to the gears. (I have had to jump in the water to show a diver how to do it.)
The diver needs to clean each of the gear teeth and the surfaces that rotate around the pivot pin. Then, manually try to pivot 180 degrees. Usually they go about 20- 45 degrees the first time, before newly engaged gear teeth stick due to debris, barnacles, oysters, whatever and stop the pivot.
So, the diver works the blades back and forth and repeats this process of cleaning and trying to pivot until it finally clears. Note that, as it pivots gear teeth on the "other" side of the blade get exposed. These also need to be cleaned.
Once the blades all pivot freely through the entire range of motion, try to get rid of any remaining stuff (e.g., with a small scraper or brush). Then, cover the gears with really sticky marine grease, pushing the grease into every nook and cranny you can find. This is effectively, the "antifouling coating" for the gears and pivot faces. You'll be surprised how well it sticks.

The blade pivoting and re-greasing should be a regular maintenance step.

One guy I know ran his boat in reverse and forward every week at the dock to get the blades to pivot. As they pivot, they kinda clean themselves.

[catalystcat]

Oh yeah. As said above, regular "exercise" of the blades can help you avoid having a diver correct the problem.

[BobFord]

I like my Gori props but maintenance in critical. Stop too long ,in a barnacle growing environment and the little fellows can grow well inside the gears. My remedy - Lanolin grease travelling and run thro' fwd & reverse each (2) weeks when parked.