Improving stern thruster efficiency

[1Mainer50]

I have a 2017 RT29 which I cruise in New England. The tight marinas, winds, tides, and river currents cause me to rely on the thrusters in many docking situations and I learned quickly that the stern thruster provided significantly less push than the bow. On the hard last week I think I saw why, that being the location of the thruster in relation to the port trim tab and the rudder, The thruster blows directly on to the tab (which is angled down toward the keel), which blocks the thruster flow when pushing the stern to starboard. The rudder has a similar effect (though less hydraulic impact) when pushing to port.
There isn't much room on the stern below water so relocating the thruster doesn't look like an option. But I could remove the two partial "funnels" now attached to the upper quarter of each side of the thruster or rotate the funnels to a different position. Dropping the port trim tab into the cruise position may improve the water flow too but experimenting that will have to wait until we get back in the water.
Has anyone tried removing or repositioning the funnels and if so with what effect?

 

[Irish Mist]

I had asked the same question and I was told the "funnels" are actually to help with the water pick up. The stern thruster would cavitate without them.

 

[Scuba Too]

We have the 2017 R29 CB and I've encountered the same issue. I make sure our trim tabs are up before engaging the thrusters and that does seem to help. I suspect that the bigger issue is that the stern thruster is pushing around the heavier end of the boat. The bow thruster is on the lighter end and the boat pivots at the stern. Interesting thing to try is see how the boat pivots for each thruster on a calm day and were that center is.

 

[Larry H]

The stern thruster on my 2014 R-27 is one size smaller than the bow thruster.

 

[1Mainer50]

Thanks for the feedback. I'd wondered about the cavitation issue as the intake is so shallow, and the point on weight distribution is well-taken.

 

[Irish Mist]

I try to not use my stern thruster a lot as the sheer pin is not fun to change. I have gotten quite good anticipating the pivoting of the boat with the bow thruster. Also conditions permitting if you are patient you can just use short bursts and let it drift.

 

[bill46]

I found the stern thruster less effective than bow. From non thruster days I learned setting the rudder and a short burst of power will make the boat wag it's tail. Rudder has little effect in reverse. Bill R31CB

 

[stwendl]

I was wondering if it would help attaching a wide hose type tube to both sides of the stern thruster and route them almost to the edge. The would prevent the stream to hit the rudder or other obstacles

 

[Irish Mist]

I was wondering if it would help attaching a wide hose type tube to both sides of the stern thruster and route them almost to the edge. The would prevent the stream to hit the rudder or other obstacles

The problem is keeping water going into the blades.. With the tube unless you could keep it low it would cavitate. I did see a large mono hull house boat once with about a 16 ft beam that put a tube through the stern of the boat with a thruster in the middle, Like the bow thrusters on our boats and he said it works great.