Shipbucket

In the interested of keeping the supply chain clean, I'd go with the TRS-16 over Variant or Sea Giraffe, simply because both the USN and the USCG are deploying the sets on LCSes and NSCes.
The pumpjet has a lot of appeal, and I don't see anything that might be problematic for shock hardening. Makes me think of hydropower turbines.

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𝐌𝐀𝐓𝐇𝐍𝐄𝐓- 𝑻𝒐 𝑪𝒐𝒈𝒊𝒕𝒂𝒕𝒆 𝒂𝒏𝒅 𝒕𝒐 𝑺𝒐𝒍𝒗𝒆

as for the schottel pump jet, those are actually in service on the dutch LCU landing craft. the drawback of them is indeed some noise (especially since, when inactive they act as large turbulence ducts) and the fact that they only work at relatively low speeds (the high torque of those big propellers are great to move big ships though)

they seem near ideal, except for the fact that I do not really see a good way to let them make less noise when not in operation. retracting them behind an hatch seems ideal, but I am uncertain if you want such complex systems on your emergency thruster.

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Drawings are credited with J.Scholtens
I ask of you to prove me wrong. Not say I am wrong, but prove it, because then I will have learned something new.
Shipbucket Wiki admin

I was thinking you could have a plate that covered only the inlet, which actuated directly downward via a concentric pushrod. I suspect the inlet is the dominant source of flow noise when the unit is not operating.



This seems like it should be simple and durable.

that plate would have to be very strong, as the water going into the outlet would try to push it out..... that might make just as much noise. no, I would really close it all down. that said, the pushrod you have drawn now would have to go trough the propeller axis, but I was pondering a rim driven propeller fitted on this thing.
I think the simplest solution would be either an sliding door or an round door fitted in the position you have now, but fixed to the pumpjet. the pumpjet would then be pushed down, opening up the water intake and outlet.

the sliding door would be the easiest both construction wise and required power wise (you could even hand operate it when needed)

_________________
Drawings are credited with J.Scholtens
I ask of you to prove me wrong. Not say I am wrong, but prove it, because then I will have learned something new.
Shipbucket Wiki admin

something similar to what the have done to the bow thrusters on Queen Mary 2 (there for speed purposes)

Much of the marketing in favor of these thrusters points out the relatively low inlet velocity and such. In any case, a mechanism that hinged a plate along the centerline does not seem like it should be a great deal harder to engineer.

the inlet velocity in operation is indeed very low (big, slow turning propeller, the shape of the outlet does the rest) but water streaming along the thing will be turbulent and thus noisy.

the reason I think hinging the plate in the middle is the fact that there is a lot in the middle already. the turning mechanism, the drive mechanism and the structural supports are all near the middle. the plate would also have to be lowered significally to clear the jet wash of that propeller, however the low inlet velocity helps here.

_________________
Drawings are credited with J.Scholtens
I ask of you to prove me wrong. Not say I am wrong, but prove it, because then I will have learned something new.
Shipbucket Wiki admin

What propeller? With respect, I don't know what you're saying.

the schottel pumpjet has an propeller internally inside the big intake (named impeller on the schematics) visible here http://www.binnenschifferforum.de/forum ... 1327178008 , http://www.schravenbv.com/media/28647/R ... ?width=460 and here http://megayachtnews.com/wp-content/upl ... mp-Jet.jpg
your construction would go straight trough that propellers hub.

_________________
Drawings are credited with J.Scholtens
I ask of you to prove me wrong. Not say I am wrong, but prove it, because then I will have learned something new.
Shipbucket Wiki admin

Never mind. I'm drawing something up right now.