erik_t wrote:With any serious after AA fire sort of dead on the vine, I'm now considering deleting the big awesome rotating X-band AESA aft in favor of a very much more modest unit like Variant, Sea Giraffe, TRS-16... Right now I'm keeping the larger unit so that you could handle ESSM illumination, but it's a frigate. I'm willing to lose that backup capability if I have to. It's a question of using a cheaper additional type of system versus having as few things in the supply chain as possible. Thoughts?
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.
erik_t wrote:I nixed the Voith units just in time to discover the pretty cool-looking Schottel pump-jet propulsor, which I'd dearly love to use for auxiliary propulsion in favor of the usual deployable unit. I don't see why it would be particularly unreliable, although I have concerns about flow noise. Perhaps you could have some sort of cover for the intake grill. The fact that these units don't seem to be in naval use suggests to me they haven't undergone much shock testing, although they don't seem to me like they should be particularly vulnerable. Anyway, I'm considering this change. Discussion and advice are appreciated.
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.
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.
Drawings are credited with J.Scholtens
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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.
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)
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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
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
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
