USS Blueback Sub Build - Page 3

magpie · 26-08-2006

Quote:

Originally Posted by Bunkerbarge

............
By the way did you realize that when you crack your finger joints and make them ‘pop’ the noise is actually cavitation inside the joint. The ‘pop’ is the gas bubble collapsing within the joint as you cause a sudden reduction in pressure by opening the joint. The more often you do this the more damage you do to the joint and cavitation erosion will eventually cause arthritis.

Very good description of the cavitation effect Bunk! Much better than the ones I've read in the past. Most interesting. There are a lot of very cool subjects involving boats/ships etc.
The last paragraph re arthritis is particularly interesting to me as I have Rheumatoid arthritis myself. I thought the clicking you referred to that kids do, was just bones clicking. My joints are all very clicky but that's mostly due to large gaps and worn cartliage etc from the RA erosion. Some of it may also be cavitation as you said.
Regards
Jason

**Bunkerbarge** · 26-08-2006

Many years ago I was sat in a class at college doing a subject called Tribology, which is the science of how surfaces react and respond to each other and how lubricants affect this relationship. The science of lube oils is not far off the mark.

Anyway the guy asked the class what people popping thier fingers had in common with erosion of a propeller and, I have no idea why, I saw the connection, stuck up my hand and said "cavitation".

The fact that I was correct has stuck in my mind ever since! (Maybe it was rare!)

I agree with your thoughts on the cool subjects. Propeller design is an unbeleivably complex subject and yet most of them are, at the best, a compromise and, at the worst, such as controllable pitch props, bloody inefficient!

As with a lot of things though the really interesting, more traditional stuff is dying out as more and more technology takes over and the intervention of the engineer with his thought process is less and less of a requirement.

Only the other day we had a problem to solve whereby we wanted to remove a section of main seawater pipe, 4 foot diameter, and fit blanks but we could not get an effective isolation. The Deputy Chief suggested we run a pump on the line to vacate the line while we fitted the blanks. It worked and we saved ourselves a very big job. It is just this sort of thinking that we are loosing as technology takes over and we become isolated from the hardware that is working for us.

I agree though, I still enjoy playing around with traditional Marine Engineering concepts and the appliance of things I learned at college that I never thought I was going to use.

magpie · 30-08-2006

I still haven't received the battery for her yet, but put a 100gram lead bar in the battery bay and trimmed her in the dog bath with foam and lead. She'll start her sea trialls with her decks awash at full flood to save losing her before I get her sorted out. I'll add more lead later on.
The pic is with half the air in her.

ajg141 · 30-08-2006

Very nice Magpie - I thought it was a real one when the pic appeared!

**Bunkerbarge** · 30-08-2006

Looks the business. I'm looking forward to seeing her on trials though.

Are there figures on the bridge? I can't quite make out the detail from the picture but it looks like there is a nice level of interest there.

magpie · 31-08-2006

Thanks guys!!!
The pics below show a bit more of the bridge. It’s not perfect, but fairly close to the real one I think. It has a hatch in the back of the cockpit and a snorkel and several masts/scopes etc. Simulated ones anyway. Like I said, “It’s not perfect”. I think it’ll look good out in the lake anyway.
Jason.

**Bunkerbarge** · 31-08-2006

Of course the downside of having the prop in all that lovely uninterupted water flow is that the rudders are nowhere near the wash. Hence the two rudders to try to compensate for this.

Compare this with a U-Boat where both rudders and both aft planes are directly in the prop wash making them very effective. I was actually very surprised at how well my Revel U-Boat steers with no modifications to any of the control surfaces.

It will be interesting to see how well this boat manoeuvres.

Mankster · 31-08-2006

Quote:

Originally Posted by Bunkerbarge

Of course the downside of having the prop in all that lovely uninterupted water flow is that the rudders are nowhere near the wash. Hence the two rudders to try to compensate for this.

Compare this with a U-Boat where both rudders and both aft planes are directly in the prop wash making them very effective. I was actually very surprised at how well my Revel U-Boat steers with no modifications to any of the control surfaces.

It will be interesting to see how well this boat manoeuvres.

I'm not sure of the theory behind this but the tightest turning sub sub I have seen anywhere is my 1/96 scale Bluback. Its about 28" LOA and can turn around inside 4" underwater (and those verical surfaces on the end of the rear planes actually slow down the turn) I have never seen a U Boat get anywhere near than ratio underwater. Maybe the props behind the rudder in Uboats are optimised for surface running?

**Bunkerbarge** · 31-08-2006

Interesting stuff. Are all three vertical surfaces fitted with rudders? I assume on the surface the central fin is doing nothing but underwater it obviously has an effect.

Mankster · 31-08-2006

The top and bottom rudders are connected and turn together. Those vertical surfaces on the horizontal planes are flank arrays on the real sub, and are fixed and inhibit turning rate as a side effect.