Scale Ship Oscar 2

[greenman407]

Re: Scale Ship Oscar 2


In this drawing supplied by Scale Ships notice the slight reduction in diameter of the Oscar at the waterline. Its a small detail to be sure and the supplied hull does not have this condition. I wonder what is the purpose of this on the full size boat???????

[raalst]

Re: Scale Ship Oscar 2

I have no real clue, but it seems to me it might have been
neccessary to fit the mechanics of the launch doors or
upper part of the launchtubes in there ? just guessing...

it certainly is an odd profile..

[KevinMC]

Re: Scale Ship Oscar 2

Hi Mark,

What you've discovered is one of the many "subtle hull features" that makes modelling the OSCAR so challenging. The hour-glass shape in the hull is most definitely present on the full-sized ship. Have a look at the photos I've attached below - you can just make out the slight depression in the hull below the missile doors as evidenced by the shadows/highlights. In contrast to the SS drawing the midline of the concave part is a smooth transition from "bulge" to "bulge", not a sharp "crease". Also, the center of the depression is well above the waterline, even with the tops of the uppper row of TT doors. This was one of many details that I had to correct on my master as I was transitioning from "blind faith in the PBP drawings" to trusting only photos or drawings that I'd thoroughly checked myself.

As for the reason it's there, your guess is as good as mine. (I'd hazzard a guess that it's there to simplify the missile door geometry, or perhaps even to accomodate parts of the door lock mechanics, but that's a WAG on my part.)

[greenman407]

Re: Scale Ship Oscar 2

So you are saying that the hull you produce has the hour glass shape? That must make pulling the hull from the mold a little more difficult. From looking at the bottom picture you can see it well. Also the waterline in these three pictures is right where the ScaleShips drawings said that it would be, right below the two upper torp tubes.

[greenman407]

Re: Scale Ship Oscar 2

After almost a week the props that Kevin is sending me have not yet arrived. When this happens your mind starts to wander and wonder what could have happened? I know! Customs has them. The guy who opened up the box(a new eager young space cadet) thought that they looked like Islamic Mujahadeen Ninja stars dipped in cyanide ready for assasination of the president. So he took them to his superior for a decision and he thought that they would make great paper weights. So I guess I will never see my new props! Hopefully we will have this project back on track soon.

[KevinMC]

Re: Scale Ship Oscar 2

Yes, my hull does replicate the "hour-glass" shape. Actually, that feature wound up significantly contributing to decisions in my mold construction. Had I elected to make hard-tooled molds I would have had to make the upper mold using a left/right half construction. Since I made my molds from RTV there's enough compliance that I can still extract the upper hull from a 1-piece mold despite the negative draft.

The waterline being even with the bottom of the upper TT doors is another "distinctive feature" of the OSCAR - it also means you can't skimp on getting the shape of the upper TT doors correct 'cause there always in plain view for everyone to see!

Don't fret about your screws yet, the folks at (Canadaian and US) Customs give everything an overly careful scrutiny these days. If they're not there by next weekend, then we'll start to worry...

[greenman407]

Re: Scale Ship Oscar 2




This is the final locations for the hull foam. These pictures are of the underside of the upper hull. With this configuration and a full ballast tank(of water) and 1 lb. 5 1/2 ounces of weight on the keel it floats perfectly with the sail just sticking out of the water. The weight starts on the keel all the way in the front just at the Z-cut extending back to just in front of the stern endcap on the Subdriver. I knew that no weight would be needed in the stern because of its tappering design and the fact that with the props and the shafts and the long bushings and linkages it was going to need not weight but foam to offset the weight.
Notice that I have two rows double stacked at the front. This was a later adjustment made onsite at the pool where I watched how it floated and stacked weight on the outside of the hull and watched its reaction. When I found the correct amount and location I marked it on the hull with a pencil and siliconed in the weight later. This procedure was also used to find the best location for the foam. Large rubber bands make this easy.

[greenman407]

Re: Scale Ship Oscar 2

I am still a kid at heart so therefore I am easily entertained. I am amazed at the difference just a few inches of water will make on the buoyancy of a model submarine. Heres the scenario. If I take my Oscar and flood the ballast tank it will just barely float with a portion of the sail sticking up out of the water. If you push it down about 10" it will become nuetrally buoyant and hover for a short time. If you push it down just 2 more inches..............its gone!............on the way to Davy Jones locker, unless you reach down and grab it or hit the blow lever. Thats why having maximum reserve buoyancy is so important when operating in deeper water.

[roedj]

Re: Scale Ship Oscar 2

Heres the scenario. If I take my Oscar and flood the ballast tank it will just barely float with a portion of the sail sticking up out of the water. If you push it down about 10" it will become nuetrally buoyant and hover for a short time. If you push it down just 2 more inches..............its gone!............on the way to Davy Jones locker, unless you reach down and grab it or hit the blow lever. Thats why having maximum reserve buoyancy is so important when operating in deeper water.

Wow, I'm wondering what's happening here. As we know that buoyancy is a function of volume alone something must be being compressed and losing its volume as the boat goes deeper. Is it the foam? What else could it be?

Thanks for your time.

Dan

[greenman407]

Re: Scale Ship Oscar 2

Dave Merriman tells me that it is the volume of the hull thats diminishing, and that makes sence because you can take the hull in your hands and squeeze it and feel it give.

[greenman407]

Re: Scale Ship Oscar 2

Found these pictures of the Kursk and thought that they might be of interest.






After all that is the vessel that I am modelling, except mine isnt going to look like this in a few years(I hope).

[Wheelerdealer]

Re: Scale Ship Oscar 2

Dave Merriman tells me that it is the volume of the hull thats diminishing, and that makes sence because you can take the hull in your hands and squeeze it and feel it give.

It may distort but it material that makes up the Hull does not loose volume. Any empty Scale ships oscar hull is just as buoyant as one thats chopped up in small pieces.
More likely its the foam, any small amount of trapped air in the hull or inside the ballast tank.

[Guest]

Re: Scale Ship Oscar 2

I am still a kid at heart so therefore I am easily entertained. I am amazed at the difference just a few inches of water will make on the buoyancy of a model submarine. Heres the scenario. If I take my Oscar and flood the ballast tank it will just barely float with a portion of the sail sticking up out of the water. If you push it down about 10" it will become nuetrally buoyant and hover for a short time. If you push it down just 2 more inches..............its gone!............on the way to Davy Jones locker, unless you reach down and grab it or hit the blow lever. Thats why having maximum reserve buoyancy is so important when operating in deeper water.

As mentioned the hull is not compressible! Your'e foam is being compressed and you are going past the neutral point.
at the surface there is no compression, so you are bouyant. push it down to 10" and you are neutral, push it a bit further and your negative.

It aslo affects compressible bouyancy tanks as well. any rubber bag type system can be compressed, along with your foam. A propel type system clearly cant, neither can a piston tank.

[greenman407]

Re: Scale Ship Oscar 2

That makes sence.

[subicman]

Re: Scale Ship Oscar 2

Ok, how much is really being compressed? it is 44 psi per every 100 ft, so 4.4 psi per every 10 ft and .44 psi per every foot (seawater, fresh is .43, pool water would be close to seawater because of the chlorine). You are saying this happens around 10" so the compression is roughly .37 psi, not very much. What kind of foam are you using? Seems to me that it could be an air trap problem and not a compression problem (or maybe a compression of air bubbles problem). Styrofoam cups have to be taken down several hundred feet to be compressed smaller then they started. I have several that were exposed to sea pressure in a torpedo tube near test depth and are the size of a shot glass. I also would look at the area that you are running, neutral bouyancy can be affected by other factors such as density of the water (salt/mineral/chemical content) and temperature of the water (warm water has less ability to support the boat, cold water will support better). I have many a time been on the way to periscope depth in the real thing and have crossed the gradient and either almost stalled out and had to pump to get up or have gotten too light and had to flood to avoid broaching the boat. The funny thing about bouyancy is it acts the same on a 7900 ton submarine or our little 10-15 lb boats I hope this helps a little.

Tim