Revell Gato 1/72 - Newbie no more Part duex

[He Who Shall Not Be Named]

just pulling your chain, Alec. And when/if you use the Pam, go easy on it, taking care not to get any on the surface of the model.

David

[alad61]

Now if I didn't know better I'd say that you, David, were being a tad sarcastic... mmm... ;) Just to clarifiy my "ah ha gotcha" meant I understood. I shall try in future to speak/type less common aussie... LOL

[He Who Shall Not Be Named]

... to break the surface tension that holds little bubbles to the inside surfaces of the model submarine. Duh!

David

[alad61]

Ah ha... gotcha.

[trout]

Pam cooking oil is used to spray onto cooking surfaces so your food does not stick - it is canola oil.

[alad61]

What is this "pam" you speak off?

[He Who Shall Not Be Named]

spray the inside of the hull with Pam. That will unglue those pesky little bubbles.

David

[trout]

I have done different tests, one person suggest I make sure all the air was out of the ballast tank - So I took the deck off while it was submerged and there was no air in there. I thought of water in the WTC, but it has been dry.
I have seen those bubbles in my kiddie pool, but in this case this water was several days old and the chlorine has dissipated.
As far as the foam absorbing, I do not think so. Here is a crayon drawing of what I think is going on.

I think by my poor installation of foam and not shaping it to fit closer to the sub, I have trapped air behind my foam. As the sub sits in the water the air slowly escapes and changes the buoyancy of the sub. It is trimmed perfectly for the first few minutes, but as time passes it slowly fills those vacancies with water.
I might be able to weigh the sub after a while and see how much additional weight I have.
Theory needs to be tested.

[He Who Shall Not Be Named]

Sometimes -- and this happens in only pool-water -- you will see 'aerated' filtered water deposit microscope air-bubbles that cling to the wetted surfaces of the model. They evidence as a silvery coating on the model. I have to think that these do much to increase the displacement of the model submarine that was likely trimmed to a near neutral state in a pool while it had this coating of tiny bubbles. At some point -- likely a function of temperature change altering the surface tension of the models surface -- these microscopic bubbles start to shed, the model looses some displacement, and it goes negative.

David

[MFR1964]

Nice test Tom,

I wonder if the foam is the problem, does the valve of the ballasttank keeps shut?, i ask this because to me losing the bouency of the foam in this amount doesn't occur with my 212, made some long runs during two hours, and did not detect any difference in bouency.
Best way is to control the ballasttank when she is submerged, simply to rule out this factor.
Other thing what you can do is, seal the foam blocks with epoxy to prevent water getting inside the foam. lead from the front sir.


Manfred.

[alad61]

Could the foam be absorbing water? That would certainly play havoc with trim. Also I found adding to much foam fore and aft played hell with the trim and listing issues.

[He Who Shall Not Be Named]

Now, that's something I never considered: displacement changer over time. Are you confident that the mechanism at work here is air trapped in and around the foam?

David

[trout]

To test out my theory about trapped air behind my foam, I placed the Gato in the pressurized polyvinyl chloride hydro test tank (aka inflatable kiddie pool) and emptied the ballast tank. She sat a little high, so I gently shook the submarine underwater to see if any bubbles came out (broke off the 40 gun barrel - we have the technology to fix her) and if the Gato would sit better. She did! She sat at the proper positive buoyancy. I left her there to sit. When I came back about an hour later.......




She had settled to the bottom of the pool. I trimmed her from this state adding foam to the bow, mid-section and aft to get her to the proper trim. Tomorrow I will test her at the big kiddie pool. The key will be to let her sit and get cozy with the water and emit her gas - such a proper lady. It's a working theory.

[KURT250]

as someone who went to sea for over 30 years, i can attest to the constant battle with rust. when i first started to go to sea we used redlead(primer) and then a final coat.when i retired in 2002 hull protection had changed to three coats of hard coating that worked much better on a clean bead blasted surface. once applied there is little rust or streaking. in the old days chipping hammers, scrapers were used to prepare the surface. two coats of red lead ether by brush or paint sprayer, then the color coat by ether method. this would last a few months then have to be scrapped of and reapplied or just painted over. modern subs get some streaking but nothing like the ww2 subs and ships did. kurt250

[He Who Shall Not Be Named]

Oh, man! I didn't even know Mike had those in stock. Sorry, Mike. Some Associate I am.

David