Hi Rogal,
We'll have a whip round to get you a bottle of Original Taste.๐
Can't recommend Diet Coke. Not much real difference in calories and various studies indicate adverse health effects from the synthetic sweeteners used.
Apart from that it tastes bl***y awful and makes terrible Cuba Libre๐
"If I used the whole internal volume as a ballast tank I would loose the buoyancy of the foam, catch 22".
The mass of the foam involved is negligible compared with 1.6kg.
I don't think that would make a significant difference Rogal. Remember, it's the submerged volume that accounts for the displacement, and swim depth. So I don't think that Captain John Yossarian's psychological problems are applicable here๐! (Yes I have seen the film and I have the original hardback book by Joseph Heller.)
You have already proven that you need 1.6kg to get Jaws to float where you want it to.
Add a few grams to compensate for the loss of the interior foam if you wish but I wouldn't bother. Mass involved is negligible compared with 1.6kg.
More important is most likely the angle of incidence of Jaws' lateral fins.
So I totally agree with Andi1, until you try towing Jaws to see if he swims, dives or porpoises you are working in the dark. A negative (downward) angle will force him under, a positive angle will force him to surface. Possibly causing him to leap above the surface (depending on the speed) and diving back down again, i.e. porpoising . Ditto repeato! Would be fun to watch though๐ But perhaps not what you are looking for. So aim for neutral incidence, i.e. horizontal.
My recommendation would be to go with ca 1.6kg (140-145cc) lead within the body.
Would either need 4 more slots like the one you have already made.
Or one plug of 4cm diameter by 11.25cm length.
Much easier to accommodate than 1600cc of water๐
Which would need a cylinder of about 10x20.5cm.
In most boating lakes a false bulb under the ventral will be visible when near the shore and detract from the visual effect and swimming - added drag! Also when on display on shore. Aggro mounting and demounting! We don't want to give away our little secrets do we?๐
Your problem reminds me strongly of a similar snag I had with my 1/72nd scale dynamic diving Type 1A U-Boat, from Krick LoA 107cm.
Built according to instructions she floated too high, despite two 6V 4Ah SLAs, dive planes were still above waterโน๏ธ
Just like you I draped weights over the hull 'til she floated right.
Then milled hull compartments fore and aft to accommodate corresponding weights of lead.
Hull construction was 'bread and butter', i.e. 4 planks of 2cm thickness.
On sea trials the dive planes would still not push her under but just threw up huge 'moustaches' of water. Spectacular but not exactly true to original๐
I then did some research at the Deutsches Museum here in Munich, where U-1 is on display with the starboard hull plating removed to expose the interior, and bought a helpful book about U-Boat designs, with scale plans. This told me that the Krick dive planes were too small.
So I made a new set. Still to be trialled as most unfortunately shortly thereafter U25 suffered a severe collision with the workshop floor๐ฎ๐ Subject for a future Blog๐
Bon chance mon ami๐คlooking forward to your progress reports / trials videos๐
Schlaf gut!๐ด
Cheers, Doug๐
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