u-47 - diving problems

[boatbuilder]

Hi everyone

I have recently finished building the robbe U-47. when I sailed the sub for the first time it took like a duck to water but I`m having problems when trying make it dive. The bow goes down nicely but the stern rises out of water enough to show the props causing the sub to lose momentum and resurface. Ive tried different settings on the bow planes but still doesnt dive. Can anyone help?

mark.

[Guest]

How far down have you

How far down have you ballasted the sub?

Fo the U47 to dive well dynamically, you have to ballast it so the decks are almost awash.

Andy

[boatbuilder]

Hi andy

The sub sits

Hi andy

The sub sits pretty low in the water, the water line is roughly 1 cm from the deck.


mark

[Guest]

Get it lower.

Andy

Get it lower.

Andy

[subdude]

If possible, move your center

If possible, move your center of bouyancy to towards the stern. Also, try this dive technique. Gently increase spead, and slowly angle the bow planes down. Try to slow down the tilting action of the boat, giving more time to get the boat under before the screws get near the surface.

Good luck!

Jim

[boatbuilder]

Hi Jim

Thanks for the tip.

Hi Jim

Thanks for the tip. Been checking out videos of other U-47`s and noticed that the subs in some of them the bow is higher above the waterline than the stern causing the sub to tilt backwards towards the sten. my sub sits completely level so could this cause the dive problems. Could you let me know the distance between the bow where the allen key goes and the front of the lead weight as I might have the weight in my sub too far farward. any other ideas welcome. thanks

mark

[subdude]

Mark,

Sorry, but I can't really

Mark,

Sorry, but I can't really tell you specifics on the U-47, as I don't own one. Actually, I haven't owned a dynamic diving boat for a long, long time. However, I can tell you for sure that my old Krick U25 would do exactly the same thing when trying to dive quickly. I slowed down my diving technique, and it worked just fine. Gently easing it under did it every time.

Jim

[anonymous]

I back up Andy 100%.

I back up Andy 100%. Get it lower.

Also use less input on the stick. That is to say let her build speed first. You should be able, with the trim tabs alone, dive the boat. Apply too much down too soon will cause this problem even if the deck is a wash.

With my old dumas Akula I even hold a bit of up. Then once to speed I release the slight up and dive with the trim tabs. Last consider and RCABS or Piston diving system. Then you will never have this problem.

Keep playing with it. You'll get it. I had the same problem when I started out with a dynamic diver.

Best of luck and happy diving.

Steve

[boatbuilder]

Hi steve/andy

Thanks guys for

Hi steve/andy

Thanks guys for help. I`ll add more ballast to make it sit lower and get it back in the water. will let you know the outcome.


mark

[anonymous]

You bet. Good luck on

You bet. Good luck on this run.

steve

[boatbuilder]

Hi Steve

I havent had the

Hi Steve

I havent had the sub in the water yet, hopefully today or tomorrow. I`ve been testing my sub in a boating lake that is fed by the sea, could the salt content in the water cause the problem i`m having? Would it be best to try a lake thats filled with fresh water & not sea water?



mark

[chuck chesney]

I would sure do my

I would sure do my submarine diving in fresh water only. The specific gravity of salt and fresh water are different, with salt being much more buoyant than fresh. Salt water can really mess up several systems on your boat as well as being death to radio waves.
As far as the salt water causing your specific problem, it could, because of the buoyancy issue, but your problem sounds much more like an over-control issue.
I agree with Andy and Steve 100%.

[Guest]

I wouldn't advise running in

I wouldn't advise running in salty or even brackish water.

It corrodes any metallic parts like the dickens, so if you're hellbent on running in the brine, then make sure you hose your boat down well afterwards with plenty of fresh water.

Also as already pointed out, you'll lose the radio signal as soon as you dive beneath the surface.

As you boat is a dynamic diver, this should initiate the freebie failsafe (positive bouyancy) and up you'll come quickly. Not much fun though.

You will need to run an external aerial that will poke above the surface of the water.

Andy

[boatbuilder]

Hi

Havent had time to

Hi

Havent had time to test the sub again. Working over & bad weather. will keep you posted.


mark

[tmsmalley]

Hi Mark -
I have had

Hi Mark -
I have had some luck in situations as you describe. Trim the sub low in the water as everyone has suggested, then as the boat starts to submerge and it's about half under, pull back on the stick (bringing the bow up) which has the effect of pulling the stern down.

I have only used this with a sternplane controlled model, but it *might* work with your U-46. What the heck, this sort of experimenting is part of the fun!