1/96 Scale Ships Akula

[anonymous]

They're coming. Stand by.

Steve

They're coming. Stand by.

Steve

[Rogue Sub]

Its been a bit since

Its been a bit since I updated this build and theres a good reason for it. I was building another boat. Seems once I got the Akula far along enough to where I could play with it, I went on to something else. There's the Seawolf I just finished, I started a PT boat, and I even gave the Dumas Akula a little TLC.

But its time to get this boat 100% SO here I go.

After having run this boat at several different gatherings one thing remains painfully clear. This boat not only looks scale.. it turns scale. Abismal turning for this boat. If your planning on running it in a pool, I would just forget about it. Unless!! you fix it. I considered a few options to fix my turning problem. I could add a piece of clear plexiglass to the end of the rudder with pins to hold it in place. I could also make a small piece that is held on with a rubberband. Both of these would probably work fine but they are not for me because it would add something that didnt belong on the boat. Now I could add bow thruster (plenty of room in this boat) only problem is bow thrusters are useless on a larger boat when there is way on the ship. This brings me to my last option.



To fix my boat I cut the bottom of my fixed rudder off and reattatched it to the moving part of my rudder with epoxy. I simply drew a line all the way around the rudder and razor sawed it off. I didnot cut the whole thing off though. I only cut off from the rudder brace down. I did this to try and give the rudder as much strength as possible while still extending my rudder. After all the rudder usually the one that takes the damage when you hit the bottom. After that was accomplished I filed everything down to ensure there was no friction while turning. Also I had to add a small piece of sheet styrene between the moving rudder and the recently removed rudder to ensure that the proper spacing was retained.



This is another shot from the stern showing my new rudder. Im not sure how much of an improvement i will get from this modification but, I will find out on Sunday when my group has our next get together.



I have also started filling in all the seems with glazing putty to remove all the gaps, as you can see from the above pictures. I have also started painting the boat and adding the rest of the resin cast details the boat came with.

[brady_d]

You'd better hope to god

You'd better hope to god that works, Skipper. And if it does you can bet the farm that I'll pull an Ivan and try to "emulate" your methods... with my own improvements, of course. I shall be watching very closely from behind my hand of cards.

[Rogue Sub]

What do you mena hope

What do you mena hope it will work. There is a question?

[brady_d]

I guess you're right... we

I guess you're right... we all can't be reactor technicians can we?

[Rogue Sub]

Well, the operation was a

Well, the operation was a success and I was able to cut the turning radius nearly in half. Anyone else out there with this model. Cut your rudder!

[cstranc]

Ok, so now I have

Ok, so now I have heard it from several people "bow thrusters don't work when the boat is underway". I just don't understand why this would be.

Let me understand. If the thrusters will turn my boat 180 degrees in 15 seconds while stationary why would they not turn it in the same time while under way?

Does it have to do with momentum...

I'll just ask the question and let the folks that know enlighten me.

[brady_d]

Ok, so now I have

Ok, so now I have heard it from several people "bow thrusters don't work when the boat is underway". I just don't understand why this would be.

Let me understand. If the thrusters will turn my boat 180 degrees in 15 seconds while stationary why would they not turn it in the same time while under way?

Does it have to do with momentum...

I'll just ask the question and let the folks that know enlighten me.

Well I don't know a darn thing about the subject, but just going off what I've gathered I think it has something to do with the slipstream of the water over that part of the hull negates the all/most of the force that the bow thrusters put out. Think of it like throwing something out a car window on the freeway; it's certainly not going to go as far straight out as it would if you were sitting still. Again I could be totally wrong...

[Rogue Sub]

Chris,

Bow thrusters dont work because

Chris,

Bow thrusters dont work because the dont posses the power to over come that slipstream brady was talking about.

Now if you ready a couple of other posts like the one from ART, you will notice he recomends bilge pumps. That is because they have alot more thrust capability.

Now if you were able to double the efficency by drilling a hole and making your own... I say try that out and let us know. If anything, in the end you will at least be able to move at slow (scale) speed. Your bow thruster construction thread was very impressive.

Kevin

ps if all else fails. Increase your rudder size. You will be surprised how even a little bit will ake a diffrence.

[Guest]

I see my mod worked

I see my mod worked well on your Akula,it sure works great an my 5ft Alfa you saw at Devils Den,just be carefull not to damage it.
The next mod would be a partial cut leaving a stationary section for protection.

Dave Amur Ship Yard

[Rogue Sub]

check it out dave I

check it out dave I already did that

[talwar]

The real answer lays somewhere

The real answer lays somewhere in between. The Slipstream of the water near the bow is indeed one of the problems for a bowthruster.
The biggest problem however is the momentum thingy. A ship turns around a point they call the Pivot Point. The Pivot point is only in the centre of gravity when the ship is dead in the water.
Once you gain forward motion, the Pivot Point moves forward, when the ship is at full speed, it lays around 3/4 of the ship's length from the stern.
When the ship moves aft, the Pivot point moves aft too.

So practically, the moment your bowthruster is creating is quite small, because the pivot point moves forward when the ship gets a forward speed, so the distance from your force/bow thruster to the pivot point is small. The momentum created by your rudder is of course at its maximum.
The other way around, if you move aft, the bowthruster has a much larger momentum and can be used as a rudder, while the rudder itself is practically useless (also because the flow of water is not really optimal around the rudder when you move astern).
Normally a bowthruster is only useable at a maximum of 3kts forward. Everything faster than that will render it useless. So at 4kts, then the slipstream of the water is not so much of a problem yet, but the momentum is getting rapidly smaller.


So far the theory of manoeuvrability of course. There are some other factors playing in this too, like the right or left handed propellor when moving aft etc.
There are a few changes you can make to improve the efficiency of a bowthruster too. One of them is adding an empty tunnel (like your bow thruster tunnel) from one side of the ship to the other just in front or behind the bow thruster tunnel. This tunnel equalizes the pressure difference between the two sides of the hull. The suction of the thruster creates a flow of water towards the tunnel and the hull, this means there is a high pressure field around the entrance of the tunnel since the water is opposing the turn of the ship. On the other side there is a low pressure created by the jet effect of the bow thruster and so you have a pressure difference which opposes the ship's turn. If you add the tunnel, there will be an equalizing effect of this pressure difference and so the effect of the thruster will enlarge.


Interesting build of a very nice ship!!!

[hakkikt]

Would this not call for

Would this not call for stern thrusters instead of bow thrusters to improve mobility at higher speeds?

[Guest]

Dave Forrest built a supplemental

Dave Forrest built a supplemental thruster for his WWI R-class boat.

It's a self contained module which clips underneath the boat, and is only used for small pond use where the R-class' turning circle is inadequate.

When it was first used, the thruster was placed at the bow, I suggested placing it at the stern for a greater moment of force. This resulted in an improvement in performance.

Andy

[talwar]

hakkikt,
not really since the

hakkikt,
not really since the rudder along with the wash from the main propellor is a very strong force at high speeds. A sternthruster is only used in some ships, for mooring operations. Same as bowthrusters actually. They are only used for ship to ship operations or mooring ops (or as part of a Dynamic Positioning system). Also the stern shape of a ship is very odd and the slipstream of the water at full speed would be too great to give a stern thruster any effect at all. (also a very difficult placement with the propellor axis running there).

How's this build advancing? Holidays I guess, my yards are going slowly too nowadays.