Last of Kevin's OSCARIIs

[Guest]

Re: Last of Kevin's OSCARIIs

The tanks you have look considerably smaller than the versions used in Engels Typhoon. That may cause you problems obtaining a scale waterline, assuming that is your aim, and taking into account that you're adapting a Typhoon box moulding.

Have you considered making a cylinder to fit the system in? That will displace a lot less than a box.

[southern or]

Re: Last of Kevin's OSCARIIs

The tanks you have look considerably smaller than the versions used in Engels Typhoon. That may cause you problems obtaining a scale waterline, assuming that is your aim, and taking into account that you're adapting a Typhoon box moulding.

Have you considered making a cylinder to fit the system in? That will displace a lot less than a box.

I did think about a cylinder, but decided against it mainly because for me at least, they're hard to work on after they're built. The tanks are smaller, at 500ml each rather then the Typhoon's 825ml each. The OSCAR is slightly over a foot shorter then the Typhoon, but the deck will be loosing close to 30%-35% of it's volume off the top just to fit. I might lower the deck too, but I haven't decided yet. The thing I like about the decks is that I can line up the motors with the props, rather then having a u-joint spin at a weird angle. I'm not a huge fan of that after I had a u-joint fail when the pin snapped, but I'm also prone to bad luck and failures happening where and when they shouldn't.

[JWLaRue]

Re: Last of Kevin's OSCARIIs

When you refer to "deck"...are you referring to the top of the WTD or the top of the hull? If the former, then assuming that the top of the WTD stays at or below the water, then it has no bearing on the size of ballast tank required.

The total moveable volume of the ballast system has to meet (or better exceed at least slightly) the displacement of everything above the surfaced waterline.

-Jeff

[southern or]

Re: Last of Kevin's OSCARIIs

When you refer to "deck"...are you referring to the top of the WTD or the top of the hull? If the former, then assuming that the top of the WTD stays at or below the water, then it has no bearing on the size of ballast tank required.

The total moveable volume of the ballast system has to meet (or better exceed at least slightly) the displacement of everything above the surfaced waterline.

-Jeff

Engel's Water tight compartment is built into the lower part of the hull so they refer to it as a "deck" rather then a compartment. Most but not all of the deck is below the water line, but only after several pounds of ballast is added. I'm not using a lead battery on this boat so I'll need to compensate for it's weight and volume, and that has to weight at least 6lbs. Take up side though is that weight can now be spread out where as before it was just the battery. I will probably get higher capacity batteries just for their size and minute extra weight.

[Guest]

Re: Last of Kevin's OSCARIIs

I'm basing my estimates on the simple fact that the engel tanks need a minimum clearance of about 3", owing to their diameter.

So you will almost certainly have to have some of the box poking up above the waterline.

Also a larger watertight area below the waterline will affect the ballast tank volume, becuase it will interfere with the last 1% of buoyancy. e.g. a boat that displaces 5kg will need a trim variance of about 50 ml, where as a boat half that will require just 25 ml.

[JWLaRue]

Re: Last of Kevin's OSCARIIs

Also a larger watertight area below the waterline will affect the ballast tank volume, becuase it will interfere with the last 1% of buoyancy. e.g. a boat that displaces 5kg will need a trim variance of about 50 ml, where as a boat half that will require just 25 ml.

If I follow you correctly, Andy......I think that's an incorrect statement. Can you expound on that 'last 1% of buoyancy" comment?

If it's below the waterline, you have to have taken into account that displacement in order to get to a correct trim...surfaced or submerged.

-Jeff

[Guest]

Re: Last of Kevin's OSCARIIs

Water varies in density dependent on temperature, mineral content etc. That variance tends to be about 1%.

Trim your boat in a cold lake, then take it somewhere warmer and it will sit lower in the water, and vice-versa

Therefore if you want to trim your boat accurately for any water density without messing about with lead weights, you should be able to adjust your boats buoyancy by about 1% of its overall displacement. The more the boat displaces the greater that 1% will be.

Some ballast systems don't allow you to do this, but the piston tanks do.

[southern or]

Re: Last of Kevin's OSCARIIs

Water varies in density dependent on temperature, mineral content etc. That variance tends to be about 1%.

Trim your boat in a cold lake, then take it somewhere warmer and it will sit lower in the water, and vice-versa

Therefore if you want to trim your boat accurately for any water density without messing about with lead weights, you should be able to adjust your boats buoyancy by about 1% of its overall displacement. The more the boat displaces the greater that 1% will be.

Some ballast systems don't allow you to do this, but the piston tanks do.

That is why I went with the TAE system over the balloons that are used in cylinders. The sub (when it's complete) will be ballasted in tap fresh water because that's what I have to work with. After that it will most likely run in the fresh water park ponds, semi treated pond by the mall, and 2 spots on the coast where it wouldn't surprise me if it was brackish or layered and depending on the tide, that can be between 1% to 3%. If it is layered, I really want to try and "float" it on the brackish layer. The nice thing about the tanks is how they supposedly can deal with silt and debris without a screen or filter. I have 2 ballast balloon pumps and a few closing celinoids, and I can tell by looking at them that they'd never survive the coast's pines, and even if I was to reverse the setup and go for air bags, the ability to trim it is gone-plus they leak. Another problem with the tubes comes down to the piston tank size and the polls. The deck allows for more stuff to be placed side by side with control rods and wires running past. I have a tube big enough for the tanks, but I tried to do a mock and discovered early on that I'd be cutting it 3-4 times then piecing it back together. Plus I don't have a bandsaw or a table saw so chances of me making a good cut are pretty slim. Chances of me cutting myself have proven to be pretty good. If the 3% proves to be too much, then all it'd need is to get the dive planes wet and the dive control system can take over and act like a hybrid static/dynamic setup. It's main home will be fresh so as long as it works correctly in fresh I can worry about salt and brackish later.

[JWLaRue]

Re: Last of Kevin's OSCARIIs

Water density! That's the missing piece of information and makes a big difference in your post. :0

I fully agree that one needs to be prepared to allow for those minor changes.

-Jeff

[Guest]

Re: Last of Kevin's OSCARIIs

I haven't seen an Oscar class model up close, but I have seen plenty of Typhoons, a popuilar model here in the UK.

The Oscar is a fairly shallow but very broad boat, bit like a flat fish. According to specifications of the real one, the draft of a 1/96th model should be about 112mm, or 4.5" in old money. Not sure what the scale waterline point is, lets say we require about a third of the boat out of the water, that leaves us with about 75mm underwater.

As the tanks are exactly that diameter, the box will project above the waterline, I would say by at least a centimetre.

Lets say we keep the box dimensions modest e.g. 30cm long by 18cm wide and lets say it projects 1 cm above the waterline. That gives us 540ml displacement. As the finished boat is likely to displace about 6 litres or more, then we need to allow at least 60ml for trim, so everything else would need to displace no more than 400ml.

In practice I think your box will be bigger than that, but that will give you some idea of how it ratchets up.

[southern or]

Re: Last of Kevin's OSCARIIs

I haven't seen an Oscar class model up close, but I have seen plenty of Typhoons, a popuilar model here in the UK.

The Oscar is a fairly shallow but very broad boat, bit like a flat fish. According to specifications of the real one, the draft of a 1/96th model should be about 112mm, or 4.5" in old money. Not sure what the scale waterline point is, lets say we require about a third of the boat out of the water, that leaves us with about 75mm underwater.

As the tanks are exactly that diameter, the box will project above the waterline, I would say by at least a centimetre.

Lets say we keep the box dimensions modest e.g. 30cm long by 18cm wide and lets say it projects 1 cm above the waterline. That gives us 540ml displacement. As the finished boat is likely to displace about 6 litres or more, then we need to allow at least 60ml for trim, so everything else would need to displace no more than 400ml.

In practice I think your box will be bigger than that, but that will give you some idea of how it ratchets up.

It is 1/96 scale.

[southern or]

Re: Last of Kevin's OSCARIIs

Interesting day today. The OSCAR and the Typhoon both got a big thumbs up from a vet.

[southern or]

Re: Last of Kevin's OSCARIIs

My shoulder is still a disaster so I haven't done anything in more then a few days now. Since I can't sleep because of it I got to wondering, don't modern subs have 2 water lines? Whenever I've seen a US Attack sub (in person) they are always docked at conning tower depth rather then being fully surfaced. I'm not an expert, but given that I'm using piston tanks, would it be possible to ballast the boat in brackish or chlorine water then if it has problems in another type, trim it to operate it at conning tower depth? Just some thoughts while I "get better."

[JWLaRue]

Re: Last of Kevin's OSCARIIs

Depends on the control electronics. the unit that I have allows me to control the piston over it's full range in what amounts to about 2-3% increments. I believe that the Engel control unit can be configured to do roughly the same thing. (I'd need to re-read the instructions)

With the unit I have, I can do an initial trim in any body of water and run from there. With the granularity of control, I can 'hang' to sub on it's periscope.

-Jeff

[southern or]

Re: Last of Kevin's OSCARIIs

I haven't finished wiring the ballast tank system yet, but it is assigned to a dial so we'll see how it works when it's wired up.

Possible good news! I "might" be able to use the pool I pay for the ballast the sub. Problem-I'm nots so goods with the math. How far off of the water line should the sub be for a pool with 3%-5% chlorine?