Question about rudders

[TexasRCboater]

Okay guys I'm somewhat new to this. I'm currantly building a battleship that is 7' long and 18" wide. I'm going to have 4 motors turning 4 props. I need some advice about what size props I need and what size and how many rudders I need. I am planning to have a bow thruster in the front of the ship. Can anyone help?

[viking north]

Wow--have you subscribed to or read many model boat magazines/articles. Track down a model boat builders club, these guys are so giving of their time and info.We have one here in Halifax that has built similar sized battleships--The Hood--The Bismark--are two that I have seen in person. Both had air powered guns that fired BB's. Somewhere far back in my memory there was a guy down your way that built a model of one of the big German battleships that fired actual 22cal bullets. Just incrediable and more incrediable the builders will show and tell for hours. --Geo.

[Submarine Tom]

Simply build them to scale. If in doubt, larger is better.

-Tom

[PAR]

If you build them (rudders) to scale, you'll never have any control, particularly considering the extreme scale difference between 100% and the 7'er you're working with. Personally, if I was building a model like this, I'd ask myself what I wanted more, scale propulsion and rudders or maneuverability. Since you're opting for the bow thruster, I'll guess it's maneuverability, so I'd use two props and two rudders. It keeps things simple, which is usually good unless you like swimming after out of control model warships.

[michael pierzga]

Wow, fantastic project. Do some googling in the UK and Europe...Germany, Netherlands. Ive come across some very good web sites, clubs, with technical and practical information for rc warship builders. Powerplants and stern gear are often discussed.

[Submarine Tom]

I strongly disagree with you on this one PAR. Aesthetics likely plays a big part in this model, with four props being turned by outrageously over powered motors (to scale) four rudders will have no problem making scale appropriate maneuvering. On top of that, he's got a likely ridiculously over powered bow thruster.

To scale or slightly larger would be the way to go here.

[PAR]

Scale models are subject to the same physical laws of similitude, as everything else in life, meaning the greatly down sized rudders and props will need to be proportionately larger in scale, then a true scale reduction. If he uses over powered engines (motors) his scale wake and prop wash will be all wrong too. A speed controller can solve the prop wash issues, but he'll still need effective rudder area. If he intendeds to run at displacement speeds, 8% of the surface area of the lateral plane will be in the general range he wants, which is clearly way over scale, but will be effective, especially with the thruster. I'll second the recommendation of looking on RC sites for a better handle on this, as they'd addressed this issue many times previously.

[TexasRCboater]

Thanks for all the info guys. I havent got any of the drive train or maneuvering components yet so I'm still thinking on all this. I can tell you that I'm going to be operating the boat in a river that has a hydroelectric dam upsteam. When they sound the horn for the water to be released I have to get out quick, hence the need for speed and maneuverability.

[michael pierzga]

Ive never seen a real warship out of the water. The radio control fighting warships seem to have hybrid stern gear. These are the ships armed with CO2-powered CANNONS that blast steel ball bearings into their enemies until they sink. Manuverabilty must be important

[messabout]

Recently a TV program laid out the details of a US carrier being built. It is to have a revolutionary new kind of launching catapult. They are to be electromagnetic instead of the conventional steam launchers. The carrier is costing us several zillion dollars but it is claimed to be the future ruler of the seas.

A shot of the aft underbody shows four screws but only two rudders. The rudders are said to weigh 20 tons each. Is the four screw two rudder layout the conventional way of doing it?

[TexasRCboater]

I'm not going to shoot BB's just water and rockets. I guess the real discription of the ship would be a Guided Missile Battlecruiser. My ship is a total creation of my imagination.

[rwatson]

Originally Posted by TexasRCboater

I'm not going to shoot BB's just water and rockets. I guess the real discription of the ship would be a Guided Missile Battlecruiser. My ship is a total creation of my imagination.

is the underwater gear purely for Go, or does it have some Show elements ?

Pars comments about the scaling effects are very important if you want the Go effect. Four props would only be for Show - so you could have some there for decoration only, and keep things simpler.

Your first big decision is Electric or Diesel. That will be a big decision that will affect the whole build.