Hulls

The hull is the obvious part of the boat. The hull makes a direct contact with the water and supports the mast and fittings on sailboats, the engine, strut, drive and rudders on motorized boats.

According to the design of the hull, r/c boats may be classified in two main types:

Mono: are those hulls which bottom surface offers a continuous wet surface when running, as can be seen on the drawing bellow The hull is a one piece, shaped like a "V"...Its the shape normally found on real boats. Their inner space eases the installation of any type of engine.

Hydroplane: all other hull types are generically called hydroplanes. They are hulls with sponsons and run on water over 3 or more surfaces not contiguous. The drawing bellow clearly shows the difference to the former model.

Note: Both upper drawings were scanned from David Thomas book Basics of Radio Control Power Boat Modeling, from Kalmbach KBooks, 1992 edition.

According to the angle of the Vee, monos can be classified as:

DeepVee: Those where the angle between a horizontal plane and the hull varies from 16° to 28°. A front view shows the most pronounced "V". By design they tend to cut the water when running and so are known for their good handling, easy drivability and the ability to handle rough or choppy water. (Paul Govostes Apache)

Monohull (shallow V) Hulls with angles not higher than 16°. Because of this design they are faster than Deep Vees, although more tricky to adjust and run.

Crackerbox

Based on the full size APBA hull the crackerbox has a very flat to 3 degree V hull. By design the crackerbox tends to side-slip on turns and requires skill to drive well. (Dumas Crackerbox that belongs to <Todd Clarkson from Katy, Texas, USA - Thanks Todd)

According to the position and dimension of the sponsons hydroplanes can be classified as:

Hydro: hull with two sponsons at the front and normally running on the prop at the rear end, thus the name 3 point hydro. They are fast boats and very critical to adjust and drive. There a few of them scaled from real boats.

Catamaran

The catamaran hull consists of two hulls called "sponsons" joined by an elevated superstructure containing the drive and control components . The elevated superstructure creates a "tunnel" and the wind passing through the tunnel creates a lifting effect on the hull reducing drag and increasing performance. Catamaran hulls are typically faster and easier to drive than other hydro hull types, although more critical than monos on those conditions.

Tunnel Hulls

Tunnel hulls are a small catamaran type hull using an outboard motor. Due to the weight of the motor at the rear of the hull tunnel hulls are less stable than a catamaran. The tunnel hull "flies" on the cushion of air in the tunnel and is more difficult to trim and drive than the catamaran. They normally use nitro engines, although can also be find with gas engines

Outrigger

The only type of R/C boat not based on a full size boat, the outrigger or "rigger" is the fastest type of hull. Gasoline powered models run over 80 MPH, Glow powered models have exceeded 110 MPH. The rigger consists of two small sponsons attached with metal or composite "booms" to a rectangular center section containing the drive and control assembly. They may or may not have sponsons at the rear. The rigger runs with only a small portion of the sponsons and the propeller touching the water. Riggers are typically difficult to trim. Almost exclusively a competition boat, even launching them at water requires special skill. (Jim Nissen's boat bellow)

Cannard: a very special type of hydro, with one single sponson in front and two at the rear. Read what Mike Gilman says about cannard below. The picture bellow is an Aeromarine Sabre Cannard.

Hydrofoil: even more special, they run over thin blades. On r/c field they are, yet, experimental boats.

Others: although seldom used, they deserve a mention for being so different - the air boat (with nitro or gas engines), the scale boat and others that I am not able to classify, which pictures are show bellow.

Nitro air boat

Gas air boat (scratch built by Marty Manross, now belongs to a friend of him)

Scale boat

Others 1

Others 2

In other words

Again, someone at Jim's board (Mike Gilman this time) posted a very good information about the subject.

Diff. between Vees, cats, hydros, tunnels, Etc.

Vees= great starter boats, run in a variety of water conditions and are easier to set-up than any other rc boat. Aeromarine Apaches fall into this category.
Mono= shallow vee race boats like Twincrafts, a little harder than a vee to set-up but the same principles, like calmer water than vees but a pretty good starting point if you have racing in mind.
Cats= Great handling boats, very easy to drive, not very good rough water boats and a little more knowledge to set-up. Stryker cats and AM sprint cats fall into this category.
Hydros= Very fast boats when set-up right, a bit tricky to set-up, no rough water at all. Stryker hydro, AM shovelnose, 1/8th scale are all Hydros.
Riggers= Capable of the fastest speed, not for the beginner, takes years of practice to even be able to race one. Very technical. SG rigger, mid-west riggers are good examples. No rough water and the frailest of boats.
Tunnels= Mostly nitro outboard tunnels are made for the K&B outboards, there are a few gas tunnel outboards. They tend to be a bit tricky to set-up as they ride bow high on a cushion of air. Windy condition makes them flip usually. Sometimes cats are referred to as tunnels but most people think of the nitro ones. Dumas makes a variety of outboard tunnels.
Canards= Very strange looking boats, kind of like a backwards rigger with the sponsons on the back. I have seen pictures but that is my only knowledge of them.
Just my opinions and hope it helps get the ball rolling for others to add more technical comments.

Mike Gilman

Engines

a. Electrics:

Electric (battery powered) boats, no doubt, have some advantages. No problems of starting the engine, smaller, easy maintenance, and the race electrics attain fairly high speeds. Although, in our opinion, their disadvantages exceeds the advantages. Class by class they are slower than the glow or gas engines, the duration of the batteries restricts run time to a few minutes and they lack the characteristic sound of a true engine, which is half the fun in driving a R/C boat.

b. Glow engine:

Derived from the engines used for model airplanes, they are usually called "nitro" engines. In fact, those engines run on fuel blended from methyl alcohol, castor and/or synthetic oil and nitro methane. They belong to 2 groups, according to the placement of the engine. Outboard, in which the engine hangs over the transom, just like the real ones (picture below) and inboards in which the engine rests in the hull and power is transmitted to the propeller by means of a shaft (see picture below); Outboards engines are mainly used in the tunnel hull. At speed, just the prop and the last third of the hull touches the water. Because of the special design, speed creates an air flow beneath the boat, lifting it from water, reducing drag and allowing high speeds. But this kind of hull demands a very calm water, because it has a strong tendency to fly in choppy water.

Outboard glow engine Inboard glow engine

d. Gasoline engine:

Our personal preference in engines. Two types of engines are used:

I - The ones specifically made for hobby use, the most well know are Quick Draw and Zenoah (pics below), both are available in a range of displacement and power.

II- The ones originated from engines developed for other purposes, normally leaf blowers and string trimmers. These are commonly known as "Weed Eater" motors. These engines are extensively modified for use in R/C boats. In USA the Homelite is the most commonly used engine, because of its availability and low price. Only your imagination, in the USA, limits the different brand of engine used. The pictures below show a stock, air cooled Homelite as found on weed eaters and the same engine prepared for R/C boating.

Quick Draw Engine Zenoah engine

Homelite engine for a weed eater Homelite engine ready to go on boat

Husqvarna engine being prepared at 6 cylinder engine
Shark Racing. v. water jacket.

Drives

Except for sail boats, all boats need a system that transmits power from the engine to the propeller. On outboards, this transmission is inside the engine and is not visible. What you see is a cylinder, much like that of an airplane motor, normally wrapped by a water jacket - although some of the more moderns K&B engines are using air cooling - and a lower end with a propeller on tip . Inside, a flex cable links the motor crankshaft to the prop. For all other engines, internally mounted in the hull, some kind of transmission must be made between the engine and propeller. Mostly used types are the rigid shaft (picture below), which demands 1 or more u-joints to allow for the inclined angle from the engine to the propeller shaft, parallel to the bottom of the hull. This kind of transmission is normally limited to electric boats or glow engines with low HP. and comes with kits for assembling this kind of boats. For engines with higher HP and for gas engines, the transmission is via a flexible cable that looks like the speedometer cable of your car, but much more larger and stronger. This "flex shaft" runs through, and is supported by a brass tube with or without a teflon liner. This tube can be bent to create the correct angle from the engine and become parallel to the bottom of the boat, linking to the prop axle. One of the tips of the flex cable links to the engine crankshaft by means of a special coupler screwed onto the engine crankshaft on one side and with a square hole on the other side in which fits the flex cable. On the other end of the flex cable we solder the ferrule, screwed to the prop shaft. In USA there are some types of drives available called "out drives" (pics below) that, besides being extremely efficient, ease the assembly of the boat. For very special applications, other types of drives known as "jet drives" are available in the USA, like the one we show in the below picture, they work like a jet ski, getting water from the bottom and directing it at fast speed out the transom.

Rigid shaft transmission

Flex cable transmission

M&D designs Racing transmission (USA)

Precision in Perfection drive. Can be adjusted by means of a third radio channel.

Water jet transmission

"Made in Germany" drive trains. What do you think?

Yet just a curiosity - the performance is less than proportional to the price and complication evolved - but really very interesting. A jet propulsion on a David Cadman boat:

Some models of drive

A- Shark Racing (under development)

B- Int'l R/C Cobra Drive

C- Enforcer

D- MDd-Drive (M&D designs Racing)

Exhaust

The most efficient exhaust systems include a special projected manifold and a tuned pipe whose dimensions take in consideration such variables as: engine c.c., RPM, exhaust and transfer ports duration, sound velocity at the pipe, exhaust temperature and so one, creating a complex equation that results in a design that vastly improves engine performance. (picture below). The cooling water for the engine, after leaving the water jacket may exit in two ways: exhausted out the boat side, by means of a outlet on the hull, or into the exhaust system, injected into the exhaust header and going out at the pipe outlet.

Propellers

When choosing a propeller, those variables must be considered:

a. diameter, thats is its size;

b. pitch: the inclination of props blades, which determines the theoretical forward movement the propeller makes at each rotation;

c. number of blades: normally 2 or 3 on RC boats, although there are special props for submarines with 5 or more blades;

d. shaft diameter: The most common sizes are 3/16 (.187") and 1/4 (.250").

Besides that, we must take in considerations whether the prop will be used in a surface drive configuration wherever the prop will be used at the surface - a situation where half prop is under water and half out of water - or subsurface, in which the whole prop is under water. The first type - surface drive - gives better performance and for that reason is used on boats where performance is the prime requirement.. Because the of the vast variety of types, sizes, dimensions and materials of props commercially available in the USA your options are only limited by your pocket.

Radio

A complete radio system for your boat includes the transmitter, which sends the command signals that open and close the carb butterfly and move the rudder to drive the boat through the desired direction, the receiver, that inside the boat receives and decodes those signals and the servos, small electric motors that, under the receiver command,move the shafts and cables that control the throttle and the rudder. Just like ordinary transmitters, that you could have at home or in your car, RC radios are allowed to transmit only in specific frequencies ranges:

27 MHZ for airplanes, boats and cars - not much used, because of the risk of putting together planes and other vehicles.

72 MHZ exclusively used for planes

75 MHZ for boats and cars.

Always use the frequencies range authorized for the vehicle you are driving, to avoid accidents. For each of those groups there are channels with different frequencies, so several pilots can use their vehicles at the same time, without danger of interfering each other. The AM transmitter is more susceptible to external interference and, whenever used on a gas boat we must filter this interference, mainly that originating from the engine, using resistor spark plugs and accelerator cables made from non metallic materials. The FM transmitter is less prone to those interferences and, according to Futaba, has a 20% longer range. The PCM type radio encodes the TX signal. At the RX this signal is decoded and so only the "true" signals are accepted by the receiver. This way, interference is drastically reduced. Additionally, the PCM radio has a inboard fail-safe that may be adjusted to kill the engine if the interference supersedes the system filtering.

Items needed for a complete R/C boat

Sail boat:

a. hull
b. finwith lead ballast
c. sail winch
d. mast
e. mast appendages
f. cables
g. rudder and axle
h. rig
i. complete radio system (transmitter, receiver, servos, batteries and charger)

Glow engine

a. hull
b. engine and mounts
c. drive system
d. propeller
e. rudder and shaftsand/or cables
f. complete radio system (transmitter, receiver, servos, batteries and charger)
g. fuel
h. electric starter and portable battery.
i. Glow plug battery

Gas engine

a. hull
b. engine and mounts
c. drive system
d. propeller
e. rudder and shafts and/or cables
f. complete radio system (transmitter, receiver, servos, batteries and charger)
g. Gasoline / oil mixture

 

Carlos Andrade