The hull is the obvious part of the R/C model 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:
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.
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 Modelling, from Kalmbach KBooks, 1992 edition.
According to the angle of the Vee, monos can be classified as:
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.
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
According to the position and dimension of the sponsons hydroplanes can be classified as:
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.
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 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
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)
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.
even more special, they run over thin blades. On r/c field they are, yet, experimental boats.
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)
In other words
Mike Gilman this time posted some 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.
Inner trim tabs are the ones closer to the keel. Besides adjusting the boat's attitude on water, they may be used to correct torque roll, the tendency the hull has to lean to the right as a reaction to the engine torque. In this instance, the right part - starboard - should be opened, lifting the hull's right side. As a consequence, the bow gets deep in the water. Eventually, closing the left trim tab - port side - could be a better alternative. attitude on water, they may be used to correct torque roll, the tendency the hull has to lean to the right as a reaction to the engine torque. In this instance, the right part - starboard - should be opened, lifting the hull's right side. As a consequence, the bow gets deep in the water. Eventually, closing the left trim tab - port side - could be a better alternative.
The outer trim tabs - far from the keel - are used to adjust boat's attitude on turns. The bigger the angle the more the transom lifting at that side, the deeper the bow and the sharper the turns. outer trim tabs - far from the keel - are used to adjust boat's attitude on turns. The bigger the angle the more the transom lifting at that side, the deeper the bow and the sharper the turns.
There is also a consensus that the trim tabs would not be lined with the hull bottom. 1/8" looks like a good distance. With this, unwanted drag is prevented and the tabs acting as a hull extension is minimized.
I seldom, if ever, use trim tabs. So, I hardly qualify as an expert on this issue. But they are sometimes necessary and answering a post at his board Jim Nissen got to the point. That was the question:
"Is there a rule of thumb that dictates how far the inner edge of the inboard trim tabs should be from the centerline of the keel on a mono? I have read or heard numbers from 7/8" to 1-1/2". Is it important that the inner edge of the trim tab be positioned so that it is outside the prop diameter?"
And the answer:
"Yeah it really depends on the angle of the mono or deep vee as well as the diameter of the prop. I have set up monos normally with the tabs just to the outside of the prop's diameter. If the hull is rather wide you can get away with a second set of tab's on the outside. The best race set-ups typically will use one wide tab per side but then split it in the middle to produce inside and outside tabs.
I would not recommend putting them in any closer to the keel than the outer prop diameter. The closer they are to the keel line the more shallow the prop will surface and less water it will have to work with. This can be a good thing in low power set-ups but be very bad for higher output motors.
Oh and remember the most important aspect of tabs. They tend to act like a hull extension. The boat will have more lift the closer they are to the keel line. Move them outside and the hull will be allowed to ride lower in the water. There is a limit though to the amount of lowering the hull will be allowed to do. The limit is the hull design itself."
Bellow, a pic of a Ron Frank's boat with out and inner trim tabs.
Should be installed at the chine line parallel to the keel and perpendicular to the hull. In a way that, when the boat leans at the turn it should be in a vertical position to the water surface or slightly tilted toward the keel. Only when turning, as the hull rolls into the turn, are they supposed to dip the water. When travelling in a straight line they should not touch the water, this is to avoid drag
Hull porpoising (up and down oscillation of the bow, when travelling in a straight line)
Normally occurs on monos with surface drive, when the prop is too far from the transom. To correct, bring the prop closer to the transom. Adjust half an inch each time, until the oscillation ceases. After correction, adjust the strut angle to determine the bow height when running.
What makes a high lift hull?
Strakes that run back pretty far and/or are also pretty sharp
A very rounded keel
As Jim Nissen says:
"The strakes are flat riding surfaces that limit the water from spilling off to the sides. As a result they act like ski's. They tend to make the hull ride on top of the water opposed to cutting through it. The further back toward the transom the strakes extend then the bigger the ski (surface area for this to occur). All high speed hulls eliminate the strakes several inches ahead of the transom or eliminate them completely. This allows the hull to lift up to the point where the strakes end. The rounded keel doesn't help much either. As Don says - it's like a rounded ride pad.
A sharp keel cuts through the water and will limit lift. Even sharp keels have limitations. Ride pads integrated into the hull bottom have to be used once you hit speeds in the upper 50-60 MPH range. At this kind of speed even a sharp strake less keel can provide enough lift to cause chine walking. Trim tabs can help but your really fighting against the physics involved and mother nature will win this one! "
Bellow, a picture of a ride pad on Ron Frank's boat
Rudders: Don Betz is a big fan of Speedmaster rudders. His choice for gas boats is a 65/90 single water pick-up, with the gas bracket (longest) and the water passage drilled to 1/8.