Hydro System Tips for RC Boats

I will explain the most important setup aspects for sport hydro RC boats. The points covered can also be applied to some outrigger hydros. I will not cover things like center of gravity and engine placement as these should be supplied by the boat manufacturer. In most hydro’s the engine will end up being considerably forward of the leading edge of the turn fin. The CG will end up closer to the leading edge of the turn fin. This is generalizing and varies from one boat to another. The turn fin is what the boat "pivots" on when the rudder is turned. Moving the CG away from the point of pivot changes the turning characteristics of a hydro considerably.

There are three (3) pieces of hardware to adjust and fine tune on most hydro’s. These are:

The strut

The rudder

The turn fin

Adjusting the Strut: 
To do this, it's usually easier to remove the rudder blade. If the rudder extends past the back of the strut you can leave it on, otherwise remove it so you can move the boat forward on the table and have the entire strut bottom over the table surface. This is important when adjusting the strut angle.

In most cases the manufacturer will recommend 0 angles on the strut. They should also recommend a starting depth for the strut, usually measured from the bottom from the boat at the transom to the center or bottom of the strut. Lightly tighten the adjustment bolt(s) and double check your height. Make sure the strut is still flat on the table. This is checked by ensuring you do not see light under the strut when looking at it from the side, parallel to the table. Fasten the adjustment bolts and triple check the strut.

Setting the rudder: 
Setting the rudder is pretty straight forward. Unless the manufacturer specifies otherwise, you will usually want the rudder perpendicular with the riding surface of the boat. In this case, this means perpendicular to the table surface you just used to set the strut. For this reason it is VERY IMPORTANT to set the strut first!
With the strut adjusted, install the rudder blade and check that it is 90degrees with the surface of the table. The boat must be sitting flat with the strut and both sponsors on the table. If the manufacturer recommends some inner or outer tilt, you can check and adjust with a protractor again using the table as reference.
Setting the turn fin: 
There are two different types of turn fins more commonly seen on hydros. One has a straight bend and the other is a curved type. In most cases the manufacturer will specify where to mount the turn fin and how to adjust it. Again this varies from boat to boat.
Tilting the fin forward will have a tendency to make the boat track to the left and exert some lifting force on the right (starboard) sponson.
Tilting the fin back will have a tendency to make the boat track to the right and pull down on the right (starboard) sponson.

I hope this will help some of you fine tune and get the best possible performance out of your hydros!