trim tabs rfs trim tabs
the new compact RocketFlap Lite is a marine trim tab system
INVENTED to boost runabout hulls onto the plane automatically
for sale

home trim tabs hard lift trim tab sysyem on the plane trim tab trim tabs how they work calculate transom angle for trim tab system for sale
  system operation ...
  Simply by utilizing a boats own forward motion while accelerating onto the plane, downward deployed trim tabs, retarded by rams, are gradually pushed up by the resultant water pressure achieving the desired LIFT to assist the boat onto the plane effortlessly ...  
    How it Works            
  The fully automatic hands free system uses the surrounding sea, lake or river water as the hydraulic source for the rams rather than oil or a gas. The power source for the system is the boats own forward motion through the water but only while accelerating onto the plane. This novel method provides the ever reliable power to activate the system.

When the boat is at rest in the water the rams are fully extended, positioning the tabs down. To operate the submerged rams must be completely flooded by the surrounding water, via upper fill ports

As the boat accelerates onto the plane the forward motion acts on the downward inclined tabs and the rams gradually collapse as the piston moves through a control zone which is a partial hydraulic lock relieved by a spiral groove (see fig. 1), this creates the HardLift that raises the stern of the boat.

As the boat achieves plane and no longer requires the high lift, the ram's internal piston crosses into a zone which has a much larger bore. This allows the water to flood easily around the pistons 'o' ring resulting in the ram collapsing very quickly - the 'blow-out' phase. Keeping the boat on the plane maintains the rams in the 'neutral position'. (limited effect on the boats trim).

When the boat is taken off the plane and brought to rest, the force under the tabs is lost. Light internal springs automatically extend the rams and return the tabs to the start position ready for the next cycle.
The Flash animation below is controlled by the links on the left.



Although the basics are fairly simple as outlined above, to fully understand the system it's necessary to explain in more detail how we arrived at such a design and why we believe it is the preferred method of operation for a fully automatic trim tab system...

As the positive effects of trim tab plates are well documented the focus will be on the operation of the rambody.

The RocketFlap is an Open hydraulic system that utilizes water from the surrounding environment to charge the rambody. Operationally, the rambody would perform equally as well if it were a closed system filled with any fluid, water, oil or gas. Of course there are some obvious advantages and disadvantages to using an Open system rather than Closed.

  • Advantages - an unlimited supply of hydraulic fluid (water). No polluting, messy oil leaks and having no oil seals means easier manufacturing tolerances.
  • Disadvantages - sand, silt, crustaceans, etc. may enter the rambody and possibly effect the function of the system.


The Disadvantages needs to be answered;
The inversed orientation of the rambody means any silt, sand or life form debris build-up, is collected at the bottom of the ram and is well away from the operation of the piston head. As can be seen in (fig. 1), the relief for the control zone is a spiral groove that the piston's 'O' ring scrapes so there are no holes to block. Also, for easy maintenance, the complete rambody and tab can be removed in seconds without the need of any tools.
control ring
Fig. 1 Control Ring with spiral groove

However, the primary reason for opting for an Open rather than Closed system was a safety issue - consider the following scenario;

A boat travels across a lake at approximately 50mph, the water conditions are flat calm. The boat encounters another boats wake and go's airborne, a common occurrence. In such a circumstance, momentarily the prop, engine gear case and trim tabs are disconnected from the effects of the water.
If the trim tabs installed on the transom are the fully automatic kind, such as RocketFlap (or any other similar product that relies on the boats forward motion through water to maintain the tabs UP position), without the resistance of the water the tabs will automatically and immediately deploy DOWN to their default start position. Subsequently, when the hull reconnects with the water, a significant load would be applied to the fully angled DOWN tabs.

In the above scenario, if the RocketFlap was a closed system filled with it's own reservoir of fluid, the rambody would reset and be fully charged for the HardLift phase. Reconnecting with the water at such speed would have a dramatic and undesirable affect on a boats stability and potentially part or the whole system could be ripped from the transom!

However, because the RocketFlap is an Open system, when the tabs drop Down, any water remaining in the rambody would be purged back through the fill ports when the rambody was extended out of the water. As described in phase 1, to function 'the rams must be completely flooded' to produce the HardLift effect...(see video below).
To conclude - With an Open system when the boat reconnects with the water the only resistance from the tabs is the dampening effect of the light 15lb return Springs and the residue of water in the rambody.

  RocketFlap on transom - demonstrating the resistance needed by the trim tabs to produce the
required HARD LIFT when the boat is going onto the plane...


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