What exactly is boat trim?
Boat trim is the correction of the hull’s angle (along the longwise axis) in respect to the sea surface (pitch). By trimming the boat, we actually correct pitch angle to the optimal, aiming to decrease resistance on boat hull and consequently increase boat’s speed.  

My boat is fine-adjusted, so why do I need a trim system?
Even with the best designed hulls, optimal cruising (which enhances speed, stability, fuel economy and comfort) is achieved only on a specific trim angle of the hull in respect of sea surface (pitch). Changing factors like height and direction of waves, wind, load distribution on deck or speed, may divert the hull from optimal geometry. A dynamic trim control system can continuously re-adjust pitch, so the boat gains maximum speed, stability and of course economy in fuel consumption.

Which types of trim systems are out there in the market today?
Traditional trim tabs are the most common systems for boat’s trim. Trim tabs are a pair of plates attached on the transom of the boat. Electric or hydraulic actuators adjust the angle of the plates in respect of sea level. This inclination of plates produces the appropriate lift force in order the position of the hull to get optimized.

During the 90’s, interceptors (or vertical flaps), a different but more efficient concept than conventional trim tabs entered into the marine market. Interceptors are a pair of blades attached on the transom extending downwards in the water under the hull. Few millimeters of blades extension can produce enough lift force applied under the stern, in order to adjust the boat’s pitch (trim) and roll (list) properly. Interceptors can operate faster, the lift force they produce is much larger than ordinary trim tabs, without increasing drag.  

Don’t interceptors work as a brake when we deploy them?
Indeed, both trim tabs and interceptors apply a small drag force against the motion of the boat. However, the drag produced by interceptors is not higher than that produced by ordinary trim tabs and this small drag force is absolutely necessary in order trim of the boat to be controlled. Though, by optimizing the trim of the hull we practically minimize friction and resistance of waterflow against the hull, which finally results to minimizing the total drag applied on the boat and increase its speed. 

Is it true that interceptors produce more drag than common trim tabs, due to the fact that interceptors extend vertically in the water?
No, it is not true. Several recent scientific studies bear testament that in order for interceptors and trim tabs to produce an equal amount of lift force, they produce equal drag. However, trim tabs may produce more friction and drag if they don’t get cleaned often to remove barnacle and marine growth.

Which are the main technical advantages of Hydrotabs over other trim products?
Hydrotab is a system of interceptors. The innovation about Hydrotab is about a simple, though highly reliable and robust, pneumatic mechanism which never fails, even under the harshest of conditions. Similar trim systems (trim tabs or other interceptors) are mechanisms vulnerable to failures due to their sensitive parts (servomotors, gears and rotating parts, seals, gaskets, etc.) and all seafarers are quite familiar with such a fact. On the contrary, with a simple but reliable pneumatic mechanism which is open to the sea water and made by premium quality materials, Hydrotab is highly resilient to harsh sea conditions and hard use like hits and bumps with floating objects or extreme temperatures. Hydrotabs are practically unaffected by barnacle and marine growth, they have almost zero failure rate and a surprisingly long lifespan.

I have been using trim tabs for several years. Why should I change them with Hydrotabs?
First of all, you should change your flaps in case your boat does not come into plane position quickly or if it does not plane at all, which means that the selection of your current flaps is not the right one. In that case, do not hesitate to choose Hydrotabs over other trim systems due to their several advantages.

  • Interceptors produce more lift force than ordinary trim tabs. This lift force is applied under the hull (not at the plates of trim tabs). This means that they can control trim of the boat more effectively, even if the boat is fully loaded or even if weather conditions are bad.
  • Planning with interceptors is quicker at lower speed than with trim tabs. Also, it is smoother even in higher speeds and they do not create porpoise.
  • Interceptors react instantly. Only few millimeters of deployment are enough to control a heavy loaded boat. In addition, because of the quick reaction of interceptors, the list of boat can be controlled easier and quicker.
  • Interceptors are installed on the back of the transom and consequently, even if they are covered by barnacle, they do not affect speed. On the contrary, trim tabs require regular cleaning, otherwise they work as a brake against motion of the boat reducing the speed.
  • Interceptors require much less space on the transom than trim tabs.
  • Conventional trim tabs have many moving parts as well as sensitive parts, so the possibility of damage is quite higher. Failures often mean high service and maintenance cost. Do not forget that a small initial price always hides big future costs due to maintenance and service.
  • There is a common problem of steering interference, when you reverse the boat with conventional trim tabs.
  • A frequent problem is that when trim tabs are extended in high wave condition, they receive high mechanical stress from boat’s constant bouncing.
  • Conventional flaps protrude considerably out of the transom and they are pretty inconvenient in activities such as fishing.

Are Hydrotabs appropriate for planning and semi-planning motorboats?
Yes, Hydrotabs can be used to trim and optimize cruising performance to both planning and semi-planning boats. Hydrotabs, like all trim systems, are effective for boats with cruising speeds greater than 17Knots.



Are Hydrotabs appropriate for a small and light motorboat like inflatables or RIBs?
Yes, different models and sizes of Hydrotab cover motorboats from 15-140ft. In fact, the smaller and lighter the boat is, the more the need for trim adjustment is, since small and light boats are more sensitive to weather conditions, speed or load changes.

Frequently Asked Questions for Moby (or 4DHC) Auto Controller and NMEA 2000 Network

I don’t have an NMEA 2000 network. Can I use Hydrotab Auto Control?
Yes, the system will make its own network, as soon as you make the proper cable connections.

I don’t have GPS Unit at all. Can I still install a Hydrotab Auto Controller?
Moby Controller has a GPS antenna embedded in order device to receive GPS signal, so even if you don’t have any GPS device installed on your boat, you can still use Hydrotab Moby Auto Controller. 

For the older 4DHC Auto Controller, you just need to install a regular passive antenna and connect it to the appropriate socket of the device.

Is Auto Controller compatible with NMEA 0183?
You can use the older NMEA 0183 system, if you have a NMEA0183 to NMEA2000 compailer device.

What are the advantages of the Auto Control system compared to other systems?
Moby Auto Controller (or the older 4DHC) have been designed from the beginning as a pure NMEA 2000 system and it only uses a network’s existing cables, making installation quick and easy. This also means that it immediately communicates with all n2k systems onboard.

Copyright @ 2019