What exactly is boat trimming?

Boat trimming is the correction of hull’s cruise angle in respect of the sea surface (pitch), and also the correction of hull’s roll angle (around the longwise axis).


My boat is fine-adjusted so why do I need dynamic trim?

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

Which trim systems are there in the market today?

Traditional trim tabs (or flaps) are the most common systems for boat’s dynamic trimming. A trim tabs are a pair of plates attached on the transom of the boat. Electric or hydraulic actuators adjust the ascent of the plates in respect of sea level. This inclination of plates produce the appropriate lift power so the hull’s geometry to get adjusted.

Within the last 15 years interceptors (or vertical flaps), a more efficient concept for trim entered in the market. They are a pair of blades (also attached on the transom of boats) extending vertically in the water under the hull. Few millimeters of extension of blades can produce a lift power exactly under the stern, so boat’s pitch and roll can be properly adhusted.

Which are the main technical features of Hydrotabs?

Hydrotab’s design is based on the concept of vertical flaps (interceptors). The innovation about Hydrotab is a simple though highly reliable and robust mechanism which never fails.  Until today, vertical flaps were mechanisms vulnerable to failures due to the sensitive parts they consisted of (servomotors, gears/rotating parts, seals. etc.). In the contrary, with a simple mechanism open to the sea water, self-cleaning, made of materials unaffected by salt water or barnacles, Hydrotab practically have zero-fail rate and needs no maintenance.

 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 quicly, 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, due to their several advantages.
  • Your current conventional hydraulic flaps require to be cleaned regularly, to avoid fouling and barnacle development, which operates like a brake against the speed.
  • Also, they often get damaged , and require spare parts and service. Very often, a small initial price hides big future costs (maintenance and service). Also do not forget that malfunctions will take place at he time you want to use your boat mostly, for example during your vacation period.
  • There is a common problem of steering interference, when you reverse the boat.
  • A frequent problem is when flaps are extended in high wave condition, because of high received stress, from boat’s constant bouncing.
  • Conventional flaps have many moving parts, so the possibility of a damage is higher.
  • Conventional flaps considerably protrude out of the transom and they are pretty inconvenient  

Is it true that vertical flaps (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 contemporary scientific studies bear testaments to the contrary. Interceptors need only few mm of vertical extension to produce the appropriate lift to trim the boat. Friction and drag power is proportional to the flap’s surface exposed to the water, so conventional trim tabs produce greater amount of drag. In addition, response of interceptors is quicker and more precise. These are the major reasons super-yachts builders use interceptors instead of common trim tabs.

 Are Hydrotabs appropriate for planning and semi-planning motor boats?

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

 Are Hydrotabs appropriate for a small and light motor boats like inflatables or RIBs?

Yes, different sizes of Hydrotab cover motor boats 20-130ft. 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 NMEA 2000 GPS Unit.

Hydrotab Auto Controller (Moby or 4DHC) has multiple GPS inputs available as a system and n2k is just one of them,

Is Auto Controller compatible with NMEA 0183?

You can use the older NMEA 0183 system.

I don’t have GPS Unit at all.

Use a normal passive antenna and connect to its own built in GPS system

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 network’s existing cables, making installation quick and easy. This also means that it immediately communicates with all n2k systems onboard.

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