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Bow Angle

In yesterday’s post, we discussed drive trim and how surface drives provide lift. There is another benefit to adjustable trim, and that is related to bow angle.

An advantage of surface drives over water jets (in particular), stern drives, and outboards (even though trimmable), is that surface drives allow a the vessel to remain level while travelling at top speed. I refer to the same graphic used yesterday:

As one can plainly see, Tau, or the bow angle, will vary based on the trim of the drive. When vessels equipped with the SDS are operated at top speed, the trim may be adjusted to minimize this bow angle (typically 3 degrees) in order to allow level operation of the vessel.

There are several benefits to this:

  1. The captain can sit while operating the boat.
  2. Full visibility without being obstructed by the bow.
  3. More comfortable ride while in rough seas.
  4. More maneuverability of the vessel.

 

With water jets or vessels equipped with other types of propulsion, the bow angle increases as the vessel goes faster, with many vessels requiring the captain to stand or strain in order to see where he is going. Additionally, with many hull designs, drag will increase as the bow rises, with the vessel “pushing” the water away, rather than proceeding through it.

When a vessel is at full plane, it should be level with only a small portion of the hull wetted. This principle can be illustrated by the photo below of a vessel equipped with SDS: The same picture that is in the banner on this site.


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More Stories By John Miele

I am currently Sales and Marketing Manager, Asia / Pacific for France Helices. Created in 1977 by Paul BEZZI, FRANCE HELICES is today an international company. French marine propulsion leader, FRANCE HELICES is also one of the international leaders. Research and development are a very important part of FRANCE HELICES program, the CAD's department is equipped with the latest computer technology, using most up to date programs. Our engineers and technicians determine from the customers specifications and designs, the type of propulsion system to suit the boat's application. They can also advise on the ideal choice of power and optimum gearbox ratio to obtain the maximum thrust. There are many FRANCE HELICES' inovations and patents such as Surface Drive System (SDS) which enable boats to obtain very high speed with excellent handling capabilities and high quality Controllable Pitch Propeller systems (CPP) for both professional use and pleasure application. The constant research using cavitation tunnel testing, guarantees high efficient propeller blade shape for our customers. More than 20 000 propellers per year are manufactured by FRANCE HELICES workshops. In all sizes from small sailing boats to large fishing vessels to navy boats or mega yachts. The FRANCE HELICES workshops are equipped with modern foundries capable of casting propellers up to 3.5 tons in NiBrAl. They are also equipped with CNC milling machines and CNC lathe machines. FRANCE HELICES has four sites which cover the complete range of production. The development of FRANCE HELICES, supported by shareholders places our company as a leader in the international market and insures a constant development, worldwide, in order to be close to the end user.