Inverted pilothouse windows

A16

Total Drag: 771 Newtons

A20

Aero Drag ... Hull: 374 (!) Newtons

 

Hi Calevi, I think inverted windows are angled to avoid broadcasting a presence with reflections from shipping and vehicles in war time.
I also like the look of them, but if used at deck level instead of high up like on a ship's bridge, I think they would fare much worse than aerodynamic orientation if / when green water thunders over the deck. The angled bases will create focused pressure regions, and more easily damage them or push them in at the base.

 

On the pilot house of a fishing boat, and other commercial vessels they are used to help keep them clearer from rain water.

At deck level, they would be helpful in redirecting spray from the cockpit.

-Will

 

Good point!

 

I think they are angled to avoid reflection of the bridge instruments which may impair night vision.

 

Hiding the hull in the water is an interesting way to reduce aero drag but since water has around 1000 times the density of air,could have unfortunate side effects when considering the 1/2 rho.V^2 aspect of drag.I have a feeling that short of building two boats with identical hulls and differing wheelhouses for sailing trials that the answer will be found either by finding a student who is looking for a good CFD project to present or building a scale model from the waterline up that has a detachable section where various shapes can be substituted and drag measurements taken at different apparent wind angles.Simply adding a feature because commercial shipping has it isn't necessarily a good idea as the big ship world normally provides plenty of horsepower to push the vessel along,in part to meet schedules and in part to overcome the hull drag of several hundred square metres of immersed surface that doesn't have a mirror finish.

 

I incorporated them in Serenity for water shedding. Extremely effective. Compared to similar boats in similar conditions where gravity pulls the water down as fast as apparent wind pushes it up, and it justs hangs there.

 

That makes a lot of sense.

-Will

 

"Hiding the hull in the water is" ... A very very good solution

Total Drag: 965 Newtons

Residual (A23): Hull Residual resistance, Rr (Wave making Drag): 75 Newtons @ 5 knots

Viscosity (Friction: Hull, keel, rudder): 154

 

Checking the numbers instead of 75 it could be 85 or more; but the point is that it does not take much effort to move a hull through the water up to a speed of 0.35 Froude (which is the "Hull Speed in practice", the theoretical one is 0.40 Froude)

Note, for example, the Drag induced by the Lift (Lateral Force) of the daggerboard/Keel and rudder blade (A24: 222 Newtons) which is independent of whether the hull is above the water or hidden in the water.

 

A 'modern' sailboat (1930-) like this "Tumlaren" (20 Squared meter, Jib + Main) sailed very well upwind heeled 30 degrees and buried in the water like a submarine; a 'modern' (2030-) sailboat can sail on top of the water with 15 degrees of heel.