Real benefits of hull/bridgedeck streamlining?

So true..

 

The drag of the boat with the vertical wall of windows may not be as bad as it would appear since the transition to the cabin top is well rounded though not as good as if the "wall of windows" was flush with the edge.

 

There was a chart of wind resistance posted just a few days ago. It showed the effect of apparent wind angle on drag and showed that a wind at about 30^o either side of the bow was the worst case scenario, which, unfortunately, is where it will be when trying to claw out under storm canvas. So streamlining from the side is at least important. you are fighting physics here. Clawing off is not a cat's strong point. Set the boat up to do well where it can and use a decent motor to overcome its weaknesses. Trying to overcome its weaknesses will probably just make it a tub all the time under sail and increase the cost of the venture more than putting a decent motor in it. (you gotta make it carry more sail in a storm, which means a heavier boat, which costs more, the rig costs more, and you gotta drag all that extra crap around all the time even though you rarely use it. A good motor is practical. Trying to set up a cat so it doesn't shake the air out of its sails while pointing into a storm is another problem.)

 

A streamlined and very low, curved roof house with minimal headroom helps a great deal, but taking the headsails down and not using furlers helps more.
Anything above the waterline is the braking effect of evil windage so less is best. Deflate the dinghy, send the crew below to the weather side etc.
A fully battened (Harken system is good) main, cut flat, will not flog so much when motor sailing out of Dead Man's Embayment in the teeth of a raging gale with your nice little Yanmar turbo diesel and constant speed prop working in partnership. With this combo of tightly sheeted main and good engine you might point high enough to not get set down on the fangy reef of death with all that nasty surf breaking to leeward.
Many cruisers get anywhere they want to go without an engine, but a strong current and adverse wind can put the most careful sailor on a reefy entrance with a little bad luck.
My area of the Pacific NW has many places with 8-9 knot tide races and lots of calm wind periods so an engine is pretty essential if you want to get anywhere and not have constant heart failure.
Being engineless inspires real practical seamanship and teaches the three holy rules of sailorizing better than anything else could.
1. Don't be stupid.
2. **** happens.
3. Bring beer.
Plenty of beer, because sometimes you wait a long time for the wind.

 

Do you remember which thread it was in? A quick search for "wind resistance" in the past week didn't turn it up.

 

Excellent advice

Although a 9knot tide run would challenge the auxiliary motor on any sailboat I've been on, so an engine isn't a total solution.

 

found it -
http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/aerodynamic-drag-coefficients-38479.html

 

Thanks.

 

Cruiser comforts or racing hopes ?

Cruiser Should be SAFE during drinks & after drinking.

NO projections. UNLESS absolutly necessary.

ALWAYS !!!!! Safety first on a enjoyable cruiser.

Straight bulkheads / walls. Handrails on both sides of stairs. People ARE left & right handed.

How many of us have ever been on a cruiser like the above one ??

 

Gentlemen, haven't read the complete thread, just wanted to drop in a piece of information, hopefully it is not too far off the topic.

When I was fanatic about motorcycles (70's) one of the leading magazines reproduced a wind tunnel evaluation on fairing a bike. The short version was that it made more difference to fair behind the rider rather than in front, by a large margin. I suspect you are looking at the wrong end if you really care. Perhaps Dick Newick's Tremolino and Argonata are better than they look?

 

Hello David and All,
I've re-posted three photos or designs which have bluff superstructures, with varying degrees of rounding. Would you mind commenting on how well you would expect air flow to remain attached to them, and thus how much drag you would expect compared to a more typical cruising catamaran superstructure?

Is there any rule of thumb on how much rounding is required to get a desired reduction of turbulence/drag?

Could you further amplify your thoughts on how the shape of the aft portion of the superstructure also needs to be considered?

Autodafe's design has a rather blocky superstructure, but the pontoon-like hulls are much lower than the hulls of a typical 38' catamaran. Will the presumably extra windage of the cabin structure be offset by the lower windage of the hulls?