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#11
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Possibly a major flaw in sailboat design?
Any considerations that the center of drag would be ahead of the center of
mass in a forward mounted rudder system? |
#12
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Possibly a major flaw in sailboat design?
"Charles Momsen" wrote in message ... Any considerations that the center of drag would be ahead of the center of mass in a forward mounted rudder system? That's what I just said (inherently unstable) but, of course, I said it more brilliantly. You're welcome. Wilbur Hubbard |
#13
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Possibly a major flaw in sailboat design?
Charles Momsen wrote:
In contemplating sailboat design I think I have found a fundamental flaw, that when corrected should yield a great improvement in sailboat performance. The flaw is that the keel is put before the rudder. I believe this legacy continues in modern designs because of accident. The rudder rightfully belongs in front of the keel, not behind it for reasons that shall become obvious upon further reading. Firstly, think of cars and motorcycles. Are they steered by rear wheels? Mostly not and with good reason, the steering is better done by the front wheels. It depends on what you wish to accomplish, there are many vehicles with rear wheel steering, usually relatively slow moving, (and aren't sailboats relatively slow?) like forklifts and other machines that move material and require great maneuverability. Cheers Martin |
#14
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Possibly a major flaw in sailboat design?
"Charles Momsen" wrote:
It was tried here in 2006: http://www.mediterraneanavenue.com/F...likeButter.pdf Some benefits are mentioned. Heck, there were America's Cup boats with forward rudders in the 1980s, and long before that. I remember a guy who raced Fireballs back in the 1960s who built a Fireball with "turret daggerboards" which was a set-up very similar to modern cassette rudders. The poblem he had was the loading on a fast planing dinghy exceeded commonly available home-brew materials back then. Too much deflection in any control linkage he could build made it impossible to control it finely enough. Plus the Fireball is a complex boat to sail, givng the skipper & crew yet one more task to concentrate on was not an improvement. As for controlling canoe-like hulls by balance, check out the St Lawrence skiffs. http://books.google.com/books?id=axf...esult#PPA58,M1 or http://tinyurl.com/6dupkp The "Rudder Like Butter" might be nice but is it really an improvement on "No Rudder At All"? Fresh Breezes- Doug King |
#15
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Possibly a major flaw in sailboat design?
wrote in message ... "Charles Momsen" wrote: It was tried here in 2006: http://www.mediterraneanavenue.com/F...likeButter.pdf Some benefits are mentioned. Heck, there were America's Cup boats with forward rudders in the 1980s, and long before that. I remember a guy who raced Fireballs back in the 1960s who built a Fireball with "turret daggerboards" which was a set-up very similar to modern cassette rudders. The poblem he had was the loading on a fast planing dinghy exceeded commonly available home-brew materials back then. Too much deflection in any control linkage he could build made it impossible to control it finely enough. Plus the Fireball is a complex boat to sail, givng the skipper & crew yet one more task to concentrate on was not an improvement. As for controlling canoe-like hulls by balance, check out the St Lawrence skiffs. http://books.google.com/books?id=axf...esult#PPA58,M1 or http://tinyurl.com/6dupkp The "Rudder Like Butter" might be nice but is it really an improvement on "No Rudder At All"? Fresh Breezes- Doug King Great Information Doug! |
#16
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Possibly a major flaw in sailboat design?
"Charles Momsen" wrote in message ... What is pitch? Propeller pitch is the theoretical forward movement of a propeller for one revolution, assuming that there is no prop slip. For example, a 21 pitch propeller will theoretically move 21 inches for every revolution. Propeller slip occurs with every propeller, but the amount of slip varies depending on propeller design. More aggressively and efficiently designed propellers will slip less. When selecting a propeller pitch for your boat, it is important that the propeller runs at the upper end of your engines wide-open-throttle RPM range. If you want your RPM's to increase, go down in pitch. To decrease RPM's, go up in pitch. As a general guide, for every 2" of pitch, RPM's will change approximately 400 RPM's. For water sports or extra people on board, you should generally drop 2" of pitch to help compensate for the added weight and drag on your boat. It makes a noticeable difference in your boat's hole shot, fuel efficiency, RPM's, and overall performance. You should ALWAYS carry a spare propeller on board, and if you're into water sports or occasionally load the boat with extra people, a spare prop with a lesser pitch is a good idea. When thinking a propeller pitch, compare it to a gear on car - lower gear, higher RPM's. The same pitch from different manufacturers will run slightly different RPM's due to a difference in blade design. Speed differences among the same pitch from various manufacturers will vary even more. For example a 17 pitch from one brand could run up to 7 mph faster than a 17 pitch from another brand. Pitch is the 2nd two digits that are listed in a propeller item description (14-1/4 x 19, 19 is the pitch, 14-1/4 is the diameter) -------------------------------------------------------------------------------- What is diameter? Propeller diameter is distance across the imaginary circle that a spinning propeller makes. It can be easily determined by measuring the distance from the center of the hub to the tip of one of the blades and multiplying that number by 2. Diameters between different propeller manufacturers may vary slightly. For example for a V6 outboard application, Turning Point uses a 14-1/4" diameter where a different manufacturer may use a 14-1/2" diameter. This small variance does not affect your performance as much as the pitch and overall design. However, larger diameter propellers - 15" or 16" diameter - are designed for larger boat applications - 23 ft +, and are not ideal for 15" - 22" foot run-a-bouts. These larger boats need more blade area to push more water. -------------------------------------------------------------------------------- What is rake? Propeller rake is the degree that a propeller blade is angled in relation to the hub. Props with higher rake typically have better speeds and greater lift. The better performing propellers typically have between 20 - 30 degree rake angles. -------------------------------------------------------------------------------- What is cupping? Propeller cupping is the curved lip at the trailing edge and/or tip of the propeller. Cupping helps the propeller to get a better grip in the water for better holding at higher trim and on turns. Cupping also increases the efficiency of a propeller and can result in higher top end speeds when properly designed. -------------------------------------------------------------------------------- What are vent holes? Vent holes are holes behind each blade designed to aid in the hole shot of a propeller. When accelerating from neutral, these holes allow some exhaust bubbles to flow through and flood the blades. The prop is then spinning through more turbulent water, thus gaining RPM's and speed more quickly. After approximately 1000 RPM's, the exhaust flows rapidly enough that is will bypass the holes and flow through the hub, eliminating any further slippage from the holes. This performance feature can only be found in stainless steel propellers. However Turning Point is the only one to offer this feature in aluminum propellers as well. |
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