Stupid question.
05-05-2013, 11:06 AM
#41
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Curious as to the case studies they gave you. Also curious if 3 or 4 steps are even more efficient.
Here's one for you which sums up step hulls nicely courtesy of David Svahn:
"The stepped hull is viewed as two regular hulls following each other closely in the
water. The first hull follows the same theory as a normal planing hull since this one
meets a calm level water surface. The second hull does however not, as it travels in the
wake behind the first hull. Because of this, the shape of the wake has been studied for
different conditions like speeds and hull shapes."
Here's one for you which sums up step hulls nicely courtesy of David Svahn:
"The stepped hull is viewed as two regular hulls following each other closely in the
water. The first hull follows the same theory as a normal planing hull since this one
meets a calm level water surface. The second hull does however not, as it travels in the
wake behind the first hull. Because of this, the shape of the wake has been studied for
different conditions like speeds and hull shapes."
So on a longer narrow boat having multiple steps does improve efficiency since the L/B ratio is rather large thus making for a small aspect ratio and an in efficient single step boat.
This does not make more steps beyond 2 ate better though as it can make the boat very resistant to pitch in a seaway which could make the boat neigh on impossible to drive effectively.
Your quote does bring up a very important issue in step design, and that is the angle of attack of the step and the length of the step. Two more extremely important variables in making an efficient stepped hull boat. Too low an angle of attack combined with too long of a step and you end up with a step that has more wetted surface than it needs and may cause the same problem as mentioned above. Savitsky presented a paper in 2009 that was based on a series of model tests to predict the wave height aft of a step to give designers an easy tool to help predict wake height and using his equations from his hydrodynamic design of planing hulls to calculate the lift the after-bodies are capable of producing.
I've posted a link to a dropbox with that paper in it.
https://www.dropbox.com/s/c0ijod7en3...%20%282%29.pdf
I don't think either of us is in disagreement with the other about the last sentence of Potgieter's essay.
As far as case studies research and such...Papers from Chesapeake powerboat symposium,FAST conference papers, HSBO papers, SNAME papers, RINA papers, Dr. Doctors UofM class notes "hydrodynamics of high-speed small craft", Faltinsen's book Hydrodynamics of high-speed marine vehicles, and class notes from my high speed hydrodynamics course.
Last edited by MIskier; 05-05-2013 at 11:14 AM.
05-05-2013, 12:22 PM
#42
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This thread is effing hilarious. It's amazing how easily things fly right over the tops of the heads of supposedly educated and intelligent individuals. Thanks to all the rocket surgeons who failed to recognize the sarcasm / humor intended by the OP.
05-05-2013, 02:37 PM
#43
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Her's one for ya, kid, courtesy of Kobus Potgieter. The last sentence sums it up quite well!
http://www.navaldesign.co.za/article...s-%20Feb07.pdf
http://www.navaldesign.co.za/article...s-%20Feb07.pdf
Personaly, I have no need for them, give me a perfect straight bottm anytime. They just arn't worth all the trouble that comes with them. But I am also a old "F"
05-05-2013, 07:10 PM
#44
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05-05-2013, 08:30 PM
#46
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I hate to say this but it doesn't matter if the boat has 1 step or up to 6 step's , they all need a responsible person at the wheel that know's how to drive .
most all the newer race boat's are step bottom and they take corner's at 80+mph because the have experienced driver's in them that no how the boat handle's .
most people that buy $ 200 k+ fancy go-fast boat's think they no how to drive but they have no clue unless it's running in a straight line and that;s what the sticker is for , they should be on all Step bottom boat's
most all the newer race boat's are step bottom and they take corner's at 80+mph because the have experienced driver's in them that no how the boat handle's .
most people that buy $ 200 k+ fancy go-fast boat's think they no how to drive but they have no clue unless it's running in a straight line and that;s what the sticker is for , they should be on all Step bottom boat's
05-06-2013, 09:22 AM
#47
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As I stated above there is a caveat when designing stepped hulls that the L/B ratio plays a very large roll in determining the number of steps.
Too low an angle of attack combined with too long of a step and you end up with a step that has more wetted surface than it needs and may cause the same problem as mentioned above.
Too low an angle of attack combined with too long of a step and you end up with a step that has more wetted surface than it needs and may cause the same problem as mentioned above.
We do things completely different if we are going over the "90" or "100" mark. Pretty much a zero angle of attack and these adjustments are what make it handle. Also we have changed the trailing edge of the forward running surface miniscule amounts and seen major changes it attitude.
Unfortunately you just can't spend that many years on theories and math with a known end result in the class room. Or for that matter in a test tank.
My point to the original post is if there is a known issue why isn't it fixed instead of a sticker warning you to "hang on, you're about to go swimming".
One thing to think about as my theory: The more times the water reattaches it self to the bottom of the boat (each step) the more resistance and confusion it creates. In a turn we only have the re-attachment at the transom. With a multi-step boat we have multiple re-attachements.
Curious as to your opinion on this.
05-06-2013, 04:38 PM
#48
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05-06-2013, 06:33 PM
#49
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[QUOTE=ActiveThunder;3919876]You would be interested to know after 13 years of building this boat and also mentioning we use an insert in a V-bottom mold,
Now that is what I like you can still build me a non-step after I hit the power ball
Now that is what I like you can still build me a non-step after I hit the power ball
05-27-2013, 04:05 PM
#50
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[QUOTE=cosmic12;3920211]Or I could build you a boat correctly engineered to be faster, more efficient and MUCH MORE user friendly since you don't need this:
