Stepped hull design concept

[batistuvan]

Could anyone me teach me the concept stepped hull boat?
My questions are:
1. What is the best location to put a single step and/or multistep?
2. What is the ideal height of the step in comparison to its length and width?

Thank you for sharing!

[Jimboat]

there is a good thread here on step design.

[batistuvan]

Thanks Jim.
An interestid post, but do you know what is the height of the step related to its length/width, I think it also important.

[Jimboat]

batistuvan - Yes, height of step is important and does indeed influence performance. Adjusting location of step and height of step can help control the angle of attack to fairly tight limits, aiding design. There is also a minimum step height required to be effective (dependant on planing surfaces configurations, hull weights/forces, and velocities).

[Captain RAH]

your website is hard to read!

[Jimboat]

Captain RAH - give me a call, and I will try to answer any questions you have.

[batistuvan]

Yes, height of step is important and does indeed influence performance. Adjusting location of step and height of step can help control the angle of attack to fairly tight limits, aiding design. There is also a minimum step height required to be effective (dependant on planing surfaces configurations, hull weights/forces, and velocities).

Do you have some sort of formulae to calculate this?

[Jimboat]

batistuvan - unfortunately there is not one simple formula that will optimize step placement. The influence of step design on overall hull performance is a function of many of the other hull performance parameters. So it is not a simple variable relationship and must be solved with simultaneous equation solutions. It is worthwhile understanding the principles of how the step design can affect performance generally. Solving it numerically is more complex. We use software to determine best solutions. And remember that a step placement can only work optimally at one velocity.

[batistuvan]

Should you put an angle after the step?
I heard somewhere that to decrease the drag, you need to incline the hull, is that right? but how much angle?
Can anybody help?

[fede]

Have been looking for "formulas" about stepped hulls for years, couldn't find anything, Hydrodynamics of high speed marine vehicles by mr Faltinsen gives the best scentific explanation of the issue but it's still not an in depth research on the topic.
Being a ultra fast crft enthusiast I?ve seen anything on race tracks,high steps small steps, 2 steps 5 steps,I?m talking 100 mph boats,all of them seem to work but until somebody does an in deep research in the tank comparing different designs and combinations of steps config/strakes/CGs/LCP/trim/watr conditions etc. none will ever know and that's a tricky and complicated/time consuming and expensive test to run that nobody will ever take into consideration.
I myself considered step design on my ribs but let the ball drop not being 100% shure of what I was doing.
The only way to get it right is to make aproto of the boat you want to make and test and modify and test and modify until the result is achieved.
Just my 2 cents...I'm none around here.

[yipster]

Originally Posted by fede

"formulas"

was just reading this formula in "fluid-dynamic drag" by Hoerner but offcourse there is more

[fede]

Cool,found a couple of used drag and lift on amazon...100 and more $ each.

[tspeer]

Originally Posted by yipster

was just reading this formula in "fluid-dynamic drag" by Hoerner but offcourse there is more

I believe the page is talking about the aerodynamic drag of steps when the airplane is in the air, not the hydrodynamic drag of a stepped hull in the water. It's not going to be of any help in designing a boat.

[fede]

Yes but I?m pretty shure the books talk also about drag reduction in water.

[yipster]

Tom, your right and good setting that straight.

recalled reading drag of surface imperfections and the scan above starts on the page before with

"steps cut into the lower side of floats and flying boats are necesairy to break the suction of the water; and to keep the airplane balanced at angles of attack desirable for take-off. the drag of these steps, plotted in fig 25 can be calculated in a way similar to that of sheet-metal joints"

but its from the chapter "aircraft components - drag of floats and boat hulls" and dont think x800 calculates.

from the chapter "water-borne craft - characteristics of planing craft" some more here but no in detail stepped hull answers.

turning the page i see hydrofoils