Steps angle

[Flysafe]

My name is Jorge Lopes and I live in Lisbon , Portugal .

I have as hobby radio control and I would like to make one miniature yacht, a deep vee hull with two steps and strakes, I made part of the hull in 3D, but I have a problem with the two steps angle, do you know how I can calculate the step angle, or indicate me a reference book, or web site where I find information about this specific area.

Thanks

[Flysafe]

This post it's to clean please, sorry.

[messabout]

I will try to understand your question. When you say that the boat is to be a deep vee with two steps are you referring to steps that are parallel to the centerline or are the steps running across the boat section (sideways)?

Sideways steps were used in fast boats in the past but they were not deep vee type boats. I suspect that you are asking about the deep vee style objects that are often called strakes. The strakes run more or less paralell to the waterline and the outer edges are turned down 4 or 5 degrees. The stated purpose for doing that is to help keep the spray under the boat. In fact the angle is there to reduce wetted surface caused by spray and splashing. For all out performance, wet surface is an important factor. Some people claim that the strakes are also lifting surfaces. They are so small that I doubt that there is much lifting effect from the strakes. In any case the most advantageous angle will probably be dependent on speed and bottom loading (weight/bottom area while planeing) of the boat.

[Willallison]

I would counter what Messabout says by simply saying that most of the fastest deep-vees have both steps (transverse) and strakes (longitudinal).
Historically, the planing surfaces of stepped hulls had their running surfaces angled at about 3 degrees. These days, most have little or no built-in angle of incidence.
There's a great deal of science / art / experience that goes into making a good stepped hull, and there's very little published info about it.
Get it wrong on a full size boat and the results can be disastrous. At least on an RC model you are unlikely to kill anyone!

[baeckmo]

There was an article reviewing the subject in the "Professional Boatbuilder a year (2?) ago.

[HJS]

More about transversal stepped hulls and how they work.
Just put the figures in your computer and push the right button and you have the right answer!:D


js

[Flysafe]

Thank you all to the replies


Messabout
I was referring to sideways steps, for now I leave the strakes by side.

Willallison
You are correct

Baeckmo
Do you know how i can find this article?

Hjs
Thanks for the information


I have been reading about this subject but it’s not easy because there isn’t a lot information. The ones that know about it don’t share it.

I already read some patents and all make mention of one step, but I couldn’t find the measure in angles for two steps.
I found the maximum height of the channel step, and the purpose for the strakes, chine and so on.
I think that this subject it is not so complicated.
And I thought the degrees for one step were one value, and for two or three step was another, but no. It doesn’t work that way.
I have the Harry Schoell patent but I didn’t read it yet.
I hope that after reading the Hjs information, I have some answers.

[HJS]

I hope that after reading the Hjs information, I have some answers.

Good luck

The clew is to understand and calculate the local trim angle and the local deadrise. With this in mind you can design how many steps you want. But I am not sure it will be better with many steps.

It is also important that the stagnition line goes over the longitunal spray chine on the forward planing surface. If not, spray will wet the aft surface and add drag.

Professional BoatBuilder oct/nov 2003 deals with some of your problems.

Also check up the Dynaplane configuration and my own midship interceptor with aft stabilizer.

hjs


www.sassdesign.net

[Flysafe]

Thanks for the help HJS ;)
Briefly I give you news.

[messabout]

If your aim is all out speed then you will want to investigate the "pickle fork" design. That type of boat is basicly a three point hydro. The sponsons extend outward away from the main body of the boat and pretty far forward. Viewed from the top they do remind one of a pickle fork, thus the name. The angle of incidence of the sponsons is adjustable. There are no steps at all. These boats in RC form can approach 180 KPH. (kilometers per hour)

[Jimboat]

Flysafe - your investigation of step design is sure to be interesting....it can be a controversial topic of design discussion. Step design - particularly mulitiple step design - can be a very tricky feature to implement effectively. From a design standpoint, steps are somewhat limited in advantages for several reasons, perhaps primarily because a properly designed step can only benefit the performance of a hull at one velocity - so all other velocities in the operating range of the hull are not benefited by the step. Steps also have some rather nasty side-effects, particularly the unexpected venting - particularly during cornering - that can cause significant lift loss and movement in dynamic CofG, often causing high speed "tripping" of the hull and even broaching.

there is more on step design in this thread (http://www.boatdesign.net/forums/boat-design/stepped-hulls-7343.html#post47245).

It sounds like you may be intent on building a vee hull design, but if, as messabout suggests, you are interested specifically high-performance hulls, then perhaps a tunnel hull design will give you the result that you're looking for?