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Old 05-20-2009, 06:21 AM
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Default Stepped Hulls... why?

What are the advantages of stepped hulls? I assume one disadvantage would be backing... are there others?

Just curious...
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Old 05-20-2009, 06:31 AM
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As I understand it, if (big if) the boat is trimmed correctly - a stepped hull reduces drag and makes the boat (1) more efficient, and (2) faster. Faster is important for racing and why a lot of offshore racing boats have stepped hulls. The major downside I have heard about (never owned one) is that stepped hulls really only provide the efficiency advantage at one trim angle which can be hard to achieve and/or maintain in real world conditions. Another downside I can think of is if the fork lift operator is having a bad day he could put a nice ding in the back of the step pretty easily.

I'm sure others with hands-on experience will chime in soon enough. My comments are based only on what I have heard.
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Old 05-20-2009, 07:05 AM
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Faster is the main advantage. I use to have a wellcraft with a stepped hull. It was a nice ride and seemed to ride better with a light chop on the water.
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Old 05-20-2009, 07:41 AM
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The step allows air under the hull...theoretically, this creates less friction which results in more efficiency and speed. I don't think there would be a problem with backing up.
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Old 05-20-2009, 07:50 AM
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Less power producing more speed equals reduced fuel consumption. The only real downside to steps is cornering at high speeds where they "can" slide then hook or roll. This would only be a concern during race or very aggressive driving conditions.
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Old 05-20-2009, 09:22 AM
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The purpose of stepped hulls is to reduce resistance at high speed. As you increase speed in a planing boat, running trim tends to decrease below the most efficient angle. Also, frictional drag increases significantly. Adding a step(s) allows a boat to maintain a more optimal trim angle at high speed while also (usually) reducing wetted surface area. Trade offs usually include a more expensive boat, and sometimes tricky handling characteristics.
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Old 05-20-2009, 09:28 AM
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I was surprised to say the least when I read an Uffa Fox book where he discussed the history of power boats and their design, the first stepped hulls were made in the 1900-1910 era. These boats were able to go in the 60 MPH range with ridiculously small engines. They were VERY narrow and had maybe four or five steps. As uffa explained it, the step's created lift, more lift less wetted surface and less skin drag. Skin drag is by far the most power consuming as compared to angle of attack. The steps each give their own little lifting surface each with it's own angle of attack or trim angle of something like two degrees or so. This recent innovation apparently is far from being recent as it turns out. I thought of the steps as "air Vents" till Uffa set me straight. I was blown away with this info when I read it. So who invented stepped hulls? well, whoever they were, they are long gone.
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Old 05-20-2009, 09:34 AM
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Quote:
Originally Posted by timo14 View Post
What are the advantages of stepped hulls? I assume one disadvantage would be backing... are there others?

Just curious...
Allow more air under the boat.
Reduce drag, increase performance.
But, not always the case.
We build them both ways.
Were quite surprised, pleasently so, when after taking the step out of some bottoms, lost no performance at all.
So, it's not an "always".

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Old 05-20-2009, 10:11 AM
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on vee hulls to my knowledge while many think it is a US think, the first stepped hulls started in Italy by the company Offshorer which was Riva owned I think they produced the first stepped boat in the 1980s
and there design winning a Class 1 Offshore championship was previously used by Tencara
something along those lines....
I think unless you go over 50 knots you dont really need a stepped hull that is why EU producers hardly use it, what surprises me how Larson uses a step on its smaller cruising model, and what are the benefits of this in a boat which cruises in mid 20 knots and has a max in the high thirties with the bigger engine choice
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Old 05-20-2009, 10:27 AM
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My Larson has the step. I have no issues backing, its great in tight quarters. My sweet spot is 26 mph burning 10 gph, I think due to the step. If I drop down to 20 mph or so, economy drops off to 2 mpg.
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Old 05-20-2009, 11:32 AM
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One issue with stepped hulls is transducer placement....
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Old 05-20-2009, 11:40 AM
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Quote:
Originally Posted by 1bayouboy View Post
One issue with stepped hulls is transducer placement....
Very true...you need to place the transducer in front of the step.

Also if you high n dry store your boat be sure the forklift operator know how to lift a step hull. If the oporator puts the forks under the boat in the water where they just tough the hull and then moves the forks from side to side to line up the forks then you will have big pieces of gel coat missing at the edge of the step. Also do not let a fork lift wraps in rope pick up a step hull.
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Old 05-20-2009, 01:48 PM
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Quote:
Originally Posted by PowerYacht View Post
on vee hulls to my knowledge while many think it is a US think, the first stepped hulls started in Italy by the company Offshorer which was Riva owned I think they produced the first stepped boat in the 1980s
and there design winning a Class 1 Offshore championship was previously used by Tencara
something along those lines....
I think unless you go over 50 knots you dont really need a stepped hull that is why EU producers hardly use it, what surprises me how Larson uses a step on its smaller cruising model, and what are the benefits of this in a boat which cruises in mid 20 knots and has a max in the high thirties with the bigger engine choice
Power,
check my earlier post, you have to go back about 70 years before the 1980's for the first use of stepped hull's, that right about 1910!! Uffa Fox's book had other references to stepped hulls in the intervening years. I think Uffa's book I have was written in the late 50's or early 60"s stepped hulls were well known back then. It is funny I think that WE have just now "re-discovered" this concept.
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Old 05-20-2009, 02:16 PM
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^ Even earlier actually. The very first stepped hull was conceived in 1872 by William Froude. Significant development of stepped hulls didn't really begin until the decade of 1910, however, when engines with adequate power/weight ratios were available.
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Old 06-04-2009, 06:36 AM
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I have a Larson Cabrio 254 with a stepped hull. I believe it really helps. I can be pushing over 6500#s and still top out at 42 mph with 250 hp.
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Old 06-04-2009, 07:27 AM
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Though not typically what springs to mind when talking about stepped hulls, Seacraft is also a stepped hull.
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Old 06-04-2009, 09:08 AM
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Stepped Hulls were around long before any boat builder started using them.




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Old 06-04-2009, 09:34 AM
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Quote:
Originally Posted by PowerYacht View Post
on vee hulls to my knowledge while many think it is a US think, the first stepped hulls started in Italy by the company Offshorer which was Riva owned I think they produced the first stepped boat in the 1980s

Dick Cole's (and Wellcraft's) airslot was a stepped hull, and was first mass-produced in the late 1960s. The Rybo-runner 30 was also a production stepped hull, and dates back to the early 1980s.

Below is a link to Dick Cole's patent. Item "S" denotes the step.

http://www.ultimate.com/omc-boats/ga...179/qtr/p2.gif
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Old 06-04-2009, 12:45 PM
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1934 weston farmer,N.A. "SURE MIKE" 1934 william atkin "U.S.A." double step 1934 harold tapken,N.A. "SPEEDO" plus many more from motor boating "ideal" series vol.16
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Old 06-04-2009, 01:09 PM
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Quote:
Originally Posted by timo14 View Post
What are the advantages of stepped hulls? I assume one disadvantage would be backing... are there others?

Just curious...
Lots of controversy around this one-

Proponents say - increased speed, mileage, and handling responsiveness.

Detractors say - the increased speed is a myth and if it all the tradeoff is not worth it, and that stepped hulls handle poorly and contribute to spin-outs.

I have detailed tests I could post but the file is too large for the site.



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