Re: step hull
 

Hi Dean;

At the Toronto show we had Evinrudes on it because they paid a promotional fee to do it. The boat was rigged with Merc 250xs motors. That boat has run 90.1 mph and thats on 87 pump gas. Now we are all excited to get the first I/O version in the water.

Re: step hull
 

TUFFBOAT:

We're looking forward to seeing the I/O version. If you are interested in competing with the best single engine boats in offshore racing , give me a call.

Re: step hull
 

Just curious why don't you see people with hydrofoils?

Re: step hull
 

People feel more stable on waterskis. :p

T2x

Re: step hull
 

That is something to be proud of Mark. When I looked at the hull and how you did the bottom the first thing I said to Cindy was I bet that boat will fly!!
I think I will do the things you showed me on my new hull. I was really wondering though when I came on this site if I did the bottom just like yours and added the steps in , it may be great. I am pretty much scard of the step hull thought. When I first started out with my first boat I was under the impression that a smooth botton boat was the way. NowI have had people tell me getting air under them in much faster!
Thats why I was realy happy to find this site. Talking to people that think they know and have never done it ,is not near as good as the people on this site that lives it. I have learned don't talk to the guy just going into the bush ask the guy coming out the other end.
Dean

Re: step hull
 

what is it that you are doing? are you building a boat from scratch? if so got any renderings? Would love to see it.

Re: step hull
 

Yes I build my boats from the ground up. I start out with a buch of lumber on my shop floor and go from there. The last one was a plan for a six meter race boat and I made it in to a 22ft bass boat. Now I am going to add another foot and go from a 18 degree to a 24 degree bottom. My wife and I have had a push pull thing happening on the length.(All in fun)I was going to go 24ft and she loves our 22ft so I have decided to go 50 50 with her.The beem is only 7ft and the length will be 23ft.
All of these bass boat compains build boats for mill ponds. (not like our ponds we fish on) Ihave seen guys in the hospitl peeing blood for a week after a ternament on Eire. That is how all the bass boats ride to. I have drove almost every comanys boat and after having a boat like a offshore hull I will never go back. My 22ft will still go in 12inch of water the same as there boats but does and not kill you getting there.
Dean

Re: step hull
 

Soon......

Re: step hull
 

Dean;

Because of the way the water moves ( displaces ), I think you will find that there is quite a bit of air under a straight bottom boat. By the way, my straight bottom boat has aeration tubes in it, just trying to get both worlds. If you re-read the thread listed near the top, all this stuff was covered by T2x alreadly.
There is not just one good idea, lots of different things work with completely different approaches.
With your boats you have the ability to try, and then change your mind, and try again.
Like the Boss said to the hit man when asked how to kill the target..."go with your hart".

Mark

Re: step hull
 

I expected someone to answer your question by now, but no, just joking around. That's OK, but here is the actual answer:

The bottom of a planing boat is like the bottom of a wing. It works by creating lift. It creates lift by having a positive angle of attack. It works well if there is a lot of lift for a given amount of drag: a good L/D (lift to drag) ratio.

Lots and lots of tank tests and full size tests over the last 150 years have shown that the best lift-to-drag is achieved at 4 to 5 degrees angle of attack -- the keel line sloping upwards from transom towards the bow at 4 to 5 degrees.

Without a step, this means the boat needs to balance on the transom. This means all the weight needs to be as far aft as possible. This can be done, especially with an outboard on a small boat.

With a step, you can have "two wings" -- one forward and one aft, both at 5 degrees angle of attack, allowing the center of gravity to be much further forward. This is much more practical for inboard powered boats, or boats that carry lots of gear and/or people forward of the transom.

Over the last 80 years, many tank tests and full size tests have also shown that the best hull shape is a monohedron -- constant deadrise across the planing surface. Its OK to let the deadrise increase a lot forward, because its out of the water at speed, so no penalty in drag, but you get a benefit by having less severe pitch accelerations in a sea way. Any movement that is not forward is a waste of energy, therefore a faster boat in waves has more deadrise forward.

It took about 75 years of step boat experience until tests could show that the optimum number of steps is one. By the 1930s, the well tested designs in fact all had one step. You'll never see a seaplane with more than one step, for example. However, having more that one step, such as the two close together used by Fountain on its bigger boats, does help as it allows the two "forward wings" (planing surfaces) to have a higher aspect ratio (shorter length .vs. span) and lift-to-drag improves with aspect ratio.

Why not have a zillion steps, like Outerlimits, Nortech, and so on? Why are the boats with lots of steps always slower (unless they are lighter and stiffer, as the new Skater boats)?

Because, as was observed during the 1910's and 1920's and finally understood by 1930, having lots of steps causes the lift to be very unstable longitudinally -- the boat porpoises unless things are done to add lots of drag (drop tabs, or do like Nortech and add way too much rocker forward).

Having lots of steps (as on Outerlimits), or even having the front two steps widely spaced (as on the early Extreme 39 hulls, and on Cigarette hulls) leads to control problems that crop up suddenly. This was well known 80 years ago, and is again being demonstrated by these poorly designed hulls today.

Re: step hull
 

Oh: I forgot. It has NOTHING AT ALL to do with getting air under the boat. Lots of people thought so originally, and many people think so today, but experiments proved conclusively long ago that air pipes leading to the bottom of the boat, or to steps, have absolutely ZERO effect. They do add weight and complexity, and more holes reduces strength and stiffness, so they actually slow the boat down.

The reason for lifting strakes that run fore-and-aft on the bottom of the boat is to cause the water layer (bow wave, or bow spray) to break away from the hull, reducing surface area drag.

But the whole air-under-the-hull story is totally bogus, and has been proven to be so over and over and over.

One of the most recent experiments I read was introducing bubbles under a planing surface via pressurized air. The INCREASE in drag was quite a lot.

Why does getting air under a hull, even a planing hull, INCREASE drag? Because each bubble introduces the force of surface tension, and the surface tension of water is quite a lot actually. You are trying, a zillion times over the bottom surface, to rip the bottom of the boat free from the surface tension of those zillions of bubbles. No single bubble is a lot of force, but a zillion is a measureable amount of force.

No, you want smooth flow under the boat, not aerated flow. No different from any other fluid flow problem: laminar flow (smooth flow) is your friend, turbulent flow (like bubbles in water) is a HUGE disadvantage.

Re: step hull
 

soon...?

Re: step hull
 

Now thats a lot of info!! Thank you guys for the help and your time. You must of been tracking boat hulls a long time crash to no all that history. It is somthing how a boat hull can be such a sience.
So what is a aeration tub Mark and what does it look like. When I looked a your boat I could only see what I call lift straps.
Another thing I did on my last hull was I cut my lift straps back about three feet from the back. I no that you had told me that I might try going all the way out the back this time Mark. Why did I do it!! Well I look at every hull I see and I seen that Scarab did that on there boat I seen. Why would they do that because after you think about it you are losing lift. I just thought that they would no best on that. But like you said crash all diferent boats run different.
Thanks a bunch
Dean

Re: step hull
 

I'm gonna need to see this proven on mythbusters. The bonus will be seeing Kari Byron in a swimsuit again.

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So why do Outerlimits and Nor-Techs have multiple steps (ex 6 or 7)
If its not for speed, it must be for production cost. These small steps must be easy to build, compared to 2 big ones. The big steps are often shaped as a pear or triangle. This effekts the strukture and stifness much more.

MTI who seems to be fast now, have 2 big steps on their hulls.

But Skaters are as fast, have multiple smaler steps. etc Baccardi Silver skater.

Anyone that know why they coose different.

Re: step hull
 

Anyone ?

Re: step hull
 

OK,
I can tell you this, I was bench racing with the owner of one of the BIG guys mentioned above and he told me when I asked about the effectiveness of multiple steps...

" I don't know if it does anything, but I'm not going to loose a sale because another builder has them ( multiple steps)"

Which means to me that we the buyer asked for them.

By the way, the aerating thing, don't confuse introducing air on to a flat surface with introducing air into a negative pressure area like behind a step or a notch.

Re: step hull
 

Were you and I separated at birth?

:p

T2x

Re: step hull
 

Now I'm just checking here, T2x,

When you built the Challenger 21 with the step in it... remember... do you recall that it went better with or without aeration tubes in it?
I remember the difference.

Re: step hull
 

Interesting. T2x, you agree with Crash?

Re: step hull
 

As I recall, George Linder told me that you did not test the aeration on that set-up. In case that is true I will attempt to recall the effect,
The step on the Challenger was a different idea, it was a small step, almost a notch that only existed between the two inside strakes. It did not extend to the outer edge of the hull. The problem seemed to be that the water around that step set-up sealed off the ability for the air to be draw in and 'release' the low pressure area created. The boat was stuck down until a wave or some 'release occurred. The solution was to allow air, via a pipe, to release the negative pressure and therefore release the boat.
I have had the same experience with a shallow notch holding on while coming on plane. Again piping in a release opportunity for air solved the problem.

Re: step hull
 

The fact that the name of that picture is "Stinson Splash" just made me fall out of my chair. Has anyone heared from him? That crash may have had more to do with He and Dick arguing at each other rather than running the boat. Best race footage I ever saw in my life was a deckshot of Sean and Dick running F-2. They kept yelling at each other and at one point Dick got SO mad he actually stopped looking at where he was going and looked over at Sean for about 5 secounds. Kinda like a father getting ready to slap his kid accross the front seat. What ever happened to the good ol days of racing?

Re: step hull
 

As I recall, the stepped 21 was actually slower than a straight bottom without the tubes...after adding the tubes,,,the vacuum was released and speeds increased but not quite up to the non-stepped speed...... with the exception of the sterndrive (heavier hull...deeper in the water) That boat had equal speed either way....... (65 mph range).

My belief is that pads and steps are not a good combo....

T2x