Stepped Hulls

I'm going to relate what I understand to be Harry Schoell's view in response to your questions, Tom. The purpose of the curved planform of his steps is most likely to bring the step at the chine forward enough that it's immersion is unlikely. It is particularly unlikely if the hull is both high deadrise and on the wide side, so it carries its chine high. Beyond this, he felt (as of 6 years ago) that additional ventilation was unnecessary, based on measuring air flow through small tubes in his models as he towed them to measure bottom pressure.

Harry felt the trim angle should decrease a little at high speeds, and for this reason he uses a centerline flat aft of the chine, but not forward of it. The data I've seen suggests that 4 deg is near optimum at most speeds, however.

Harry also believes that most control problems occur because curvature is immersed forward, and addresses it with his "delta-conic" bottom surface, which puts the straight ruling lines of the developable bottom shape approximately along the flow/spray path.

Harry's typically used spray strakes, but believes that they are far less important than getting the bottom shape right, and I think a number of other experienced designers would agree with him there. Mostly what they do is reduce the bottom area whetted by spray.

My reason for favoring a narrow flat along the centerline is that I think it improves lift and prop flow with a minimal impact on ride (as long as it is not too wide). "Pads" near the stern have become quite common. I favor carrying the flat farther forward.

The issue with cats is getting them to lean into turns. Any thoughts on that?

 

I don't know much about power cats. Perhaps using the same logic that works with monohulls may help. In a turn with a V bottom monohull, the lateral movement causes the inside half of the hull to stall and lose lift while the outside half creates added lift due to the steep angle of attack. How about making the cat hulls an asymmetric V with the outside part wider and the inside of the V just wide enough to avoid having the hull on the inside of the turn dig in too much.

Multihulls, even more than other boats having very high length/beam ratios, don't turn very well no matter what.

 

On second thought, lateral asymmetry of the hull bottoms may not be a good thing on cats. It could cause extra stress on the hull connection by an off vertical force due to the lift of the two sides not being equal. It could also make for steering problems in waves when the hulls receive different lift vectors and there are lateral accelerations because of this.

Another thought that occured is that trim tabs geared to the rudders could add lift to the outside hull and down force to the inside one in a turn. This might result in a twisting moment on the hull and that could be bad .

At any rate what is needed is some way to make the outer hull lift more than the inside one, but of course you already knew that.

 

In the latest Professional Boatbuilder that came today, there is an excellent article on powercats. There is mention of asymmetrical hulls to help the boat bank inward while turning so I guess I was not far off. They don't mention any of the possible negatives that I was concerned about but I'd still be interested to know if such problems exist.

 

HARRY'S DESIGNS

DID YOU KNOW THAT HARRY HAS DONE TWO CATS WITH A SINGLE STEP? ONE IN NEW ZELAND AND ONE IN THE STATES.

 

ONE OR TWO OR THREE STEPS

I THINK THAT THE REASON FOR MORE THAN ONE STEP IS THAT IF YOU GET A SINGLE STEP THAT WORKS THEN YOU WOULD BE INFRIGEMENT TO THE HARRY SCHOELL PATENT. I AM SURE THEY WILL ALL HAVE ONE STEP WHEN HIS PATENT IS OVER.

DOES ANYONE ALSO KNOW THAT HE HAD THE PATENT ON STRAKES OR LONGITUDINAL STEPS?

 

If you happen to remember the builders or have a link to their web sites I would love to have a look.

And welcome to the forums!

 

Reply

Thank you.

The one in the US was Caiman Cats. Awesome in the Great Lakes, the turning at that cat at speed (40mph). Do not know if they have a web site, do know that a major boat mfg. was looking to buy the molds for there line.

The other one was in New Zealand in conjunction with Wright-Lavarnos design team for a boat builder named Haines Signature out of Austrialla is promoting that boat. They are also doing a larger one in design now with Harry. They are in the process of building the first one and in design on the second.

Frankie

 

The earlier comments on strakes and chines reminded me of some things I have been told over the years. When I worked for Bertram in the late 80's, Lee Dana told me they had done some tank tests of their hulls and determined that on large, heavy boats, the strakes provided no benefit. Thus the reason why Bertrams developed during that period had smaller strakes on each new boat. Why were they there at all? Because they were Bertrams and the sales department thought that the customers would have a negative reaction to Bertrams without strakes. We finally did do away with them on the 72, but later design teams (owners?) brought them back. Ask ten designers a question, get ten answers!

Later I worked for Pro-Line and was told By Dan Attwood, the founder of Pro-Line, that when he and his father worked for Glastron in the sixties, they had also tested boats with and without starkes and found little difference. I was designing a twenty footer then and we built it without strakes to make production simpler (a popular saying at Pro-Line was "I saved you ten minutes with that change!"). Such is life at 50 boats a week. I haven't heard any complaints about that hull and in fact it has been modified and used on a number of their models, no strakes have been added.

I personally don't think they add much lift on slower boats, although high performance boats probably benefit due to their reduced wetted surface at speed. I generally use them for spray control nowadays.

 

STRAKES

Yes You would use them as spray rails and the other purpose is to reduce frontal area. Water will stick and continue to run up a surface until there is something to break it off. This will continue along the entire boat through the different stages. Of course the ones further to the bottom would not do as much on a slow boat as it never gets that far out of the water. And you are right the faster boats will benefit more from this.

Love this.

 

IBEX-2003

There is going to be a forum at IBEX-2003, on Stepped Hulls, of which Harry Schoell and two others will be moderators. You might try to make it. Also, a boat with the DDC will be available at the Marriott for a ride.

PM me if you would like a ride.

 

attorney site on step hulls

http://www.bfca.com


Go to the above site click on Publications and look under advisories and click on It's Hard enough to Make Boats.

Makes for some interesting reading.

 

Interesting reading. The thing that always makes me wonder is how someone can get a patent for something that has been in common existence for many years. Stepped hulls have been around since the early part of this century, had anyone built a single step hull before Harry Schoell? I don't know, but I would guess someone had. This isn't to take away from Mr. Schoell as I find his designs and construction techniques more interesting than most. My understanding is that A.E. Luders designed the first Deep-Vee around 1905, he just didn't have an engine with the required horsepower:weight ratio to get it on plane. This reminds me a little of the current Hinckley Picnic Boat nonsense where they have taken ownership of sweeping sheerlines, tumblehome and C-shaped aft sides of houses. All these things have been common on SF boats for decades, yet somehow they are now claiming to have the rights to these things when used together. We surely have way too many lawyers in our midst!

 

yes you are right.

Yes step boats have been seen as far back as 1905. But the handling charatristics were very bad. It took Harry 20 years towing models to come up with the right geomotry for this step boat to have the best handling charateristics and most efficent plus he can go from drawing board to mold to boat without testing as he did this already in his R&D for the patent. There have been other boat companies trying to do the step but not have the right formula and have to drop the design and just put vents in the chine (ie Wellcraft). I do not see anything wrong with someone getting paid for their R&D to make something better. How about the guy at GM that invented rocker arms? The engine was already built and running but he made it better.

Thanks for the opportunity to discuss these issues.

Harry's patent is a Mechanical Patent and not his only in this field.

 

patents

I haven't looked into the step hull patent or history that you're discussing, though I am somewhat familiar with the Hinckley deal.

What I am more fluent in is patents themselves as I've collected a few over the years. Design patents are known to be the easiest to obtain. I'm told all you need is a drawing..not even a working model.

There are three questions that must be answered to even open the discussion on whether to seek patent protection. Is it obvious to those skilled in the art? Is it novel to the art? and Is it useful for something?

I'm guessing you think the step hull or Hinckley deal is obvious and it may well be, but apparently the patent examiner at the USPTO (US Patent & Trademark Office) didn't think so. Any patent can be contested in court, the problem is that it's pricey to do so. Only people/corporations with a big chunk of money at stake will take up the fight. The problem with the obvious clause is that during the patent application examination there is no push-back from people that would claim obviousness(the examination procedure is confidential in the US...not so in EU where applications are published prior to granting the patent)...there is only the patent applicant(attorney) and the patent examiner. Patent examiners are paid by the number of cases they complete....

Is it novel to those skilled in the art? This is a bit tricky in that you can take 5 "things" that are well known & have existed for years and combine them in a new way...if you can make the case that the combination is new (and useful & not obvious), then you've met the criteria & you move forward. Part of the novelty clause is that whatever the new combination that is claimed is, it can't physically exist in the public domain or be discussed in the literature. If you can pull up an old hull or a journal/magazine article discussing the combination then the issued patent may be invalid. If you feel that you have a solid case (seek a patent attorney's advice) you can, & people/corporations do, knowingly "infringe" on the patent with the knowledge that if they are taken to court they have a better then even chance of invalidating the patent. If they aren't pursued for infringement then they carry on. The down side can be that if they are taken to court..and they lose...the costs you'll see will be brutal. You may have to pay all profits you've gained through the infringement to the holder of the patent.

Is it useful for something? This one is easy to meet, usually.

There are strategies of offensive & defensive patents, but that is another whole discussion.

Be advised I'm not an attorney & I'm not suggesting you break any laws..I've just dealt with these issues as a part of what I do for a living.