Eliminating High Speed Slides for Offshore Boats

I know this really hits home for you Dave, as you raced an Outerlimits and so many of these guys are your friends. Our thoughts and prayers go out to the families involved.

In reading through this, I understand the boat was entering a turn when the bow dug-in. I guess this is as good a time and place as any to address this...

People have long complained about step-ventilating bottoms sliding out in turns, where the forward deep V has better grip, because the aft section of the hull is recessed. (further accentuated when the drives are trimmed in) causing the boat to hook violently in turns. This puts more downward pressure on the forward section of hull, leaving the aft “loose”.

This isn't rocket science, it's simply applied hydrodynamics.... REVERSE THE CHINES in the aft section of the hull. Or use some sponsons/rails that are mounted vertically to the sides of the hull to add grip when cornering. The Sea Doo guys figured this out 10 years ago! If you don’t follow this visually, think about the dagger used on the left (inside) sponson of today’s modern unlimited hydroplanes. Same concept. Another example… offshore cats aren’t known for the cornering prowess, but did you ever wonder how Formula-One tunnel boats are able to make such incredibly sharp turns? The inside of each sponson (on the inside tunnel) is creating a slot in the water that adds a leverage point (or grip) that allows the drive to pivot against and around this point.

If you really want to make these hulls work better, follow Peter Hledin's lead and use multiple small steps. This will reduce the dramatic amount of recess many manufacturer's are using in stepped hulls. Multiple small steps will ultimately keep more of the hull in the water when cornering. In addition, the oversize dual-steps that most manufacturer's have adapted (one builder copies the other!) are creating as much turbulence, as they do aeration. It's simple... aerate the boundary layer of the hull. Don't turbulate the water the hull is running on. This increases drag. For reference, do you remember how your hull slows down when following another boat on his wake table? This is partly because your traveling over propulsed water that’s moving in the opposite direction, but it’s also because of turbulence! Reduce the turbulence and you will increase your speed.

There's another way to accomplish this too, although it's theoretical and we never conducted any tank tests. Generally, the high speed basin at Carderock will only allow testing of models running in a straight line, but the software we used on the Cray’s allowed us to experiment with some unusual ideas. One of the projects at the time was to develop a high speed, light assault vessel (similar to today’s PWC’s, but much faster). The ability to make quick, high speed evasive maneuvers without ejecting the operator was one of the protocols.

We came up with a concept that allowed a conventional mono-hull to make radically tight high-speed corners with limited slip. Essentially, we created a hydrodynamic slot in the water, by reversing the pad. This wouldn’t work with jet pump applications, but it was perfect for outdrives or surface piercing applications. Let me explain…

Today’s offshore deep-V’s lean to the inside when turning. The amount of lean, expressed in degrees, can often be equal to, or exceed the deadrise of the hull. The result is, when you’re banked over, you’re riding on what is essentially… a flat surface. This is compounded by strake aeration and of course… steps! BUT… there’s a way to counter this. By recessing the running bottom of the hull (for example: the pad) all the way to the transom, we gained two valuable elements. Lift was generated at high speed due to compression in the recessed area and it generated considerable grip when banked over in a turn. The best part about this design was you could still utilize steps and strakes for aeration, but you maintain a constant running surface all the way back to the transom. (which is like having a longer boat in rough water!)

In doing this, "ledges" are created along the inside section of the recess, that is again running longitudinally down the pad area. If you don’t follow me, imagine looking at a deep-v from the rear. The hull comes to a point at the bottom of the hull. It is this point that is inverted, or recessed. The section could by tunnel shaped, inverted pad shaped, or reverse-v shaped. I’m leaning toward the later two. We never built proof of concept models, but we didn’t have to… it’s simple common sense and the computer (remember, a Cray 9000, the world’s most powerful at the time) supported the concept.

For what this is worth… it may help save lives and reduce insurance rates. If you want to pass this link along to the guys at OSO, you are welcome to.

Again, my sincerest condolences to the family and friends. Like Mark Lavin’s death, maybe something positive can come from this.

Carl Camper, Admin
www.YachtForums.com

I find that these episodes upset me. Racing is one thing, the risks are anticipated and part of the reality check. Racing incidents are unfortunate but all involved know that it can and will happen.
Casual boating at high speed is a whole other deal. When I got to the part where the PFDs had come off I stopped reading. What a ****ed crying shame.

Of course the ejection problem is why the serious offshore race boats now have cabins with harnesses. Very high speeds in open boats will always be high risk (I suspect).

Carl, interesting proposition with that inverted keel pad. A few production builders (Campion comes to mind) have been using a mildly recessed pad for years. Though I believe their goal is still lift, rather than cornering grip. Also interesting to read your take on the multiple steps seen on some boats. When I first saw one of those it struck me as rather silly, but now I understand the reasoning behind it.

Thanks,
Kelly Cook

Carl I put your post up on OSO.

Good point Kelly. By the way... it's not actually the impact that kills you. It's the sudden stop.

I attended the Toronto International Boat Show about 10 years ago, (one of my distributors asked me to come up and work the booth with him). I met with factory reps from Campion at that time. I always liked their designs. Good looking boats. If I remember correctly, they won a PowerBoat magazine award a number of years ago too. I'm not up-to-speed on their current hulls, but I'm glad to hear of manufacturer's trying new ideas.

Thanks Kelly.

Let's hope something good comes from this. We've lost TOO many friends over the years. In my offshore days, we lost Dick Fullem, Mike Poppa and Mark Lavin. Had the pleasure of hanging with Mark a few times at Lake-X, while his conquest cat "Jesse James" was being tested. These were WAY back in the Don Schwebe days. It's been too long...

Mike Poppa's daughter is on OSO now. Her board name is kpoppa. Steve gave her a VIP membership.

I never met Mike's daughter. I knew Mike & Dick when they raced a 30' Velocity, built by Steve Stepp.

Sure takes me back in time. Stepp's 22' Velocity had some merit (and de-merit). On the positive side, they used a running bottom that was quite long for a hull this length. On the negative side... that 12" wide pad-hull was a chine-walking nightmare. I remember Gene Whipp (remember Team Gulfwind) using K-planes from a 30 footer to control that little rascal. Gene could drive it! But less experienced drivers... got a crash course in controlling chaos.

I still think George Linder's original work, i.e. challenger, shadow, superboat, etc... we're among the best "little" offshore hulls ever conceived. But, time goes on and our boats get a little bigger... and a lot slower.