Ragged Chine Hull

It is my first season with my boat Ragged Edge on the water. She was built in 1982 by Kappa Marine in Milan under licence to G L Watson. I bought it without engines so put a pair of Ford Dover Mermaid Marine engines in her. She goes well showing about 16 knots but I don't know anything about the design specs. Does anyone have any information about this type of vessel. She is 8.4m long and 2.9m beam originally built with twin Iveco engines.

Greetings,
Welcome aboard.

Hi RJim

Don't have any info but a few questions that may provide some help for comparables.

Do you have a picture of the stern? What is boat weight and draft? What HP are engines?

I found a little information on the Kappa Marine Shipmaster 840 and 850 of about that vintage. Power was listed as Aifo-Iveco (2x135 HP) - Diesel. The multi-chined hull and sponson-exhaust looks like your photo. The cabin is a little different. With the Iveco power, the top speed is listed as 27kt and cruise is 20kt. The draft appears to be 0.7m and displacement 3.5t. Fuel is listed as 700l - 850l.

Here is the 840

And here is the 850

That's all Google would tell me . . . .

This is a picture of our kappa marine 8.5.
She has twin 120hp sabre's

Actually it isn’t a multi-chine hull.
But she has a whole sack full of spray rails.
I’ve seen boats like this before .. pics that is.
The maze of spray rails turn solid water into fine spray if there’s any wind and when there’s waves there’s wind. The wind has it’s way with the spray generated by chines or/and spray rails and it comes aboard.

At least that’s what will probably happen if there’s much wind and sea. But I’ve never even seen one of these boats much less seen one in action. And often what seems obvious is not. Perhaps it only happens under certian conditions.

But what is clear is that the hull will be heavier and the wetted surface will be greater. More drag and more weight are not friends to performance. But advantages from the many spray rails may outweigh the advantages of a more common hull. For example if the water is allowed to run up the bottom and the sides of the hull there will be much more wetted surface and water higher on the hull. My boat has no spray rails and it’s quite a dry boat. But my boat goes very slow. Many variables make a complex situation.

Something we do know is that very few boats have been built w so many spray rails. Lift strakes like what most all deep vee boats have reduce wetted surface and increase lift. Ray Hunt’s boat proved that in 1961 in a powerboat ocean race that it worked and very quickly most fast powerboats became deep vee boats w lifting strakes on the bottom. It was an industry revolution.

But the man that owns the boat has experience that should shed light (or water?) on this unusual boat design. I hope he’s not tired of talking about it. Many many people have almost certainly asked him about it.

John Teal discussed ragged chines at some length in his book Fast Boats.
An interesting and underutilized idea. He goes on to say that that it only takes a rail 10mm thick to peel off water running up the hull and anything wider is for lift also. If you want to plane, you have to get the water off the hull ASAP.

Nomad Willy said:

...But what is clear is that the hull will be heavier and the wetted surface will be greater. More drag and more weight are not friends to performance....

Click to expand...

Interestingly, the hydrodynamics may not agree with this age-old assumption. We imagine water molecules sliding easily along a smooth hull, but in reality laminar flow over a smooth surface creates chaotic, drag-inducing vortices. It's why a golf ball has dimples.

It would be interesting to see comparisons of tank models with and without the ridges.

Smooth sailing: Rough surfaces that can reduce drag
January 17, 2014
American Institute of Physics (AIP)

Summary:
From the sleek hulls of racing yachts to Michael Phelps’ shaved legs, most objects that move through the water quickly are smooth. But researchers have found that bumpiness can sometimes be better. They modeled the fluid flow between two surfaces covered with tiny ridges and found that even in turbulent conditions the rough surface reduced the drag created by the friction of flowing water.

The hull design is a confusing mix of features, deep vee combined with round bilges squared off again by exhaust/spray rails, then that handful of reversed strakes, WTF??? Oh yeah, it has a keel too!
I smell weed burning...

Doubt about the weed kapnd. I designed a stranger boat w no weed at all.
I don’t think the actual deadrise is enough to be a deep vee. I thought so at first too. I think fuel is burning overcoming the extra drag.

Yes Anson rough surfaces have reduced drag at times on various shapes. The surface on this hull is more like jagged or lumpy that dimpled or micro grooved. Closser to surface obstructions than texture reducing drag.

Brooksie,
Yes flip the water off ASAP. But this “Ragged Chine Hull” is not about to shed water underneath the hull.
I’ll look up John Teal ..... thanks.

Re this design I personally think the strakes/rails should start at the bow horizontal ... not swooping up. The water then meets the rails at a much shallower angle causing less spray .. and less drag. This applies to other boats that have swooping up spray rails.
Also (and what may seem obvious) is that the spray rails have no use under the boat. That part of this design I can actually label dumb. It’s just not going to do any good. It’s just 100% increased drag and weight.
Re why there aren’t more boats like this think for a minute about building this. Those strakes/spray rails cannot be made in the male mould so lots and lots of exrtra weight and man hours went into this hull. Did it pay off?????


Other than the spray rails I like the rest of the boat a lot. Even the red paint and white boot stripe. The cabin looks very nice too.

You have to wonder if the NA wasn't inspired by the ventral pleats of the Blue Whale. Supposedly, when excited, they can attain 20 mph submerged. I wonder if that is 'because of' or 'in spite of' the pleats. I'll bet the folks at the Naval Submarine Base New London in Groton, CT. might know a thing or two about that.



"For about 20 years it has been known that special microstructures (“riblets”) can lower drag by up to 10%. A new process for the production of such microstructured coatings on large surfaces is presented in this article. This process allows coating application, embossing, and partial curing in a single step. The coating material consists of VOC-free nanocomposites that give the coating the necessary abrasion resistance and weathering stability.

Drag measurements have been carried out in a ship model basin and in a wind-tunnel respectively. In these experiments, smooth coatings were compared to riblet-structured coatings. These structures were adapted to the flow-parameters of the fluid. A surface-drag reduction of 5.2% for a torpedo-shaped specimen was measured in a large hydrodynamic and cavitation tunnel. In a wind-tunnel experiment a reduction of the total drag of a wing-profile by 6.2% was measured.

Both experiments indicate the high potential for fuel savings in the transportation sector."

http://www.sciencedirect.com/science/ar ... 4010003206

Or the latest in performance swimmer's gear . . . . "Secondary function being whale's skin has parallel lines which help eliminate turbulence and allow it to swim faster and more efficiently. Laminar flow occurs when fluid flows in parallel layers, eliminating disruption in the flow, also known as called turbulence. The Finishline’s parallel ribbed chest, back, and legs significantly reduce flow turbulence while increasing speed and efficiency, improving hydrodynamics and speeding your passage through the water, with less fatigue."



Just some food for thought

So if the little riblets on the wetsuit are there for performance, did they research the effect of embossing the logo right thru the middle? And what do the little blue rectangles do?

The small blue bits are from Moms apron, a good luck talisman.

So the Ridges on Ruffles potato chips contribute to the speed at which they can be consumed, boosting sales!

In the reality of a small Boat’s bottom in use in the sea, compromise is everything, and the most intricate designs go to hell as the Boat pitches and rolls along.
As long as it is built stoutly and meets the SOR, it is likely satisfactory to those who have put their money into them.

My first awakening with stepped hulls was about 20 years ago with several different go fasts. As best I remember the boats were faster with the same power and turns much sharper. Most builders say the benefits of stepped hulls appear above 35 mph.

But back in the 1920s Gar Wood and Chris Columbus Smith really got into stepped hulls with their single hull and eventually others with 3 point hydroplane designs ( another type of stepped hull). Speed went up dramatically. Fascinating stuff was done with notched or stepped hulls 100 years ago with no CAD designs, just plain old slide rule engineering talent. Even 100 years ago, single hull speeds of 125 mph were realized, with 4 engines. OF course the Cat hulls of the past few decades rule offshore now.

But back to the OP. Neat and interesting looking boat.