New Vee Hull Design Pics!

[sharkeymarine]

Pictures of this NEW VEE HULL DESIGN are now up on my site
under "BOAT BUILDING" at: SHARKEYMARINE.COM (http://www.sharkeymarine.com)

[chares-haske]

Very nice!

Who did the design work?

I have never seen a vhull constructed in halves before. How come you chose to do it this way?

[chares-haske]

Also the "Ram Air Ventilated Triple Stepped Hull w/a Notched Transom and Large Strakes" is quite a distinctive design!

I see the steps are movable during the construction, and the transom too? How are the different step positions determined? Is this so you can modify it based on the real world performance? Is this commonly done?

[chares-haske]

> I have never seen a vhull constructed in halves before.

I should say I have seen molds which are done in halves, but never the actual fiberglass hull layed-up in halves. I've always seen the mold joined first.

[Stephen Ditmore]

I've heard Art Paine refer to this as "ventral seaming," and it's common among open 60 solo 'round-the-world race sailboats. Joining the two halves takes the place of a hull/deck joint and puts the heavy taping along the keel where you want reinforcement anyway.

[tom28571]

Many builders use keel joined hulls, especially for boats with tumblehome. I've known a Lancer sailboat that was joined this way and later split down the middle. Lancer is, or was, definitely not a quality builder though.

Questions:

Was any wind tunnel work done on the ram air inlets to determine whether they are optimal? It is not clear that the air flow is enhanced by the location of the inlets.

How much of the air flow is driven by step suction and how much by the ram effect?

The strakes are notched to allow air flow from the sides. What percentage of the air is provided by each source?

Where are the air channels located in the hull that feed the steps? I did not see them.

These are just curiosity questions. If any are proprietary, just ignore them.

[Stephen Ditmore]

I like the Sharkey boat, but the thinking behind the steps differs from the ideas I picked up working for Harry Schoell. Here're some of my thoughts on step design:

Like wings, most planing boats tend to generate their best lift/drag numbers at about a 4 degree angle of incidence, and tend to generate most of that lift along the leading edge of the whetted surface area. The problem is that, once into the planing regime, the faster one goes the more the boat lifts out of the water and the farther aft this leading edge moves, altering the trim. A boat without a step relies mostly on the LCG (defined as the distance of the center of gravity forward of the transom) augmented perhaps by trim tabs or a trimmable outdrive unit, to maintain its proper planing angle. For every hull shape and speed there's an optimum LCG, but as speed increases the optimum LCG moves aft.

The best body of theoretical work on planing hulls has been developed by Daniel Savitsky at Stevens Institute's Davidson Lab <www.stevens-tech.edu>. Most of his papers are available from SNAME <www.sname.org>, as are proceedings from the biennial "Power Boat Symposium" presented in Florida by the Southeast Section of SNAME. I have the proceedings of the fifth (1993) symposium in front of me, and in addition to a paper on the history of his research by Savitsky there's a good paper by Donald Blount <www.dlba.com>, two papers on stepped hulls, and a short but informative theoretical paper by John Almeter, who succeeded Blount in his Navy job when Blount left and set up his own firm.

Savitsky's method is more than I can wrap my head around all at once, and I've found the Almeter paper to be a more accessible introduction to the parameters important to planing boat analysis. The stepped hulls in the Clement / Koelbel paper are very oddball, but the type discussed in the paper by Morley Smith is basically the type I'm familiar with from working for Harry Schoell <www.pulsedrive.net>. Bob Hobbs was quite ill by 1993 and did not present a paper, but he authored papers and was highly regarded as an expert on stepped hulls prior to that.

Stepped hulls have two advantages - they can maintain near optimum trim across a wider planing speed envelope, and the amount of whetted area that is not near the leading edge, and is therefore not producing lift efficiently, is reduced. Boats with a step or two aft of the LCG are achieving this by effectively moving the transom forward as speed increases. The type that Schoell, Smith, and I prefer has a single step forward of the LCG, so the running trim is more dependent on the size of the step than on the exact location of the LCG. As Smith points out in his paper, these hulls are at their best in combination with a surface drive, and do not work well with a jet drive since the intake would tend to ventilate.

Aerating the bottom may help performance some, but I think the more important issue is optimization of the running trim over a range of planing speeds, and in my experience a single step forward of the LCG works better than multiple steps.

[tom28571]

Stephen,

I will probably expose my ignorance here somewhere but this subject interests me as an amateur with no training or professional exposure. Lou Codega sent me some of Savitski's work on planing and I had the same experience as you, only more so.

I played with a single step hull in the fifties and was always impressed with its speed on low HP, relative to other boats that I drove. The single step does maintain almost the same trim angle for a wide range of speed. In fact, the longitudinal stability is so high that the ride of a single step hull gets downright rough or unbearable when at speed in rough water. Maybe that is the reason for multiple steps. That is, a compromise of ultimate performance in favor of handling. With no one step controlling the attitude of the hull, it could approximate the motion of an unstepped hull in waves.

Just a guess, but theory often has to give way to practical use.

[Stephen Ditmore]

In my experience the Schoell designs with low deadrise (under about 20 degrees) do ride a little rough. Those with a deadrise of over 20 deg ride well once you take into account how fast you're going (which is often pretty fast). The Schoell designs have a flat "pad" along centerline aft of the step.

[sharkeymarine]

I just want to clear up a misunderstanding. The Manufacturer is "HYDRA POWERBOATS". I believe the builder and an outside Marine Engineer had come up with the design. I used to get contracted to do work for this company till I decided to move into a different career. Since I saw this project, I thought I should get the word out to parties that may be interested. ;)

[Jeff]

Well, congrats to Hydra Powerboats then. And thanks to you for providing the pictures. Steps always seem to generate an interesting discussion here, and the ram air inlets are something unique too... it's always nice to see something new.

I hope you'll get some more pictures as the project moves forward.

[sharkeymarine]

I will try to keep up with their progress and add more photos as I get them...;)

[sharkeymarine]

I just added more photos of the NEW HULL DESIGN . They are located under "BOAT BUILDING" at SHARKEYMARINE.COM (http://www.sharkeymarine.com)

[sharkeymarine]

He has it home now. Graphics guy was there today. After seeing some photos, I'll tell ya, expect alot!