Examples of wave piercing hulls, please?

I appreciate your comment and can see why you feel this way. Unfortunately this started off as a simple discussion reviewing the issues that influence seakeeping. That is to say, rather than relying on ones “feelings” or “thoughts” or “beliefs”, as naval architects we need to understand the true mechanisms. Without an investigation of the actual mechanisms that affect seakeeping, how can we make informed decision and understand why XX or YY occurs on one boat and not on others? Also, as I have said from the outset, this is a terribly complex field of NA and what we are discussing is just one aspect, a major one nonetheless. But it has been flip-flopping, owing to one poster refusing to accept simple well established and known science that is used to describe the theory of seakeeping because it does not agree with his preconceived beliefs.

You’ve have succinctly summed up the issue here with a nice analogy. And the trouble is that in the use of the term myths are formed which is not supported by science, no matter how loudly one may protest. Erroneous myths and incorrect statements must be dispelled; otherwise charlatans shall take advantage of the myth for their own gain. Often financial gain at “your” expense.

If you have any questions, please feel free to ask away. I’ll do my best to answer if and where I can. If I can’t I’m sure BMcF, or baeckmo et al can.

 

Great videos D

At around 1:19 in, you can see what occurs when bows without sufficient buoyancy that starts to entering or piercing into a wave(s) at an angle of trim, they keep on going until disaster strikes. Not good!

That was the reason for the simplistic child like questions here:
http://www.boatdesign.net/forums/bo...piercing-hulls-please-44789-3.html#post583082

This simple Archimedes principal is lost in the fog of debate. A floating object remains afloat or it does not, and if it does, it does not always remain at level trim just because it is floating, not matter what it is doing on the surface. The distribution of the buoyancy is importnat too. But I don’t need to tell you that as you already know

 

In simple general terms, the WPA/displacement ^(2/3) is the indicator.

Most boats, small or large, fall into the 5-ish ratio. From the little runabout to the QM2.

You'll get the odd boat here and there that is less. Those semi-whatever you wish to call them are in the 3.0+ ratio. (BTW this debate semi or otherwise has been going on since the late 80s, when the term MWATH was used instead of SWATH. MWATHs being above 1.5 but less than 2.0).

SWATHs fall into the ratio of 0.8-1.5 range. The 1.5 being close to the upper limit. There are some that are a tad higher. The extreme, the LM SLICE is below 1.0, which is a truly unique vessel.

Thus, the WPA/displacement ratio is the indicator of where the vessel 'sits' in the "able to pass through waves" relatively untouched debate.

 

Thanks for explaining things in terms a normal non-naval architect can understand...

Ive noticed that when comparing 2 different designs, design A might perform better than design B in certain wave spectra, whereas design B might be better in a different wave spectra. So it all just depends in the end doesnt it...

Adhoc, thanks for explaining the WPA/displacement swath ratio. However can you please clarify whether its;

(wpa/displacement)^2/3 or
wpa / (displacement^2/3) ???

 

Most assuredly it does. That is why the more savvy and experienced of ferry operators will have a credible company perform a route analysis prior to making their final decisions on selecting a vessel for a particular route.

Many the high-speed ferry operation has suffered and even failed outright by virtue of having the wrong vessel in their service.

 

So, in that paper you posted, the WPC has a ratio of roughly 4.7 and the mono of roughly 4.9. Very little difference.

 

I have read this thread and the others concerning "wave piercing" hulls and am as confused as ever. Probably not relevant, but just for fun I made a box ,tapered the ends width wise , then made a copy and tapered it's top both in length and breadth ,and then manipulated the tapers until both models had the same volume and surface area. Presumably the blue model would be the same weight as the white model but twenty percent longer and draw slightly less water. The length to beam ratio could be made to be greater or not, but the length to displacement ratio would be greater. These are crude and exaggerated models and not intended to be real hulls but I have to ask. Which model would pitch less?

 

Both. Or neither. The point is that they would pitch differently.

The conditions (wave height and period, vessel speed, and relative wave heading) that would promote resonant (sometimes called "synchronous") pitch behaviors in each of your models would be different since the resonant period of each model would (probably) be different as well; perhaps quite different.

 

This company is betting the bank of wave piercing technology http://transonichullcompany.com/

I bet they will argue that wave piercing is the best thing since sliced bread.

Here is a paper they published. Check out the pictures on page 5.

 

Peter Payne spent a lifetime trying to defeat the basic physics inherent in the fundamental works of Archimedes. As have many others. It remains a popular pursuit for many to this very day.

 

Hi BMcF
Here's a thread from another site..... http://www.cruisersforum.com/forums/f48/beaus-boat-9093.html ........ is this following "transonic" theories, the builder quotes "triflection principles". The builder "trialed" a dinghy sized model apparently successfully, the "full sized" model didn't reflect the modeling results.

Regards from Jeff.

 

Ad Hoc,

With all due respect, that AC boat was simply driven under by being over powered. I looked at this multiple times and there were no waves to pierce when they went over.
I have been in exactly this situation on a Tornado and it survived due to the large full depth bow. The deck did not go under water. They were quite late in releasing the main, never released the jib. Crew error possibly brought on by trusting the wave piercing concept. But racing you take chances. No doubt if the deck was flat like the Tornado they would have gone over quicker or actually pitchpoled.
The interesting thing is that this hull shape (rounded deck) was used by Nacras in the 70's to help keep the pitchpole from happening too easily. I have seen boats recover from this attitude with quick enough crew work. The bow can just pop up if sail load is reduced quickly.

Nothing new here. Americas Cup has finally caught up with beach cat sailors.

Not trying to suggest your comments are not right overall, just the observation of the video.

 

How a boat finds itself in the situation is irrelevant. It is what occurs, once it does, that is of interest.

Perhaps you missed this bit:

Either the boat is moving, or it is not. If it is moving, how it moves or propels itself in a fwd motion is not the issue. Over powered, under powered or otherwise.

If it is moving, what occurs when a boat trimming by the head, enters a wave(s). Or when a boat is running at level trim but enters a wave which has a wave length between around 1/4 to 2 times its length. Where said boat has minimal or no reserve buoyancy in the bows of each hull.

 

This video does not illustrate your point. I am not disagreeing with your point in a situation where there are waves.

Any idiot can see the boat was moving. What are you talking about?

On a boat driven down by the head by a gust or changing direction and suddenly generating more power than can be handled the boat will pitchpole or at least stop rapidly, even if the water if completely flat.

The sailors failed to control the boat and drove it past equilibrium.
Been there, done that, have you?

You keep accusing many people of not understanding basics. Perhaps you should think about yourself in this case.

 

My take is that Ad Hoc is pointing out the cost of lack of reserve buoyancy.

Watch this video, no lack of reserve buoyancy here. These skippers have "attachments" made of steel.

http://www.youtube.com/watch?v=ec3ovHTpiL4&feature=fvwrel