Examples of wave piercing hulls, please?

Then we beg to differ.

You raised the issue of being “over powered”.

This is ostensibly true only for sailing multihulls which have no deck between the hulls, as pretty much most racing yachts are arranged as such.

This is not the case for powered vessels; these have “foredecks” between the hulls up fwd and “deck dive” or “bow dive”, they do not pitch-pole as such. This discussion is, in general, about powered multihull per se. All references on this thread to date, save for Daiquiri’s videos, refer to the classic WP hulls used on fast ferries et al ; which has a 3rd bow up fwd, ergo, not an open deck. Even that vessel posted at #4, falls into said catagory. And as such these vessels exhibit different behaviour once the hull(s) enter a wave.

 

Ad Hoc,

When I lived in Japan we were always concerned about miscommunication due to "Japanese English".

I am going to attribute this little "discussion" to that problem and withdraw.

My point was very simple and it had nothing to do with anything but the video in post #87.

I have thought that you had something useful to say, but now that I am on the receiving end of you not paying attention, I understand the irritation of others.

 

Great video

What you are seeing is significant reserve buoyancy being put to good use, rather than a lack of; the amount of "hull" above the waterline. Without the reserve buoyancy as such, these trawlers would have capsized.

 

These guys might disagree with you



http://www.lomocean.com/

I will alert them to this thread so we can get the navel arc,s and professionals to quantify.

 

BMcF, I'm curious about the linear code you use. Are the coefficients used the theoretical ones which result from assuming small amplitude oscillations, or are they from experiements, or something else?

On a somewhat related note at IBEX tomorrow Eric Giesberg and Michael Morabito are presenting an approach to obtaining empirial equations of motion for planing craft. They use Euriqa software which finds a "best fit" of the form of the equations to data. I don't know if their equations are linear or non-linear: In this advanced seminar for designers and engineers, we’ll consider the effect of planing boat parameters, speed, and wave height on the resultant motions and accelerations. In irregular waves, quick prediction of planing-boat performance is helpful to verify concept designs and to visualize the effect of speed, wave height, and other parameters on motions. Currently, simple empirical equations exist for estimating vertical accelerations and added resistance but not for heave and pitch motions. Here, we’ll describe how genetic algorithms have been used to develop an empirical method. You will learn how data sets are derived from prismatic model tests, and how free software, Eureqa, generates equations for heave, pitch, and accelerations at the center of gravity and at the bow. We’ll detail how the final equations are selected, and how they compare with other methods for predicting heave, pitch, and accelerations. http://www.ibexshow.com/seminar-series2.php

 

Our code was almost 100% "physic based", with only things like the lift on appendages and some added-mass damping terms having any connection to emperical sources. The software included no means or facilty to "insert or modify" various matrix coefficients like so many others do or have. Everything was based on "small perturbation" modeling.

The USN insisted/specified that it be that way; the program development was started back in the 70s (not be me then..I'm old but not that old) by people like AW Ernest and was specifically intended to provide insight in to the behavior of novel and advanced ship concepts (SES' in particular)...concepts for which no previous basis or model testing even existed in so many cases.

After nearly two decades of quasi-continuous development, refinement and extension, it became a very accurate tool for the prediction of the motions of any twin-hull vessel excepting SWATHs.

Still officially "USN Property", the code was never made public domain and has languished in recent years as the USN users have retired and the compiled versions became platform-obsolete.

 

That company has built some very impressive boats. I have been studying the Planet Solar boat for a while. I hope to build something similar but about half size and diesel powered. The general layout of the design has many features I like but will not go into here.

I am not remotely qualified to comment on the design on a technical basis but I can comment on it's demonstrated performance.

One thing I have noticed is the boat rides like crap. The first time I saw a video I said to myself that thing needs the buoyancy distributed much better, specifically the hulls need more buoyancy in the bow. There may be other variables at work but I'm sure the hulls don't help. It looks like they hired a designer from the Americas Cup to design hulls that would average 5 knots around the world.

Here is an example video that shows it bobbing along in very mild seas at about 0:16. http://www.youtube.com/watch?v=4N3bUpscm_U

Here are couple pictures of the hulls.

 

My guess is that they had an imperative of minimizing the structural weight of the boat, so the volume enclosed by the hulls topsides is shrink to a minimum. That's the only so-so valid argument I can see for completely getting rid of the topsides, and hence of the reserve buoyancy.