Wave Piercing Bows

[ImaginaryNumber]

Originally Posted by waynemarlow

...True wave piercing shapes are very different to a raked back bow, nature certainly has designed some pretty good wave piercers and they certainly don't look like the shapes we term as wave piercers.

What does a nature-made wave-piercer look like?

[sean9c]

I don't know anything, and even less about multi's, so feel free to tell me I'm wrong but doesn't the Tornado cat with it's more traditional looking bows stand up well in performance comparisons to the newer more vertical bow designs?

[Petros]

Originally Posted by hoytedow

Thanks for the inspiration. My boat will be named Sea Cups.

How about "See Cups"? OR "See pair" perhaps?

From the time I once spent racing catamarans many years ago, when a lee bow goes under two things happen, there is no more increase in righting moment because the whole bow is under, and the drag goes way up. so risk of pitch-poling goes way up (trust me, it happens so fast you usually do not have time to react to it). Lee hull goes down, windward hull goes up, catching more wind under deck to lift it higher, sudden increase in drag at the lee bow causes boats inertia to want to roll the boat up and over, wind in sails and under deck help drive it up and over. No stopping it once bow is fully submerged.

If the function of the swept back bow is to prevent pitch-poling I do not see how, the righting moment goes DOWN as it goes under faster than in a vertical walled hull with no flair. Drag would be reduced as the rake-back bow goes down, but the tendency to dive deeper and faster is actually higher. This can not prevent pitch-poling, it appears it would to make it worse.

But something missing from this discussion is the effect on winding on the bows, which I think is the real reason for the rack back bow. It is very difficult to tack quickly in fast catamaran in my experience as compared to typical modern racing monohull. As you try and bring the bow around, dragging those two long hulls (usually with little rocker) slows the boat very rapidly, and both the effect of the wind in on the jib and acting on tall vertical bows also very noticeably slows the change in direction of the boat since you are turning into the wind. This sometimes stalls you in irons before you can get across the eye of the wind. This is a very aggravating because a failed tack is very time consuming, you have lost all forward speed and need to back wind the sails just to get moving again, in the wrong direction. This made worse if there is a lot of chop also splashing against the bows against you.

Any attempt to reduce windage in the front of the boat will greatly reduce the risk of a failed tack, and greatly improve your chance of wining. I suspect that is considered a better trade off against the risk of pitch-polling since that does not happen very often, while failed tacks are a very real possibility every time you change directions against the wind.

For a cruising it cat it likely makes little difference unless you drive it so hard you start flying the windward hull. Something I suspect does not happen in a cursing cat, but I have never been on a cursing cat, only beach cats.

So it comes down to what the owner wants, or in this case, what he might perceive his typical customer would like to see, or willing to pay for.

[BobBill]

Originally Posted by waynemarlow

My understanding of raked back bows was that it had very very little to do with wave piercing but everything to to do with getting the designed maximum flotation as low as possible and keeping weight out of the ends of the boat to stop hobby horsing. The raked back bow was just an asthetic side issue that happened due to other factors.

True wave piercing shapes are very different to a raked back bow, nature certainly has designed some pretty good wave piercers and they certainly don't look like the shapes we term as wave piercers.

This may help...was put up in earlier post...as Par said, faddish perhaps. After all look at sea-going mammals and find your bliss.

[souljour2000]

The "Ady Gill" bat-boat that Sea-shepherds had for brief period seems to have had alot of wave-piercing hull shapes...sadly it was not designed to be rammed by 200-ft whaling ships though it looked good. until the end ...definitely one for the boat porn file...

[Corley]

Originally Posted by souljour2000

The "Ady Gill" bat-boat that Sea-shepherds had for brief period seems to have had alot of wave-piercing hull shapes...sadly it was not designed to rammed by 200-ft whaling ships though...but it looked good ...definitely one for the boat porn file...

While the "Andy Gill" was a good wave piercing design the Japanese had the superior hull piercing design.

[waynemarlow]

You miss the point here guys, raked back bows have nothing to do with wave piercing, they came about from the design function of having the upper part of the hull being smaller in profile to the lower hull profile ( and that design was for a whole host of other reasons ).

As an aside they seem to allow the boat to have less drag when entering into a wave or such like, which every one then went Eureka we have discovered a new form of bow shape, a wave piercer.

Didn't we somewhere on this forum have a very long detailed discussion on the pro and cons of this very subject a couple of years back where some very eminent designers labelled wave piercing as being just a myth.

As to nature, think of the fastest animals in the water such as sharks and the likes and look at their frontal shapes, it certainly doesn't look like the shapes we are creating.

[rapscallion]

How would a cat hull shaped like a baraacuda be any better? Whales travel through water and air, maybe using their bodyshape as inspiration would make more sense. In my opinion, the foremost expert in aerodynamic biomimicry is Colani. His whale inspired yacht hull design is quite unusual. Im not sure it would provide a performance advantage over current design.

[Ad Hoc]

Originally Posted by waynemarlow

Didn't we somewhere on this forum have a very long detailed discussion on the pro and cons of this very subject a couple of years back ....

Indeed, here:
Wave-piercers - marketing myth or design ingenuity?
and here:
Reserve Buoyancy
and here:
Proa questions...

[BobBill]

USA 17 or BMW Oracle tri should offer some insight, you view that boat in the air on one ama ripping though the seas - doing 19 knots and faster.

[waynemarlow]

Originally Posted by rapscallion

How would a cat hull shaped like a baraacuda be any better? Whales travel through water and air, maybe using their bodyshape as inspiration would make more sense. In my opinion, the foremost expert in aerodynamic biomimicry is Colani. His whale inspired yacht hull design is quite unusual. Im not sure it would provide a performance advantage over current design.

We also need to look at efficiency at the same time, whales need huge amounts of energy to push a relatively blunt frontal area through the water, to harvest more energy, they have to have a bigger body to store and digest, which means even more energy to propel it to find even more food. Sometimes nature doesn't always get it right.

[daiquiri]

Originally Posted by waynemarlow

We also need to look at efficiency at the same time, whales need huge amounts of energy to push a relatively blunt frontal area through the water, to harvest more energy, they have to have a bigger body to store and digest, which means even more energy to propel it to find even more food. Sometimes nature doesn't always get it right.

Is this your personal opinion or do you have some studies to back them? I find it very hard to accept that nature would allow a creature which "didn't get it right" to survive in a similar form for nearly 5 million years (http://en.wikipedia.org/wiki/Cetotherium) and actually believe they are very energy-efficient creatures, due to some particularities of their methabolism.
Some facts:
http://www.thewildclassroom.com/ceta...aptations.html
http://www.seaworld.org/animal-info/...daptations.htm

[BobBill]

Daiquiri +1. Exactly what I thought. Suckers seem to go pretty good, as do the big subs, must be the water...eh?

And, Waynemarlow, exactly right and on Anarchy too. Both made a believer out of this dodger, but, as Par notes, it remains to be seen, it does.

[waynemarlow]

I thought Rapscillion's use of an immitation whale design was a bit far from the point of whether a raked back bow boat was wave piercing or not, that I resorted / made the mistake, to using back ground knowledge of an article that I had read some years ago by who knows who, only to be slapped over the wrist by an internet search on why nature has adapted very strange shapes into very strange looking beasts. I will bow to greater, more informed knowledge.

Still, so called wave piercing hull shapes, actually have very little to do with wave piercing in my uninformed personal opinion.

[ImaginaryNumber]

Originally Posted by waynemarlow

...As to nature, think of the fastest animals in the water such as sharks and the likes and look at their frontal shapes, it certainly doesn't look like the shapes we are creating.

Sharks spend most of their time underwater, and thus don't need a wave piercing shape. Traveling on the surface requires a different hydrodynamic shape than traveling totally submerged. I understand it can take less energy to travel submerged than to travel on the surface. When swimmers dive off the edge of a swimming pool at the start of a race they dive underwater and coast underwater for as long as they can...within reason