Jake gives a very good summery




Don't let the raked back bow mislead you, the differences between say a Bim 18HT wave-piercer and the Blade F16 wave-piercer hulls is enormous. They are really two different hull designs. Also I really dislike the wave-piercer name as that is totally not linked to why these hulls work (or don't work). It has nothing to do with wave-piercing. Actually the Taipan 4.9 bow is far more wave-piercing than most hull designs out there and nobody recognises it as such simply because it doesn't have the raked back bow.

Actually the raked back bow is not important as well. It is merely the logical result of making the deck narrower than the hull at maximum width. This choice is totally linked to dive recovering and not to any increase in speed or reduction in drag. In fact you can not have a straight bow when you have a deck that is narrower than say the hull at 2/3 above the keel. Notice the bow shape on the Dart Hawk F18 ? This is totally the result of the very rounded decks gunwhales on this design.

So lets put an end to the wave-piercer name and the raked back bow fashion trend. Lets call these hull shaped flyer hulls after the first design that used this setup.

Flyer hulls work because the volume in the hulls have been redistributed relative to the older style hulls. Reserve bouyancy have been repositioned and even been interchanged with active bouyancy. The net result is that the force required to press the bows down rises far quicker than with conventional hulls. This means that the boat feels and behaves alot more stable in gusty conditions. A direct result is that the rig is moved about throught the air less; the platform oscillates less. This has nothing to do with waves being present of pierced. As if waves wear earrings ? (joke)

Anyways. Another result is that a Flyer hull shape bow requires MORE energy to be fully submerged than the bow of a normal hull design. The dive resistance has been increased. Now you can do two things. Either cut away bow volume to get back at the older conventional hull dive resistance (when that was more then enough) or leave it there and take the extra dive resistance as an improvement against diving and as improved dive recovery. Three guesses what the Blade F16 design has done ? Now make a similar guess about the FOX and FX-one. Nils was and is an A-cat sailor and their ratio between platform width, rig power and hull length is quite small so they can cut away the volume. However the Fox and FX-one have different ratios as the F16's and F18's have. Nils cut away the volume and the end result is predictable. As some may remember ; Phill has always said that the hulls shape needed to be adjusted to the F16 hull lengths; you simply can;t just copy the Flyer A-cat shape and expect to get a good hull. If you still do that than you simply don't understand what is going on.

Some designers (Bim 18HT) thought that the amount of volume was important and simply took an old conventional hull shape and trimmed the deck lines and cut the bow to a raked back bow to get with the trend. The end result is now well known among cat sailors. Boats with small dive resistance; beams hitting the top of waves and speed loss under spinnaker.

So it is not about reducing volume it is all about repositioning the volume in both vertical and horizontal directions. In some instances you may even decide to increase the volume while reducing the reserved volume.

What you want as a designer is a boat that has more than enough volume to lift the whole boat quickly over a wave when travelling at top speed WITHOUT the boat making a to big pitching movement or to sustain such a pitching movement for too long.

So what you want is a larger damping factor combined with a volume distribuation that feels to the wave like it is localized relative close to the centre of the hull. (this sentence is correct but I'll leave some of the secret covered, we don't want anybody to start popping out superior hulls)

What you want is that when a boat at top speed encounters a wave that it is quickly accellerated upwward (so it doesn't pierce the wave so much) while staying relatively level. This is exactly what the Flyer hulls do. They do in fact only pierce the waves a little in the front part before the hull is raised up above the wave again. The sterns then sink back a little in the top of the wave that has just passed. Thus keeping the boat relatively level but hugging the surface.

Any imitation flyer hull that has reduced the hull volume will simply enter the wave much deeper, probably take it on the beam and try to dive through the wave instead of going over it. In small wavelets this system will keep the boat level while not really reducing its drag, but in big waves this is system will stop a boat dead in the water.
If you concentrate to much volume under the mainbeam (FOX etc) and have too little volume in the extremeties than you'll also get into the wave to deep and risk taking it on the beam. An additional drawback is that you have rather inferiour dive resistance; possibly even have agrivates oscillation after a gust because the damping factor is too small. So such an imitation will have hot spots where it performance relatively well while in most other conditions it is inferior.

I personnally noticed some of these drawbacks in the FX-one several years back and Phill understood it immediately. Phill took great care not to fall into this trap of having too little volume or having it too centralized under the main beam.

So yes indeed they Blade F16 has relatively more volume in the bow than most other Flyer-imitations however this is not really the most important aspect. The Blade F16 hull design has distributed the volume in the right way and this makes a noticeable difference.

The Blade F16 does indeed have taller bows as well and this is important as well. I on the FX-one and Phill on other boats found that water running up the inclined decks at speed could hit the beamlandings and initiate a violant pitchpole. By having truly faired beamlanding and a raising the deck with taller bows the Blade F16 doesn't take as nearly much water on the deck and beams. This makes a huge difference as well.

One more advantage of not having the volume so centralized (FX-one) is that you don't end up with such a stern dragger. That was the other dislike I personally had about the FX-one. In aggerated wording ; it felt as if the FX-one either wanted to drag its stern or dip its bows. The FOX has a little less of this as far as I can tell. I haven't sailed the FOX that often.

I hope that both the Bim sailors and Hobie FOX/FX-one will forgive me for using their boats as examples but these did provide a good way of explaining what is going on.

In the extreme cases (Both the Bims and FX/FOX are more of a compromise) the centralized volume boats are the worst performing flyer imitations (sorry hobie sailors) and the reduced volume boats are good in some conditions and inferiour in most other conditions when compared to true Flyer style hulls. At this moment it appears that Flyer, A2, Object (Tim Kirkhams A-cat design), newest Bim XJ, Capricorn F18, Blade F16 and Blade F18 are the only designs that have gotten it right. Ventilo's designs are yet to young to pass comment upon. The other imitations went wrong somewhere along the way.

What to take away from this post. Forget the name wave=piercer, talk only of flyer style hulls. Forget about the generally accepted phenomenon of wave-piercing; it is actually inferior to thinking behind conventional hulls. Think only in terms of proper volume distribution and wrong volume distribution. Don't believe the hypes or look up to big names to much; Even guys like Nils Bunkenberg, Lalo Petrucci and Jim Boyer can get it wrong.

I hope this explains a few things.

Wouter