Bow design – Theory or Looks?

Wave piercer looks so much cooler.

Definitely.

Maybe look to the dollars spent on research and design for the America's Cup boats and leverage your design on that(without spending the same dollars).

If you really want to dig into this-

http://www.boatdesign.net/forums/sailboats/wave-piercing-pitching-damping-marketing-18037.html

Bows with volume at the water line and finer at the top recover easier from submersion as the drag is lower as it rises vs. diving. Stick a conventional bow in that is wider at top, drag goes up faster, the bow slows down vs. the rig and over you go. The Bimare Javelin 2, 18Ht hulls are plumb, but have this configuration, volume low and skinny at the top. The N20 has tall bows for extra volume but are quite fine- different approach.

18HT

Ben Hall on his winged A cat-

bow shot of HT

On my Stealth I have canoe bows. You forgot those in your list <img src="<>/smile.gif" alt="smile" title="smile" height="15" width="15" />

I've never seen those on any other cat, they look funky, but like a canoe the buoyancy is at the bottom and the top is all skinny.

Most significant effect of

wave piercing

bows on sailing multihulls is windage reduction...

wave piercing

benefits are marginal (and maybe negative, particularly if poorly designed)...I don't believe resistance will be less with the bow under the water...in my opinion.

I think it is more fashion over function in smaller boats.

Read comments by MalSmith in above boatdesign forum link.

My main hull bow come to a fine point at the tip then grows wider. The bow height is the highest
point of the hull. Also it has a bowsprit on the starboard side of the bow for the screacher and spin.
I have a flair that starts just past the bows very slight at first then significant to the stern.
The family will be back from vacation, they took the camera, I hope to pull the foam out of the mold
again and get some shots of the half hull foamed out to show the shape of the hull and posted it on
the web site.

Today I laminated a foam strip to form the bow stem and started to bog the inside of the hull to fair
it out. What a job there are compound curves and the foam strips lay worse on the inside. The outside
will not be as bad to fair out. I also have a drawing of the ama lines to post I update the website next.

Mike

Your effectively making the water line longer as well. If the longest point is always in the air, its not doing anything usefull.

TMS, what about utility?
After all you may want to be able to stand on the bow tips when docking (or, if push comes to shove, fend them off). What about being able to see how long you really have before you hit the dock etc? I can't offer any solutions, but you may want to think about the bow shape from a practical point of view also.

You should checkout the discussion over @ SA about the BMWO bow-down pics and wave piercing amas:
http://forums.sailinganarchy.com/index.php?showtopic=93626

I thought AC boats were designed to a box or formula, which may influence their design. Maybe something like Open type boats, but those are monohulls designed with heel in mind.

Is there a class of trimarans not limited by some formula? ORMA 60's?

Only a self imposed box. BMWO's challenge document said their boat had LWL of 90' and a beam of 90' . The only constraints on the swiss is lwl<90' if a sloop or LWL<115' if its a schooner or ketch.

The Race

boats weren't restricted.

Don't take too much technical stuff out of the SA discussion, it's more of a pissing contest between pro-Alinghi and pro-BMWO posters.

For the record, I don't like the look of those submerged hulls and Alinghi doesn't have a trim problem! hahahaha!!!!

Wave piercer looks better stationary

Nothing beats the sheet of spray that comes of a Tornadoes bow at pace.

Lots of spray = lots of energy wasted.

Sailing Math

Lots of spray = lots of energy wasted

Lots of energy wasted < Looking Cool

Therefore:

Looking Cool > lots of energy wasted

And so furthermore:

Lots of spray = Looking Cool, and cancels out any concern for energy wasted

I don't care what everyone says about you Don, you're a Genius.

Wettest ride has to be a Supercat 20 I wear goggles and a snorkel

Bow view and stern view. Remember this is the roughed in foam

Few more views with side laying flat. It's about 3 feet tall for an idea of the size

10762
10763

Love it!

The stingray has to be one of the coolest cats around then.
Not only does it have the tornado bow, but also a front beam. When the front beam touches the water at speed it produces a very spectacular cartwheel. And cartwheels are cool too right?

I remember my amazement at how the Nacra 5.8 handled differently to the stingray. Whereas the the stingray would go up and over the wave. Mostly. With enough wind the 5.8 would just say F#$% ^#F, and go straight through, just like a wave peircer should i guess.

Then moving to the Taipan, I found that it would slice through those waves so easily compared the 5.8.

I cant be sure, but I think my current boat, an ozBlade, needs a bit more energy than the taipan, but much less that the 5.8, to get through a wave. If it does dig in though, it definitely recovers much easier than both.

The G-Cat 5.7 is great in the waves. I think that is why I kept it all these years. It was once given the “Cadillac of Rides” rating. There was a string about a boat to ride up on beach with. I went through 3 bottoms hitting the beach over the last 25+ years; each time I had to lay-up more glass on the fine V-Hull bottom, as the years of beaching would sand it away. When we (the boat and I) were younger I’d land on the beach flying a hull.

It was easier to sail up the beach then to pull those dual knife-edges through the sand. I have never pitch poled the boat even when buried up to the center beam front tramp and all. I’ve done a few cartwheels with it though.

Mike

Agree with the smooth ride on the G-cat 5.7 AND the

joy

of trying to pull that sucker up a fine sand beach! IMO the Nacra 5.0 and 5.7 also are pretty smooth (fine/deep hulls) but not as smooth as the G-cat. Heard Hans is back building boats??

Kirt

Thank you sir, could not have said it any better myself <img src="<>/grin.gif" alt="grin" title="grin" height="15" width="15" />

Mike,
The wave piercing bow is the end result of moving more volume down to the waterline while keeping surface area constant (or reducing it.) The Acat designs did this because once you've moved the volume down to the waterline you need to remove surface area or you will end up with a boat that is too heavy for the box rule. Other designs moved volume down to the waterline in an effort to reduce wetted surface area that generally results from loading up traditional multihull shapes. Traditional multihull shapes have always suffered from adding weight as the surface area increases quickly as compared to a traditional mononhull shape.

So the net effect of moving volume down to the waterline is a pear shape with the topsides being thinner than the waterline. Once you take this shape to the bow, your classic bow shape is upside down and becomes what is being referred to as a wave piercing bow. That description is a bit misleading because even though the bows may seem to pierce a wave, the rest of the boat doesnt actually pierce the wave and the boat if affected by the wave at some point in a way thats pretty much the same as a boat with regular bows. The designers were/are more concerned with the waterline shape/volume than the bows and the bows are really just the end result of moving the volume down to the waterline.

The side benefit (and I own a wave piercing Acat) is that you can submerge the bows and the boat wont pitchpole as easily. See the recent BMWO trimaran shots for illustration. Sailing around with submerged bows like BMWO probably isnt fast, but if this happens in a gust, or during a bear away its a nice feature to have the bows keep moving underwater with little or less drag than traditional flat top bows. The boat doesnt really pierce a wave, the wave affects the boat in basically the same way. Think about a H16 and how the bows slow dramatically when they are submerged, this is what the wave piercing bows resist/avoid.

The downside of a bow with a pointy topsides is that you lose a bunch of utility, you cant walk on it, you cant attach hardware to it easily, etc.

So when you ask the question, you really need to talk to the designer and see what he thinks, and look at how he has the volume in the ama's and what the whole picture looks like. Having ama's that dont pitchpole as easily is a good idea for a 20 ft tri and something that I would consider having.

Deciding on the bow shape should be done in concert with the rest of the hull shape and boat design and not as a separate design decision.

Bill

Nice work by the way.

Yes, last year he built a 35' g-cat power boat... (its for sale)
He is now building a few F-16's for this years nationals.

He has been doing some pretty cool R&D last weekend too...

Thats amazing... I have seen several G-cats pitchpole... and i sail with a guy who says if you get his more than 3 or 4" above the decklid... over you go.