Pete Melvin from Morrelli and Melvin provides some good insight for you.

Q: You sometimes articles where an inquisitive amateur asks a question and an "expert" provides an answer. I was reminded of this issue again with the recent picture of the BT Team Ellen fleet showing two multis with varying degrees of reverse rake bow and a monohull in the background with a plumb bow. You may want to include this picture as part of the article if you choose to run with it. I think others curious minds would like to know:

I have been curious for some time about the trend toward reverse rake bows on multihulls. It seems counter-intuitive that multihull designers would want to give up reserve buoyancy in the forward sections on craft that have a tendency to pitch-pole. Yet, there must be some net gain besides just looking cool. What are the pros & cons of reverse rake bows on multihulls and why has this design characteristic not been adopted by monohulls?

Thanks,

Jonathan Smith
Mystic, CT

A: There are several reasons to consider designing a boat with reverse rake or "wave piercing" bows. The primary reason we consider this hull shape is to reduce pitching motion caused by waves of certain amplitude and frequency. I think an easy way to explain it is this: assume you are sailing along in smooth water with no pitching motion. Along comes a single wave. As your bow starts to penetrate into the wave, you pick up buoyancy in the bow region. The boat reacts to this increase in buoyancy by pitching bow-up. As the wave passes under the boat, the bow then must fall back to equilibrium.

The more reserve buoyancy the wave sees as the bow penetrates through the wave, the more pitching moment is imparted onto the boat by the wave and the greater the potential for pitching motion. So if your bow has a lot of flare (vertical angle of the hull sides), then you naturally have a lot of reserve buoyancy high up in the bow region and this may result in excessive pitching motion.

Why do we care if the boat pitches? Because pitching increases hull resistance, reduces the efficiency of the rig and underwater foils due to unsteady flow, and causes motion discomfort for the people on the boat.

In order to keep the boat from pitchpoling, you need a certain amount of buoyancy forward. On a wave-piercing type bow, this buoyancy and lift are achieved by making the hull fuller down low. On some wave piercing designs, the hull is wider at the waterline than at the deck, especially near the bow. The wider, flatter underwater shape provides lift at high speeds and dampens pitching at all speeds.

Other benefits of wave piercing bows are reduced weight and windage. You can really feel this difference on light weight multihulls like the A Class catamarans. The older designs with tall bows got really pushed around in higher wind and sea states whereas the newer designs are easier to steer and maneuver in waves.

We have developed several very successful racing catamarans with wave piercing bows including the A3 A Class catamaran and the NACRA Infusion F18. Variations of these shapes are now making their way into some of our larger racing and cruising designs.