boat design

We just got an interesting question from Françoise and Jean-Michel who are looking at buying a new boat.

Question

Boreal’s daggerboards can be broken as you can see on the n° 42 ep ” Bushpoint ” on You tube. It was last year on a Boreal 55 in the north of Norway. Even if it was not a great issue , it can happen. The owner fix it himself.

My wife and I are looking to build a new boat to change our Ovni 43 and we ask Patrick Lenormand, the yard manager of NYS ( Caen France) to build it .

We have chosen a Cordova 45 ( design of Jean-François André , well known french architect ) . His choice of a twin rudder system concern me .

He said that he put two strong skegs welded on the hull to prevent any damage. My worry is also about the drag of these skegs in front of the rudders.
I know that a boat is always a trade-off but I don’t want to make a mistake.

Answer

You are right to worry about the twin rudders and that’s a great question because it exposes something we are often told: that we can fix a basic design problem by just making it stronger.

I used to believe this, too, until the engineers that comment here helped me understand it better.

Sure the boards on the Boréals can break. Boréal themselves talk about this.

But that’s a a good thing, not a bad thing. It’s a feature, not a bug.

A key thing to understand about boat engineering is that saying we will just make it stronger, is actually bad engineering.

There is no way to build a skeg strong enough to withstand even a six-knot impact from ice, a rock, or a big log (big problem in many places). The key point is that something must flex and bend to absorb force.

So if we make the skeg super strong and it does not flex, then maybe it rips right out of the hull and the boat sinks. The force must go somewhere.

So based on that, here are the key points that I think about:

• When a Boréal board gets damaged, it breaks and the hull is fine. With skeg-hung twin rudders, a bad collision with a rock or ice can hole the boat and the stronger we make the skeg the worse that problem gets.
• A Boréal can operate fine with no boards (I have sailed one that way). You could even sail all the way home with no boards. Bend a twin rudder and skeg and the steering is jammed until we can haul the boat and then we need skilled metal workers to fix it.
• When in tricky waters (rocks or ice) on a Boréal, we can pull up the boards and the rudder is protected by the huge keel box. We can never pull up twin rudders, they are always down there ready to get damaged.

For me, based on some 30 years of cruising, particularly in the north, I would never do so in a twin-rudder boat. Heck, I would not own a twin-rudder boat for cruising, but that’s me.

And by the way, the reason Boréals will never have twin rudders is because the chief designer, Jean-Francois Delvoye, went to Chile in a twin-rudder boat and broke a rudder on a rock.

After that he sold the twin-rudder boat, and designed and built a boat with a single rudder and keel box for himself. That was the first Boréal.

A good example that will help to explain this point about the force being absorbed by bending is the A40 keel.

As I have said many times before, I’m agnostic about the number of hulls a cruising boat should have. There are benefits and drawbacks to one, two, or three.

That said, I do have a soft spot for some boats with three hulls, but that’s another post.

Anyway, I came across this good article comparing the options that’s worth a read.

I think the author does a very good job of pointing out that condo-cats are great for hanging out on, particularly in rolly anchorages, but if we want a cat or tri that sails well, we gotta keep her light, and if we are not willing to do that, the overloaded multi will have a hard time keeping up with a similarly loaded mono.

That was certainly our experience over the years we sailed our McCurdy and Rhodes 56, and is also why our friends Steve and Linda Dashew turned away from cats (their first love) in favour of long thin monos.

Real selection criteria to think about, instead of engaging in the silly which-is-best argument.

Much more about how to cut through all the noise and blather to end up with the right boat for our needs.

The photo shows our new-to-us J/109 and AAC member Frank’s Ovni 435 hanging out together in the workshop at East River Shipyard here in Nova Scotia.

It would be hard to imagine two more different boats, and yet I like both boats a lot.

Which is best? Wrong question. They are designed for different purposes.

Sure, this is a radical example, but it does serve to illustrate how silly the all too common “best boat” meme is.

I will bet this keel was designed shortly after Australia II won the America’s Cup.

It’s a dead ringer for Ben Lexcen’s revolutionary keel.

But here’s the thing, while end plates are good and bulbs can make shallower keels more efficient than they would be otherwise, Australia II‘s keel was designed to get around or fool the 12-meter rule, not because there is anything intrinsically good about this design.

And yet a bunch of cruising boats at the time ended up with keels like this that will catch any piece of floating debris and have large vulnerable wings, just because it was fashionable.

Watch out for the results of trends like this when buying a boat.

People often think that I must be a multihull hater, just because I own a monohull.

Not true, I love well-designed catamarans (and tris, too) like this way-cool Chris White 42.

But here’s the key point:

To be safe, and deliver on their speed potential, cats must not be overloaded.

Check out how thin the hull of this same cat is. It won’t take a lot of weight to push this hull dangerously low in the water.

Overload this boat, and she won’t be much faster than a mono, and, counterintuitively, will be much more likely to end up upside-down than if kept light.

So to have a safe cruising cat, and to be able to carry a reasonable load of cruising comforts, we will often need a bigger cat than we might at first expect.

One of the things I look for when looking at boats out of the water is a nice fair curve of the bottom of the hull from bow to stern.

Contrast our J/109 (above) with the boat below.

The knuckle at the bow does not bother me, but check out the lump in the line just forward of the prop strut. I’m guessing that’s there to provide the buoyancy missing from the pinched stern.

I always prefer boats where the designer has focused on keeping the water happy, not the rating.

Who on earth thought it was a good idea to fit the boat with a bulb extending forward creating a setup to catch every stray piece of gear floating around our oceans, never mind the risk of snagging her own anchor rode or mooring chain?

You gotta seriously wonder.

Here’s a nice looking vintage Nautor Swan.

But look at the strange distortion of the stern.

You think this looks weird? Check out the next shot taken from off the quarter.

When shopping for boats, it’s worth looking for this result of designers cheating the station measurements of the IOR racing rule.

Such distortions don’t necessarily ruin a boat, but they sure as heck don’t help, particularly with tracking when sailing downwind in big breeze, just what we cruisers want to do.

Generally, boat design got better under the influence of rules that imaged the whole boat, starting in the early 90s with the MHS that became the IMS and then the ORC, still used today.