Good Cat, Bad Cat

LowBridgedeckWhat is Wrong With This Picture?

What’s missing is the bridge deck clearance! The single, most important factor is the load carrying capability! This affects everything else. Find out more below…


Good Cat, Bad Cat! What Do We Mean By That?

We don’t mean a boat is bad quality, or doesn’t sail well. What we’re talking about here is what makes a catamaran well suited for long distance cruising with a good sized load aboard. What makes a boat suitable for extended stays aboard.

This page was put together from interviews with builders, designers, delivery captains, owners, charterers and from our own personal experiences delivering boats up and down the East Coast, offshore and vacations aboard with both experienced and inexperienced catamaran sailors. It’s both practical and technical. The information is not intended to support any particular product, though we obviously have chosen Fountaine Pajot because we believe it is a good example of our discoveries. Many people get referred to this page by other dealers and owners.

Let’s Take a Look

Please read all of this document‐there’s some really great stuff at the end‐don’t short change yourself!

Why It Matters…

The sun doesn’t always shine. The seas aren’t always calm. Find out why it’s important to have nets forward that let the waves through. Those are lighter and reduce pitching. Why load carrying is so important for safety, comfort and for you to accomplish your goals. And much more…

For Charterers…

The information provided here shows the difference between a comfortable boat and a disappointing vacation. Sure, in protected waters most anything will do. But if you’re planning on chartering in the Caribbean‐‐this is information that will make a difference in how well you enjoy your vacation!

For Used Boat Buyers…

Many of the older boats literally got away with murder! There was no competition. Much has been learned. New technology has perfectly matched the needs of catamarans to be light, but strong. Use these criteria to choose the best compromises if you simply can’t go for the latest and best.

For New Boat Buyers…

Surprise, Surprise. This is the age of spin doctors and marketers. What looks good at boat shows, isn’t necessarily what will make a serious, offshore cruiser. Many, so called, new boats are actually re‐hashes of very old designs‐‐sometimes 10 years old or more. Often with a couple of feet slapped on to the transom! Buyer beware! You will find information here that will narrow the search.

Learn how to offset 80% of the costs of a new yacht with tax advantages and income here.

What Are You Doing For The Rest Of Your Life?

It all depends on what you’re planning to do! Staying at the dock, venturing out for weekends in protected waters? More ambitious? Coastal cruising? Or are you combining coastal cruising and watching the weather, with serious offshore cruising? Your plans affect what you need and you need to plan for the most adventurous cruise you plan.

How do we know what’s required? Because we arrange delivery of many boats every year‐‐trans‐Atlantic, and East Coast to the Caribbean. We talk to the captains who have sailed all kinds of boats. We’ve talked to the designers. Visited the plants. What I’m sharing with you here is the distillation of 100’s of hours of talks based on hands on experience with some of the most knowledgeable sailors out there in all conditions.

This discussion is directed towards offshore sailing. But even if you only want the capability, here is where you’ll find out about what to look for. Remember, even if you don’t plan to venture into long distance cruising, the person you eventually sell to may want to so your selection now, may affect your boat’s resale later. Why cut off any market potential? A “Good Cat” can sail inshore AND offshore.


Looking at What’s Important… Good Cat, Or Bad Cat?

Is it built for inshore or offshore sailing? With the advent of new technology the high tech necessary for ocean cruising catamarans is now affordable. The appeal of comfortable sailing without healing, of privacy only attainable with good separation of living and sleeping spaces, and a panoramic view with extraordinary deck space‐‐not to mention shoal draft… Catamarans have come of age. (If one has any doubts, he simply hasn’t visited a boat show lately!)

As with any new phenomenon, there are plenty of promoters anxious to jump on the latest trend‐‐whether they know anything about what’s required or not. This paper is designed to highlight the 4 important distinctions that will help you understand the builders’ intent. Is he offering an inshore or offshore Cat? The 4 important criteria to consider (aside from overall quality and integrity) are:

  • Stability. Beam to Length ratio and Static Stability
  • Pitching. The comfort factor
  • Bridge Deck Clearance 
  • The Control Cockpit. Flybridge or deck-level?
  • Load Carrying Capacity

There are other factors we’ll be discussing as well and I urge you to pay particular attention to #4‐all of the others hinge on this being right first.


Static Stability Diagram
Stability of a Catamaran

A catamaran generally has no ballast. It primarily depends on beam and individual hull buoyancy for stability. The wider it is, the more stability‐‐however, at some point excessive beam becomes unmanageable. In addition a narrower hull is more easily depressed and prone to tripping in heavy seas. The same wider body hull that gives you better load carrying ability, also gives you more total stability. Of course at some point, you lose performance… Finding the balance is the key.

Virtually all of the experienced builders, especially the European builders who must sail their boats transatlantic to their bases in the Caribbean, have settled on a minimum length to beam ratio (L/B) of approximately 50%. That’s a 20′ beam on a 40′ boat. As the boat gets larger, over 50′ or so, you can back off from this ratio a bit and still have adequate stability. These same experienced builders put enough beam into the individual hulls to give more than adequate load carrying ability. One sign of an older design (often resurrected these days and promoted as new) is narrow individual hulls, sometimes supplanted by (needed) extra beam because the hulls no longer have the required buoyancy.

(By the way, you can often recognize these designs from inside because the berths will be high and spanning the bridge deck‐‐the hulls don’t have enough volume to carry 4 full size double berths! Watch out!)

Static stability is a measure of a boats stability. The factor was developed by sign builders (what strength wind will blow our sign over?!) A bad cat (for offshore) might have a static stability in the 25 knot range. A good Cat in the 50‐60 knot range. This is a static measure. In reality, the boat would slide sideways and round up if you were foolish enough to leave all sail up and this would approximately double the figure.


Pitching Diagram
Catamaran Pitching Explained

Imagine two children on a sea‐saw. If they’re both near the center of rotation:

  • It’s very difficult to get the board going at all. And if they did and you came by, you could grab the end with two fingers and stop them. Imagine the same two children moving out to the end of the board.
  • Now it’s easy to get the board moving (pitching). And once the children got started, you wouldn’t want to try grabbing the end to stop them‐you would probably get your hand broken!

SeasawPitching is caused by too much weight in the ends of the boat. Accommodations and storage areas that extend much forward of the mast. Solid fiberglass decking forward (Fiberglass is heavy compared to netting‐‐that’s one reason you see netting on all serious cats!) Engines and storage too far aft. Not enough stern or bow hull area extending aft and forward of the nacelle. See the drawings below.

Pitching can make your life miserable. Tire you out so you take unnecessary chances. Dampen your appetite. However, solid decking forward does more than just contribute to pitching. In offshore conditions when you might be semi‐surfing down waves; your bow can overtake the wave system ahead of you and plunge into the wave. Nets simply let the water through and allow the bows to recover. Solid decking can trip the boat and cause a catastrophic pitch pole‐mid‐ocean. Netting forward rather than solid decking is crucial for an offshore cat‐for comfort and for safety!

Good Catamaran Left, Bad Catamaran Right

Good Cat Left…

Long overhangs fore and aft. Accommodations concentrated in center of boat (weight kept out of the ends). Beam/Length ratio 58%, Static stability about 55 knots.

Bad Cat Right…

Short overhangs. Solid decking forward. (Heavy, and doesn’t let the water through‐‐can trip in large ocean wave, surfing situations.) Accommodations spread into the ends. Beam length ratio of 46% or less, Static stability about 23 knots.

By the way, the last thing you want to do is have decking and/or footwells forward. The extra weight forward is bad enough, but if the foot wells and lounges fill up with water when you surf down a wave at sea, for instance, you can have real problems.

Did you know that if you measure these forward wells there can be up to 100 cu. ft of water-catching, enclosed foot well? A cu. Ft of water is 7.48 gallons. A gallon weighs  8.5#  (62.4 pounds/cu.ft.). So 100 cu. ft of water combined with additional structure means you could easily add 7,000 lbs of water forward when your nose dips into a large ocean wave. Think about it this way. That’s like carrying a Pick up truck on your bow when you’re sailing offshore. (Okay, if you’re just chartering in a 50 mile circle–but is this how you want to sail offshore?)

Bridge Deck Clearance

This is generally referred to as the height from the water to the underside of the nacelle. If it is too low, waves will slap and bang under the living accommodations. Sometimes literally knocking the plates off the table in a poor design. The noise prevents sleeping. But I amplify this view. When I talk about bridge deck clearance I want to be sure there is adequate volume for smooth passage of seas between the hulls and also that the separation between the hulls isn’t exaggerated.

Catamaran Bridge Deck Clearance
Example Showing Bridge Deck Clearance for a Catamaran

Imagine pushing two pipes through the water as in example (Cross sect. A&B). The pipe with the small hole must create much more resistance; literally forcing a wall of water before it. Pipe A easily allows the water through.

You need the combination of:

  • the highest possible bridge deck clearance
  • Adequate beam between the hulls‐‐but not too much distance
  • and smooth transitions between the nacelle and hulls…

…to allow the smooth transition of waves with minimum resistance, impact and effect on forcing the bows up into the start of pitching motions.

Catamaran Bridge Deck Clearance Example
Catamaran Bridge Deck Clearance Example

Catamaran Bridge Deck Clearance Example

A good cat, left, has a higher bridge deck clearance, with no protuberances interrupting the water flow. The wider beam between the hulls also contributes to uninhibited water flow between the hulls.

Note the difference for the bad cat on the right. We have heard this as one of the biggest negatives from owner’s who owned boats like those on the right. This is also one of the biggest reasons for them selling. (This style is typical of many of the older generation of boats, and also some new ones where marketing types take over from the designers).

Why not too much beam? Have you ever observed the wake coming off the bows of a boat? (Actually if you watch a power boat, the effect of a heavier boat at higher speed exaggerates the effect I’m talking about.) The wave curves up and away at an angle about 150 degrees back from the bow. If you measured diagonally outwards from the bow, you would see that the wave increases in height as it curves away from the bow. Keep this in mind.

Now, imagine an older design catamaran with narrower hulls (The waterline beam of each hull being narrow.) The hulls don’t have the buoyancy to give the stability that comes from buoyancy (see above) so the designer is forced to gain stability the only way he can‐‐he increases the overall beam. The trade off? Several and all bad:

  • The two bow waves come together under the nacelle as they angle back from the bow and the distance is longer (with the wider hulls) so the wave is bigger‐‐the result is excessive pounding under the bridge deck! In other words, the self generated waves combine with even a modest chop causing pounding in relatively moderate conditions.
  • The narrow hulls don’t give you the load carrying ability a serious cruiser needs.
  • The narrow hulls don’t allow the berths to nestle comfortably (and low) in the hulls, forcing berths to be uncomfortably high and overlap the bridge deck in some way in order to make them full size (or allow the charter company to advertise king sized beds!.
  • Being so far apart, the hulls sometimes sail in two different wave systems imparting a very uncomfortable motion.

Why would anyone design a boat this way? The answer is that today they probably wouldn’t. However some charter companies or marketing companies trying to take advantage of today’s catamaran popularity, and wanting to keep costs down choose older designs whose tooling cost is already amortized (or choose inexperienced designers) primarily to reduce the cost of the boat. The problem is that a bad design will always be a bad design and the cost will long be forgotten while the discomfort will linger…

Remember, charter companies ask designers for parameters suitable for people staying on‐board for short times and equipment (load carrying capacity) needs are minimal for these short times. These boats, typically only need to sail in a 50 mile circle.

Whether you’re looking to use our investment program to pay your boat off early, or getting it for some serious cruising we take the long view. We represent up to date designs that feature boats with the load carrying ability you need for care free, serious cruising (This is my only advertising plug in this piece, but I feel I’ve given you enough information to earn the right.)

Load Carrying Capacity

This may be the most important point of all. It’s not just that the boat goes slower, when you immerse the extra hull depth, the boat gets sluggish. It won’t come about without turning the

engine on. It is difficult to maneuver in tight situations or when docking. This hull submersion also decreases the bridge deck clearance, which promotes hull slamming as well! What a shame‐‐because a well-designed catamaran should be a joy to sail in all conditions and much easier to maneuver than a monohull with it’s widely spaced twin engines.

When you sail offshore you will carry 1,000’s of pounds of extra water, fuel, stores, safety equipment and amenities. (Whether you plan to or not, consider resale value‐‐the next owner may want the option!) Here’s what manufacturers do for marketing, which reduces load carrying capacity:

  • Install inboards in too small a boat, or in a boat originally designed for outboards.
  • Start with a performance hull and try to make it all purpose (too narrow a waterline beam). (Or, as mentioned above, simply start with an older design, narrow hull with deep “U” sections.)
  • Put in too many accommodations (charter boat!)
  • Build the boat too heavy‐Use low tech construction. Needless weight in the building takes away from load carrying.

Some dead giveaways. At a boat show, look at the lower transom step‐‐especially when there are a number of people in the cockpit‐ ‐ is the step awash (actually underwater?) Not enough load carrying. Is the waterline at the water (or below it) at either end or entirely? Not enough load carrying. Sure, you can move it up, but believe me, that doesn’t solve the problem!

NOTE: We had the Fountaine Pajot Salina 48 above, recently at a Blue Angels exhibition in Annapolis. over 50 people, full tanks, full equipment and catering for 50 aboard. Note, the waterlines on both sides are still well above water! A good cat! P.S. note Blue Angels in back round. Maybe next time you’ll be there!?

The central nervous station–the control cockpit

There are several bad compromises that happen with a flybride helm, right.LagoonFlyBridge

1. The boom has to be higher to give headroom. Much higher. Out of reach for tucking in the sail or handling tangled lines. It greatly raises the center of effort of the sail plan introducing increased jiggling motion, and compromising safety in heavier air.

2. The helmsperson is out of touch with the cockpit. Beverages, food, conversation–all require participants to negotiate steps.

3. Helmsperson is not at deck level–not in a position to help with docking maneuvers–incomparable with short-handed (couples) sailing–a charter boat affectation.

Saba364IndexA deck level helm station (left and close up, right) is the answer to all of the above. LowSaba 50 Helm Station boom and center of effort. Helms-person in touch with the cockpit, and just a step away and at the same level of the deck. This deck level help promotes short handed sailing where the helmsman can step on deck to help with lines without stumbling up and down steps. As a bonus–the crew from the galley or cockpit can pass up a drink! A serious cruisers choice.


Whether you actually go offshore or not, you may meet bad weather conditions. Your comfort, enjoyment and safety, (and ultimately resale value) are dependent on proper design.

Most of the criteria I have shown here, you can easily evaluate yourself. If what others tell you doesn’t make sense, or if what I tell you doesn’t make sense, then make your own evaluation. There’s no magic here. Good design really does make sense and you can see the telltale signs.

A Test…Putting Together What you Know

Look at the boat from the transom. Are the individual hulls narrow (is the transom narrow)? Is the bridge deck clearance low? Are the hulls too far apart? Or too close together? Are the transoms already in the water with no overhang showing (overloaded aft)?

  • Look at the boat from the side. Is the boat, while lightly loaded, already on her waterline or below it!? (There should be several inches of hull showing below the waterline!
  • Inside. Are the berths spanning the hulls?
  • The bridge deck? About right? Why?
  • Service. Can you get to the engines? Easily? At sea?
  • Are accommodations pushed into the ends?
  • Is there a net forward? Substantial overhangs with no weight in the ends?

Eric Smith

Senior Sales Consultant, Partner
More from Eric >> Boat Business Webinars, Videos, Blogs, Learning center and more.

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