“Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.” – Mark Twain

Sailing a Modern Hull


Last weekend we were at a friends yacht club for some nautical bingo.  Fun night and we won an eco air horn and spare dockline.

During the evening I got to talking to a prospective member of the club.  He has been sailing a Catalina 30 out of a nearby marina for 8 -10 years and was trying to become a member of the club and purchase a bigger boat.  He was looking at boats similar to the Catalina 36.  After talking to him about what he was looking for in a bigger boat (i.e. larger master berth, more room for short term guests, bigger cockpit, bigger head, etc.) I suggested he should look at the Catalina 350 as many of the layout aspects may be better for his intended use.  He responded that he had ruled out the C350 because he heard it didn’t point or track well.  Ugh!

This is one of those things that you hear and that is perpetuated by the internet that drives me crazy.  How you sail a boat has a lot to do with the hull shape, the rig and the conditions.  You just simply can’t sail a Catalina 310 the same way you would sail a 1970s Cape Dory or a Lyle Hess Bristol Channel Cutter. Understanding the hull’s stability curve is paramount to sailing the boat efficiently.  This requires having some basic knowledge about form stability vs. overall stability vs. dynamic stability.  In this day and age of computer designed boats and boat designers willing to help the public learn it’s never been easier to get this general understanding.  Here are some of my favorites:

Bray Yacht Design, Stability – What Is It and How Does it Work?:

Stability is the ability of a vessel to return to a previous position. Positive stability would then be to return to upright and negative stability would be to overturn. Stability in it’s most basic form is the relationship between the center of all floatation in your hull (center of buoyancy, or CB) and the center of all weight (vertical center of gravity, or VCG). In other words, the downward pull of Gravity and the uplifting force of Buoyancy. These are the primary characters in this scene and all others play minor roles. Once you understand how their relationship works, understanding stability becomes a simple matter.

M.B. Marsh Marine Design, Understanding Monohull Sailboat Stability Curves:


Righting moment with KG's scaled for hull loading

Righting moment with KG’s scaled for hull loading

  • Hull A, the narrow one, will have a hard time flying much sail. She’ll heel way over in a breeze. But she can’t get stuck upside down.

  • Hull B, a moderately slender cruising shape, also can’t get stuck upside down- her AVS is 170 degrees. Her extra beam causes the centre of buoyancy to move farther to leeward when she heels, so she has more initial / form stability than hull A and can carry more sail.

  • Hull C, which is typical of modern cruising yachts, has over twice the sail-carrying power of the slender hull A. She’ll heel less, and since her midship section is much larger, she’ll have more space for accommodations. The penalty is an AVS of 130 degrees. That’s high enough that she can’t be knocked down by wind alone, but wind plus a breaking wave- such as in a broach situation– could leave the boat upside down until a sufficiently large wave comes along.

  • Hull D, the broad-beamed flyer, can hoist more than three times the sail of hull A at the same angle of heel. She’ll be quite a sight on the race course with all that canvas flying. Her maximum righting moment, though, is only 37% more than hull A’s, which leaves less of a margin for error- hull D is more likely to get caught with too much sail up, and will reach zero stability at a lower angle of heel. If she does go over, she has considerable negative stability, making it unlikely that she’ll get back upright.

Wavetrain blog, Modern Sailboat Design: Form Stability:







Stiff boats with good form stability in one sense are more comfortable, especially for novice sailors, than boats that heel easily. In another sense, however, they can be very uncomfortable. Though they are rolled to less severe angles, they snap back from those lesser angles more quickly and abruptly than boats with less form stability that are rolled to greater angles. The resulting motion can seem jerky and violent, and this is reflected in a boat’s motion-comfort ratio. This quick motion, combined with the tendency of a flat-bottomed boat to pound in a steep head sea, may lead some to conclude that there can be such a thing as too much form stability.

The most important thing to remember about form stability is that it does not translate into ultimate stability. A sailboat’s hull form can help it resist heeling up to a point, but past that point all bets are off. A boat that depends too much on form stability to stay upright will be capable of supporting an enormous sail plan in moderate conditions, but when caught in a sudden squall with all its sail up, it can be laid over and capsized very quickly.

Ted Brewer Presents a Primer on Yacht Design:

The terms and ratios that follow are used by all yacht designers so it’s a good idea to have an understanding of them if you are considering buying a boat, or having a custom design created (of a classical style, of course!).

You may need to work out some of the ratios for the boats you are considering for purchase from the available information but the formulas are simple and can be handled by an inexpensive scientific calculator. The one I use in my design business is a Sharp EL-520, almost old enough to vote, and cost less than $25 new, too many years ago.

Robert Perry (my personal favorite designer), Keel Design According to Perry on the Sail Far Live Free blog:

I have designed a series of full keel boats (Baba 30, Baba 35, Baba 40, Tashiba 31, Tashiba 36) and all of these boats sail quite well. But I have pulled the leading edge of the “full” keel aft and tried to give it a reasonable leading edge in terms of shape. Some people call these designs “modified full keels”. That’s OK but those labels can be pretty nebulous. Probably my biggest complaint with full keel designs is that they seldom if ever back up well under power. They also add a lot of wetted surface and that can kill light air performance. Plus, they are so long in chord that if you give them a good efficient foil say with a thickness ratio of 10% (width of the keel compared to the chord length) you will end up with a fat keel that adds too much displacement to the boat. And the funny thing is, and it’s not intuitive, all that keel volume is on the wrong side of the righting arm when the boat heels over. So technically a big full keel can reduce your righting moment.  Go ahead and love your crab crusher full keel boat but don’t try to justify the design on technical terms. Some traditional full keel designs have a lot of subjective, aesthetic appeal. That’s good enough reason to love your boat.

We don’t have to guess anymore about keels and draft. I use a Velocity Prediction Program (VPP) to analyze my hulls and keels. I can try various keels and drafts and pick the one that gives me the best combination of performance results. We reduced the draft on CATTARI 6” after doing a series of VPP runs.

I included this last bit from Robert Perry to highlight a point I often make.  Too often we fall in love with a look of a boat or how salty we think it makes us to have certain aspects of a design.  But seldom do most people actually understand what that feature actually does for performance.  Also, I often get chastised from old, salty types for bringing up that boats designed by computers have advantages over older designs done by hand.

Several weeks ago I came across this blog post: How to Sail a Morgan Out Island 416.  Many of the characteristics described in this post are similar for modern cruising boats like the Catalina 310 and Catalina 350.

All yachts are a compromise. As such, each design has its strengths and weaknesses; the Out Island 41 is no exception. She is very beamy to allow for more living space below and more room to enjoy the pleasures of being on deck. In addition, her draft was kept relatively shallow so as to allow her owners to enjoy many anchorages and gunk holes. These can be enjoyed only by dinghy when sailing deeper draft yachts. As a beamy, shallow draft yacht, she must be handled on some points of sail in a slightly different way than a deeper draft yacht with less beam. The most prominent distinction exists on the wind and close reaching. Sail trim on both these points of sail is critical for optimum performance.

This post goes on to describe some specific techniques for different points of sail and conditions.  Almost all of these tips hold true for our Catalina 310 and some other modern designs like Jeanneaus that we have sailed.

The way I often describe it to people is you have to sail a modern cruising boat almost like a catamaran.  My Catalina wants to sail flat footed.  We typically stay between 10-15 degrees of heel.  If we are heeling over 20 degrees we can see a noticeable reduction in our speed.  Compare that to a Pacific Seacraft 36 that feels like it will heel to 25 degrees with the slightest breeze but can’t get pushed over 40 degrees in gale force winds. This gets back to the form stability vs. overall stability discussed above; it’s like comparing Hull A (Pacific Seacraft) and Hull C (Catalina) in the article from  M.B. Marsh Marine Design.

If you sail a beamy, modern hull over heeled it will not point well. The keel is designed to stay deep in the water and not be up closer to the surface.  With the keel up high, you will have sideslip and your will not point well.

So REEF!  Reefing is not a sign of defeat or the sign of a beginning sailor.  On most points of sail we need to reef at around 18 knots or we lose significant speed.  The good thing is that Catalina designed our boat to make this easy.  We have factory installed, single line, slab reefing.  This means all you need to do to reef the main is ease off the sheet until luffing, release the main halyard and ease it down while taking up the reef line, once the reef point is down to the boom lock it in and retention the main halyard.  All of this can be accomplished from the cockpit in under a minute if you are well practiced.

There are many other small pointers such as sail trim, lead positions, etc. but the article on sailing a Morgan Out Island already does a great job of listing these so I won’t repeat them here.

In my opinion there are very few bad boats.  Boats are designed for a purpose and a price point.  Add to that some aesthetic characteristics.  To balance all of these you need to make compromises.  I always say that a boat is a series of compromises and it’s finding the balance of these that best fit your wants and needs that will make for a good match between the boat and owner.

6 thoughts on “Sailing a Modern Hull

  1. You hit the nail on the head, Jesse. We have sail our boats with an understanding of its particular underwater shapes, beam, and ballast to sail it effectively and efficiently.

    My boat (Watkins 27) has similar beamy issues. It has to be sailed flat-footed, or it drifts off to leeward badly. This means sail reduction earlier, and a balanced sail plan is better the headsail alone or main alone (no matter how lazy I’m feeling). Also, those of us with much older boats need to give attention to the age and condition of our sails. Good sail condition is essential to good performance and, if like me you are moving away from roller furling headsails, a reasonable inventory of sizes or reef-ability is required.

    A couple of years ago, I sailed with a friend on his Norsea 27 – a quite narrow boat. That boat would carry through any amount of chop, and is a great sailor. However, there is very little room down below, and the cockpit is very uncomfortable – so we also have to choose the elements that are important to us wrt design. For me and my wife, it’s more comfort than a narrow boat would afford, and since we are not “blue water” sailors (Chesapeake Bay only, at this point), a narrow hull has very little advantage for us. But with careful sail management, our boat sails acceptably well. A broad beam doesn’t exclude us from careful blue-water passages, as many of these boats have accomplished open water voyages. However, we need to understand the issues and cautions when taking to blue water in a boat like ours.

    Great post!

  2. Rick,

    Excellent additions to the post. Thank you for adding them.

    Nice write up on the NorSea as well.

    It’s all about finding that balance that is comfortable to you. I could never live on a boat with an uncomfortable cockpit. Once the weather warms up we spend so much time in the cockpit. But unfortunately it’s down to single digits again today. Can’t wait to take off the bubble and be able to enjoy the sun in the cockpit.

    Fair winds

  3. Gee, I dunno. I sail a Snipe which, as you likely know, is a small one design class racer. I want to get a cruising boat to sail out to the islands and up and down the coast. I had my sights on an old Mac 21 with damn near no hull draft and a deep swing keel. This boat has a small cabin for camping out and almost 30% sail area to displacement ratio, which is why she will get up on a plane. I figured it would make for a good intermediate transition from dinghy sailing towards cruising. Then I read Marchaj’s second book “Seaworthiness”. As you may know, this books talks about the issues mentioned above and a whole lot more in excruciating detail and with enough charts, graphs and quadratic equations to choke a physicist. The short of it is that after reading this book I decided to forget about speed and focus on a boat that would handle most conditions up to maybe a full gale without undue worry of an easy capsize. So know I’ve reversed course and look at fin keels with disdain and full keels with appreciation, like on a Cape Dory.

    • Marchaj’s book “Seaworthiness” is nice but it’s extremely date. Marchaj was born in 1918. He published “Seaworthiness, the forgotten factor” in 1986 at an age when most people have retired. All of his experience and knowledge came from the pre-computer aided design days. It completely ignores advancements in design and modeling that come about from being able to model hull, keel and rudder forms on a computer.

      Not to mention modern construction techniques like vacuum bagging didn’t even exist until he was isn his 80s. Forget about multi-directional glass or materials like kevlar.

      But hey, get a Cape Dory if that is what you like. They are nice boats and there are lots of them on the used market. Just know that if you do it because you feel they are safer you are willfully ignoring the last 30 years of advancements in boat design, construction techniques and materials.

  4. Jesse,
    Thanks for the reply. Marchaj does come across as a bit of a grumpy old man criticizing the young whipper snapper’s newfangled contraptions. I also was wondering what advances had been made in the interim since 1986 that addressed his main points of critique about modern racer/cruisers built to IOR specs. I know IOR has been superceded but I don’t know to what extent the newer rating systems address seaworthiness and I don’t know what design changes have been made towards the same end with the new tools available. If you read the book, you know that Marchaj was a Finn racer of distinction when he was young and his first book also gets into the nitty gritty of the elements that make a boat sail faster, so he wasn’t always so focused on seaworthiness. The impetus of his second book was the disaster of the 1979 Fastnet race where so many lives were lost on boats that were ostensibly fit for ocean racing but faired so poorly in a storm. I understand that every boat has its own handling and sea weathering characteristics and there is no perfect all around boat. But some of the points he hammers home are that thousands of years of trial and error worked to evolve very seaworthy boats such as the Bristol Channel Pilot Cutter. That the various yacht racing rating schemes that started in the mid 1800s undid a lot of what was so painfully gained. Also that much of the study on seaworthiness done by designers using models in tanks (as he did), on drafting boards or by computer end up confirming the seaworthiness of design elements found in boats of long ago. There were a great many racing designs of the 1800s that used flat bottoms, skimming discs, fin keels, center boards, etc. These boats were not intended for the ocean but for the greatest speed in sheltered waters and faded out when rating rules changed. The old ocean racers of that era were generally heavy full-keeled boats. They wouldn’t beat a modern ocean racer but they could survive a storm. But hey, if there is a 25′ to 35′ sailboat out there that has decent cabin accommodations, won’t broach in a large following sea under proper sail, won’t capsize while heaving and rolling on the top of a 30′ wave, will come back up if it does turtle, can handle force 8 or 10 in the North Atlantic without resorting to an EPIRB and will still do 15 knots on a reach, please let me know! Really, I’m not being snotty, I really don’t know what’s available in state of the art yacht design.

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