Krogen 48' AE

Architectural Integrity

Design Tenets – Capability AND Liveability


Why is a Kadey-Krogen the trawler yacht of seasoned mariners? No doubt because Kadey-Krogen Yachts builds trawlers that combine globetrotting capability and at-home liveability. Some yachts are designed and built for the single-minded purpose of bluewater capability (often at the expense of creature comfort), while other yachts are built primarily for liveaboard comfort, never mind the dream voyage. Only a Kadey-Krogen yacht accomplishes both aims better than any comparably sized yacht in the world.

True Architectural Integrity in Every Kadey-Krogen Design


One of the most important yet often ignored marine design concepts is Architectural Integrity, which essentially means keeping a vessel true to its original design parameters. Naval architect James S. Krogen once said, “To produce a successful design, you must make an honest determination of how the vessel ‘really’ will be used and then prioritize every design decision to favor that outcome.” In the case of a Kadey-Krogen full displacement trawler yacht, that “outcome” is a sea kindly, live-aboard ocean crossing yacht.

James Krogen’s pronouncement has often been ignored and in the last few years we have seen notable manufacturers stretch a 41 footer to a 49 footer, a 47 footer to a 52 footer, and a 55 footer to a 60 footer. This disturbing trend compromises the performance of the resulting hull design. Perhaps the best-known example of violating architectural integrity occurred back when SUVs first became all the rage. Manufacturers simply took the chassis of another vehicle and put a large boxy structure on top, thereby raising the center of gravity. Remember all those early stories about SUVs rolling over?


So why do manufacturers violate the architectural integrity of one hull design and stretch it to make another model? Simple. It’s a relatively low cost way to introduce another model, and with more models there is a greater chance a builder will have a vessel that appeals to a particular customer. Keeping costs down and building and selling more boats equate to greater profits.

Why not stretch a boat? To design a boat with optimal performance involves a mathematical formula where everything is a variable and the goal is optimal efficiency and stability. Like any formula, if you change some of the variables without changing others, you will get a different result. This is inescapable.


If you take a boat that was designed at 55 feet and “stretch” it to 60 feet, all of the engineering is changed. You simply can’t design the proper curvature and shape of a hull, stretch the middle by 10% or more or stick a larger cockpit on, and have the physics stay the same. You can’t determine, using sound naval architecture principles, where to place the propellers, rudders, etc. on a boat, and change its length by 10-15%, add a larger engine and prop, and then expect the same handling results. Like most bad ideas, this one tends to magnify itself. It’s hard enough to get a big heavy boat to turn, and in my example above for the first few moments when the rudder is turned, the boat’s going to try to push sideways until the reduced torque available finally starts the turn. This may result in just an unpleasant ride but at some sea state it will approach the line between difficult steering and being unsafe.

Hull Form

bow-fine-entry-of-krogen-58_crBesides the Architectural Integrity of a Kadey-Krogen, the hull design is perhaps the most important reason why seasoned mariners are attracted in the first place and also why so many come to love the brand. Each and every Krogen yacht begins with Kadey-Krogen’s exclusive Pure Full Displacement ® (PFD) hull-a masterpiece design for full displacement pleasure yachts, originally created in the 1970s by James S. Krogen. This is a hull form with ideal displacement-to-length ratios, a fine entry, and characteristic end-to-end symmetry including the signature “wineglass” transom-all producing a ride that is truly without equal.
We are singular in focus and only build this proven, reliable seaworthy and sea kindly cruising hull form. The Pure Full Displacement hull design does what it does so well, that cruisers are ensured a safer and more comfortable time aboard when compared to vessels built upon other hull forms. Only the pure full displacement hull provides the stability for comfort plus ample room for the fuel and supplies needed to make long passages or cross an ocean. And only the exclusive Kadey-Krogen hull form allows us to combine the elements to deliver capability and liveability so perfectly.

Hull Form Symmetry

The Pure Full Displacement hull is differentiated from other hulls based upon two form fundamentals: longitudinal symmetry and displacement to length ratio (D/L).  Longitudinal symmetry refers to the degree to which the stern shape matches the bow shape. The image of a barge quickly enters the mind. A barge is highly symmetrical and seaworthy, but does not have ideal longitudinal symmetry and therefore is not very sea kindly. A simple way to describe what is desired is that a hull with good symmetry will have V-shaped sections and sharp waterlines at both ends. The Kadey-Krogen is on the left. Which entry form do you think moves easiest through the water? Which form do you think has a softer ride?hullform-symmetry-1-1




So why do you want a vessel with a symmetrical hull form? There are four compelling reasons. First, the fine entry has superior wave cutting ability making it more efficient compared to blunt, stout-looking forms. The fine entry also yields a softer ride, which means less pounding in head seas.Second, symmetrical forms track better in a following sea. The V-shaped sections aft slice following seas rather than surfing them, making for a safer and more comfortable ride.

Third, the aft V-shaped sections also offer less resistance and drag than the broad waterlines of asymmetrical hulls. This results in better fuel economy.

hullform-symmetry-2And fourth, symmetrical forms roll less. Yes, contrary to popular belief, an asymmetrical hull with an immersed transom and/or relatively flat aft sections will actually tend to roll more than a symmetrical hull in a following or beam sea. Why? Simple physics. The leverage (upward force) that wave action has on those flatter sections is greater than on a hull that is more rounded and/or tapered. The upward force on one side creates a downward force on the other side and voila, you have roll. It is this roll (the downward pressure on the opposite side) that will then cause the vessel to veer off course (yaw). Those of you that snow ski or water ski will understand exactly what I mean. The appropriately symmetrical hull form is much more sea kindly than one that is not. Vessels roll and heave as though they are on springs, with less symmetrical forms having stiffer springs (lots of force per immersion) whereas the Kadey-Krogen transom effectively rides on softer springs. Comfort-wise, you can think of operating a wide-transom boat in rough seas as trying to drive a sports car through deep potholes.

Hull Form Displacement

The displacement-to-length ratio (D/L) indicates whether a given displacement is carried over a long waterline length or a short one. It reflects the load the vessel has to carry on a per-foot of waterline basis. Lower ratios tend towards lean and slippery forms with fine ends, and higher ratios tend towards full-bodied and less efficient forms with blunter ends. The lighter the load per foot of waterline length the better the economy and hence the better the range will be.

Low D/Ls result from either long waterlines or streamlined underbodies, or a mix of each. Both characteristics serve to improve hull efficiency and therefore fuel economy. Longer waterlines permit higher displacement speeds and streamlined sections result in a hull more easily driven through the speed range. For example, if a given displacement is stretched over a longer waterline, two things happen: The LWL increases (higher hull speed) and the ends get finer and sectional areas less full, i.e. streamlined (less hull drag). Of course, reducing a vessel’s fully loaded weight (displacement) will lower D/L and improve economy but the fully loaded displacement requirement is usually already more or less locked in by the voyaging requirements (living quarters, fuel supply, provisions, etc.).

This long waterline low D/L approach (those in the 260-325 range) can be compared to a bank account earning compounded interest. Reducing D/L yields a more easily driven hull form thereby improving fuel economy and allowing for the use of smaller engines. The improved economy reduces the weight of fuel that must be carried for the desired range and the use of lower horsepower engines will reduce the weight of propulsion machinery. All this weight reduction now results in even greater fuel economy resulting in more weight savings resulting in even better economy, and so the benefits compound.

You may be asking, what about strength? Isn’t strength compromised by this weight savings approach? Not in a Kadey-Krogen, which one could argue is actually stronger. Why? Because while the boat is solid fiberglass below the waterline, the coring material is vacuum bagged in place everywhere above the waterline. Utilizing core materials and the vacuum bagging process creates a stronger and lighter weight result.

So Kadey-Krogen yachts are strong, yet lighter in weight. This is accomplished by using proven structural design techniques and conventional lightweight materials.

Interestingly, D/L has had an opposite and incorrect application in the evaluation of long-range trawlers, and many inaccurate conclusions can be made using this ratio. It is important to understand that low D/L does not mean lightweight, or a less substantial structure, or a long and narrow form. How did these misconceptions come to be?

Back in the “early days” the market consisted predominantly of shallow flat-bottom coastal craft with insufficient internal volume for the fuel and supplies needed for long-range voyaging. These craft had very low D/Ls. To help separate the wheat from the chaff, Captain Robert Beebe published very useful minimum values of D/L below which the vessel was said to have insufficient “heft” or carrying capacity for long-range voyaging. Therefore, D/L was used to verify that a vessel had sufficient heft instead of being used to rate hull efficiency. Heft was rightfully considered to be a good thing in that context. And back then, since most boats’ D/L ratios were way under the minimum for long range, the higher the D/L the better. Beebe and other experts agree that the minimum D/L should be around 260. With many modern passagemakers in the 350+ range, that makes those in the 260-325 range seem “light” and some builders’ marketing guys have tried to capitalize on this incorrect assessment.

Hull Comparison

This computer animation illustrates why a trawler with flattened aft sections of the hull is difficult to steer, especially in a following sea. Many if not most trawler brands have some form of flattened aft section of the hull, so it’s important to understand these principles if you are looking at a trawler.

Flybridge, Boat Deck and Pilothouse

Standard Salon and Accommodations Arrangement

Optional Asymmetrical (Widebody) Arrangement

Optional Three Cabin Arrangement

Brief Specifications

  • Length Overall (LOA) 53′ 0″
  • Length On Deck (LOD) 48′ 6″
  • Length at Waterline (LWL) 45′ 5″
  • Beam (Molded) 16′ 8″
  • Beam (Over Rub Rail) 17′ 4″
  • Draft (Designed Water Line – DWL) 5′ 0″
  • Displacement (DWL with Half Load) 56,450 lb.
  • Ballast (Encapsulated Lead) 4,500 lb.
  • Fuel 1,000 gal.
  • Water 400 gal.

Bridge Clearance

  • with Mast Up 29′ 3″
  • with Mast Down 14′ 7″ (DWL to top of flybridge coaming)
  • with Radar Arch Up 20′ 9″
  • with Radar Arch Down 15′ 2″


  • 6 knots: 4,730 Nautical Miles
  • 7 knots: 3,020 Nautical Miles
  • 8 knots: 1,980 Nautical Miles
  • 9 knots: 1,390 Nautical Miles

NOTE: Calculated with a 10% reserve. Ranges are approximate.

Specifications and equipment are accurate at time of posting, however, are subject to change.

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