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The 45' Widebody Motor Yacht


45' Widebody Mootor Yacht - Kasten Marine Design, Inc.
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Perspective Above Aft | Perspective Above Forward | Perspective Portside
Pen Drawing Aft | Side Rendering | Fwd Rendering  

Copyright 2016 Michael Kasten


The request for this design was to create a trawler yacht suited for a couple to live aboard with occasional guests.  A vessel suited to ocean travel, and for an active pursuit of life on the water.  Low build cost, a simple layout, and low maintenance were priorities. Propulsion via a four cylinder turbo diesel assures modest machinery weight and good fuel economy.

I've called the design Gannet after the beautiful white and yellow pelagic seabirds found on many oceans. The lines of the vessel reveal an easily driven hull. The Gannet interior layout is similar to the 40' Widebody Coaster and the 43' Widebody Dive Yacht, where the "Widebody" main cabin provides plenty of interior space for four to six in the saloon and two in the galley. The transom is designed for optimum access to the water in order to best enjoy the water.

Particulars are:

Stability will be excellent due to the raised fore-deck and the widebody house structure, both of which provide quite a large reserve buoyancy and outstanding large angle stability. The 45' Gannet will easily meet the EU RCD "all ocean" category.


Hull; deck; cabin and pilot house construction are planned for aluminum construction. Scantlings will be according to the ABS Yachts Rule - 2015, and will also comply with ISO rules used within the EU.  It is anticipated that plating and framing will be detailed for NC cutting. For more information about our use of CAD for NC cutting, please see our Design Stream article.  


The engine specified is a John Deere 4045 TFM - 4 cylinder turbo diesel that produces 120 hp at 2,400 rpm (M-2 Rating). It will be mated to a Twin Disc gear using a 3.5:1 reduction to drive a three blade propeller.  An alternate stern gear arrangement would be to use a Sabb HVP-65E gear at 3.8 : 1 reduction and a Helseth or Nogva Controllable Pitch Gear.  Theoretical hull speed is 8.7 knots.  Due to the relatively light Displacement to Length ratio, the John Deere 4045-TFM should be able to provide a top speed of around 9.5 knots, depending on load. 

The optimum cruising speed for long range voyaging is 7.0 to 7.5 knots.  Assuming a tank capacity of 800 US gallons and a 12% reserve, according to the Beebe algorithm the range at 7.0 knots should be around 3,500 NM.

Adequate space has been provided in the engine room for a small generator, plus all the ancillary machinery that is usually expected such as water maker, filters, pumps, fire extinguishers, muffler, electrical panels and so forth - plus the bulk fuel tanks...!

Aft of the engine room is a large storage area below the saloon and galley. Items slated for this area are dive equipment, tools, spares, and stores for long range voyaging. Below the aft deck is the lazarette, plenty large enough for all the myriad lines, fenders, fishing gear and the usual "stuff" that accumulates onboard...  


The aft deck, saloon and galley are all at one level.  In the cockpit area aft, a ladder will lead up to the "boat deck" and Flying Bridge via a hinged hatch.   An additional means to access the boat deck and flying bridge will be located just aft of the pilot house side decks.  On the house top, there is a low profile Flying Bridge to provide good conning, with seating for four to six.

The exterior side decks outboard of the pilot house are at the same height as the pilot house sole.  The foredeck spans the full width of the vessel forward of the saloon / galley, extending all the way to the bow.

Exterior watertight doors are located on each side of the pilot house, and on center aft of the saloon. The aft deck is surrounded by substantial bulwarks to each side, and there is a center bulwark right aft. To each side of the center bulwark a stairway leads down to the swim platform right aft. On the aft swim deck will be mounted a removable dive ladder, and a hinged passerelle plank for ease of boarding when moored stern-to.

There will be an A-frame mast for a pair of A-frame paravane poles.  A boom will be provided to allow easy placement of a shore boat on the house top above the saloon. 


I arranged the stations at regular 28 inch intervals. That is a favorable module for the interior arrangement, since conveniently four frame bays make a perfect size for a sleeping cabin (9’ – 4”) with room at the end of the master berth for a walkaround, or in a guest suite for a desk, etc. From there, three frame bays (7’ – 0”) make a generously sized berth, two frames (4’ – 8”) make a very adequate head compartment or galley, and one frame bay (2’ – 4”) is perfect for a closet or apartment sized washer / dryer, etc.  This is very much the norm for our metal boat designs...!


With that in mind, I made the forward cabin four frame bays (9’ – 4”) in length to achieve a walkaround island berth forward on center, flanked by shelves, with ample room for a pair of large wardrobe cabinets outboard with a dressing area on center. An arrangement of that kind can be seen on the Far Horizon 54 in both the forward and aft cabins.

I also dedicated four frame bays (9’ – 4”) to the guest cabin (to starb’d) and head compartment (to port). There is enough length in the head compartment for a WC, sink, and separate shower compartment, or if desired, a bathtub… Then depending on the arrangement used for the head, there is a closet in the hallway which could be used for a compact apartment sized washer / dryer. There is enough length and width in the guest cabin to have it arranged with an extendable couch forward, and an office desk and closet aft.  

Aft of that, on the lower level another four frame bays (9’ – 4”) are given to the engine room. Beam is 15’ – 6” so with roughly 2’ – 0” on each side used for bulk fuel tanks the ER interior is then just over 11’ wide inboard of the tanks. With a 24” wide engine, that leaves some 4’ – 6” outboard of the engine on each side. With a 24” wide wrap-around seat facing toward the engine, that leaves a reach of 30” to the engine. That allows ample space to pass through and around the engine by scooting around on the seat. We have used this arrangement successfully quite often. 

Moving farther aft on the lower level, just aft of the engine room is a storage room occupying two frame bays (4’ – 8”) in length by the full width of the vessel. Aft of that, and below the aft deck is a Lazarette, which is also two frame bays in length. Aft of the Lazarette are a pair of lockers outboard for gas / propane so that they can be vented overboard, and a center area below the swim platform for the steering gear. 


This being a Widebody layout, there is not a walkway down the side outboard of the aft house, nor any need to go forward outboard from the aft deck.   So starting from aft, there is the swim deck, then the aft cockpit deck, then an “L” shaped seat against the house on both sides, with a BBQ / Sink just forward of the inner transom. Alternately, a bench seat would be nice there. 

Inside, six frame bays (14’ – 0”) are dedicated to the saloon and galley. Since the ‘widebody’ extends all the way outboard on both sides, the interior of this space would be approximately 14’ square.  

If two frame bays (4’ – 8”) at the forward end of the house were dedicated to the galley, that would allow an “L” shaped galley with a peninsula extending inboard between the galley and the saloon. With the usual 24” counter top width, that leaves 2’ – 8” between the counter and the forward bulkhead. If there were also a counter extending forward of the bulkhead (i.e. below the Pilot House accommodations) that would provide a full-on U-shaped galley.  A refrigerator would be ideal in that location, tucked under the Pilot House seating.  

To port of the galley there is a stairway up to the pilot house, and toward the centerline from that there is a stairway leading down to the accommodations below forward, with headroom provided within the pilot house seating. Outboard of the stairway leading up to the pilot house, there is enough room for a full width counter, which would make a perfect spot for a top-loading chest freezer.  

With the galley arranged like that, it leaves a full 9’ – 4” of length for the “saloon” itself, which I have envisioned as being arranged with a soft and comfortable couch to starb’d, and a pair of easy chairs to port, more or less as shown on the Widebody Coaster layout sketch, or possibly there would be an entertainment center to port. One important difference between the 45' Gannet a nd the Coaster 40 Widebody is that there is quite a bit more length and beam available in the saloon. Given that, I did not envision having a dinette located there, but instead a large cushy couch to starb’d, and coffee table just off center. 


With the layout described above, within the pilot house there would be a stairway leading up into the PH from the galley, located outboard to port. Then located outboard on both sides forward, a door would lead out to the side deck.

The pilot house sole has three full frame bays' worth of fore and aft length (7 – 0”).  With that, there is enough room to provide a generously sized “L” shaped raised dinette in the starb’d aft corner of the PH, which would extend approximately 7’ – 6” athwartships, right over to the stairway that leads to below aft. The table should be large enough to seat six (three or four on the dinette seats plus two or three on director style folding high-chairs). The raised dinette allows persons seated there to be at eye-level with a person standing in the PH, affording them all a commanding view.

If the dashboard forward of the PH is arranged in a semi-U-shape there should be sufficient room for a wheel and helm seat on center. It should then be possible for the helm seat to swivel around to face the table. If necessary, the forward portion of the table could be arranged as a drop-leaf for a bit more room to pass through forward.


Ideally there would be a forward facing bench seat on the fore deck right forward of the pilot house – a good deck locker…!

A stairway is planned on both sides which leads up from the each forward side deck to the Flying Bridge deck. On the Flying Bridge, there is enough room for generous seating, a commanding view, and still enough deck aft for stowing the shore boat. A Bimini cover could be easily rigged, and can also be taken down when needed. 

The saloon house top on either side of the Flying Bridge provides a convenient stage for managing the paravane rig.


The layout described here fits nicely into an overall length of just under 45 feet. In my view this layout has accomplished quite a feat..! 

For one, it seems ideal to have the galley within the ‘saloon’ cabin. The galley is always the center of attention socially, therefore having it integrated with the saloon seems ultimately sensible. In this location, galley activities need not disturb the helm, for example when running at night. With the dining area located in the Pilot House, a dimly lit dining table should be a fairly good companion to the helm, or if that were not desired, certainly a meal could be served in the saloon… 

In all, the 45' Gannet Widebody Trawler Yacht will be economical to build, simple to maintain, and a pleasure to travel with... 

For other similar designs in this series, please see the following:


45' Widebody Trawler Yacht GANNET - Kasten Marine Design, Inc.
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