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The 43' Widebody Dive Yacht


43' Widebody Dive Yacht - Kasten Marine Design, Inc.
Perspective Above Aft | Perspective Low Aft | Side View Above | Perspective Above Fwd | Portside Cutaway Perspective
Widebody Preliminary Interior Profile | Widebody Preliminary Interior Plan View

Copyright 2011 -2016 Michael Kasten

General Concept

The request for this design was to create a steel trawler yacht suited for living aboard, ocean travel, and for an active pursuit of diving. Low build cost, simple layout, redundant systems and low maintenance requirements are a priority. Propulsion using a four cylinder turbo diesel assures modest machinery weight and good fuel economy.

I've called the design Petrel after the graceful pelagic sea-birds found on all oceans. The lines reveal an easily driven hull. The Petrel interior layout is similar to my 40' Widebody COASTER  and 45' Widebody GANNET in terms of their interior layout. The "Widebody" main cabin provides plenty of interior space for four in the saloon and galley. The transom is designed for optimum access to the water in order to best enjoy active dive adventures. Having relatively short ends, the WL is all of 40 feet..!

Particulars are:

Stability will be excellent due to the raised fore-deck and due to the widebody house structure, both of which provide quite a large reserve buoyancy. When completed, the 43' Petrel will easily meet the EU RCD "all ocean" category.


Hull; deck; cabin and pilot house construction are planned for aluminum construction.  An alternate would be to build the hull in steel with the house in aluminum. Scantlings will be according to the new ABS Yachts Rule - 2015, and will also comply with ISO rules used within the EU. Plating and framing will be detailed for NC cutting. Check out this image of Coaster's Frames, ready for nesting. Though built in aluminum, the Coaster's frame layout is very much the same as will be used on the Petrel. For more information about our use of CAD for NC cutting, please see our Design Stream article.

Power, Range, Equipment

The engine specified is a John Deere 4045 TFM - 4 cylinder turbo diesel that produces 107 hp continuous at 2,400 rpm. It will be mated to a Twin Disc gear using a 3.5:1 reduction to drive a three blade propeller. Theoretical hull speed is approximately 8.5 to 8.7 knots. Cruising speed for long range voyaging is 7.25 knots. Range (assuming a 15% reserve) at 7 knots will be around 3,000 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 tanks...!

Aft of the engine room is a large storage area below the saloon and galley. Items slated for this area are the dive compressor, storage tanks, extra dive gear 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...

Exterior Arrangement

The aft deck, pilot house side decks, saloon, galley and pilot house sole are all at one level. Aft in the cockpit area aft a ladder leads up to the "boat deck" on top of the house through a hinged hatch at the top of a ladder. The exterior side decks outboard of the pilot house are at the same level as the pilot house sole. The PH side decks step up to the foredeck, which spans the full width of the vessel forward of the pilot house, extending all the way to the bow.

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.

Exterior watertight doors are located on each side of the pilot house, and on center aft of the saloon. There will be a mast for the paravane poles, which will also be provided with a boom to allow easy placement of a shore boat on the house top above the saloon.

Interior Arrangement

The accommodations are planned in order to provide comfortable cruising for two people on extended summer cruises with another couple as guests for dive adventures. Taking the interior from right forward, the layout is as follows:

At the forward end of the owner's cabin is an "island" berth with walk-around space surrounding the foot of the berth. To port and starb'd are shelves and lockers with reach-hole access. A hanging locker is located on each side of the owner's cabin aft. A door just off center leads aft into the hallway.

To starb'd of the hallway is a guest stateroom containing a double berth and lockers at each end. The guest berth can be arranged as a "berth in a box" for combined use of this cabin as an office, in which case there would be a 5" deep box occupying what would otherwise be the depth of a typical desk drawer. On raising the hinged desk-top, the mattress is exposed - and the desk-top lashed in the up position outboard against the ceiling to starb'd. This allows complete dual use of the guest cabin.

To port of the hallway is the head and shower, containing a vanity cabinet with sink outboard and a marine toilet forward. At the aft end of the hallway a ladder leads up and aft into the pilot house. Behind the ladder a door is provided to access the engine room.

In the pilot house, a built-in double seat is located to starb'd, and a single helm seat is located to port. The "dashboard" forward will hold navigation instruments and engine controls.

Aft of the Pilot House is a bulkhead with a door into the galley / saloon cabin. In the galley to starb'd is a peninsula counter, defining the aft face of the galley. To starb'd is a cabinet arranged lengthwise, and to port is another cabinet of similar proportions. The portside cabinet will hold a deep freeze. The galley peninsula will be equipped with a double sink. A three burner propane range with oven will be located outboard to starb'd. Along the forward face of the galley is the pilot house bulkhead. There will be doors in the bulkhead to allow access to the space below the pilot's seat. This will house a 12v DC refrigerator and an under-counter style combo washer / dryer. Aft of the galley there is a full width saloon. A pair of easy chairs are located to port with a small table between, and to starb'd is a dining table with wrap-around settee.

See the following images to view the preliminary layout below:

The interior will be styled very much like the 40' Coaster, but with a "widebody" saloon and galley. Please see the following images which show the Coaster 40 as-built interior:

Design Summary

In all, the 43' Petrel Widebody Dive 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:

Widebody Dive Yacht PETREL - Kasten Marine Design, Inc.
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