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The 49' Low Profile Steel or Aluminum Trawler Yacht


The 49' Trawler Yacht - Black Jack - Kasten Marine Design, Inc.
Interior Plan | Interior Profile | Portside Perspective Aft | Perspective Aft Low | Perspective Aft Above

Copyright 2011 Michael Kasten

General Concept

The 49 foot 'Black Jack' has a semi-displacement hull form that has been derived, interestingly, from that of a sailing Skipjack... thus the derivation of the name. The original sailing hull type has been modified as needed - made less wide, and freeboard increased - for suitability as a motor yacht hull. The Skipjack hull type provides a good combination of easy construction, excellent hull speed and propulsion economy, combined with ultimate seaworthiness. The rather short overhangs maximize the WL length for the sake of being able to achieve greater vessel speed per overall boat length, and for the sake of having more accommodation space below.

The accommodation space is envisioned as the ideal small vessel layout for two couples - possibly as co-owners. The forward and aft cabins are essentially equal in size and accommodation, with the galley, saloon, and pilot house at deck level. See below for a more detailed description of the interior.

Particulars are:

Hull, decks and cabin are ideally shaped for construction in steel or aluminum, with all scantlings according to the ABS Rule. If built in steel, ideally the house top would be cold molded wood laminated into a single monocoque structure and sheathed in GRP. Alternately, the whole pilot house could be built in aluminum alloy, including the house top and the brows. Of course if the vessel were built in aluminum, the entire cabin structures would also be in aluminum. All plating, framing and internal structures are ideally shaped for NC cutting, which would include the integral tanks, engine girders and major bulkheads.

Given the chined hull shape, certainly construction in plywood is a possibility. Yet another advantage with this kind of shape is that a female hull mould can be very quickly built using flat sheet mould sheathing throughout, with the cabin structures being made using flat-sheet GRP panels made on a flat layup table. Quick and easy.

Power and Range

The engine specified is a John Deere 6 cylinder diesel for 175 hp at 2,400 rpm, mated to a Twin Disc gear using a 3:1 reduction to drive a 34" propeller. The "cruising speed" for long range voyaging with this hull is assumed to be around 8 knots. Theoretical hull speed is around 9.5 knots, however due to having relatively light displacement the hull should reach around 10.5 knots with the planned horsepower. Although higher speed can be achieved with this semi-displacement hull, it would be less economical to push the hull faster.

For example, using a modest amount of power with 1,250 USG of fuel and keeping a 12% reserve, the Beebe algorithm shows the range in the average load condition to be around 3,200 NM at 7.5 knots. One knot faster and the range drops by some 800 NM..!


To see the interior that has been planned, please review the Interior Plan and the Interior Profile preliminary sketches here. The sketches in these links are taken from the Rhumb Runner prototype's interior sketches - an example of being able to wrap a variety of different exterior hull forms around a given interior layout. In this case, the interior is an exact fit for the "Black Jack" hull form, which uses the same cabin configuration as the original. A description of the interior follows:

Beginning forward, the layout below contains a large owner stateroom with head and shower to port and starb'd respectively. A ladder on center leads upward to the Pilot House. The pilot house is spacious, with a nav station to port and pilot seat to starb'd. The pilot house also contains the galley and dinette seating. Below the Pilot House sole is the engine room and the bulk fuel tanks.

A companionway leads aft and down to another large stateroom which contains a large berth, cabinets and an en-suite head. Both staterooms are equally well appointed and have nearly the same area, so really it's tough to decide which should be the "master" stateroom. This is an ideal layout for two couples - possibly making the vessel a good candidate for co-ownership with another couple, or possibly making the vessel suited to charters...

Motor Yacht prototypes using this same interior layout:
Black Jack | Double Eagle | Rhumb Runner


On the aft deck an aft facing seat offers a great place for fishing or just for watching the wake. The aft seat also provides a bit of extra headroom for the head of the double berth below. Just forward of the aft deck seat, the top of the aft cabin is envisioned as a 'chariot' style exterior bridge, therefore the aft sweeping 'wing' walls. The overall rationale there is to keep the height of the house and coamings below the EU canal clearance limits, but to also allow an exterior steering station. It functions just like a flying bridge, it is just not 'flying' as it would be if located on top of the Pilot House...

Design Summary

The intent of this design has been to fit the maximum accommodations into a seaworthy long range cruiser under 49 feet LOA. This keeps the length within the 15 meter boundary for easier ownership and licensing within the EU countries. The height to the top of the Pilot House is just under 10' - 8" which opens up access to most of the canals in France, Germany, Holland and much of the rest of Europe. Few people realize for example that Geneva is a port city..!

Black Jack is so-far a preliminary design, having been modeled by computer and the preliminary hydrostatics calculated. The rest remains to be detailed in order to create a completed set of Building Plans. For further information, please inquire.

The 49' Trawler Yacht - BLACK JACK - Kasten Marine Design, Inc.
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