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The 48' Fast Aluminum Trawler Yacht

'Rhumb Runner'

The 48' Fast Trawler Yacht - RHUMB RUNNER - Kasten Marine Design, Inc.
Interior Plan | Interior Profile | Larger Perspective Aft | Larger Perspective Forward | Perspective Above Aft

Copyright 2002 - 2011 Michael Kasten

General Concept

The 48 foot all aluminum "Rhumb Runner" has a fast semi-displacement hull form. The long and fine run and light displacement will yield an excellent combination of speed and economy. Relatively short overhangs maximize WL length and therefore vessel speed and accommodation space below.

Average waterline length is 46.75 feet. Beam is 13.5 feet. Displacement will be around 32,000 lb. light and around 44,000 lb. loaded. Draft is 4.5 feet light, and around 5 feet loaded. Draft could be significantly reduced without having to reduce propeller diameter, via the use of a tunnel drive... an excellent solution for a single engine in shoal waters.


The displacement to length ratio will vary from around 142 to 192 depending on the load case. This is quite light. The result is that hull speed will be right around 12 knots. In order to achieve this relatively high "displacement" speed, power required will be around 160 hp, assuming the average load condition. At 12 knots, with 600 US gallons of fuel, range will be something like 720 NM in the average load condition, with a 12% fuel reserve.

At typical "voyaging" speeds of around 8 knots, with 600 US gallons of fuel, range is calculated to be over 2,600 NM, assuming the same 12% reserve. At this speed, power use will only be around 40 hp...!

For such a wide range of power for these differing purposes, a Controllable Pitch Propeller will be the ideal choice.

For higher semi-displacement speeds one could easily make use of 450 or more hp, which would yield vessel speeds in excess of 20 knots (depending on fuel load and other vessel loads). The top speed achieved with greater horsepower will be more or less in proportion to the power applied. Of course range will be exponentially reduced at higher speeds.

Engine choices for Rhumb Runner are therefore numerous, and the amount of horsepower provided would depend entirely on the top speed required.

Although it is possible to apply sufficient power for true planing, if that were the goal the hull form should be changed. In other words, for true planing performance, the hull should be given a run that is flatter yet, along with a wider transom...


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 quite 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 the ideal layout for two couples - possibly for co-ownership...

To review the interior in greater detail please see the Interior Plan and the Interior Profile preliminary sketches.

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


On the aft deck, there is a seat that offers a great place for fishing or just watching the wake. The aft seat also provides a bit of extra headroom for the head of the berth below. Just forward of that, the top of the aft cabin is envisioned 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 there to be an exterior steering station. It is like a flying bridge, but 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 fast cruiser under 50 feet LOA. Additionally, the requirement for excellent sea keeping has encouraged keeping the cabins low. Height to the top of the Pilot House is under 11 feet, which opens up access to most of the canals in France and the rest of Europe.

This vessel type has also been developed in a smaller design, the Wave Runner 36. Having the same hull form as her larger sister, the Wave Runner 36 makes use of the interior layout of the Greatheart 36. The Wave Runner 36 allows a wide range of powering options, and best of all, it is small enough to be easily trailered from one cruising site to another.

In addition to the 36' Wave Runner this prototype has been further developed into a few other types, including the 48' Coast Runner, the 49' Ocean Express, and the 70' Express Cruiser.

Rhumb Runner 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 48' Fast Trawler Yacht - RHUMB RUNNER - Kasten Marine Design, Inc.
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