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Is A Motorsailor The Ideal Combination...?

Copyright 2000 - 2008 Michael Kasten

Although I've always found sailing to be very pleasant, having lived for more than 25 years in a nearly windless part of the US (the Pacific Northwest during the summer time) I have seen the light: A motor vessel is simply more convenient. Nevertheless, I would ideally still want a good sail rig on a boat of my own, thus the concept of a "motorsailor" becomes quite attractive.

Many will say though that a motorsailor is neither fish nor fowl, neither motoring nor sailing very efficiently. While this may be true with many such vessels, it need not be so. There is no reason for "motorsailors" to end up being characterized as an oversized sailboat with broad beam, high freeboard, short masts, and huge "raised salon..." In truth, even though these may be fairly common features, none of them except a modest pilot house is desirable for a true seagoing passagemaker.

Regardless of the many popular notions to the contrary, it seems to me that the idea of a motorsailor makes ultimate good sense.

Why? To name but a few reasons...

Let's consider a few of the reasons one might favor a proper motorsailor...

Just What Is a Proper Motorsailor Anyway?

Among the most fundamental of issues with the concept of a motorsailor is the commonly held notion that such a vessel must be 50% motor boat and 50% sail boat. This approach only allows the vessel to be only half as good at each task...

Emphasis on Sail: A motorsailor in its ideal form will be 100% sailing vessel, and 100% power vessel. In other words, with a boat such as this, if it will be desired to motor most of the time then one may simply provide an engine of adequate capacity and enough fuel for true passagemaking. With an uncompromised motor-sailor such as this, the boat will absolutely function well as a sail boat. After all, the requirements for moving through the water efficiently at what is essentially sailing speed are not much different in a true displacement power vessel than in a sailing vessel.

Naturally there are optimizations for a motorsailor that will be powering most of the time... One of the first and most obvious choices will be to provide a comfortable pilothouse rather than the open cockpit of a sailing vessel. The design may be given a higher bow for the inevitable times spent powering into the weather. Freeboard, within reason, is to be desired. However, excess freeboard provides windage, weight, and vulnerable structure up high... structure that cannot be reefed when the weather kicks up.

Broad beam is often equated with comfort. It is not so. Excess beam makes a vessel's motion more harsh due to higher rolling accelerations, and excess beam increases the overall resistance per ton.

Emphasis on Power: One may certainly take an alternate approach and create a motorsailor that has a slightly greater emphasis on power. One can for example design a power vessel with a good hull form for both powering and sailing, with a "powerboat-like" layout, and with a modest "get-home" sail rig. This combination will offer the simplicity, silence and joy of sailing when the wind favors, in addition to the peace of mind that comes with knowing that a mechanical failure will not jeopardize the safety of the voyage.

For examples of several motorsailor types please see the links at the bottom of the page.

Power Vessel Hull Form

At the opposite extreme to a pure sailing vessel is a boat that is strictly a power vessel. Such a boat will not need a deep keel like a sail boat. A power vessel will always benefit from some sort of roll dampening scheme. A power vessel will have several hull shape differences from a sailing vessel. For example, a power boat will not require as much beam, and a power boat will benefit from optimizing the prismatic coefficient in terms of a higher expected operating speed on a voyage.

As excellent as Beebe's book is with regard to power vessels (and also Leishman's rewrite of it), if you study the vessel designs presented in either issue, there are very few of them specifically optimized for making passages at efficient displacement speeds (the optimum long range voyaging speeds between S/L 1 and S/L 1.2).

Many of the examples offered in either edition of Voyaging Under Power as prime passage makers are instead prime coastal cruisers, i.e. vessels intended for optimum speeds above the efficient passage making "groove." In other words, a large percentage of the examples offered in both editions of Beebe's book (and in the re-write of it) are designed for short duration cruises where fuel use is not an overriding issue.

Naturally, there are many valid reasons to make use of a "semi-displacement" hull form. It must be realized though, that semi-displacement shapes are not necessarily optimum for long passages. Instead, their place is coastal cruising where rapid transit is the primary requirement, and where fuel use and survival in ultimate conditions are secondary considerations.

Semi-displacement types require more "lift" in the after body to give them higher speed potential. Therefore, a semi-displacement boat will have fairly straight and fairly flat buttock lines aft. This is the vessel type exemplified in Voyaging Under Power.

While greater speed will certainly be possible, that boat speed comes at a much greater cost in fuel, and often in the displacement required to carry that fuel. While speed is improved, range is diminished considerably. For many travelers this is the correct choice, since they may only have weekends and short vacations to spare. For the true long distance voyager however, quite different requirements exist.

For seaworthiness in ultimate conditions there is little question that a true displacement vessel is the most suitable platform, having a more sea kindly behavior, a deeper hull, less beam, and ordinarily a larger range of positive stability.

A common misconception is that a displacement vessel must be "heavy" and must consequently be slow. Whether a vessel is or is not a displacement type is partly a matter of her weight, but also a matter of her shape, mostly in the after body. If you study good sailing vessel shapes, you will be looking at what are also essentially excellent hull types for making voyages under power...! By this we mean to say the hull itself, rather than the appendages (keel, etc.).

One common change made when optimizing such a shape for power rather than sail is to widen the stern. This is beneficial for power vessels, and if the change is modest, sailing performance will not be adversely affected.

Roll Dampening

As noted, all ocean going power vessels will require some sort of Roll Attenuation scheme. Aboard a motorsailor, this is to a large extent provided automatically by the sail rig itself. The sails also contribute, but the weight of the rig itself provides an effective roll stabilizer even with the sails furled due to the added inertia of the spars and rigging.

Sailing Synergy

On all points of sail, the synergy between motor and sail produces a net gain in speed over what would be possible with either alone. When motor-sailing, 6 knots worth of fuel gets you 7 or 8 knots of boat speed. Of course when under sail alone there is zero fuel use. At today's fuel prices, that is saying something...!

Naturally, the rig must be set up to be easily handled. Once that's accomplished, the sails will not be any more hassle than paravanes... If the hull shape is designed for maximum efficiency rather than just simply to enclose an enormous volume for accommodations, she will also be a real blast to sail!

When motor sailing, if the desired course is not perfect for sailing, then "tacking" downwind accomplishes roll reduction, produces a big gain in comfort, and a very welcome gain in speed and efficiency.

Controllable Pitch Propellers

For this kind of motoring, there is much to be gained by using a Controllable Pitch Propeller and a slow turning engine. With a CP prop, one can get the optimum performance out of both sails and engine, rather than making the engine do it all.

One can make slight course changes, adjusting the apparent wind to get a "good return" rather than just only motoring. Alternately you can speed up or slow down the engine to increase or slow down your "boat-made-wind" to change the apparent wind angle. Toward that end, a CP prop gives ultimate flexibility when motor sailing, allowing the engine to remain at the "sweet spot" in terms of RPM, and just feathering the propeller to match the difference in power required.

Rig Type

Is there a reason to prefer one rig type over another? Of course each sailor will prefer one rig type over another, and wherever there is a strong preference there is ordinarily little point in arguing the point further. For one perspective on the choices involved, please have a look at the web page, "What's the Ideal Sailing Rig...? "

Overall Efficiency

Based on my own experience with this combination, I prefer a good sailing rig over stabilizing fins and paravanes for most conditions. Dragging paravanes through the water seems to generally knock almost a knot off the boat speed. That said, we have developed a series of streamlined, NACA foil shaped paravanes that cut the usual resistance by more than half - an excellent choice if paravanes are required.

Paravanes or active stabilizers however will not bring you home in the event the machinery stops. A good sailing rig will bring you home, and usually adds a knot or so. With that difference, 7 knots' worth of fuel gets you only 6 knots on the motor vessel with paravanes, but yields 8 or more knots on the motorsailor! In 2008, with fuel prices pushing USD $4.00 per gallon, two extra nautical miles is welcome in the extreme...!

In this sense alone, practicality certainly seems to favor the motorsailor.

A Few Motorsailor Examples...

The 56' Ketch, Shiraz | The 50' Schooner, Lucille
The 44' Schooner, Redpath | The 'Dream Yacht' Renegade 50
The Motor Ketch, Greatheart 48 | The Motor Ketch, Greatheart 60
The Motor Ketch, Swallow's Nest 60  | The Motor-Schooner, Chantage 64