Messing about in boats since 1975. Online Since 1997.
Home | Intro | Our Design Process | Stock Design Info | Motor Yacht Designs | Sailing Yacht Designs | Prototype Designs
Plans List | Articles | Our CAD Design Stream | Maxsurf | News..! | SITE MAP..! | Site Search | Design Team | Contact Us
Please see the AVAILABLE BOAT PLANS web page
Is a Motorsailer The Ideal Combination...?
Copyright 2000 - 2016 Michael Kasten
I've always found sailing to be very pleasant. But having lived for so long 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 "motor-sailer" becomes quite attractive.
Many will say though that a motor-sailer 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 a "motor-sailer" to end up being characterized as an overweight sailboat with broad beam, high freeboard, short masts, and huge "raised salon". In truth, even though such features may be fairly common, none of them (except a modest pilot house) are desirable for a true seagoing passagemaker.
Motor sailing yachts are becoming more popular these days, primarily because they make ultimate good sense.
Why? To name but a few reasons...
- For propulsion backup
- For the sheer fun of sailing
- For roll reduction
- For efficiency of propulsion
- For the synergy of employing two modes of propulsion simultaneously!
- The cost of a get-home engine or second main engine can just as well be put into a good sailing rig...
Let's consider a few of the characteristics inherent in a proper motor-sailer...
Just What Is a Proper motor-sailer Anyway?
Among the most fundamental of issues with the concept of a motor-sailer is the commonly held notion that such a vessel must be 50% motor boat and 50% sail boat, implying that the vessel will be only half as good at each task...
Emphasis on Sail: A motor-sailer in its ideal form will be 100% sailing vessel, and 100% power vessel. When it is desired to motor most of the time then one can simply use the engine, assuming it is of adequate capacity and there is enough fuel for true passagemaking.
With an uncompromised motor-sailor such as this, the boat will also have been designed to function supremely well as a sail boat. It turns out this is not so difficult to achieve, since 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 motor-sailer 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. This is decidedly not so. Excess beam makes a vessel's motion more harsh with higher rolling accelerations. Excess beam also increases the overall resistance per ton. There must be sufficient beam for good sail carrying power, but no more.
Emphasis on Power: Certainly one can create a motor-sailer that has a greater emphasis on power. One can for example design a motor 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.
Power Vessel Hull Form
At the opposite extreme from a pure sailing vessel is a boat that is strictly a motor vessel. Hull form differences are as follows:
- A motor vessel will not need a deep keel like a sail boat.
- A motor vessel will always benefit from some sort of roll dampening scheme.
- A motor vessel will not require as much beam, and
- A motor vessel will benefit from a higher prismatic coefficient, optimized for a slightly higher average operating speed.
As excellent as Beebe's Voyaging Under Power is with regard to information about motor vessels (and the Leishman re-write of it), if you study the vessel designs presented in either edition there are very few designs presented that are specifically optimized for making passages at efficient displacement speeds, with the optimum long range voyaging speeds being between S/L 1 and S/L 1.2.
A large number of the examples offered are instead prime coastal cruisers, i.e. vessels intended for optimum speeds above the efficient passage making "groove." In other words, boats designed for short duration cruises where fuel use is not an overriding issue. I call these boats the "transom draggers" because they have a substantial part of the transom immersed, a shape that is optimized for higher "semi-displacement" or even "semi-planing" speeds well above S/L 1.35.
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, and ordinarily part of the transom will be immersed. To the greater degree this is so, the more the hull shape is optimized for speeds well above the most efficient passagemaking speeds. While greater speed will certainly be possible, higher 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 can be the correct choice, since their voyages may be only coastwise and they may only have weekends and short vacations to spare.
Unfortunately, this type of vessel is over-represented in the first three editions of Voyaging Under Power (both Beebe and Leishman). But for the true long distance voyager, quite a different set of 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. In the most recent edition of Voyaging Under Power (Fourth Edition by Denis Umstot) it is good to observe that several new designs are presented that have hull forms much better suited to efficient long range passage making.
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 excellent hull types for making voyages under power...! I'm referring to the hull itself, rather than the appendages (keel, etc.). You will not find any "transom draggers" among displacement sailing vessels because that is quite an inefficient shape for traveling at displacement speeds under sail..!
One common change made when optimizing the hull shape for motoring rather than sailing is to widen the stern. This is beneficial for motor vessels in order to prevent squatting under power. If the change is modest, sailing performance will not be adversely affected.
Roll Dampening
All ocean going motor vessels will require some sort of Roll Attenuation scheme. Aboard a motor-sailer, 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. For more information about why this is so, please see the article on Beam vs. Ballast, specifically the section under Roll Moment of Inertia.
Sailing Synergy
On all points of sail, the synergy between motoring and sailing produces a net gain in speed over what would be possible with either alone. The speed gain is in fact greater than one would expect. When motor-sailing, 3 knots worth of fuel gets you 7 to 10 knots of boat speed...!
Naturally there must be optimization of the sailing course, since in this mode you are operating primarily as a sailing vessel, with motor assist, and the heading must be suitable for sailing. And of course when under sail alone there is zero fuel use. At today's fuel prices, that is saying something...!
The sailing rig must be set up to be easily handled. Once that's accomplished, the sails will not be any more hassle to handle 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 to windward or on a reach, the sail rig accomplishes roll reduction, produces a big gain in comfort, and provides a very welcome gain in speed and efficiency. On a reach or off the wind, there is little need for the engine.
Controllable Pitch Propellers
For this kind of motoring, there is much to be gained by using a Controllable Pitch Propeller. With a CP prop, one can get the optimum performance out of both sails and engine.
One can make slight course changes, adjusting the apparent wind to get a "good return" rather than just 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 adjusting the pitch to match the difference in power required. And when under sail alone, a fully feathering propeller will offer the least resistance.
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. 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 motor sailing, I prefer a good sailing rig over stabilizing fins and paravanes. Dragging paravanes through the water generally seems to 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 several knots to your boat speed. With today's fuel prices, the extra nautical miles per gallon are welcome in the extreme...!
In this sense alone, practicality most definitely favors the motor-sailer.
A Few motor-sailer Examples...
The 42' Ketch, Lucille | 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
Please see the AVAILABLE BOAT PLANS web page.
Home | Intro | Our Design Process | Stock Design Info | Motor Yacht Designs | Sailing Yacht Designs | Prototype Designs
Plans List | Articles | Our CAD Design Stream | Maxsurf | News..! | SITE MAP..! | Site Search | Design Team | Contact Us