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Diesel Duck Article in the June 09 Passagemaker Magazine



Motorsailing - Some Thoughts

Builder's Notes - Mandarin Motorsailer

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Motorsailing - Some Thoughts


Based on my experience the motorsailer is the most practical and comfortable vessel for serious ocean passagemaking. However these days power-only long range cruising yachts seem to be the rage. We sell about 8 power boats for each motorsailer we build. I personally can not understand the long range powerboat skipper generating a beautiful 7 to 9 knot wind, at some cost, and than just throwing it away - while worrying about fuel?

I would like to share with you some thoughts about motorsailers, power-only trawler yachts, and sailboats.

Passagemaking has many areas of concern. Three of the most important ones are:

FUEL ECONOMY, both to keep costs down and provide the range needed for longer cruises,

STABILIZATION, good stabilizing is the difference between a voyage out of hell and one of the most pleasant experiences of a lifetime, and

RELIABLE PROPULSION, who do you call when the engine stops.

These three concerns are addressed in a power-only vessel buy utilizing a variety of conflicting contrivances. More fuel is carried for long cruises the weight of which causes more fuel use. Extra "wing" engines are employed to back up the main engine which increases weight and hull drag causing more fuel use and are of no use in rough conditions or in case of total fuel loss. Stabilizing means dragging cables and paravanes or powered fins through the water, both of which slow down the vessel and require even more fuel. And they will not bring you to a safe harbor following total propulsion failure.

Solutions to the problems of stabilization, propulsion redundancy and fuel economy are inherent in the very concept of the motorsailer.

A properly designed sailing rig stabilizes the vessel better than any mechanical device without inducing hull drag or relying on fuel dependent energy.

And the rig provides total propulsion redundancy allowing the vessel to reach a safe harbor if the fuel runs out or there is a mechanical failure.

Plus the sailing rig increases the speed of the vessel so less fuel capacity is needed. This weight savings coupled with the additional propulsion power available results in faster passages and excellent fuel economy.

How can this be? Well most power-only trawler yachts cruise at around 6 to 8 knots per hour depending on power, weight, hull shape and water line length. All these vessels are creating, at some expense, a wind equal to their speed. This wind, a vital and reliable source of energy, combines with and adds to the true wind to create an apparent wind across the boat which is just thrown away. The motorsailer, on the other hand, uses its rig to regain this energy resulting in increased boat speed, up to 25% above a stabilized powerboat, without increasing fuel use.

At the same time the pressure of the wind impinging on the sails stabilizes the boat very well and, of course, sail only propulsion is always available if needed or desired. Life should be so good.

While Beebe's book, "Voyaging Under Power" is the bible of the power-only crowd it is interesting to note that his vessel, "Passagemaker", was a motorsailer with small a rig. Bob wanted a larger more appropriate rig but settled for the smaller rig because of its, and a suitable folding prop's, cost. (P.20 bottom, Seven Seas edition; P.28 top, Leishman rewrite) In actual practice I feel motorsailers do not need a folding prop unless extensive sail-only passage making is planned. It is my experience that most of the time motorsailers work best in the engine running mode.

Beebe's design 103 is a true 50/50 motorsailer, similar to the MANDARIN 52, which, to quote Bob, "...eliminated the faults we found in "Passagemaker". Bob called Design 103 "Passagemaker II".(P.84 2nd paragraph, Seven Seas edition; not in Leishman rewrite)


You may think I'm talking about a sailboat with its motor on here. Not so! A sailboat using sails and motor is, in fact, motorsailing, but it is not a "motorsailer". Some sailboat builders put a pilothouse on their sailboats and call them motorsailers. Even the newest motor sailor knows they are just trying to fool you.

A sailboat is designed to sail well on all points of sail and this means upwind. Racers can not use their motors and sailing purists love to surf up and down a multi sail inventory while sitting outside ( ! ! ) enjoying the ocean gods dumping 55 gallon drums of seawater over their heads. I've been there and did that and, at the time, even enjoyed it, sometimes. But a sailboat that's sailing well upwind carries, to varying degrees, three rather serious design compromises.

First Compromise: When a boat sails upwind part of the wind's energy is making the boat move forward, that's good; but most of the wind's energy is trying to tip the boat over, that's bad. To keep the boat from tipping way over we need ballast, like heavy heavy lead, lots of it. So this extra weight is our first compromise.

Second Compromise: Because this heavy ballast can not keep the boat from tipping over some, we need nice water planes, efficient hull bottom shapes, right up the side of the hull so that the boat can sail while heeled. This results in pinched sterns causing user unfriendly interior spaces and less form stability decreasing the effect of all that ballast.

Third Compromise: Now to make the ballast really work we need to get it low. This means deep draft usually in a fin shaped keel with an exposed rudder. Deep draft limits available cruising areas, our third compromise.

Bummer #1, you have to carry these three compromises all the time, when sailing up wind where they are needed, and when sailing on a forward reach, a beam reach, an aft reach, downwind and even at anchor, when they are not.

Bummer #2, cruising sailboats, despite carrying all these design compromises, almost never sail upwind! Cruises are carefully planned, weather systems are waited out, motors are run, all to avoid ever having to actually sail a long cruising leg upwind.

So what's different about a motorsailer? The motorsailer is a vessel that sort of sails with out a motor pretty well, but not real close to the wind, and can motor along without sails OK, but may be a little stiff. A stiff hull is shaped to resist rolling. It carries sail well but it likes to float with its beam water line parallel to the water surface. A lumpy sea presents many inclined water surfaces and a stiff hull will snap around trying to parallel each one as it passes. However with the sails up and the motor quietly ticking over the motorsailer comes into is own. Providing its crew with fast, stabile and fuel efficient passagemaking.

Of course, the designer of a motorsailer has to make the decision to exclude good upwind performance. And accepting that compromise allows a lot of neat things to happen, lighter weight, shallower draft (5 feet is the max for most canal systems) and a more yacht trawler like hull shape with its large accommodations, especially in the aft cabin.

But the neatest thing of all is the way the large motor and large sailing rig of a true motorsailer, designed with a nice slippery hull, work in harmony, the motor taking over in the lulls and the rig taking over in the puffs, to provide a surprisingly fast, fuel efficient and comfortable passage.

Note: By "Slippery" I mean a cp (prismatic coefficient) around .60 which favors the 7 to 9 knot. range.)

Comments are welcome.

Bill Kimley


I have to share with you one small thing that occurred to me as I read your article about motor sailers. Something you didn't mention: With the sail up, the motor off, and a starlit sky, the motor sailer can offer the quiet romance of the sea. There is nothing like a quiet passage at night on a sailing vessel. Yet you still have the full ability to turn a key and head in whatever direction you would like. A vessel that delivers all the romance of sail.... without giving up the control of a motor vessel.

Charles Bell
Belgoes Filtration Systems Inc.




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