For years now I have been toying with the idea of a stern mounted mast on a sailboat. I believe it is time to present my thoughts,
for criticism, both positive and otherwise. I may learn that the theories are wrong, or that the idea is unworkable for some reason. I might receive some reinforcement for my idea as well. Either way, I am bound to learn something...and that is the benefit behind any outlay of thought.
Firstly, let me get you a photo, so you have an immediate concept of what I propose.
Here you see the "Future of Sail".........in my mind, at least.
Is "Why?" your next question? It would be mine.
On many occasions sailing, I have noticed the mast seemingly getting-in-the-way of the wind as it flows to the sail. The physics I have studied say that air usually takes 7 times the distance it deviates, to flow back to its 'original' surface. In simple tests I have taken, this seems to be accurate. On a 34 foot sailboat, the mast might be six inches wide at the base and 4 inches wide at the top.
Imagine the area of,
let's use 5 inches (for the mast)
times 7 (given above) equals 35 inches,
times the height of the mast, let's say 38 feet or 456 inches.
That is 110.8333 square feet of sail which isn't being used efficiently, all because of the mast at the leading edge (luft) of the sail.
Here is a crude graphic to explain the main reason again.
My proposal is to build an aft-mounted mast and lean it forward over the deck. For obvious strength reasons this should be built into the boat, incorporating its base into the main structures of the hull itself. (An 'add-on' mast might not be rigid enough for this as the hull in the attachment area, might not be able to handle it.) I do believe we now have the technologies to create a strong enough mast of this type, keeping in mind what can be accomplished with wind-generator blades of 80 and 90 feet, and flag poles of 150 feet these days.
Now, two headsails can be hanked on with only the thickness of their forward edges to hinder the wind flow. With two sails, a slot can be created as is always the wish on a normal sloop or cutter. The halyards for these sails may run up through the mast for raising and lowering, right from the aft cockpit area, where the base of the mast is.
Now, let us take on other concerns and aspects of this idea...
Would this 'arm' cause any unusual motion in the boat due to its being mounted on the stern and 'hung' over the deck?
The mast should be weighted carefully to try to put its Centre of Gravity above the centre of buoyancy of the boat. The hull I have in mind for this boat has a fine entry and a full, wide hull, aft of the keel, for stability, and If this is accomplished, there shouldn't be any strange motion. (NOTE: This is an area of study which could use more time and testing, but models have shown great promise.)
What is the inner construction of the mast?
Since a normal, straight mast, in this new position would be supported by an aft-facing spreader and a stern shroud, I would have this engineered into the body of the mast. Today's Kevlar and carbon fibre constructions, using cutting-edge techniques, the new epoxies and stainless steel should be able to fashion a mast capable of doing the job. ****Gougeon Brothers report here*****
How will the profile of this new mast be affected by the wind?
Using my calculations, the profile presents an area equal to the square footage of a normal mizzen sail from a yawl of the same length. The 'sail' will automatically head a boat up into the wind if the rudder fails. It will allow you to point the boat into the wind, when hoisting sails, if you are single-handing the boat. The mast stepped in this rear position will give the rudder more 'bite' and allow less rudder, hence less drag, in order to make a turn. Any yawl sailor will agree as to the wonderful advantages of a mizzen sail...me thinks! (The leading and trailing edges of this mast will need more study to determine the best shape for all wind conditions.)
And...just think of all the 'stuff' one could attach to the mast, for protection, for convenience, for use over the cockpit area, or just to add to the futuristic look of the ship. No longer would there be any need for a boom-crutch or rest; no more fear of that jibbing boom sending you to the promised land; no more mast and all of its inherent lines in the view all the time, only sails and wind (with the sails down, you have a perfectly clear view); no spreaders to catch and tear the sails on.
Let me just throw in a photo to show the more traditional use of a mast and spreaders and shrouds, while using the aft-mast idea.
Note the mizzen hung on the shroud.
Allow me say here that this concept must have been thought of long before I did, so it can't be my idea. I must add that it DID dawn on me one day, without seeing it anywhere else before that day. Since then I have found numerous references to the aft-mast on the internet but I still have the same excitement for the concept and am still trying to advance it, in my own way, with my own perceived improvements and revisions.
"Man! What I'd give for a benefactor or investor who would finance a full sized experiment."
"I would create a ship like no other."
