Designing  My First Sailboat

 

            As a young teenager, I had spent many hours on the nearby bay (Seatuck Cove) and one day my Dad decided to build me a ten foot "scow" which was easy to handle and pull up on shore when not in use.  I had a lot of fun with it and experimented with crude sailing rigs and soon found that anything could sail with the wind but not across or into the wind without some extra device besides a flat bottom and a rag-tag sail.

 

            I read everything in sight about small sailboats and decided to design one of my own.  My Dad , who was a carpenter, had previously built many small rowboats and had, in fact, a small boat business some years before my time.  So Dad indulged me and agreed to build it to my design, perhaps with some unexpressed misgivings.

 

            It is important that a sailboat has a "balance", that is, the center of effort of the sails should be in harmony with the center of lateral resistance of the submerged part of the hull.  If this is not accomplished, the boat will require that the rudder be applied to compensate for the imbalance thereby causing considerable drag and discomfort for the helmsman.  It is furthermore dangerous to have a "lee helm", that is, a tendency for the boat to turn leeward when sailing across the wind.  In a strong gusty wind situation the boat would tend to upset as it wouldn't automatically nose into the wind to relieve the pressure on the sails if one were to be lax in managing them.   A "weather helm" was more to be desired, but no boat can be perfectly balanced under all conditions, so the ideal compromise is one in which the boat has a slight lee helm when the wind is light and a weather helm when the wind is strong.  A boat that would tend to sail straight while upright, tends to turn into  the direction of the "high" side when heeled, as the  underwater curvature of the hull becomes unequal in this mode   This is all  to the good.

 

            Following the recommended procedure, I determined the center of area of the sails by drawing lines from the three corners of the triangular sails to the centers of the opposite sides.  The intersections of these lines approximated the center of area of each of the two sails.  The center of area of the combined sails would fall on a line drawn between these two centers.  If the sails were of equal size the center would be  on this line, halfway between them.  If the jib were 30% of the area of the mainsail, it would fall 30% of halfway, measuring from the larger sail. The center of effort  of the sails would fall at a distance of 15% of the waterline length forward of this, according to formula  The center of area moves forward as the sails are deployed from a perfect fore and aft profile to an "average" sailing position, creating an center of effort ahead of the center of area as determined from the profile.  It is this center of effort that must be balanced with the center of lateral resistance in order to have the location of the sails in the proper relation to the hull.

 

            Since the form of the hull is much more "fixed" than the rigging, it follows that any balance might more easily be achieved by designing the rigging to accommodate the hull, rather than the other way 'round.

 

            The "center of lateral resistance" is the midpoint of resistance if the boat were pushed sideways through the water which is what the sails try to do when sailing across the wind.  Imagine shoving a boat sideways through the water with one hand.  If the hand were too far forward it would tend to push the bow around to a leading position , whereas a hand too far aft would do the opposite.  To find this "midpoint" using this method might not always be practicable and so another solution has been devised to replace it. 

 

            The underwater profile, the center of which approximates the center of lateral  resistance, is an irregular configuration at best, and might seem to pose quite a challenge to determine its center geometrically.  However, a very simple method of determining this to a reasonable degree of accuracy can be used as follows:  Make a cardboard cutout of the underwater profile and balance it laterally on a knife blade.  Be sure the centerboard (if any) is in the "down" position, but do not include the rudder.  The position of the knife blade, if transferred to the plan view of the boat and sails, would become a vertical line crossing the boat in a location that would intersect where the "hand" would be when shoving the boat sideways so that the fore and aft resistance of the hull were balanced.  

 

            The center of effort of the sails (CES) must now be coordinated with the underwater center of lateral resistance (CLR).  In other words, our CES which has been moved a distance of 15% of the waterline length forward of the center of area of the sails, must coincide with our "knife blade" line which indicates the CLR in order to achieve a good balance in the average situation.  Therefore, in order for these two vertical lines to become one, the rig may have to be moved in relation to the hull.  This may be accomplished by adjusting  the position of the  mast, changing the configuration of the sails, lengthening of shortening the bowsprit, (if any) changing the length of the boom, or any other reasonable means.                                                                    

 

            Another dynamic factor that enters into the balance is the tendency of the hull to turn into the wind when heeled.  Imagine a hull progressing through the water in a level position.  The water  pressure on both sides of the bow would be equal.  However, if the hull were heeled to one side, there would be more pressure on the "low" side and this would tend to push the bow toward the "high" side, (to windward when sailing) across or somewhat into the wind).   

 

The distribution of the weight of the occupants is another factor, as it changes the underwater profile and therefore, the CLR.  There are so many variables that no perfect balance can be achieved under all conditions, but the formula described is the best "educated guess" that I am familiar with.  Of course, some post-design changes might be desirable, but they should not be major ones if some proven system is followed.

 

To return to the "lee" or "weather" helm situation, one can only expect a good balance when  the boat is sailing across, or angled into the wind.  Fortunately, the stronger the wind, and the more the boat is heeled, the greater the tendency to turn into the wind, thereby relieving some of the pressure on the sails.  This is a safety factor if one is lax in tending the sheet, or if an unexpected gust is encountered.  The trim of the sails will also influence the lee or weather helm situation.  For example, if the jib is trimmed "flat" the boat will tend to turn off the wind.

 

Having only designed one boat, I have to believe that some considerable amount of luck was involved because of the inexact nature of the procedure I followed, but that was, and possibly still is, the best and only system to work with in determining what I had to know.  I would not necessarily expect to so lucky at another try.

 

            I enjoyed sailing my boat around the bay/  The main difficulty I had was getting out of a narrow pocket of the cove where I kept the boat, when the wind was southwest.  That was the prevailing wind in the summer.  At low tide, there wasn't enough room to maneuver with the centerboard down, and I sometimes had to pole the boat out to deeper water and where the cove was wider.  This was no fault of the boat however, but I did have another problem with the wooden centerboard.  I had not included a piece of lead to stop it from floating up when there was no side pressure to keep it in position, especially when going from one tack to the other.  I solved this by using a stick to shove it down initially and wedging the stick so that it wouldn't come up when turning into the wind.  I don't remember why I omitted this item, but it was probably difficult to obtain the piece of lead in a convenient form.  I could have neglected to include it out of my inexperience, but Dad wouldn't have.  Anyway, it wouldn't have been difficult to fix, but I never bothered.  The centerboard pivot was a substantial hardwood peg (probably oak) driven into close fitting holes in the centerboard trunk.  Where it went through the

centerboard itself, It fitted loosely.  The swelling of the peg from the water took care of any tiny leaks that might have occurred at first.

 

One thing I forgot to mention, the obvious fact that I had to design the sails so that the sailmaker would have something to go by.  I was disappointed when I first hoisted the mainsail.  It appeared to be too short along the "luff" (next to the mast) and the outer end of the boom appeared to sag downward.  I had not realized (as the sailmaker obviously did) that the line, to which the luff of the sail was sewn, would stretch.  He had "gathered" the sail in this area and when the line stretched, the profile assumed the proper configuration.

 

When I had to move away, I had to sell the boat.  I sorely missed the boat and my frequent contact with the bay for a number of years.  Later, I was to re-establish my association with the bay to some extent, but I found that cruising around with the noise of an outboard motor was not quite the same as silently sailing along near the shore and hearing the birds sing.  The tranquility of the bay was no longer there.  As the years went by the number of boats multiplied to the extent that many of the "locals" preferred not to go out on the weekends during the summer season.

 

            Along with many other things, the gross overpopulation of Long Island and the ever increasing influx of summer people, changed things to a very distasteful level for those of us who grew up in a more pristine Long Island.  I guess that's the price of "progress."