Obsolete Outboards  

by Max Wawrzyniak - St Louis, Missouri - USA

Fitting a Sailboat with an Outboard Motor
When the Boat was never Intended
to Have an Outboard Motor

Well, it's the morning of April 15th, 2007 and the sun is shining. Although a mite chilly outside now the temp is supposed to rise into spring-time range in just a few hours. A beautiful morning and I am thoughly "bummed-out."

I was supposed to be running in a marathon this morning but a knee injury has kept me side-lined.

So I guess I will write another column and later will work on my self-designed kayak I have been building. I have a cup of hot coffee handy, have the Destin (Florida) Pass webcam open on another screen, and have a subject to address with this column.

A few years ago I decided to build a sailboat. My experience with sailboats at that time was severly limited so I selected what I felt was the simplest and most practical sailboat design that I could find: a Jim Michalak AF3. It was certainly simple and easy to build, but after overnighting on it a few times I decided that I really should have built something a little bigger, such as an AF2 or a Normsboat, but the basic concept of the boat was a good choice. After a few years I sold the AF3 and at some point will build a slightly bigger boat in the future.

click to enlarge

The fixed (non-adjustable) bracket that was given to me some time in the distant past.

Although some of Jim Michalak's sailboat designs such as the Normsboat and the Mayfly 16, for example, feature mounting arragements for a small outboard motor, the AF3 did not. Being an inexperienced sailor, I felt the need for the "security blanket" of an outboard so I had to devise the mounting arrangmeents on my own. After picking over my collection of outboard motors I finally decided on (2) that I felt would be suitable for the AF3. The first was a 1945 Neptune 2hp while the other was a 1949 Gale 1.5 hp. Both engines were already in running condition and neither engine was so "collectable" or valuable that a dunking during a capsize was result in a major finacial hit. The Neptune, in fact, had a damaged crankshaft and I felt it's time was limited anyway, so it became the primary engine for the AF3.

The usual mounting arrangment for outboards that Jim shows in his plans is a motor "well" between the transom and the "lazarette" compartment. I considered incorporating such a well into the AF3, but this would have greatly reduced the size of the lazarette compartment, and the bouyancy of this compartment was key to the "self-rescueing" aspect of the the AF3 design. I decided that a bracket mounting of some sort would be best.

Most of you will be familar with the adjusting motor brackets so often seen on production sailboats. These brackets lift the outboard clear of the water when the motor is not in use, and lower the outboard when it is to be run. These brackets are readily available but they do cost money and they are a bit big and bulky for a boat as small as the AF3, which has a very small transom. Someone had given me a fixed bracket, one that does not adjust up or down, and I decided to use that bracket with some modifications. I could also have constructed a fixed bracket from wood, with long bolts passing all the way from the transon to the motor mounting board.

click to enlarge

A new motor mounting board would be made just barely wide enough to handle the small outboards chosen to power the AF3.

Jim M usually suggests mounting the rudder off-center to one side, and mounting the outboard off-center to the other side, on boats with narrow transoms. Being a traditionalist, I wanted my rudder mounted on the centerline, with the outboard off to one side, which was going to complicate matters. With only half of a very narrow transom to work with the total width of the bracket had to be minimized.

One of the attributes of the (2) outboards that I selected was very narrow transon clamp spacing, meaning the the engines required a minimum of width of area upon which to be clamped. The motor bracket that I used consisted of (2) cast aluminum arms with a wood motor mounting board bolted to them. I removed and discarded the wood board and replaced it with another board witch I laminated from plywood. This new board was much narrower than the original board and in fact was just barely wide enough for the small motors to clamp to. Many other small motors, especially modern ones, would not clamp to such a narrow board.

Deciding exactly where to mount the bracket was another concern. If the bracket was mounted too close to the centerline of the boat, the propeller would hit the rudder when the rudder was hard-over. The further away from the centerline the bracket was, the more likely the motor would get dunked in a capsize to that side.

click to enlarge

Once the proper postioning of the outboard was determined, the outboard was clamped to the bracket so the exact postion of the bracket on the transom could be found.

Another concern was how high to mount the bracket. The AF3 has a lot of "rocker" to its bottom. A lot of rocker and the small size of the boat means that a person moving forward or aft is going to cause a large change in the trim of the boat. In other words, If I walked forward into the cabin "slot," the bow was going to go down and the stern up. If I went to the rear of the cockpit, the bow would rise and the stern would drop. Both of the motors that I intended to use were so-called "short shaft" engines, meaning that they were intended for planing boats with transoms about 15 inches tall. Since the AF3's hull is not a planing hull, this measurement is not particularly useful. Here is what is important: When I walked forward and the stern rose, I did not want the propeller or the cooling water intake of the motor to come out of the water, When I went aft and the stern fell, I did not want to submerge the powerhead of the engine. Finally, I needed to be certain that there was enough clearance between the outboard and the transom so that the motor could be tilted-up, and so that the starter rope could be pulled. An outboard mounted on a bracket very low on a transom often can not be tilted-up, and often requires a "vertical pull" starter rope.

The final concern was structural. The AF3's transon was not designed to take the weight or thrust of even a small outboard motor. As I also intended to use foot holds on the rudder for reboarding the boat, I built the transom much heavier than designed. I used 1/2 inch plywood instead of 1/4 inch, and I increased the size of the framing a bit.

The waterlines on Jim's plans are usually marked, and utilizing a straightedge laid across the drawings I made a guess as to the vertical position of the outboard. I used the straight edge to simulate stern-up and stern-down conditions, keeping the center of the straight edge on the marked waterline at the center of the boat. Not being a naval architect, I had to guess just how far the stern would rise or fall with the weight of one or two people, but at least I had the range of motion fairly established.

click to enlarge

There needs to be sufficient clearance between the top of the outboard and the transom of the boat for the outboard to tilt up.

There are computer programs available that can predict the results of just such a shift in the longitudinal center of gravity, for you "geeky" guys who want a more precise prediction. .

Next, I clamped the motor to the bracket (not yet fastened to the boat) to establish the position of the bracket when the motor was at the correct height. With the motor still clampled to the loose bracket, the motor was tilted-up in order to estimate the clearance between the transom and the motor.

Taking measurements from the transom and rudder, It was apparent that even with the narrowed bracket there still was not enough space to one side of the rudder to mount the outboard without the propeller hitting the rudder when the rudder was put over more than about 30 degrees. I did not want to install rudder stops limiting the swing of the rudder to that side so I decided that I would just have to be carefull when motoring not to swing the rudder too much to that side. In practice this was not too much of a problem. although the rudder blade did show the signs of occasional "rudder-propeller interface."

Once the desired position of the motor bracket was decided upon, I drilled one hole and bolted the bracket to the boat with one bolt and mounted the outboard to double-check the clearances. Since all seemed well I drilled the additonal (3) bolts and bedded and bolted the bracket on. While everything looked good with the boat on the "hard," I could not truly check the vertical clearance of the motor until the boat was launched.

click to enlarge

Bracket "arms" bolted to the AF3. The motor mounting board has not yet been added. Also shown is the fixed mast crutch: not one of my better ideas. The lower blade of the rudder has not yet been attached.

The first time on the water revealed that I had postioned the motor about as idealy as possible. Walking all the way forward in the slot raised the stern to the point where the outboard's propeller and water intake were just barely in the water. Sitting at the very stern still left the powerhead a comfortable distance above the waterline, and the motor could be tilted-up to just clear the water before the motor powerhead hit the transom, limiting the amount of tilt.

Another concern in the installation was keeping the sheet from becoming entageled in the outboard, a common problem. I also needed a way to store the struck mast on the boat where it would not be in the way of rowing or other activities. My solution to these problems was not so successful. I incorporated a mast crutch into the motor bracket mounting. The crutch was not removable, and the sheet was routed through a metal ring on top of the mast crutch. Although the crutch was very handy for storing the mast, the sheet not only still became entagled in the outboard, it was also become entangled in the crutch.

A much better arrangement would have been to mount the rudder off to one side, so that the motor could be moved more to the center where it wouild have been much better protected from submergence during a capsize. The propeller and rudder would have both benefited from the increase distance between the two. Don't know if this would have helped the sheet situation but it could not have been any worse..

In the end, I probably could have gotten by without the outboard motor at all. I had the oar ports and oar locks that Jim shows on the plans, and used the boat a few times on a lake where gasoline motors where not allowed, and once rowed the boat a couple miles when the old Neptune overheated. The boat was surpisingly easy to row.

And I am a little bit better sailor now.

Happy Motor'n


click here for a list of Columns by Max Wawrzyniak