Outboard motor well for a Taipan 28 sailboat
A version of this article first appeared in Good Old Boat Magazine
The Inside Outboard
An evolution of outboard motor wells for the small voyaging sailboat.
When our boats were hauled for routine maintenance at a Trinidad boatyard in 1999, my friend Theo asked me for suggestions on how to improve his outboard motor installation. On his 1972 Hong Kong built Taipan sloop, Islander, instead of an inboard diesel engine he had a 5 hp 20" long-shaft Mariner outboard motor hung on a standard adjustable transom bracket. "You know I dont like inboard motors," he said, "But this outboard can be a real pain. In any kind of sea the motor's prop lifts out of the water one minute and then as the bow lifts, the motor gets dunked under water and sometimes stalls out. It's also difficult to lift it out of its storage locker and hang over the stern to set it up when the boat is bouncing around. There must be a better way."
We both have similar modified full-keeled 28-foot fiberglass cruising sailboats. Both of us had removed our ailing original inboard motors years ago and replaced them with outboards. I had removed my Pearson Triton's venerable gasoline Atomic 4 partly because it had become a maintenance nightmare and occipied valuable space and partly because I wanted to have a pure uncomplicated sailing experience. For over five years I cruised far and wide with only sails and a sculling oar and proved to myself that engineless sailing was as practical and rewarding as it had been before motors for small sailboats were invented. When my cruising style changed from making mostly long offshore passages to doing more coastal cruising and river trips, I reluctantly re-entered the motoring world by purchasing a 3.3 hp two-stroke long-shaft outboard. The noisy little beast normally lay forgotten in a cockpit locker. When needed, I hung it on an adjustable stern bracket. It did work - sort of. Besides the problems Theo mentioned, there is the question of esthetics; its plain ugly, hanging there on the stern like some tacky add-on afterthought. And there is the possibility of theft; some envious Brazilian fisherman had pinched my outboard a year earlier.
So I had been thinking about this problem for some time. It occurred to me that the overhanging transoms of many classic older sailboat designs might permit a modification to allow the outboard motor to function in a cut-out well in the afterdeck within the lazarette locker. When Theo asked for help, I was ready and enthusiastically leapt aboard Islander with tape measure and notepad. Theo eyed me quizzically as I crawled around measuring the overhang of the transom, emptying his lazarette locker and disappearing inside it head first. When I emerged I revealed my plan: "I can make an outboard well, or box, inside your aft cockpit locker." After discussing the extensive modifications necessary and the estimated cost, he said, "Do it," and left his cherished Islander in my hands while he flew home for a spell of work in Switzerland.
The Dirty Work
From my measurements I knew the well would need to be placed as close as possible to the forward vertical bulkhead of the lazarette, or aft cockpit locker. The access hole in the deck needed to be as large as practicable to allow adequate ventilation while the motor was running and to permit access to the furthest recesses of the locker while the motor was in place. Its probably best Theo wasnt around to see the destructive stage of the job beginning when I cut a huge hole into Islander's afterdeck. "It looks much worse than it is," I replied when one neighbor asked, "Does he know what youre doing to his boat?" Once I cut this large section of deck out with a reciprocating saw; the real dirty work began.
The outboard well box with motor and covers removed.
Motor in place with storage room alongside well box.
Using #36 grit pads on a grinder, I took most of the inside of the locker down to bare fiberglass. To protect skin and lungs from fiberglass dust, I wore a full Tyvek suit with hood, goggles, and respirator. Next, I carefully measured for the placement of the hole in the hull needed to accommodate the motor's shaft. Originally I planned to cut a circular hole so that the motor could easily pivot to provide side thrust when needed to turn in tight quarters such as when a current has you pinned against a dock. Unfortunately, further measurements indicated that because of the angles involved this might not be easy, so I went ahead and cut as small a hole as necessary to allow clearance for the prop. I saved the slightly wedge-shaped rectangular fiberglass cutout, cut it in half fore and aft, and shaped it to fit around the outboard shaft at the appropriate height. I stiffened the cutout pieces with extra layers of epoxy-saturated fiberglass and attached them to the shaft with angled stainless steel brackets and 1/4-inch bolts. Although the outboard will not always be kept in its well, these new flanges are meant to stay permanently attached to the motor. When the motor is lowered into position, these flanges make a flush fit with the hull, ensuring minimal turbulence and preventing waves from entering and flooding over the inside of the well into the stern locker. The slight gap around the edge is sufficient to allow the motor's cooling water to drain out. (On later tilt-up designs I made sliding cover boards instead of attaching anything to the motor's shaft.)
Holding the motor temporarily in place, I measured for its exact placement. Ideally, the motor should sit as low as possible to ensure that the prop remains underwater when choppy seas cause the boat to raise her stern. The motor should also sit low so that the deck hatch box does not need to be built excessively high to fit over it. On the other hand, the motor should be situated as high above the waterline as possible to prevent it from being flooded by following seas or when the boat is heeled under sail. I struck a reasonable compromise by placing the prop about 10-inches below the boat's at-rest waterline. This motor was a 20" long shaft. A 25" extra long shaft will provide better performance but may be too long to stow easily in a locker. That required a different desgn that I;ll discuss later.
Working with cardboard and scissors, I made templates for the four sides of the well. The top of the well's box in this case worked out to be about 12-inches above the at-rest waterline. Three of the templates were then transferred to pieces of 1/2-inch marine plywood and cut out. The fourth piece, which was the forward end of the box to which the motor would be mounted, needed to be stronger, so for it I used 3/4-inch plywood. At the top portion of this piece, where the motor clamps would rest, the thickness of the wood was doubled to 1 1/2-inch. The plywood was then sealed with epoxy resin and glassed into position using several layers of medium weight fiberglass mat and cloth. Although considerably more expensive than polyester resin, I used only epoxy laminating resin because of its better strength and adhesion. Vinylester resin would also be suitable. To fill gaps and corners I mixed talc-thickened epoxy to the consistency of peanut butter and applied it with a putty knife. In later years I used colloidal silica such as West System 406. Prior to applying the epoxy, I used rags soaked in acetone to thoroughly degrease all surfaces. To complete the box I block sanded the top edge level and epoxy-bedded four 1/4-inch bolts into holes drilled 2-inches deep into each top corner. The bolts stood proud by 1-inch and their heads were cut off so that they could be used as alignment studs for a lid held down with wing nuts. This lid has a rubber gasket under it to seal the box and prevent incoming water from entering the boat when the motor is not installed.
To prevent unwanted turbulence, or drag, the hull also needed a flush-mounted plug to seal the cutout when the motor is not in place. This I made by cutting out a piece of plywood from a paper template that matched the hole and glued it onto a larger plywood backing piece. With the plug held in place by a similar system of inward facing 1/4-inch studs, I ground the plug's outside surface to match the contour of the hull. The plug was sealed against moisture with 3 coats of epoxy resin and then painted. Because this plug is so near the waterline I did not attempt the difficult task of making it 100% watertight. Instead, I expect it only to stop the main force of surging water and provide a smooth surface for water to flow past undisturbed. Whatever water does get into the box can seek its own level and will, in any case, ultimately be stopped by the gasket-sealed top lid.
Before going further, I had to modify the stern locker's bulkheads to ensure this locker was entirely watertight and isolated from the bilge in case of accidental flooding over of the well. I filled all gaps in the bulkheads with my epoxy filler mixture and then used fiberglass mat, cloth and resin to make it all watertight. Then I installed a drain hose leading from the locker floor to the bilge with an in-line shut-off valve accessible from the cabin. This way the locker could drain normally into the bilge or be shut off if there were ever any uncontrolled flooding. Ever since experiencing my first storm at sea Ive realized that all cockpit lockers should be constructed this way. When a boat is knocked down, pooped by a following sea, or held over flat by force of wind, the cockpit lockers may fill the bilge so fast with water as to risk sinking the boat, or at least require near-constant pumping out. At least with the drain valves shut off there is a limit to how much water can enter the boat.
The next step was to construct a box around the access hole in the deck to raise the hatch high enough to clear the top of the motor. Because of the motor's height I needed to add about 5-inches along the rear over the afterdeck and 9-inches along the front edge where the hatch intruded on the cockpit seat area. Trinidad had its own sustainable teak farm which sold teak at less than half the cost of teak sold in the US, so I lavishly used 1-inch thick teak planks for the box sides. The upper lid of 3/4-inch plywood was then fit over this, trimmed with teak, latches, and rubber gasket. Note that when measuring for the height of the hatch box, you need to take into account any extra clearance required by the throttle arm, although usually the handle can be operated in a folded back position. A round plastic access hatch is located on the forward side of the box to provide access to the motor's starter cord. Final detailing involved painting the inside of the locker with epoxy primer and 2-part urethane paint. The locker lid got a finish coat of nonskid polyurethane. I coated all teak with four coats of clear polyurethane. It took about 70 hours to complete this job and we were both pleased with the results.
How it all works
The following year I had an opportunity to test the practicalities of this installation when Theo asked me to sail Islander from Venezuela to Brazil. The system performed better than expected on the 6,800 mile voyage which took us to the eastern tip of Brazil via Bermuda, the Azores and the Cape Verde Islands. When approaching landfall the motor was easily placed in the well and sea water never flooded over the well into the locker. On each offshore passage, once clear of land, the outboard was removed and stowed in a cockpit locker to eliminate drag and the chance of snagging seaweed or other floating debris, as well as to protect it from the corrosive effects of sloshing seawater. For this reason, and to save your back, I would not choose a motor that is too heavy or too large to lift out and place in another locker. This fixed well works because the two-stroke 20" shaft 5hp motor is lighter and more compact than the 4-stroke 25" shaft motors we commonly use today. Since in a fixed well the motor cannot pivot back if caught on an obstruction, it makes sense to reduce the risk of unnecessarily dragging it long distances through the sea while under sail. In this case the flush-fitting hull plug is locked in place to present a strong smooth external hull surface. The top of the well is then sealed with its gasketed lid. Although there should not be any appreciable water intrusion into the main locker, the locker drain valve is left closed and can be checked and drained occasionally as needed. Around the sides of the well there is ample storage space for ropes and fenders, nearly as much as before the well was added, because with the larger hatch, more of the locker's corner space is accessible. This motor had an internal gas tank but the well also can work with an external tank. The upper hatch is held firmly in place by sturdy lockable latches on either side.
Outboard motor surrounded by a flush fitting hull plug.
The cover is normally set aside for increased ventilation when running the motor.
When the motor is needed, the top and inner hatch lids and the hull plug are removed, the motor set in place and secured. The main hatch lid is set aside and the plastic access hatch for the starter cord is removed. These hatches are normally left open to provide the engine with enough ventilation to operate properly. To protect the engine and locker from rain and spray we can prop open the hatch slightly to provide the motor with the fresh air it needs to run. Alternatively, a hose could be led from the air intake to an outside vent to allow the motor to be run with the hatch closed. The motor operates in forward and reverse as normal and steering is done by the boat's tiller. A minor annoyance in this first desgn was that in order to turn the motor for side thrust it must be put into neutral and the boat brought to a stop. Then the motor clamp screws are loosened and the motor raised 1 1/2-inch by setting it on a spacer block. This raises the motor shaft flange clear of the hull and the motor can now be re-clamped, engaged and swiveled. Normally, I would not bother with this unless doing really close quarter maneuvering. Still, it is possible to use this swivel function, which is one of the advantages outboards have over fixed inboards. Another reason not to have the motor normally able to swivel would be to prevent it from accidentally turning sideways when sailing at speed, causing high side loads on all components. With the motor seated into its normal position, its flush rectangular-shaped hull plate totally prohibits any accidental swiveling. To safely remove the motor when under sail, it is necessary to bring the boat nearly to a stop by heaving-to.
Details of other projects on this boat are on the Taipan 28 Refit page.
This project was such a success that I planned to repeat it on my own boat. Unfortunately, my Triton lacks enough clearance between the forward lazarette bulkhead and transom for a 5-6 HP motor in a closed well design without extensive modifications (in 2014 I eventually did complete an enclosed tilt-up well in Atom's enlarged lazarette similar to the one in this video.)
In 2008 I constructed a different version fixed outboard well on an Alberg 35. The aft cockpit bulkhead was cut out and the motor sits further forward in a well that is open to the cockpit. It was not ideal because the owner chose a 20" shaft instead of the extra-long shaft model and the heavier 9.9HP motor was awkward to lift in and out of this non-tilting well design. This type open well can work on the Triton and other boats that lack a large lazarette locker but it reduces the total watertight locker volume that I was trying to maximize on my earlier voyages. For better reserve buoyancy on some boats the lazarette can be divided into three sections with port and starboard sections sealed with additional bulkheads, but this may mean the motor can no longer be stored on its side in the locker, even if the transom is wide enough to permit this.
Obviously, this alteration will not be suitable for most modern boat designs lacking deep and long overhanging lazarette lockers. Careful measurements need to be made of rudder location, waterline height and existing locker layout before any work is begun. The advantages of the well versus hanging the motor on the stern are obvious. For those who do not need to motor long distances or require high thrust, this system even has advantages over an inboard diesel. An outboard saves a great amount of space and weight. It is cheaper to buy and maintain. It will not spew oil and fuel into your bilge. It will not radiate unwanted heat into the cabin in hot weather. Repairs are easier. When it comes time for a new motor, installation is a snap. If you are going to have an outboard motor for your dinghy, the one motor might serve both purposes. Or you can carry two outboards of different size for the boat and dinghy and always have a standby ready in case of breakdowns. Try doing all that with a diesel inboard! With the outboard now located inboard, we feel we have the best of both worlds.
Alberg 35 outboard well:
The motor in operating position on the Alberg 35. When the hull plates are removed by loosening the wing nuts, the motor can swivel some 25 degrees for limited side thrust if needed for departing a marina slip in a strong cross wind.
The 9.9 motor is too big to fit entirely within the lazarette since it needs to be this far forward to have the prop low enough in the water so this slotted cover board is used. A vinyl motor cover is available to protect the motor from sun and spray if left installed.
In 2010 I went to the next step in outboard well design evolution by extending the prop hull cut-out with a narrow slot up the transom to allow the motor to stay permanently in place tilted up to keep the motor shaft clear of the water. An example of this is the open-faced tilt-up well I built on Triton #503 Salty.
This was a big design improvement.The open tilt-up well is a good compromise, especially for a Triton or similar boat of limited locker space using a 4-stroke motor.
Tilt-up well installed on the Triton Salty:
In 2014 I made another modification to my design by moving Atom's lazarette bulkhead forward as close to the rudder head fitting as possible in order to keep the outboard well fully enclosed. I had already done enclosed tilt-up wells on several Alberg 30s, which have idealy sized lazarette lockers. Many of these can be seen in the Video Gallery page.
Atom's enclosed tilt-up outboard well
|In 2011, the owner of this Able 32 sent me these photos of a tilt-up outboard well conversion he has nearly completed based on my design.|