Diesel Repower From Scratch Pt. 1

This is a multi-part article detailing the installation of an inboard diesel engine into my modified Cape Dory 36 Far Reach. I rebuilt the Far Reach from bare hull over a six-year period maximizing her sailing performance and minimizing complexity, including removal of the inboard engine. I relaunched her in the spring of 2015 and subsequently sailed her 8,000 nautical miles without an inboard, including two round-trip offshore voyages to/from the Virgin Islands from NC. While I occasional used a sculling oar and custom, side-mounted outboard bracket, the boat was for all intents and purposes engine-free.

I enjoyed sailing the boat engineless. I found the challenge immensely rewarding. I loved how simple the boat was, and the significant increase in interior storage space. But there were four reasons that led me to the decision to finally install an inboard engine.

First, I came to the conclusion many boaters don’t understand the “rules of the road” for powerboats, much less sailboats. Maneuvering a 17,000-pound boat under sail often requires more time and space than power-boaters appreciate. Power-boaters often don’t know what to do when a boat is under sail near them except to act like it’s not there.

Second, there are an increasing number of places I would like to visit in the Far Reach that involve long rivers and canals where sailing is not very practical. Third, as depressing as it is to think about, one day I will part with the Far Reach and an engineless boat no matter how strong, capable, or lovely will attract a very small number of interested buyers. Last, and probably more important to me is that while I found the outboard and its clever bracket marvelously effective, I could never make peace with its unsightliness hanging off the port stern quarter.

THE OUTBOARD ENGINE WELL

I considered two main options: 1. An integrated well built into the stern of the boat to accommodate a more capably arranged outboard engine; or, 2. a more traditional inboard diesel engine.

Many small-boat cruising sailors are familiar with James Baldwin and his superb website Atomvoyages.com and Youtube channel Atomvoyager. Baldwin, a two-time circumnavigator aboard his 28-foot Triton Atom, has modified many sailboats to incorporate a clever seaworthy outboard-well design he has perfected. His design permits the engine to be tilted up with the shaft completely clear of the water minimizing drag while under sail. When the engine is operating, it can be swiveled in normal outboard fashion to provide thrust vectoring, dramatically increasing the maneuverability of the boat under power.

The design also incorporates “doors” around the shaft to reduce the amount of water that can enter the self-draining engine compartment when sailing offshore. It is a unique and capable design providing an inexpensive but capable power option for small cruising boats yet eliminates many liabilities associated with inboard diesel engines.

Pros. The extra-long shaft Honda 9.9 hp I used on our side bracket was perfect for the design and with its 2.25:1 reduction gear and 10-inch four-blade prop was capable of powering the Far Reach on flat water at 4.5 knots at half throttle, 5 knots at 3/4 throttle, and 6 knots at wide-open throttle (WOT). I estimated it would cost less than $500 to build. I would not lose the great amount of storage space that I would with an inboard engine and fuel tank. I would also not have to drill a hole for a prop shaft or seacock for engine cooling or cut a hole in the transom for the raw water exhaust. Best of all I could simply pull the engine out of the well when I did not want it aboard and sail engineless.

Outboard Engine Well Cons. I would have to replace the Cape Horn Windvane because it incorporates the steering quadrant inside the lazarette, which would interfere with the outboard, with a vane such as the Monitor which has an external quadrant.

The surgery required to install the outboard well is extensive requiring the after part of the cockpit and lazarette to be completely cut open and modified. Additionally, major cutting would be required under the stern counter to allow the outboard shaft to reach the water. Furthermore, when the outboard shaft is tilted up clear of the water the shaft extends backward and is visually distracting, though less so than the side mount outboard bracket I already had. Additionally, outboard engines are not as reliable as diesels nor can they charge battery banks as effectively as diesel engines. Lastly, such an unusual modification would not help the resale value.

INBOARD DIESEL

The CD 36 was originally equipped with the large but very capable 50 hp. Perkins 4-107 naturally aspirated diesel engine and a 50-gallon fuel tank. But it was a tight fit in the engine compartment, and access to the engine a common complaint among owners. I could not install a similar sized engine even if I wanted to because the modifications I made to the boat’s interior during the rebuild reduced the available engine space. Any engine I installed would need to have smaller dimensions.

I also did not want to open up the old propeller aperture in the keel/rudder because it would degrade the sailing performance of the boat which was at the heart of the rebuild.

However, it occurred to me that if I could install the diesel engine incorporating a slightly offset prop shaft above the rudder I could eliminate the drag associated with an aperture and install a folding propeller.

Pros. The diesel engine is reliable. Modern diesels are smaller and lighter than their predecessors. Diesel fuel is not as explosive as gas. Diesel engines like to be run and are capable of long continuous run times. They last far longer than an outboard engine especially in salt water environment. With an appropriate alternator, a diesel engine can quickly recharge a boat’s battery bank to power other equipment. A diesel engine and offset prop could incorporate a low-drag folding propeller. An inboard would increase the value of the boat over that of an outboard in a well.

Cons. An inboard diesel engine is far more expensive and heavier than an outboard engine. It takes up valuable space used for storage. It requires a hole to be drilled in the hull for the shaft and another seacock to be installed for the raw water for cooling. A fuel tank is required to be permanently mounted inside the boat taking up space. There is the chance for diesel smell to invade the interior.

An inboard engine complicates the boats with a major mechanical system as well as more complicated supporting electrical and plumbing systems. A diesel engine is far more expensive to install then building the outboard well. Lastly, it takes more skill and is a far more complicated project to install a diesel engine than to modify the boat for an outboard well.

ELECTRIC PROPULSION

I considered electric propulsion for both the outboard (Torqeedo cruise 6.0—10 HP) and the inboard electric engine options. I even called Torqeedo before I purchased the 9.9 hp outboard in 2015 to discuss how a small Honda generator could be used to run a Torqeedo outboard, but they were not interested in discussing this. I looked into inboard electric propulsion as well. But the cost, weight complexity, and expense of the battery system was staggering for the limited range. The cost of the 10HP Torqueedo with a single 48 volt battery was the same as a 25 HP Beta diesel.

No matter how many benefits electric propulsion has (clean, quiet, no odor, smaller foot print) there is no escaping the limited range. Either dockside recharging or a significant increase in solar panels wattage is required to properly charge the battery system, adding cost and complexity. Operational range is directly tied to the size of the battery bank and the larger the bank the more significant the charging requirements. Electric propulsion is perhaps a reasonable option for those sailors who expect to return to the dock for shore side charging. For extended cruising such an option does not exist. I read up on regeneration by allowing a spinning prop to charge batteries under sail but that means more drag and less performance under sail, and the actual benefits of regeneration are over-hyped.

Many proponents of electric propulsion advocate for Lithium Ion batteries because they are smaller and lighter than wet cell or AGM batteries. However, they are more expensive and require specialized charging systems to include “smart alternators.” Who was I going to find in foreign ports to fix a needlessly complicated charging system? These were not the kinds of challenges I wanted to deal with on my keep-it-simple, built-for-adventure voyaging machine. For these reasons I decided the electrical propulsion was not practical for me.

THE CHOICE

Though I conducted substantial research for every reasonable option, the final choice was not difficult. I admired the simplicity and practicality of Baldwin’s brilliant outboard well design, but I was not willing to part with my proven Cape Horn Windvane, nor could I bring myself to chop up the stern of the Far Reach. The diesel engine was the best and really only choice for me. I could keep what I had, of course, but I didn’t want to look at the outboard on the stern of the Far Reach any longer. I was reminded Keat’s timeless observation “A thing of beauty is a joy forever.”

With the decision made to install a diesel engine it was time to build a plan to make it a reality. This was not going to be a simple engine replacement. There was no shaft log, engine beds, raw water intake, battery system or wiring to support an engine. This would be an installation from scratch.

I would never pay a boatyard to undertake such a project. This decision was not so much driven by cost but by the overall quality of the installation itself. I believed no one would be more thoughtful or careful about such a task than me.

After spending six years rebuilding the boat and making two major voyages, I not only had a lot of confidence in my skills and ability to achieve high quality results but to learn as I went along when the need arose. I would also know the entire system inside and out, a distinct advantage for a self-sufficient sailor. Lastly, I had a superbly capable mentor to guide me along.

GOALS

An important step of any upgrade is to define your goals. My aim was to install a diesel engine that would meet five goals.

1. Attain a target speed of 5 knots cruising speed at ¾ power.

2. Provide a range of 250 nautical miles on flat water.

3. Provide maximum access to the engine for maintenance and repair.

4. Minimize loss of valuable storage space so critical on a voyaging sailboat.

5. Prioritize sailing performance over power performance.

It was obvious to me my goals would best be met by incorporating a design developed by the legendary sailor Hal Roth for his famous Spencer 35 Whisper—a small diesel incorporating an offset shaft exiting the hull above the rudder but closely aligned with the boat’s fore-and-aft axis as well as its centerline.

PLANNING CONSIDERATIONS

I spent considerable time mapping out the engine installation geometry to address the following questions: Where precisely would the shaft exit? Would there be room inside the now smaller engine compartment for an engine sized to meet my requirements? Could the propeller be submerged far enough below the waterline so it would not ventilate? Where would the fuel tank be located so as not to interfere with valuable storage space and would it give me the desired range?

Geometry. Even boats with the engine on the centerline want to turn, no matter how slowly, due to the effects of a spinning propeller. I reasoned a shaft not on the centerline would cause a boat to turn even more so. I read up on engines and props. I learned right hand turning props turn or “walk” the boat to port, pushing the stern to starboard. Just the opposite occurs in reverse, though I was not concerned about reverse as full keel boats don’t steer well in reverse anyway and also because I would spend 99 percent of my time going forward.

I had more space on the starboard side of the engine compartment. But, if I aligned the shaft perfectly fore and aft on the starboard side of the rudder post, the effects of forward prop walk would be exacerbated, causing the boat to turn even more to port than if the shaft was dead on the centerline—like a twin engine airplane flying on one engine. However, I reasoned with the engine so far aft, if I angled it slightly to port the effect of prop walk would be reduced because the thrust of the propeller, like an outboard would push the bow to starboard. How far to angle the engine to port to balance the forces out? I estimated 3-5 degrees.

The shaft also needed to exit the hull above the top of the rudder but deep enough so the propeller would not ventilate (suck air from the surface down to the propeller). When I mapped it out, the top of a 16-inch-diameter prop would be only 8-inches below the static waterline. That did not seem deep enough. The solution was to cut five inches off the top of the rudder, and epoxy that section to the hull above the rudder. Then the shaft could exit the hull lower in the water column.

Another part of the geometry equation to solve was how low the engine could be positioned in the boat while achieving the lower shaft position. Because the hull narrows below the engine, the lower the engine was positioned, the farther forward it would need to be located. If it was mounted too far forward,the engine would project into the saloon and interfere with the positioning of the companionway ladder. If I raised the engine too high, I would not be able to get the prop deep enough in the water.

Angling the engine and shaft down could both help and hurt. The original Perkins was angled down about 15 degrees. That seemed a lot to me. I reasoned more downward angle would perhaps decrease forward thrust and increase prop walk. I decided five degrees down angle would allow the engine to be a little higher in the hull and thus a little further aft while still contributing to putting the prop deeper in the water. Also, when moving forward the stern wave would rise under the counter putting more water over the top of the propeller.

All these measurements when combined together revealed I could position the shaft 18-inches below the waterline. This would put the blade tip of a 16-inch diameter propeller about 12 inches below the waterline and provide a minimum of 2 inches of “tip clearance” between the tips of the prop blades and the hull.

What all this meant is I had to carefully balance all the factors involving the positioning of the engine, the prop shaft, and the shape of the hull and rudder.

THE ENGINE CHOICE

My observation is most sailors want as big an engine and fuel tank as they can fit in their boat. One of the first questions sailors are asked about their boat is “How big of an engine do you have?” instead of “How much sail area do you have?” or “What is the ail area/displacement ratio? Seems backwards to me. I worked hard during the rebuild to keep my boat simple and the focus on sailing performance. The difference in horsepower required to get from 5 knots cruising speed (my goal) to 7.08 knots (the theoretical hull speed of a Cape Dory 36) is dramatic. The VicProp online calculator reflected I needed only 12 hp with a 2.6:1 reduction gear turning a two blade prop to achieve 5 knots in flat water. But I needed a minimum of 35 hp to achieve hull speed. I did not want to run an engine wide open to get five knots. Thus, I reasoned a 16-20 hp engine would meet my needs.

Additionally, a smaller engine would use less fuel. I desired fuel consumption to be closer to a quart per hour versus the original Perkins 4-107’s one gallon per hour. Lower fuel consumption would mean a smaller tank which would take up less space.

I did not care about hull speed or the common view that a boat needed “reserve power” to make good headway into a chop. My view is if there is a chop there is wind. If there is wind, I will sail. If the course is too restricted for sailing I will wait for the conditions improve. There is no free ride. Even simplicity, like most choices in life, comes with compromises.

In the 1950s it was thought 1 hp per ton was enough to serve as an auxiliary engine on a sailboat. That number gradually grew to 2 hp per ton, then 3. Now it seems to be around 5-6 hp per ton, which is right where the Perkins fit. Why do we need all this power and engine weight for a sailboat? My observation is many sailor’s think like powerboaters— horsepower equals safety. I disagree. Safety is more about what’s between your ears and less about what’s bolted to the deck.

I briefly considered a Yanmar because they have a good reputation. But I heard from some experienced friends that Yanmar parts could be hard to get in remote locations. Also, I heard complaints that Yanmar’s interest in small auxiliary engines had waned and their focus and support seemed more oriented on larger more profitable turbocharged engines. My friend and mentor Tim Lackey recommended a Beta Marine diesel because his experience with them had proven them to be well made and reliable.

It turned out the Beta Marine US HQ was just down the road in Oriental, NC. So, I visited with them and discussed all this in person with the very professional Farron Peffer, a highly regarded Beta Marine tech rep. He initially recommended a 38 hp to 43 hp (of course!) to achieve maximum performance.

When I explained my goals and thinking, he acknowledged my math was correct for my goal of 5 knots. A 20 hp engine, would give me 5 knots with something left over. And with a steeper reduction gear (2.6:1), I could use a bigger prop providing more torque, so long as I had the room for the larger diameter propeller. I was ready to select the 20 horsepower engine, when he reminded me that a 25 hp has the same footprint as a 20 hp engine. In the end, the 20 horsepower would save me just 27 pounds and 300 dollars.

While I recognized the 20 hp would meet my powering needs, I understood when it came time to sell the boat (it hurts to writes those words) a 25 hp would appeal with more buyers than the more diminutive 20 hp—just a fact of life. Peffer informed me that with a few exceptions, most of the parts on the engine are Kubota tractor engine parts and can usually be purchased worldwide and at less expense than “marine” parts. Beta gave me a 20 percent boat show/veteran discount. I paid $10,870 tax included for the 3 cylinder 25hp diesel’ a TMC 40 transmission, and upgraded control panel with a full engine gauge cluster, along with the larger 75-amp alternator.

THE PROPELLER CHOICE.

I never considered anything but a low-drag folding propeller. Any fixed blade prop was too much drag. A feathering propeller would have been a good choice if I had a propeller aperture that could not accommodate a folding prop. I researched folding propellers on-line. I called Martec and talked with their rep. I looked at the Gori, a well thought of propeller. But, ultimately, I chose the Flexofold two-blade folding propeller. I liked the geared design. There was a lot of praise for the prop in the on-line forums. The interaction with Nina von Bergen, a sales rep, at Flexofold in Denmark, over a two year period was superb. Flexofold was always responsive to my email questions.

Since my offset shaft engine installation was unique, I was concerned about Flexofold being able to specify the right size prop. If Flexofold did not get the prop calculations correct on the first shot, it would be expensive and time consuming for me to swap propellers with the company located in Denmark. Nina assure me if their prop size recommendation did not achieve the specified engine RPM, as long as I did not leave the prop in the water more than two weeks, they would exchange it for free until it was right. She suggested I leave the hub on the shaft and remove the blades in the water and ship them back to be exchanged.

I filled out the form Flexofold provided to me which required I list the engine and reduction gear as well as info about the boat—length on deck, waterline length, displacement, beam, draft, hull shape, etc. Flexofold recommended a 16X12R prop (a right-hand turning prop with a 16-inch diameter with 12-degree pitch).

With the engine and propeller decisions made, it was time to refine the installation plan.

ENGINE TEMPLATE

Beta marine provides detailed schematics for all their engines. I used the diagram for the 25HP and my woodworking skills to build a precise engine template which replicated the length and width of the engine. I placed the template in the engine space and played with the positioning determining approximately how far forward it could be located while leaving adequate room for the engine box, the work bench over the top of the engine, and space for the companionway ladder.

I also wanted room behind the engine for the shaft, stuffing box and flange, and needed to position the engine low enough in the hull for a sufficiently deep shaft that would exit at the correct angle as depicted in my drawing. I established reference points on the hull to measure from, both inside and outside the hull, to eliminate guess work. But, the only way to know for sure where to locate the shaft log was to drill a test hole.

Once I decided where I thought the shaft would be located, I drilled a hole with an extra long ¼-inch drill bit through the hull about four inches below the top of the rudder and aligned on the same 4 degree downward angle as I planned for the prop shaft. To my great relief it entered the engine space about where I thought it would. This hole determined the position of the shaft log and it became the single reference point for all subsequent work— the engine beds, engine box, shaft log, and rudder modifications.

Now it was time to cut the top off the rudder so the shaft long could be installed and fabrication of the engine beds begun. All this and more will be covered in Part 2.