Going Gas to Diesel is Not Always One for One


Note: The Waterpomptang family is fictitious and occasionally a Waterpomptang story appears on the M&O website. Some say their adventures resemble real events, but that is just a coincidence.

Marina, Will, Shruti and Polara had joined Opa and Oma for an afternoon run.

They all met at Froetjers, which was peacefully tied up at the Molly Pitcher on a beautiful calm late summer day. There was no real plan for the run yet, and Wim and Truus had simply asked their grandchildren to join them to get caught up with the latest in their lives.

Wim had already pre checked the engine and Polara decided to take the wheel. She ran the fan and started the 350 small block which, as usual, fired right up without a hint of smoke.

Once they were off the berth and in the channel, Bolle joined Polara at the wheel to check temperature and oil pressure and for Bolle to mark the info in the log.

Polara who was the quietest of the grandchildren showed her deep thought frown a little and said, “Opa, I am just wondering”.

“About what meisje?” Bolle replied.

“This boat has a gasoline engine right?”

“Yes, it is the same engine that it was built with in 1980 and it still runs great.”

“But with newer technology would it not make sense to retrofit something that is cleaner and more efficient?”

Will had listened in to the conversation and said, “Yes, Opa there are beautiful new diesel engines out there today that weigh almost the same, run real clean, are safer and are about 30 to 40% more fuel efficient. Overall it should work really nice.”

“All true,” Wim agreed, “I suppose I could swap to a diesel, but it would not be cheap and we all know how to run a gas engine safely, Mostly we simply don’t burn enough fuel on this boat to make it worthwhile financially or even environmentally. I have occasionally considered it, because Froetjers deserves the best, but decided against it. Some people have fitted diesels in Sea Bright Skiffs like this, but it never really turned out well, although those were more primitive diesels.”

Wim slid into the settee that was positioned to port of the helm station and Will sat down on the facing bench.

Wim went on: “I remember an interesting issue I encountered a number of years ago that shows things like this are not always as simple as they seem.”

We were called by a client who was a diesel engine importer and service provider. Excellent people, good friends actually. Their attorney called us and told me that they had imported and installed four super fancy European high performance diesels in an out-and-out offshore racing boat.

The builder/designer had secured an Owner who wanted to win races with diesels and converted one of their standard designs with a diesel installation. It kinda made sense. These diesels were only a little heavier than the gas equivalents and, since they burned less fuel for the same power, on long runs they should be competitive. Once the diesels were installed our client performed the start-up. They ran well but after the first race one engine died and then another and then another.

The Owner was not happy and our client had shown up every time trying to figure out what was going on. The engines ran well, the boat performed well, and then the engines just imploded.

This started to look like a law suit, but our client’s attorney asked us to attend to try to figure out what the problem could be.

So I humped it out to North Carolina where this top end racing boat builder did his magic. Our client’s attorney and a service tech also joined me. It was a nice shop, clean, a few boats with fancy graphics on trailers, some molds outside, nice Craftsman toolbox walls, pin up calendars and in the middle of the shop the boat with the fancy diesels.

The installation looked fine and I figured that maybe somebody had made a design error. I asked the designer/builder to provide me with a copy of his calculations. He became very defensive, and told us that was a trade secret. Our lawyer explained that we were trying to resolve a problem and if it did not get resolved there would be litigation, and if there was litigation he would have to show us what he did anyway.

After a bit of back and forth he went into his office and printed out a spreadsheet.

It listed every boat he had ever built and for every boat he listed all up weight, horsepower, gearbox ratio, prop sizes, top speed and if I remember correctly he also calculated slip. It was actually a really nice list with about 30 boats. If I were building boats like that, I would not want to hand it to every Tom, Dick, and Harry either, since it contained valuable data. Your father especially likes lists like that, and while this seemed rather primitive for boats that do around 110 miles per hour it was at least something to ponder.

So I look at the list, and note that according to this list the diesel boat was nothing really special. Basically the same everything as the gasoline boats. Except that the engine’s reduction gear ratio was half of the gasoline engines. That also makes sense since the diesels ran at about half the rpm of the gas engines.

I turned to the attorney and said: “There is nothing wrong with the engines, there is something wrong with the design. They are over torqueing these engines, they can’t handle the torque from the drive and the propeller.”

The builder came back right away: “You know nothing about this stuff. These are the same drives and propellers I have used for all the other boats and these diesels have way more available torque. If I am over torqueing these diesel engines, I would never be able to keep the gasoline engines running in these boats.”

“Rotzooi”, I went on, “The device that provides the moment, or resistance, that tends to overload the engine is the propeller. In other words, if the propeller is too big, the engine will go in overload and that may be at low rpm or actually any part of the speed range. Over time you and your competitors, with trial and error, have found just the right props to keep the gasoline engines from coming apart. However, you have never worked up this experience with diesel engines and these props are hurting the diesel engines.”

“But how can that be if these diesels have much higher torque ratings?”

“Yes the engines themselves have higher torque ratings, but the maximum torque delivered to the props is changed through the reduction gear. If you reduce the engine rpm by half through a reduction gear, it can deliver twice the engine torque to the prop. But since these diesels basically are direct drive, they can only deliver the engine torque to the prop and no more. So if a gasoline engine can deliver 400 foot pound torque and this diesel can deliver 600 foot pound torque, the gasoline engine can deliver 800 foot pounds to the prop and the diesel tops out at only 600 foot pounds. You need to match the props against the boat drag curve, the torque curve and the horsepower curve.”

The builder became physically agitated now. “Why did the engine supplier not tell me that?”

“The engines are what they are and they gave you all the data you needed. It is the boat designer’s job to make the propeller and gear match based on the boat’s drag curve.”

“But I don’t have a drag curve.”

“And you apparently did not need it until now, but I am betting dollars to donuts that you will need it here to get this set-up to run properly, or go through a lot of trial and error and probably a lot of engines. I suggest you stay nice with the engine supplier because they can help you by monitoring the engines during trial runs, but engine suppliers have little knowledge of what needs to be done once the horsepower and torque leaves the bellhousing.”

We left, leaving the builder rather unhappy. The attorney and the engine tech were much happier at first until we further discussed this matter at lunch. While the engine supplier had done nothing wrong, I cautioned them that possibly these engines would never be a good match in this application. If that were the case, they would have to be very careful in how they deal with this builder because bad news spreads very quickly and it would be easy for the builder to blame the engines.

“So what happened?” Polara asked.

Wim shrugged, “When I got back to the office, I asked Willem to run some numbers. He made some suggestions, but it would be quite an effort to get it right, and in the end the whole thing faded away, and as near as I know these engines were never used in racing boats again. It is a shame, since they were really nice engines, and, if they had done their homework at the start of the project, they might have been quite competitive.”

“So the old Chevy stays”, Will smiled.

“Ja Will, no reason to mess with something that works, maybe when you kids take over the boat, you can switch to another iron horse”

“We’ll keep it running on this pony Opa, until we can switch to hydrogen” Polara said, and Will nodded in agreement.



Wim (Willem Fokko) Waterpomptang, originally a blacksmith, but became a Chief Engineer in the Dutch Merchant Marine (this would be Hoofdscheepswerktuigkundige Waterpomptang) and mostly sailed to the Great Lakes and the Mediterranean. No fan of the English, but loved the Scots. Referred to as Oudopa by his descendents. Passed away in 1992.

Wim Waterpomptang, President Emeritus, Watt & Fulton, Ship Surveyors and Engineers

Started as a sailing engineer at Holland America Line and then started to work for an American Ship surveying company in Rotterdam.

Transferred to the United States with his family just before the Bicentennial.

Joined Watt & Fulton in 1980 and bought the company with his son, Willem, in 1993.

Owns a 28 foot Olson Sea Skiff named “Froetjers” and drives a 1993 Dodge K car. Hates cars. Keeps his boat at the Molly Pitcher.

Nicknamed “Bolle” by his old friends (Means “round one”). Called Pa by his kids and Opa by his grandchildren.

Any stranger he meets he calls “My Friend”. Anytime somebody says something that makes no sense he says: Rotzooi! (A not too rude word for mess, mix-up or confusion)

Loves his wife Truus and bacon, hates to travel. Drinks Lairds and cold beer. Is distrustful of people that eat porridge and oatmeal for breakfast. Hates melted cheese.

Willem (Willem Fokko) Waterpomptang President Watt & Fulton, Wim’s son

Sails and iceboats. Aerospace and Ocean engineer and Professional Engineer. Is somewhat autistic and sometimes has trouble figuring out what people mean. Helped by his partners and office staff in maintaining human contact.  Nicknamed “Dutch Uncle” due to his inability to behave tactfully. Married to Anne Gardiner, fortunately of Scottish descent.

Marina (Marina Gretchen) Waterpomptang. Economist and Environmental Scientist with a Masters degree in System Engineering from Columbia.

Daughter of Willem. Works for the company as an independent consultant. Travels the world and does weird things, sometimes for W&F.

Will (Willem James) Waterpomptang

Son of Willem. Mysterious Character. Also an engineer but now works as a lawyer in mysterious acquisitions and deals. Married to Shruti a big data engineer from India.

Polara (Polara Ruth) Waterpomptang

Daughter of Willem, marine biologist, artist and environmental activist.

Watt & Fulton, an ancient ship surveying and engineering company, founded by descendants of James Watt and Robert Fulton and world renown for dealing with the thornier maritime issues.

The company used to be based in New York City, but moved to Red Bank, NJ after the Whitehall Club closed.

­­Today W&F is located across the railroad station above a packy store in the Mexican section of town.