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Date: 16 February 2015. Stainless Manifold Ordered (tractor motor adapted for boat)


The problem: how to turn the standard tractor motor into an engine that can propel my boat. Mine, a Kubota 18hp came from Yanmar Tractor Parts and is a gem. Progress on various fronts has been made. The latest, how to build a cooling system, has taken time with loads of input from a variety of sources.

Patrick and Steve move Betsy (the Kubota 18hp) into the pilothouse via a chain hoist.

She is a boat. Everyone has an opinion. Designing a cooling system for the exhaust of the Kubota certainly offered a ripe opportunity for a multitude of choices.

All of us know an automobile motor is cooled via an anti-freeze and water solution in a radiator with a big fan blowing air on said radiator. At the other end of the car engine is your exhaust and muffler. The exhaust is air-cooled and the mufflers are h-o-t, far too hot to touch and certainly not something I wanted inside my Seaweed.


For the folks that like old cars, to the right is another picture of the brown vehicle shown above. As always, click (or double click) to get the full sized version of the picture. Enjoy... J.

One concern is that I do not want any salt water running through my motor. She's a tractor motor and few tractors (none!) are designed to have salt water in their innards. I did not want to take a perfectly good Yanmar Tractor Parts Kubota engine and ruin her.

Many of the problems related to motors (say "risers" if you've a gasoline engine) or manifolds on diesels can be directly related to salt-water. Corrosion occurs and no motor is happy with salty water running through it. That is why many of the yacht-boats have devised closed systems for cooling.

Our 40'er had a closed cooling system though I do no recall the details.


The final decision on the Kubota exhaust has been made. What Just Right Marine in Carrabelle along with a welding shop in Tallahassee came up with is a manifold attaching to the starboard side of the motor. This item was ordered and should be ready on Monday. I am thrilled, though my credit card is cringing.

It's custom built, from heavy duty stainless steel... A once-in-a-lifetime build that should last forever...


Manifold Design for Tractor Motor Used in a Boat



My sketch could be better, so let me clarify a bit. First of all, there's a heavy duty big stainless box that surrounds the pipes. Those pipes carry the exhaust from the engine. Fluid, a combination of anti-freeze and fresh water, will fill said box. The solution will flow in from the bottom left corner and exit the top right. That water/anti-freeze concoction will go into (and come out of) a separate tank.

A sturdy stainless box encloses the Schedule 40 (heavy, thick walled stainless) 1.5" pipe. The stainless pipe carries hot exhaust air through the cooling manifold box. A nipple at the top will deliver raw water to further cool the pipe. The blue arrows and stars show water and antifreeze as they flow through the stainless box. There will be an external closed fresh water tank.


Addendum April 2015: My drawing is a bit off from the final result. The changes you will note are the box (aka manifold) is now U-shaped. That will allow better flow of the fluids through it.

Also, the coolant goes in at #1 and exits at #2.


As you can see, no salt water will be able to get into the motor. She'll be totally 100% fresh water and air cooled. That's why I won't be dealing with corrosion issues. The difference between stainless pipes and elbows as shown was just more than $100 extra over black iron. I opted for stainless, 'cause I like it better.

The final cost of this custom built box is not yet in. We are talking a day of labor, plus parts. It will not be inexpensive, though this should be a one-time purchase item. Like many others, I would rather pay once for a superior job. This work should last until I am 90 years old. By then, I just *might* be ready to come ashore -- but I hope not!

Happy cruising.

Tractor motors can be bought from Yanmar Tractor Parts in Tennessee. Shipping is via pallet and not terribly expensive.

In Carrabelle, Just Right Marine designed the manifold and is having it custom welded by a professional.

Side Note: Through the *coconut grapevine I have heard that some diesels in boats have had exhaust elbows that failed. An option for replacement is offered by the Exhaust Elbow in stainless at a good price. I've heard nice things about the quality and speed of delivery too.

*Coconut grapevine is a boater's radio net. We all listen in and it's a source of information for cruisers.

Have you ever replaced your exhaust manifold? How frequently has that occurred?
Was yours custom-built or off-the-shelf? If custom built I'd be curious as to location and price paid.

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2015, 2023

Categories: Boat Talk, Characters, Gear, In the Bilges, Locations

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