Boat Engines

[JC77]

While having several cups of coffee with the guys I work with talking about my mini tug boat project, several questions were asked about what motor I would use. I have no idea. I'm going to stretch the boat a little bit, I want to run AC power and would like to be able to push around a little bit if necessary. So inboard vs outboard, gas vs diesel, how much horse power do I need? Which also brought up a question about HP on land vs HP in the water. Is there a difference between say 15 HP on land and the same 15 in the water? I've had several different ideas about using electric motors, 500cc 4 stroke or larger motorcycle engines, outboard engines or small inboard diesel engines, please provide help.

[Breakaway]

JC77
Welcome to the WB Forum.

First, most boat designs have power recommendations. Indeed, many designs are built around a specific power plant. Is this a self-designed vessel?

You want to run AC power. How much? Once you determine that, you will need to install either a generator or an inverter. Propulsion engines produce DC power, but can by various means be used to produce some amount of AC if required.

Inboard, outboard? What does the design call for? Besides propulsion, where the engine sits in the boat will affect how she handles, drains, and more. This is one reason propulsion factors large from the get go.

Horsepower is horsepower. Its a value of the rate of work, and used to compare and rank engines. Torque is another matter. Torque is what actually does work. Its the force that turns a propeller. For a tug-- a real tug, whether diminutive or full size--an engine with more torque, to swing a larger prop is desirable. For faster boats, less torque, but higher RPM works well.

Do you want to go fast? Or slow? Both? Really tow other boats and stuff? Or just look the part? (nothing wrong with that). These are questions you have to answer.

Outboards produce less torque than inboards for the same horsepower, generally. Diesels produce more torque at the same horsepower than gas engines, generally.

Kevin

[Woxbox]

If you're going to push something with it, a little diesel with a good sized, low-pitch prop will do the job best. And it will sound like a tug boat. Otherwise, it's not so critical. Electric would be most agreeable, but running time would be limited. And gas is gas. At any rate, a single-cylinder diesel would be cool if you could find a used one. The diesel will easily turn a big alternator, too.

[JC77]

Good info, thank you for the reply. The Boat I'm looking at with some modifications is the Berkeley Candu 14. The original plans call for a 10HP electric motor. I've seen them lengthened with small outboard engines. I agree that HP is HP land or water, the right term would have been torque. I'm looking to get about 10 knots, with a little extra if needed. I intend for this to be more of a pleasure craft with all the look and sound of a tug with some of the functional features. All the AC power would be for lighting, small search light, run some GPS or depth finders and maybe a coffee pot.

[Breakaway]

You can run GPS, depth sounder, lights and a spotlight on DC. They used to sell DC coffeepots in marine and RV stores--sure you could find one.

Electric motor is called for? An inboard electric motor or an electric trolling motor?

Kevin

[JC77]

You can run GPS, depth sounder, lights and a spotlight on DC. They used to sell DC coffeepots in marine and RV stores--sure you could find one.

Electric motor is called for? An inboard electric motor or an electric trolling motor?

Kevin

Couldn't tell you about inboard electric or electric trolling motor. I ordered the study plans just last week so I'm sure it talks about it. Everything I've seen online show little gas powered outboards. We'll see what happens. Good to know about the DC powered equipment.

[M. J. Notigan]

I bought the plans for the Can Du EZ but my Microtrawler build is enough right now on it's own. The plans are very well drawn out and nicely detailed. Mr Eastman did an excellent job with this boat design and David Cronk did a simply superb job in doing the drawings. This is not a 3 or 4 page design sheet like the Bolger Microtrawler; no, this is a step by step, page by page process in building this boat. As much as I like my Microtrawler, the Eastman tug really captures the spirit and feel of the real deal!

I don't have the plans in front of me right now, but Mr Eastman does call for a golf cart electric motor and a proper main shaft. He even lists suppliers for the gear required.

As Kevin correctly states, 12 volt gear is available for everything you will require. Good luck in your build; welcome aboard and hope to hear from you once you start your project!

Take Care
Mike

[JC77]

I'm really excited! My wife has no idea what she is in for.

[Cogeniac]

Most of the boat electricals are DC. GPS, lighting, bilge pumps, horns, etc. Consumer stuff is all typically AC, and DC variants can be both expensive and generally not very good. However, you can get an inverter that will generally power things like laptop chargers, coffeepots, etc. from the DC battery/alternator. The proper setup is to use a shore power setup so that the AC is provided by shore power when in port and is provided by the DC house batteries via the inverter when underway. I got a small inverter capable of supporting 2000 watts for about $100 at West Marine. You should start with an inventory if what you need to power. I suggest you get a copy of The Boat-Owner's Illustrated Electrical Handbook by Wing. He describes all these systems and how to go about figuring out what you need.

S