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Old 07-02-2018, 03:23 PM   #1 (permalink)
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Anybody in here mess with getting better FE out of Boats?

Boats are pretty thirsty an inefficient. I'm looking into ideas to get my 1538 1970s fisher water rover with a 1989 yamaha 30hp outboard to get better mpg. What ideas have you guys tried?

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Old 07-02-2018, 04:21 PM   #2 (permalink)
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There are really only two areas you could look at.

The first is engine efficiency.

The second is your hydro-dynamic drag.

Both are complex.

I prefer sailboats but if you want to optimize on the water fuel economy, you have to design from the water up.

Foils that lift the hull out of the water reduce hydro-dynamic drag tremendously. Then, with reduced drag, you can outline an engine design that minimizes fuel use at that reduced drag.

If speeds get high enough, then you can start down the road of reducing your aerodynamic drag.
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Old 07-02-2018, 08:57 PM   #3 (permalink)
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Water drag is much worse than aero drag and you have both with the boat. I assume with just 30hp it doesn't come up on a plane but I could be wrong. If it does plane you want to get it on a plane and then back off some to save gas but maintain the plane. If it isn't planing but the hull is designed to you need more power to make it happen or lighten things up and hope. Make sure its operating in the motors designed range as well, if it over revs you need more pitch on the prop and if it never revs all the way you need less pitch.
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Old 07-02-2018, 10:40 PM   #4 (permalink)
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I took the Jetski out on a new-to-me lake last summer, got to the end, and turned around to head back. 5 minutes into the ride back, I had to switch over to reserve. Thinking I would conserve fuel I backed off to about half speed. 15 minutes later I was out. 3 hours later I had swam the boat back to dock.

Someone told me 2-stroke motors want to run at near full-throttle to get the most power out of the fuel. I'm not sure what is most efficient, and haven't seen a BSFC for 2-strokes.

All that said, I think reducing weight is probably most important if you can't change the hull shape.
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Old 07-03-2018, 02:15 AM   #5 (permalink)
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Diesel engine?
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Old 07-03-2018, 02:41 PM   #6 (permalink)
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Bingo!

Quote:
Originally Posted by Stubby79 View Post
Diesel engine?
Fuel efficiency in a hot pocket pouch.
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Old 07-03-2018, 06:06 PM   #7 (permalink)
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https://newatlas.com/yanmar-dtorque-...utboard/51675/

Its great but $25,000+ for 50hp buys an endless supply of gas.
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Old 07-04-2018, 06:34 AM   #8 (permalink)
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Some years back I found I intriguing a 30’ turbodiesel with Anderson drive prop a “high” mpg commuter. Hawaiian Islands, IIRC. Both of those were new enough (fir a small package).

One has to start from scratch. And optimize steady state cruise. It’s start and stop that kills boat FE.
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Old 07-11-2018, 06:23 PM   #9 (permalink)
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Operating at the interface between air and water, you want a hull that optimizes for both.

https://www.brighthubengineering.com...ull-technolgy/
Quote:
Construction and Working
The design of M hull consists of three main features as follows:

the central displacement section
the planing tunnels
rigid skirts
The central displacement section is what supports the vertical skirts that are attached through out the structure. The design is made in such a way that the skirts are able to capture the hull waves inside the planing tunnel. The incoming bow waves spirals along the planing tunnels and trap the incoming air, forcing it towards the aft.

The planing tunnels also have a slope moving downwards to compress the aerated water for forming the air cushion and reducing the drag. This air cushion increases with the speed of the boat, thus providing additional thrust to the vessel and also reducing the fuel intake.
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Old 07-13-2018, 02:44 AM   #10 (permalink)
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Apparently typical bsfc is on plane 5000rpm at throttle valve fully open (volumetric efficiency) with a mpg prop... big prop that wont let the motor rev up. So currently I run 100% throttle, 5000 rpm (max hp is 5500... max rpm is 6000 rpm). And.... I get a whopping 9 mpg lol. 15' flat bottom 25 mph. 90s yamaha 2s 30hp.

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