Running one engine on twin inboard

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RWS
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Re: Running one engine on twin inboard

Post by RWS »

My earlier post now has actual data inserted for a 1983 10 Meter International

454 engines and 4 blade props

The data was collected with Floscan, GPS and a digital tach/sync.

FYI, I resized the image by e-mailing it to myself.......

Hope this data is helpful to the Forum.

RWS
1983 10 Meter SOLD after 21 years of adventures
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Re: Running one engine on twin inboard

Post by RWS »

prowlersfish wrote:At idle I go about 6 knots on both engines , with one I go about 5 knots , so I can burn half the fuel just by losing a knot . With only a slight increase of rpm I easily get 7+ knots on one engine . With only one engine in gear the stern will squat down as much and seems to glide though the water easier . The fact I put off much less wake seems to verify this . That may canncel out the added drag of the rudder at angle .
======================================================================================


Perhaps this is due to the higher torque and larger props on the diesels ?

This may indicate that the diesels may offer an higher rate of savings burning fuel on one engine only.

I never tried that........... but need to do so.

Taking into account what Todd said, I wonder what that would do for a 100 mile run through the intercoastal?

RWS
1983 10 Meter SOLD after 21 years of adventures
Yanmar diesels
Solid Glass Hull
Woodless Stringers
Full Hull Liner
Survived Andrew Cat 5,Eye of Charley Cat 4, & Irma Cat 2
Trojan International Website: http://trojanboat.com/

WEBSITE & SITELOCK TOTALLY SELF FUNDED
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RWS
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Re: Running one engine on twin inboard

Post by RWS »

todd brinkerhoff wrote:RWS, I didn't see your attachment on your post.

I don't have an exact LWL for the boat, but assumed it to be in the 35 to 36 range, since my LOA is about 39. Based on that, I calculated a max hull speed to be between 8 and 9 mph. At approximately 1500 to 1600 RPM's with both motors, I cruise at about 7.8 to 8.2 mph. I do not have a flow meter, so I do not know what my current burn rate is at that RPM. With one motor, at again 1500, I slow to about 6 mph. Both my carbs need to be rebuilt, so I will probably put the flow meters on then.

If I do run one motor, I can adjust my packings to drip more, and I am not concerned about the Velvet drive Free-wheeling. Its the Walter V-drive that I am more concerned about. If I could run 8 mph (1550 RPMs) and burn 7 to 9 gph I'd be happy. Gas prices in this area are about $4.95/gallon.

At this rate, a 40 mile trip will take 5 hours, and you would burn 35 to 45 gallons of fuel. At $4.95/gallon, you're looking at $173 to $223.

At 3100 to 3300 RPMs, I'm running about 20 MPH, and probably burning 32 to 38 gph (I'm taking this off a previous post of someone running a flow meter on a 10 Meter Mid-Cabin, which is probably lighter than my boat). I'm down to 2 hours of travel. Now you're burning 64 to 76 gallons of fuel over that 2 hours. At $4.95 gallon, I'm looking at spending $316 to $376. That's about $143 to $153 MORE in fuel.

If this is all accurate (which I need to buy a flow meter) that is certainly some significant savings.

Now lets see, a diesel boat would burn about 2 to 3 gallons per hour and only costs $4.25/gallon. Although at about $100,000, that may take awhile to make back in fuel savings.

==============================================================================================

Todd,

Your numbers indicate a far higher burn rate than those I have provided.

Different hulls, gears, props yes, however at displacement speeds, the burn rate should be reasonably close as the engines are identical.

Tony Athens over at BoatDiesel maintains that it is the PROP that moves the boat, not the motor.

I wonder, if you installed a floscan you might be surprised that your actual hull speed fuel burn may be more similar to mine.

Plus it would be interesting to see the actual hull speed data with one engine only vs. two.

My planning sweet spot shows up on a 2004 test after doing all the modifications.

I will convert that spreadsheet and post it here shortly.

At 2800 RPM I was running 17.3 kts, getting .81 NMPG - not bad for a gas burning vessel of our size .

RWS
Attachments
THS IS THE FINAL DATA AFTER DOING ALL THE MODS
THS IS THE FINAL DATA AFTER DOING ALL THE MODS
RWS_GAS_ACTUAL_DATAONLY_DETAIL.jpg (152.27 KiB) Viewed 8329 times
1983 10 Meter SOLD after 21 years of adventures
Yanmar diesels
Solid Glass Hull
Woodless Stringers
Full Hull Liner
Survived Andrew Cat 5,Eye of Charley Cat 4, & Irma Cat 2
Trojan International Website: http://trojanboat.com/

WEBSITE & SITELOCK TOTALLY SELF FUNDED
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Re: Running one engine on twin inboard

Post by prowlersfish »

Both engines at 800 rpm idie 6 knots 1.6 GPH (3.75 nmpg ) 1 engine 5 knots .8 gph (6.25 nmpg) speeds are real life , The fuel burn is from a fuel burn chart with a prop curve . Once I hit hull speed the numbers will drop fast .
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Re: Running one engine on twin inboard

Post by summer storm »

Paul, do you have the one engine at 6 knots number?
Doug

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Re: Running one engine on twin inboard

Post by prowlersfish »

I believe its right under or at 1.0 gph . Remember the gph is off 2 charts with a prop curve so its not exact but very close the speeds of 1 vs 2 are from my boat . It only take 100 rpm to bring it up 1 knot + with 1 engine . Once you get at hull speed the advantage of 1 engine is gone .

I used a cal on boat diesel and a Cummins chart , both agreed and have been right on at cruse speeds .
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Re: Running one engine on twin inboard

Post by Svend »

Interesting post!

I have a 1977 Trojan F30 Express with dual 318's. Does anyone know if they had freewheeling ability/transmission?
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Re: Running one engine on twin inboard

Post by prowlersfish »

Svend wrote:Interesting post!

I have a 1977 Trojan F30 Express with dual 318's. Does anyone know if they had freewheeling ability/transmission?
If you have Borg Warner Velvet Drives you can .
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Re: Running one engine on twin inboard

Post by jimbo36 »

Savings at hull speed is minor considering drag from the dead running gear and the rudder turned hard to steer the vessel. Running both engines also provides better tracking with counter rotation. You will use more fuel correcting your course possibly covering twice the distance through the water. Oh,..and it is not very seamanship like, lol. :roll:
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Re: Running one engine on twin inboard

Post by prowlersfish »

Jimbo , I would have to disagree on the fuel savings IF you keep it below hull speed . It may vary boat to boat . Getting to or past hull speed forget any savings . With that said I would not recommend it in crowed areas or were there is a need to do a lot of maneuvering .
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Re: Running one engine on twin inboard

Post by Svend »

I went out this weekend on Lake Winnipeasukee in NH and tried a few different things. I ran for a couple of hours under hull speed with 1 engine and boat ran fine, steering was easy once you hit the sweet spot. My fuel gauge barely moved all day.

I also test out an electric outboard I had kicking around, and it was able to move my boat at 2+ knots. This was not much at all, but with a properly sized electric outboard running at 48V, I could get to 5-6 knots which would be great for much of my trips where I really enjoy just putting around. But then when I need to get somewhere quick, I can aways fire up the 318's (which in turn will charge my battery bank for more electric motoring! - also note, I get shore power for a fixed cost of $100/year so the electric get topped off each night)

A few electric motor companies have suggested a 20HP electric for my goals of hull speed cruising.

Thanks for thoughts on 1 engine boating with a 2 engine setup...
1977 Trojan F30 Express, With Dual 318's with Electronic Ignition
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