Fuel efficiency

tsawyer · Post by **tsawyer** » Sun Jun 26, 2011 7:19 pm

I took a trip this weekend from my home in Pompano Beach, Fl to Bimini, Bahamas. The trip is roughly 55 miles.

I've not run the boat too much and was less than pleased with my fuel burn.

It was 55 miles against the gulf stream at 3000 rpm and approx 14 knots avg. I burned 150 gallons of gas. Gas there was $6.19 per gallon.

Coming home with the current we ran the same 3000 rpm at approx 17 knots and burned 112 gallons.

So for the weekend I'm out about $1700 for fuel.

In had read a boattest.com article in a 10 meter conversion and that boat was getting .72 mpg at 3000 rpm with the Crusaders.

I was not getting anywhere near that.

I'd like some feedback on what I should expect.

What can I do (other than cruising at 2000 rpm) to improve this?

Thanks.

prowlersfish · Post by **prowlersfish** » Sun Jun 26, 2011 9:38 pm

I would think that boat would be in .5-.6 MPG max range , I could not find any test or info in boattest .com on a Trojan .

What to do to help the fuel burn ?

clean clean clean Bottom and running gear When I say clean I dont mean it was clean a month or so ago I mean now a few weeks in Fla. water and the gear can be loaded, Loose the weight , All that stuff we add to our boats hurts the MPG , Clean flame arestors , engine tune . are the props right ? (can you turn the max rpm range you should ?)

Or do what I do , and thats all the above plus Diesels

RWS · Post by **RWS** » Sun Jun 26, 2011 11:11 pm

Tom:

Something is not right.

Based on your numbers you ran .36 SMPG on th eway out and .49 on the way back.

I'm sure you had a full load of fuel and numerous other items, however these numbers are not even close to where you should be.

Paul is right on regarding the bottom & props. The worst fuel burn I ever had was due to what I thought was just a wee bit of barnacles on the props and shafts on a trip to Ft. Myers where we averaged .6 NMPG

I don't have a mid cabin so my props and numbers will be somewhat different, but I'll get some dat posted from before the refit. I was running flowscans that were deadly accurate to 3-4 gallons between fillups.

Here's some numbers:

Let's see if this transfers well...

Vessel 33' Trojan International, 13' beam, 12,500 lb dry,
Delta Conic Hull design, year 1983
Props: 4 blade 18x21 part# 0940 37171 and 37172
Prop Shaft is 1 1/4 diameter
Power - twin Crusader 454 cubic inch, 350 HP w/ Rochaster 4 bbl carbs
Velvet Drive transmission with 2:1 ratio
trim tabs 100% retracted
sea conditions - very smooth, winds variable
carrying 113 gallons of fuel in a 250 gallon tank
test conducted 7-15-02 in Charlotte Harbor
running gear 90% clean but not shiny
calculations done using digital tach/synchronizer, flowscan & GPS Difference from Summer 2002

Jul-02 Nov-03
kts nmpg kts nmpg nmpg increase

2700 15.0 0.67 15.5 0.82 22%
3000 17.1 0.53 17.2 0.70 32%

Here's the chart with NMPG data with the 454's

RWS

TurboTim · Post by **TurboTim** » Sun Jun 26, 2011 11:35 pm

I was just going to post a question but I am wondering if its more efficent to run on one motor and can it be done with velvet drives? Also what is the cheapest/best value to get into a setup that does MPG. I am assuming you need a GPS and a flow meter to go with it.

todd brinkerhoff · Post by **todd brinkerhoff** » Mon Jun 27, 2011 10:47 am

Running one motor would not be good. Too much strain on one engine and drive system. Plus you would just be running in circles.

How bout a sailboat?

RWS · Post by **RWS** » Mon Jun 27, 2011 11:25 am

todd brinkerhoff wrote:Running one motor would not be good. Too much strain on one engine and drive system. Plus you would just be running in circles.

How bout a sailboat?

+1

two options

1. run at displacement speed and "pick your moments" when to run at planing speeds, keeping her in the "sweet spot"

2. invest in a flowscan (not expewnsive if you have no return fuel lines) and dial in the correct RPM & tabs for the best efficiency.

Running RWS as in #2 above yielded me efficiencies of .8nmpg which equates to .81 NMPG at 2800 RPM at 15 knots - this is the equivalent of 17.1 MPH 18.5 GPH and that is the equivalent of .93 mpg (statute miles)

Not too shabby for a 33' vessel with a 13' beam !

RWS · Post by **RWS** » Mon Jun 27, 2011 11:42 am

Here is the raw data from when she was a gas burner.

This is an EXPRESS CRUISER - not a mid-cabin version of the species.

Keep in mind these are NOT fresh motors, they were on the low end of the compression scale and the port engine had a very, very sloppy timing chain.

Because the engines were tired, I chose NOT to wind them up too high for this final run.

These numbers are REAL, ACTUAL DATA.

RWS

prowlersfish · Post by **prowlersfish** » Mon Jun 27, 2011 12:10 pm

If running very slow you could save fuel on one engine . on 1 engine I hit 5 knots at idle on 2 its 6 knots a 20% gain of speed and a 100% increase of fuel burn, Pick up the rpm and it will loose the fuel advantage.

jddens · Post by **jddens** » Mon Jun 27, 2011 12:55 pm

Prior to the new engine, I ran my 30' Sea Raider on one engine most of the time......I ran slow and easy at about 2000rpm and 6-8 knots. Took longer to get anywhere and I don't have any hard data but fuel consumption was way better.......however with the new engine I prefer 3100rpm and 20+ knots............I get close to 1mpg at 3000 with twin throttle body injected 350's, again no hard data, just my GPS, around 1000lb boat and a sharp pencil......John

RWS · Post by **RWS** » Mon Jun 27, 2011 12:57 pm

Other changes made prior to that posted data include:

1 repairing the mechanical advance mechanisms in the distributors.

2. machining out the "diverters" in the cast iron exhaust tees (as reccomended by John Leed at Marine Tech (if I remember correctly)

3. messing with the pitch on the 4 blade props

4. disposing of the rediculous 1" tall spark arrestors and getting larger ones from Marine Tech/Beacon.

5. correcting the metering rod problems in the carbs which showed one engine using 5gph more than the other

we'll have to see what else I can think of !

RWS

k9th · Post by **k9th** » Mon Jun 27, 2011 1:30 pm

RWS wrote:
2. invest in a flowscan ....

Just so everyone will be able to find it, it is actually spelled Floscan and they work very well.

http://www.floscan.com/html/blue/index.php

tsawyer · Post by **tsawyer** » Mon Jun 27, 2011 6:25 pm

Wow. I was gettin 18 gph per engine and you had 21 total.

The bottom is fairly clean (it gets cleaned monthly) but I'm do for a bottom job soon.

My props are 17 x 17.

I had full fuel, water, cooler, etc but I can't imagine the total extra weight was more than 400 lbs. Most of the personal crap was forward of the helm in the cabin. My kids combined don't weigh 200 lbs.

The boat does seem to ride a bit bow high even at full tab.

Maybe a bigger set of tabs is a good idea. Did you replace the whole setup or just the fins?

RWS · Post by **RWS** » Mon Jun 27, 2011 9:22 pm

Tom:

couple of ideas:

1. get a inexpensive inclinomoter at Wm or somewhere else.

2. get a full load of fuel and water and set the inclinometer up at zero when floating in the canal. Now yiou have a reference point to start from.

Think of it this way, if the bow is UP the props cannot do the kob they were intended to do efficiently, you need to get her ass out of the water. Could be a prop issue or a combination of manu items.

3. The mid cabin has different geometry than the express cruiser I have including different prop sizes and different final gear ratio. You should share info with the other mid cabin guys here on the website.

the floscanis a great sirst step, that way you can measure your results instead of guessing.

bottom, timing, advance issues, floscan, tabs, props, carbs, etc.

took me some time to get from .6nmpg to .8nmpg!

While these hulls will never see 1.0 nmpg you really do have lots of room for improvement.

These are great boats, the ride is that of a 40 footer and the beam makes foe tremendous usable space. Add in the solid design and engineering/construction and you have one helluva boat there.

Dial in the details and stay on top of the issues and your numbers will get much better.

RWS

PS - the drop fin tabs are simple bolt on replacements - contact Bennett

S.A.M. · Post by **S.A.M.** » Tue Jun 28, 2011 10:20 am

The midcabins are a different boat from the express'. The center of gravity shifted to the rear. They are heavier, due to the wood interior in lieu of the fiberglass inner liner of the 330 model.

BobCt had his weighed and with water and fuel came in 18,500lb. Far from what the spec sheets show.

Our midcabins will never perform like the express. So I have resigned to accepting that you burn a lot of fuel to hit that 18k speed or you accept 14k-15k or you spend 80 grand and put diesels in. If I were to keep the boat for the next 15 years and did a lot of long range cruising, I would put Yanmars in like RSW.

I always say opinions and recommendations are free, so you get what you pay for.

todd brinkerhoff · Post by **todd brinkerhoff** » Tue Jun 28, 2011 1:34 pm

Look at it this way...You could own an 10.8M express with weight over 20,000 or a 11M with a weight probably in the mid 20s with gassers. I'm scared to get floscans, as it will only solidify my stupidity.

My boat is treated as a full displacement boat with a nice 10 mph cruise at 1800 rpms.