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Old 11-06-2012, 10:06 PM   #1
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Fuel Usage

We have recently purchased a 35' CT Sundeck Trawler with twin 85 hp (not turbocharged) diesel Perkins (Detroit Diesel) engines. Does anyone have an idea regarding how much fuel consumption I should expect. We haven't really used to boat enough to determine how much fuel we are using, but we are conservative and don't push the engines, probably cruising around 7-8 knots. Any communications are welcomed...Thanks..
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Old 11-07-2012, 08:24 AM   #2
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For a start go to boatdiesel.com and plug in numbers using one of their calculators. One of the outputs is gal. per hour at a certain power setting. It has choices for type of hull, displacement, hp of engines, rpm setting, prop size, length at water line, etc.
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Old 11-07-2012, 01:15 PM   #3
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fuel usage

I have the same perkins 4-236 engines (85hp) in a Californian 34. Two year average fuel burn is 10.2 liters per hour. ( 3.8 liters in a US gallon). This is at 7 - 8 knots, you may do better than that since about 25% of the time I am towing one or two 24 sailboats behind the Californian.

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Old 11-07-2012, 06:05 PM   #4
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I'm on a 35 PT Overseas, largely the same boat but I have twin Cummins 210 Turbos. Averaging about 9.5 knots I get 5.7 GPH total, 2.85 GPH per engine.
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Old 11-07-2012, 06:14 PM   #5
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If you don't push the engines, as you say you do not, then probably about 3 GPH. That is what I get, with the same engines.
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Old 11-19-2012, 11:54 PM   #6
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Thanks for all the replies. I'll be monitoring the fuel consumption, but now I have a fair idea of what I should be expecting. For you folks with the same engines, are there any specific issues I should know about with this model? Any information is greatly appreciated.
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Old 11-20-2012, 06:01 AM   #7
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I'll be monitoring the fuel consumption,

For easiest trade off between speed and fuel burn ,Fuel Flow Gauge | FloScan.com

www.floscan.com/

One should do the trick, no need for a pair .
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Old 11-22-2012, 03:13 PM   #8
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The next time you take the boat out, try this:
Put the trans in gear and slowly begin to accelerate, this in open water. Keep a sharp eye on the BOW RAIL, as soon as it begins to RISE, do not accelerate any more.
Check the rpm's and the speed indicated on the GPS, that, my freind is your most economical cruise speed. Period.
Of course you can go faster and commensorate with that dig a hole in the water that burns a lot of fuel.
At this point I usually add the caveat "YMMV" but cannot on this one!
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Old 11-22-2012, 03:28 PM   #9
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Charles--- Not disputing your point at all, but I've actually done this with our boat even going so far as to tape a pencil to the flying bridge cable chase in front of the lower helm and aligning the point with the base of Lummi Island six miles away across Bellingham Bay. And what I found is that the bow of our boat starts to rise as soon as I start adding power.

I attributed this to the buildup of hydrodynamic pressure under the hull. As the forward speed of the boat increases, the pressure under the forebody increases, and the bow begins to rise immediately albeit it certainly not dramatically.
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Old 11-22-2012, 06:59 PM   #10
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3 choices....
1. Install a floscan or equivalent
2. Rig a small tank and get actual numbers.
3. keep an accurate log of speed/rpm/miles covered, etc...etc....

There may be more but these 3 usually cover it...

Basing cruising speed till you know what kind of burn/economy you want on hull rise is just one tad of science from alchemy.
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Old 11-23-2012, 06:26 AM   #11
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"There may be more but these 3 usually cover it..."

The simplest is to operate at the Sq RT of the LWL in Knots.

This gives enough accuracy at no cost to not justify extra expense for a .01 improvement in range..
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Old 11-23-2012, 06:51 AM   #12
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Quote:
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"There may be more but these 3 usually cover it..."

The simplest is to operate at the Sq RT of the LWL in Knots.

This gives enough accuracy at no cost to not justify extra expense for a .01 improvement in range..
while it gives the best efficiency....not sure that it answers the question of burn rate....at least without more math than most adults like to use..
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Old 11-23-2012, 07:47 AM   #13
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.at least without more math than most adults like to use..

AHHH ,,the Joys of Unionized Publik Edukation!
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Old 11-23-2012, 12:32 PM   #14
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Fred:

Once in a while you come out with a good one. That was a great one!!!

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.at least without more math than most adults like to use..

AHHH ,,the Joys of Unionized Publik Edukation!
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Old 11-23-2012, 01:25 PM   #15
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Originally Posted by charles View Post
The next time you take the boat out, try this:
Put the trans in gear and slowly begin to accelerate, this in open water. Keep a sharp eye on the BOW RAIL, as soon as it begins to RISE, do not accelerate any more.
Check the rpm's and the speed indicated on the GPS, that, my freind is your most economical cruise speed. Period.
Of course you can go faster and commensorate with that dig a hole in the water that burns a lot of fuel.
At this point I usually add the caveat "YMMV" but cannot on this one!
Will one not gain more MPG by operating at a speed lower than the bow starts to rise speed? I once thought that was hull speed. One thing is for sure and that's that that is the speed whereas the boat starts to climb out of it's own wave and leave behind it's own following wave.

One can see clearly here that if Willy was to run any faster she'd leave that beneficial "hump" of water at her stern behind.
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Old 11-23-2012, 01:54 PM   #16
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Will one not gain more MPG by operating at a speed lower than the bow starts to rise speed? I once thought that was hull speed. One thing is for sure and that's that that is the speed whereas the boat starts to climb out of it's own wave and leave behind it's own following wave.

One can see clearly here that if Willy was to run any faster she'd leave that beneficial "hump" of water at her stern behind.
Eric - Each pict you post of your pretty craft is better than the last... Now I opt the one with dink on top as she cruises along... to be your avitar! - Keep them cool picts comen! You really do like being south, don't cha!!
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Old 11-23-2012, 03:37 PM   #17
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Thank's Art but the present avatar pic is better as it is real contrasty and Willy stands out well. I think an avatar that maximizes the size of the boat in the small space given and shows of things like the basic lines of the boat, configuration and brand type and points into the page is best. I also think one should keep his avatar the same or extremely close to the same over time as it helps a great deal to identify the poster/member. Walt used to change his avatar every week and ya never knew what he was looking like so he was hard to find and recognize.

This is pure personal opinion but I think the avatar should be a pic of one's boat or of one's self. Pics of pets, babies and other trivia should be left to Face Book and again personally I don't even like it there.

We once talked about a split avatar w boat AND mug shot. With a bigger avatar that would be nice but we don't have a bigger avatar. Perhaps we could have odd months for boats and even for muggs but how many would go for it and take the time to do it?
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Old 11-23-2012, 06:34 PM   #18
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... I also think one should keep his avatar the same or extremely close to the same over time as it helps a great deal to identify the poster/member. Walt used to change his avatar every week and ya never knew what he was looking like so he was hard to find and recognize.
I like to change my avatar frequently.

Perhaps use of a non-anonymous username counters any confusion who I am.
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