Oil burner consumption

A special section just for steam engines and boilers, as without these you may as well fit a sail.
TriangleTom
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Re: Oil burner consumption

Post by TriangleTom » Sun Aug 11, 2019 11:35 pm

DetroiTug wrote:
Sun Aug 11, 2019 10:23 pm
Quote: "On a related subject, how do we think that total boat weight is related to fuel consumption? My reflexive response is that is should be directly related."

In my personal experience and observation, they are directly related, more work requires more fuel and water. You and I came at the problem from different directions, you are designing in fuel economy, I built a big heavy boat and had to make improvements to the system to improve performance and economy. My boat with it's hull design can't be built light, it needs so much ballast to get the deep belly of the hull down in the water. The first time I launched it, it was like a fishing bobber/float on the water, I was seriously concerned about it rolling right over, I've added enough weight to it over the years that it is siting about right and stable for rough water. The Tug weighs around 8000 pounds, when I pull in, the trees shiver :)

-Ron
Have you added solid ballast or are you using water tanks? And how much did you have to add when you converted from a VFT to an Ofeldt?
RGSP wrote:
Mon Aug 05, 2019 8:02 pm
"Falcon", a late Victorian launch that many of us know, used to have a quadruple steeple compound engine, which was certainly not the right engine for the boat. She now (as of this season) has an excellent twin compound, and I will be interested to hear how coal consumption compares between the two engines.
Looking at the registry, it looks like this was a two-crank Simpson Strickland engine. Do you have any information on what issues she experienced?
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Re: Oil burner consumption

Post by RNoe » Mon Aug 12, 2019 3:50 am

Boat displacement/weight related to fuel consumption?
Absolutely. Straight physics.

A given weight of water displaced requires a specific amount of energy.
Displace more water, use more energy. Work done.
It's probably not a directly proportional relationship due to hydrodynamic friction issues.
I'm sure someone here can share the actual equations involved.
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Re: Oil burner consumption

Post by RGSP » Mon Aug 12, 2019 7:28 am

TriangleTom wrote:
Sun Aug 11, 2019 11:35 pm
DetroiTug wrote:
Sun Aug 11, 2019 10:23 pm
Quote: "On a related subject, how do we think that total boat weight is related to fuel consumption? My reflexive response is that is should be directly related."
RGSP wrote:
Mon Aug 05, 2019 8:02 pm
"Falcon", a late Victorian launch that many of us know, used to have a quadruple steeple compound engine, which was certainly not the right engine for the boat. She now (as of this season) has an excellent twin compound, and I will be interested to hear how coal consumption compares between the two engines.
Looking at the registry, it looks like this was a two-crank Simpson Strickland engine. Do you have any information on what issues she experienced?
Falcon was and is run by a group of very hard working volunteers, who are also very nice people. I'm therefore reluctant to say anything that reflects at all badly on them. I think it's public knowledge though, that the 2-crank quad would not reverse at all easily.

Wave-making hull resistance certainly always increases with increasing payload, but the relationship between the two varies quite a lot with hull type. Of course sometimes by shifting weights, or even adding weights, to alter the trim of a hull can actually decrease hull resistance over a small range, but only under very limited circumstances. It's very obvious with racing sailing dinghies that a lightweight crew has an advantage in light winds, but in stronger winds the heavier crew using themselves as movable ballast can have the advantage.
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Re: Oil burner consumption

Post by RGSP » Mon Aug 12, 2019 7:29 am

TriangleTom wrote:
Sun Aug 11, 2019 11:35 pm
DetroiTug wrote:
Sun Aug 11, 2019 10:23 pm
Quote: "On a related subject, how do we think that total boat weight is related to fuel consumption? My reflexive response is that is should be directly related."
RGSP wrote:
Mon Aug 05, 2019 8:02 pm
"Falcon", a late Victorian launch that many of us know, used to have a quadruple steeple compound engine, which was certainly not the right engine for the boat. She now (as of this season) has an excellent twin compound, and I will be interested to hear how coal consumption compares between the two engines.
Looking at the registry, it looks like this was a two-crank Simpson Strickland engine. Do you have any information on what issues she experienced?
Falcon was and is run by a group of very hard working volunteers, who are also very nice people. I'm therefore reluctant to say anything that reflects at all badly on them. I think it's public knowledge though, that the 2-crank quad would not reverse at all easily.

Wave-making hull resistance certainly always increases with increasing payload, but the relationship between the two varies quite a lot with hull type. Of course sometimes by shifting weights, or even adding weights, to alter the trim of a hull can actually decrease hull resistance over a small range, but only under very limited circumstances. It's very obvious with racing sailing dinghies that a lightweight crew has an advantage in light winds, but in stronger winds the heavier crew using themselves as movable ballast can have the advantage.
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DetroiTug
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Re: Oil burner consumption

Post by DetroiTug » Mon Aug 12, 2019 1:28 pm

Quote: "Have you added solid ballast or are you using water tanks? And how much did you have to add when you converted from a VFT to an Ofeldt?"

Increased weight was by adding ancillary devices, i.e. pumps, battery etc. and with additional gear, water tanks in the front for hot and cold water storage. Then about a thousand pounds of wood in the bunker.

I still have the firetube boiler, never did switch to the Ofeldt and I fully intended to. However, the loss of ballast weight would have been an issue, subtracting about 500 pounds which would have had to have been replaced. I decided against it. And too, the firetube is a more traditional boiler for the type of boat. The firetube is very easy to fire versus the Ofeldt, affording the fireman long intervals between tending, the Ofeldt would be a full time job tending the water and fire. Basing this off of operation of the Ofledt in my car.

-Ron
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Re: Oil burner consumption

Post by fredrosse » Mon Aug 12, 2019 9:37 pm

According to my hull software, considering maximum displacement speeds (Knots .LT. 1.3*SQRT(LWL-ft), this is a linear function of the general form HP = M*(Displacement) + B. Therefore the function does not go through zero horsepower at zero theoretical displacement, which makes sense, because even at the imagined zero displacement the hull bottom is still producing drag forces and requiring horsepower.
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Re: Oil burner consumption

Post by Lopez Mike » Tue Aug 13, 2019 3:38 am

So it's a mixture of wave making and skin friction?

Any guesses at the ratio for a 25 foot 2000 lb. launch hull? Say at two speeds, half hull speed and hull speed.

I did some coasting tests on my sailboat years ago. Measured the deceleration at various speeds, assumed an additional 3-4% mass due to entrained flow. I made several coasting runs and averaged the deceleration by graphing. Took a tangent to the resulting curve at whole knot speed intervals to come up with the deceleration at that speed. Then used the formula F=MA. It was amazing to see the numbers change over a few months after fresh bottom paint. And to find out how sensitive the deceleration was to rocking the boat.

Of course you need a knot meter, a stop watch and an assistant. I don't know if a GPS would react fast enough even if you were careful to test in zero current and wind conditions.

This is covered in Oceanography and Seamanship by VanDorn.

I guess when I get the new hull up and running I'll have to do some tests with and without some of my rather large neighbors along for the ride.
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fredrosse
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Re: Oil burner consumption

Post by fredrosse » Thu Aug 15, 2019 2:29 am

According to the DEFTSHIP hull software, for the Margaret S., the following results show linear functions for propeller horsepower vs displacement. While the Margaret S. is a sidewheeler, the software only considers screw propeller propulsion, so the computer results are comparable to typical steam launch practice.

Margaret S. is a typical Sharpie type hull, flat bottom, hard chine, 19ft-3in LOA, 18ft-6in LWL, 5ft Beam, and 9 inch draft at one long ton displacement, fully loaded with one person aboard. The most displacement I have ever had is about 1.4 tons, six people aboard.

Cruising at a moderate speed of 4 knots, one ton displacement, 0.8 propeller shaft horsepower required, and at 1.4 tons, 1.0 horsepower. The linear function is HP = 0.5*TONS + .3

Steaming at maximum hull speed of 5.5 knots, one ton displacement, 2.1 propeller shaft horsepower required, and at 1.4 tons, 2.6 horsepower. The linear function is HP = 1.3*TONS + .8

These numbers are for calm and deep water, with no wind resistance considered. Note that going from 4 knots to 5.5 knots requires 260% of the slower speed horsepower.
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Lopez Mike
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Re: Oil burner consumption

Post by Lopez Mike » Fri Aug 16, 2019 3:03 pm

So now to design a new ultralight boiler made of titanium honey comb. And maybe look into the possibilities of balsa wood in 19th. century engine designs.

But first some investigation of reduced mass skippers. I'll think about that after breakfast.
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Re: Oil burner consumption

Post by malcolmd » Sat Aug 17, 2019 12:05 pm

Lopez Mike wrote:
Mon Aug 05, 2019 5:06 am
Thanks Malcolm. Figures out to around 3 g.p.h. in imperial units. And comparing boats my little launch should use more like 2 or less.
Mike, just re-read this... I may have misunderstood your comment, but my figures were already in US Gallons - so I think (given on v off time) the consumption should be 1.3 US Gallons an hour or maybe a little more.
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