What kind of range can one expect from a 15 hp diesel on a 28' boat with 18 gal capacity? Say, 6 knots cruising speed. Is it usually referred to in terms of miles per gallon? Gallons per hour? I was looking at Southern Cross 28 with 11 hp diesel and the owner claimed 20 mpg.
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On powerboats
I have always expressed it with gallons per hour. I have read it commonly refered to on sialboats by how many miles they can travel on a certain amount of fuel, depending on the size of the fuel tank. I think it is uncommon to express it by miles per gallon. Is he refering to a Nautical mile when he says miles per gallon?
I have always expressed it with gallons per hour. I have read it commonly refered to on sialboats by how many miles they can travel on a certain amount of fuel, depending on the size of the fuel tank. I think it is uncommon to express it by miles per gallon. Is he refering to a Nautical mile when he says miles per gallon?
sounds about right
i have a 15hp diesel and i burn about .3gph @6.5knts on a 30' boat that weighs in at 11000#. there are a lot of variables that will affect fuel consumption. but this sound to be in the ball park given avg conditions. with this as a ballpark I'd say about 325nm. but i wouldn't push it that close.
i have a 15hp diesel and i burn about .3gph @6.5knts on a 30' boat that weighs in at 11000#. there are a lot of variables that will affect fuel consumption. but this sound to be in the ball park given avg conditions. with this as a ballpark I'd say about 325nm. but i wouldn't push it that close.
GPH
Gallons per hour is the standard, even for powerboats. An 11 HP diesel should burn about 1/3 to as little as 1/4 GPH.
This spec is usually right in the front of the engine manual.
Cruising speed won't matter right up to hull speed. Any more power beyond what is required to maintain hull speed is wasted fuel.
If its a Universal 5411 11HP engine, the fuel chart shows 0.25 GPH at 1200 RPM to 0.80 GPH at 3000 RPM (almost a straight line); 'though I doubt you'll ever see 0.8 GPH.
A 15 HP is about 0.3 to 1.1 GPH.
Note these assumes a load.
20 MPG on a 28 with 11HP sounds about right: 5 kts., 4 hours, 0.25 GPH.
I find I use a lot less fuel than the charts indicate, since I am seldom making much power, even though I'm spinning the prop at 1700 RPM or so.
Remember, a diesel doesn't really have a throttle, it has a governor. You set the engine speed with your "throttle" lever, and the governor adjusts the amount of fuel injected in order to maintain this engine speed, as the load increases or decreases. So if you move the lever towards "FAST" with the boat standing still, it will inject lots of fuel to keep the prop spinning against the load of accelerating the boat, and will gradually reduce the fuel fed as the boat speeds up and the effort required to spin the prop diminishes. As an example, of your prop is over pitched, and you set the speed lever to spin it faster than is appropriate for the hull speed of the boat, you will be just wasting fuel (and sooting up your transom).
Gallons per hour is the standard, even for powerboats. An 11 HP diesel should burn about 1/3 to as little as 1/4 GPH.
This spec is usually right in the front of the engine manual.
Cruising speed won't matter right up to hull speed. Any more power beyond what is required to maintain hull speed is wasted fuel.
If its a Universal 5411 11HP engine, the fuel chart shows 0.25 GPH at 1200 RPM to 0.80 GPH at 3000 RPM (almost a straight line); 'though I doubt you'll ever see 0.8 GPH.
A 15 HP is about 0.3 to 1.1 GPH.
Note these assumes a load.
20 MPG on a 28 with 11HP sounds about right: 5 kts., 4 hours, 0.25 GPH.
I find I use a lot less fuel than the charts indicate, since I am seldom making much power, even though I'm spinning the prop at 1700 RPM or so.
Remember, a diesel doesn't really have a throttle, it has a governor. You set the engine speed with your "throttle" lever, and the governor adjusts the amount of fuel injected in order to maintain this engine speed, as the load increases or decreases. So if you move the lever towards "FAST" with the boat standing still, it will inject lots of fuel to keep the prop spinning against the load of accelerating the boat, and will gradually reduce the fuel fed as the boat speeds up and the effort required to spin the prop diminishes. As an example, of your prop is over pitched, and you set the speed lever to spin it faster than is appropriate for the hull speed of the boat, you will be just wasting fuel (and sooting up your transom).
Speed Matters
Hull speed is not a precise speed like a wall. In general the slower you go the farther you go on a gallon of fuel. Hull speed is a result of the hulls shape but you also have plain ole drag. Drag does not increase in a linear fashion. More like if you double your speed you have 4X the drag. Then as you start to approach hull speed you have that drag also. A clean bottom and a clean prop make a huge difference in MPG. But conservatively my volvo MD11C burns about 1/2 gallon/hour and I get about 10 MPG these are the conservative number that I use for calculating range. This is running the diesel at about 1800 rpm.
Another factor is that fuel use is not linear with RPM. 2500 rpm uses a lot more than double the fuel at 1250RPM. A diesel's governor injects just enough fuel to maintain a set RPM. At the higher RPM there is more resistence so it takes more fuel.
Sailboats are SLOW!!!!! Trying to make them fast burns a lot of fuel and strains the engine etc.
Hull speed is not a precise speed like a wall. In general the slower you go the farther you go on a gallon of fuel. Hull speed is a result of the hulls shape but you also have plain ole drag. Drag does not increase in a linear fashion. More like if you double your speed you have 4X the drag. Then as you start to approach hull speed you have that drag also. A clean bottom and a clean prop make a huge difference in MPG. But conservatively my volvo MD11C burns about 1/2 gallon/hour and I get about 10 MPG these are the conservative number that I use for calculating range. This is running the diesel at about 1800 rpm.
Another factor is that fuel use is not linear with RPM. 2500 rpm uses a lot more than double the fuel at 1250RPM. A diesel's governor injects just enough fuel to maintain a set RPM. At the higher RPM there is more resistence so it takes more fuel.
Sailboats are SLOW!!!!! Trying to make them fast burns a lot of fuel and strains the engine etc.
Generally diesel engines consume 285 grams of fuel per horse power per
hour. It takes about 4 hp to push my boat at 4.5 knots. and close to 9 hp to get 5.5 knots.
hour. It takes about 4 hp to push my boat at 4.5 knots. and close to 9 hp to get 5.5 knots.
Question: Relationship of Speed/Load/RPM And Carbon Build-up in Mixing Elbow
Informative Thread -- Analogous to experiences with our 2000 Prius. 50-55 mpg on flat road, windless day at 55-60 mph. Only 35-37 mpg when driving Highway 5 at 75-80 mph. More wind and tire drag = lower mpg.
Question, which although not directly related to the primary range/fuel consumption topic of this thread, I would be good to know:
What engine load (% of max speed or % max rpm while underway) is sufficient to prevent carbon build-up in the mixing elbow?
Will motoring at say 60-75% of rated rpm (which for my 2 cylinger engine feels as the best range of fuel economy, acceptable speed, and lowest vibration) be sufficient to keep the elbow clean?
I know its generally accepted that idling the engine for long periods (for the purpose of charging the batteries) is considered to promote carbon build-up ... (presumably because there isn't enough enough exhaust velocity to force all the carbon along?). Conversely, some recommend its necessary to frequently motor at full rated rpm to clear out carbon soot before it cements against the mixing elbow walls.
Is full rpm motoring necessary?
thanks,
rardi
Informative Thread -- Analogous to experiences with our 2000 Prius. 50-55 mpg on flat road, windless day at 55-60 mph. Only 35-37 mpg when driving Highway 5 at 75-80 mph. More wind and tire drag = lower mpg.
Question, which although not directly related to the primary range/fuel consumption topic of this thread, I would be good to know:
What engine load (% of max speed or % max rpm while underway) is sufficient to prevent carbon build-up in the mixing elbow?
Will motoring at say 60-75% of rated rpm (which for my 2 cylinger engine feels as the best range of fuel economy, acceptable speed, and lowest vibration) be sufficient to keep the elbow clean?
I know its generally accepted that idling the engine for long periods (for the purpose of charging the batteries) is considered to promote carbon build-up ... (presumably because there isn't enough enough exhaust velocity to force all the carbon along?). Conversely, some recommend its necessary to frequently motor at full rated rpm to clear out carbon soot before it cements against the mixing elbow walls.
Is full rpm motoring necessary?
thanks,
rardi
I think that mixing elbow build-up is brand specific
I have only seen reference to it with the Yanmar engines. Never with the old Volvo's , Lister's, Beta's or Westerbeakes.
I have only seen reference to it with the Yanmar engines. Never with the old Volvo's , Lister's, Beta's or Westerbeakes.
Fuel Consumption while traveling
I had a 15 HP engine and at 6 knots you should figure on a 1/2 gallon per hour but to play it safe but I would use 3/4 or 1 GPM. You don't want to run low on fuel and gum up your tank. Using 3/4 per hour your range would be
18 Gal * ( 1 Hr / .75 Gal) * (6 Knts / Hr) = 144 NM.
I would use 1 Gallon per hour but have a bigger boat and larger engine.
Jim
I had a 15 HP engine and at 6 knots you should figure on a 1/2 gallon per hour but to play it safe but I would use 3/4 or 1 GPM. You don't want to run low on fuel and gum up your tank. Using 3/4 per hour your range would be
18 Gal * ( 1 Hr / .75 Gal) * (6 Knts / Hr) = 144 NM.
I would use 1 Gallon per hour but have a bigger boat and larger engine.
Jim
Jim, While we are on the subject of your comprehensive knowledge
what have you learned about the proceedures for opening the Amtrak bridge at Havre de Grace? By the terms of my challange you have 18 minutes left.
what have you learned about the proceedures for opening the Amtrak bridge at Havre de Grace? By the terms of my challange you have 18 minutes left.
Jim, My challange was for you to find and post the number to call to make
the necessary notification 24 hours in advance of the need. I have called the CG and got passed from one phone to another and no one came out with an answer. You Sir, told me that I was simply ignorant in not knowing that the bridge opened. I know that I is built to open and the coast pilot states that it opens on signal with 24 hours notice. You have failed to meet the challange. You are no better than I.
the necessary notification 24 hours in advance of the need. I have called the CG and got passed from one phone to another and no one came out with an answer. You Sir, told me that I was simply ignorant in not knowing that the bridge opened. I know that I is built to open and the coast pilot states that it opens on signal with 24 hours notice. You have failed to meet the challange. You are no better than I.
if it's anything like
flying an airplane, you will likely need a little more than what you have in any case.
flying an airplane, you will likely need a little more than what you have in any case.
Brian, I am sure that commercial interests can get the bridge opened
but there is no compelling reason for pleasure craft to travel up river if they require a bridge opening. This particular bridge is on the mainline between Washington and Philadelphia. The trains run about every 15 minutes. during morning and evening commuting times and about every 30 minutes for the rest of the day and night.
but there is no compelling reason for pleasure craft to travel up river if they require a bridge opening. This particular bridge is on the mainline between Washington and Philadelphia. The trains run about every 15 minutes. during morning and evening commuting times and about every 30 minutes for the rest of the day and night.
Your range is roughly around 30 hours of fuel.
How far you can go on that depends on the strength and direction of wind and current.
How far you can go on that depends on the strength and direction of wind and current.
Dan, It simply doesn't much matter what the rated
hp of an engine is . What matters is how much of that HP you use.
hp of an engine is . What matters is how much of that HP you use.
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