Fuel consumption: sail/motor. are you serious?!

[newhaul]

Originally Posted by mvweebles

Excellent. How come you prefer sail? I meet a lot of people who migrate to power and prefer it. Not many go the other way so I'm genuinely curious. Personally, if I wanted go cross an ocean, I'd go sail. Or figure out how to put a sail plan on my trawler which wouldn't be too hard. But even though my Garden designed boat is tough as nails, it's not really made for sustained Force 8 or more. But that's a practical explanation, not a preferential one. So curious your reasoning.

Mainly sound. And everything sailing brings with that relative silence.
I don't see to many dolphins or whales happily swimming within 20 ft of a power boat.
My cruising grounds here in the pnw we actually have our own breed of dolphins .
It's great to see them swimming just in front of my bow as I quietly sail along.



With driving the trawler I'm thinking about the approach to the destination and procedures to dock without any issues .
With a sailboat I'm immersed in the now what's happening on the boat the sIls and the wind.
For me it's a thought process. I think more when sailing than when motoring about what is happening around me in the moment.

There is also a certain pleasure when leaving an anchorage At daybreak under sail. Nobody k ows you are leaving.
Under power many are cursing you for waking them up that early.

[Simi 60]

Originally Posted by newhaul

Mainly sound. And everything sailing brings with that relative silence.
I don't see to many dolphins or whales happily swimming within 20 ft of a power boat.
My cruising grounds here in the pnw we actually have our own breed of dolphins .
It's great to see them swimming just in front of my bow as I quietly sail along.



With driving the trawler I'm thinking about the approach to the destination and procedures to dock without any issues .
With a sailboat I'm immersed in the now what's happening on the boat the sIls and the wind.
For me it's a thought process. I think more when sailing than when motoring about what is happening around me in the moment.

There is also a certain pleasure when leaving an anchorage At daybreak under sail. Nobody k ows you are leaving.
Under power many are cursing you for waking them up that early.

Not everyone has a screaming jimmy in their vessel.
Or a diesel that runs at 2800rpm

Our Cummins diesel buried deep inside a thick timber hull and well insulated ER is almost inaudible at startup and in the wheelhouse when underway @ 1150rpm cruise

We also have plenty of whale and dolphin encounters and video of them surfing the bow wave

[newhaul]

Originally Posted by Simi 60

Not everyone has a screaming jimmy in their vessel.
Or a diesel that runs at 2800rpm

Our Cummins diesel buried deep inside a thick timber hull and well insulated ER is almost inaudible at startup and in the wheelhouse when underway @ 1150rpm cruise

We also have plenty of whale and dolphin encounters and video of them surfing the bow wave

Then there is the whole I can go anywhere at a moments notice on my own bottom.

Would like to go back your way but life got in my way. Last time was in April of 1990 on your west coast in fremantle. Sydney was in 1988 on a navy ship.

[boatpoker]

Originally Posted by newhaul

Mainly sound. And everything sailing brings with that relative silence.
I don't see to many dolphins or whales happily swimming within 20 ft of a power boat.
.

Short sighted ? We seen them all the time alongside. We have actually patted them a couple of times as they come along midships and look up at us.

[newhaul]

Originally Posted by boatpoker

Short sighted ? We seen them all the time alongside. We have actually patted them a couple of times as they come along midships and look up at us.

Looks like a relatively narrow area your cruising through. Don't have much of that in my area .


Most areas are 5 to 7 miles wide and we have a wide variety to observe .

orcas, gray whales, humpback whales, minkes, fin whales, and pacific white-sided dolphins

[boatpoker]

Originally Posted by newhaul

Looks like a relatively narrow area your cruising through. Don't have much of that in my area .


Most areas are 5 to 7 miles wide and we have a wide variety to observe .

orcas, gray whales, humpback whales, minkes, fin whales, and pacific white-sided dolphins

I guess between Manhattan and Antigua or once to Honduras is narrow to some.

[Simi 60]

Originally Posted by newhaul

Then there is the whole I can go anywhere at a moments notice on my own bottom.

.

We go anywhere at a moment's notice on our own bottom all the time
Why wouldn't we?

Takes us seconds to start the engine
And minutes to pull the anchor
Push lever forward and we are underway

[mvweebles]

Originally Posted by newhaul

Then there is the whole I can go anywhere at a moments notice on my own bottom..

Funny you should mention this. It's one of the reasons I didn't care for sail. Putting away the sails at the end of the day was a pet peeve for me. And the lines. Just seemed like if I had a couple hours after work and I wanted to get out, sailboat was a PITA. When I first got a small trawler, it was great. Underway 5 minutes after I arrived at the dock. But like I said earlier, I love being on the water - sailing was good but not so fantastic that it offset the negatives for me. Plus, being in San Francisco, it was easy to catch a ride on friends' sailboats (several of whom converted to trawler after they crewed for me on deliveries)

Your comment about dolphins avoiding powerboats is way off base, as is the noise from a motor. Certainly a powerboat with its engine on will have some noise, but as long as the owner chose wisely for sound insulation, a large diesel ticking over at 1750 rpm (or less) is more of a drone. When I hear sailors complain about the noise, it's almost always because sailboats often have poor engine installations with higher RPM engines that rattle the fillings out of your teeth. They've been aboard go-fast outboard or ski boats, but never a proper trawler.

Are you sure you have a trawler? Honestly, doesn't sound like you've used it much. And doesn't sound like it's even modestly equipped. Nobody likes noise, not even trawler owners. There's no reason to tolerate it on a trawler. If that were part of the tradeoff, I'd lean towards sail too (though why sailors tolerate their loud, shaky engines is beyond me - decent foot massage I suppose).

[Lee Jerry]

Originally Posted by Adelie

You are correct, the article I cited is fuzzy about speeds. There isn't enough info there to say what max speed is with any of the OEM engines nor can we really determine what speed they were going to get 1500nm from 1000L of fuel. I made my best guess.

I would add, though, that I think we know enough to say that it is not more efficient than the FPB 64 (and probably less so).

Regarding the engine curves for your vessel. 4 of the 5 curves in that graphic, including the fuel consumption curve, are for max output, that is the max output possible by the engine at any given RPM. I have lightened and rotated your graphic.

Yes, you're right. It is labeled as "max output." So it may not prove my point, but also doesn't mean it's wrong.

We could develop our own SFC curve at prop load. Looking at three Yanmar engines at random* of various powers and their fuel consumption at two points, max RPM / power and "roughly" half power (rounded to nearest convenient rpm). (You could look at more, I'm only doing two points, but of course it could be done for more to better define the curve and reduce chance of error. Also, I'm using the metric side since they correspond to the grid making it a little easier to read / estimate values.):

4JH4-TE*
3200 rpm - 53 kW - 16 L/hr ==> 16L/hr * 850 g/L / 53kW = 256.6 g/kW-hr
2400 rpm - 23 kW - 6.25 L/hr ==> 231.0 g/kW-hr

4LHA-HTP(Z)
3300 rpm - 142 kW - 43 L/hr ==> 257.4 g/kW-hr
2400 rpm - 64 kW - 17.5 L/hr ==> 232.4 g/kW-hr

6LY2M-WDT
3200 rpm - 235 kW - 67 L/hr ==> 242.3 g/kW-hr
2400 rpm - 100 kW - 26 L/hr ==> 221.0 g/kW-hr

* This one wasn't so random. I picked it because I think it is the closet engine in their current lineup to my 20 y.o. one.

As you can see, all three have lower SFC at "half" power than at full power. It's possible that 3 out of 3 is coincidence, three is not a large sample size, but it certainly is evidence for my point. Also note that the change in SFC is <10%.

When installed on a marine vessel turning a fixed pitch propellor (including folding and feathering) the engine produces approximately the power shown by the bottom curve labelled "Propellor Power Curve". This power curve very different from the max power curve.

If propellor curves were similar to the max power curve, then the specific fuel consumption curve (top) would be a good approximation of efficiency. It's not so you need to look elsewhere to determine the fuel efficiency of your engine.

The prop curve is a theoretical power curve that has been shown to be a good approximation to propellors that are normally installed on displacement marine vessels.

From Gerr's Propellor Book
Prop-hp = C x RPM^n
Where n = 2.2 to 3.0, with 2.7 being normally used.
For a given engine the manufacturer knows max HP and at what rpm that is at. Using that info C can be determined, and then HPs can be determined for other rpms.

If you look at the fuel efficiency map, you can see that following the max output line from low rpm, specific fuel consumption improves until around 50% of max rpm then falls off.
This is similar to the curve from your engine where efficiency improves until about 60% of max rpm then falls off.

If you follow the WHITE prop curve on the fuel mat you will see that as rpm decreases from max, specific fuel consumption increases or is flat as rpm drops, briefly improves, then increases significantly.

Again, thanks for the tutorial but I already know this stuff. For example, in the same prior post I referenced above for fuel consumption I also talk about prop curves.

I do note that your example plot is a torque curve (and gasoline engine), as opposed to power curve. I haven't seen that and I'm not sure how that affects the nominal prop curve; I haven't really thought about it. Not sure I need to though, considering above and would rather use a power curve.

If you look at thrust requirements, SL-1.34 requires about 4 times the thrust as maintaining SL-1.0 and therefore about 4x the hp. But on most people's boats, there is about 2x times the fuel usage at SL-1.34 as at SL-1.0. If it takes 4 times the thrust and hp why does it only require 2x the fuel? Because fuel efficiency drops as rpm and speed drop.

The specific fuel curve would be great to have and use if the prop demand followed max output curve. That's not possible with a fixed pitch prop (FPP). It is possible with a Controllable Pitch Prop (CPP), or at least it's possible to run the engine at nearer to it's most efficient rpm for given load. In Europe a lot of boats use CPPs and have for decades. This is because fuel prices have historically been much higher than in the US. The extra cost and maintenance of a CPP was more than made up for in fuel savings. In the US fuel prices have consistently been low compared to the rest of the world and the cheaper price and lower maintenance meant that FPPs were similarly economical and were more reliable than CPPs.

This conclusion was disproved above. At least "as a rule." Maybe we can talk about this analysis later, but it's a nice Sunday (even if a tad hot) and the boss is already yelling to get off the computer and onto the honey-do list. (Plus I have one more post to make. )

It would be cool if engine manufacturers provided a specific fuel consumption curve for the prop curve but that would require spending more money on engine testing and nobody is really demanding it so it doesn't happen.

They have the data, they used to provide it in the past (at least as full engine maps). It wouldn't cost them anything. Don't know why they stopped.

[ranger58sb]

Originally Posted by newhaul

The big difference between sailing and power boating .
A power boater is going somewhere special. The sailor is already there.

Sounds good on paper, but not universally true.

Originally Posted by newhaul

Mainly sound. And everything sailing brings with that relative silence.
I don't see to many dolphins or whales happily swimming within 20 ft of a power boat.

The main noise we hear on the bridge -- when we're "trawlering" -- is water flow over the hull. That might be an artifact of our hull shape, which is of course much different from a full displacement sailboat. I do also appreciate the reduced noise when sailing (rarely, these days), but I dunno that I'd really call it "quiet" -- and can't remember it being quieter than water noise we hear now.

We almost have to dodge all the dolphins that play along side, behind, and just in front of the boat.

-Chris

[newhaul]

Originally Posted by mvweebles

Funny you should mention this. It's one of the reasons I didn't care for sail. Putting away the sails at the end of the day was a pet peeve for me. And the lines. Just seemed like if I had a couple hours after work and I wanted to get out, sailboat was a PITA. When I first got a small trawler, it was great. Underway 5 minutes after I arrived at the dock. But like I said earlier, I love being on the water - sailing was good but not so fantastic that it offset the negatives for me. Plus, being in San Francisco, it was easy to catch a ride on friends' sailboats (several of whom converted to trawler after they crewed for me on deliveries)

Your comment about dolphins avoiding powerboats is way off base, as is the noise from a motor. Certainly a powerboat with its engine on will have some noise, but as long as the owner chose wisely for sound insulation, a large diesel ticking over at 1750 rpm (or less) is more of a drone. When I hear sailors complain about the noise, it's almost always because sailboats often have poor engine installations with higher RPM engines that rattle the fillings out of your teeth. They've been aboard go-fast outboard or ski boats, but never a proper trawler.

Are you sure you have a trawler? Honestly, doesn't sound like you've used it much. And doesn't sound like it's even modestly equipped. Nobody likes noise, not even trawler owners. There's no reason to tolerate it on a trawler. If that were part of the tradeoff, I'd lean towards sail too (though why sailors tolerate their loud, shaky engines is beyond me - decent foot massage I suppose).

No not mine I just am the engineer and deck crew

Yes It is quite well equipped for what we do with it. Now the twin tamd41s are not quiet but not all that noisy either can't hear them on the flybridge. 2200tpm gives 8.5 to 10 knots depending on catching current or not.

Mainly it's home base during the summer crab season cruising the San Juan Islands
A few shots but don't actually have any whole boat shots .

[newhaul]

Originally Posted by mvweebles

Funny you should mention this. It's one of the reasons I didn't care for sail. Putting away the sails at the end of the day was a pet peeve for me. And the lines. Just seemed like if I had a couple hours after work and I wanted to get out, sailboat was a PITA.
).

No problem roller furling and lazy Jack's sails are put away and stored by the time I'm ag a dock or 10 minutes after I set the anchor.

[Lee Jerry]

Originally Posted by Na Mara

As an additional data point my 43ft 12 metric ton pilothouse sailing yacht gets 0.75l per nautical mile out of her 90hp yanmar going 7.5kn at 2800rpm.

Another good example confirming mvweebles observation in Post #119 about owners' reports being optimistic.


I don't see where Yanmar currently makes a 90hp engine. However, they make this 80hp engine; it uses about 11 L/hr at 2800 rpm. That would be 1.5 L/nm at 7.5 kt. And they make this 110 hp engine; which uses about 13.5 L/hr at 2800 rpm. That would be 1.8 L/nm at 7.5 kt.

Common sense would suggest that your engine should have consumption somewhere between these two. What data or evidence can you provide to support your claim of 0.75 L/nm, or more than 2x better? Is your prop demand curve (i.e. resistance) that different than normal?

I too have looked at the total cost of cruising and come to similar conclusions to those who have commented earlier: total cost of typical holiday cruising per mile is about the same between a sailboat and a displacement motorboat of the same displacement. There are, however, two very important points that definitively tip the decision toward sailing boats imho.

1. If you are voyaging, anything transoceanic, then the cost and environmental damage of doing that under engine, never mind the vulnerability of it, is a show stopper for many. 3000l of diesel to get the nordhavn over the pond is 60000 sek in Swedish money. Do that twice and you have bought my boat a new suite of sails that will last her 10-15 years.

It might cost that much in fuel travelling west. But it would be close to half that (maybe 60%) travelling east.

Sail life is measured not only in years, but also in nmiles. The former more for weekenders (i.e. those who sit at the dock more) and the latter for cruisers (i.e. those that actually use their sails). So that round trip trans-Atlantic would have taken more life out of the sails (especially the main) than the 4 total weeks of elapsed time would otherwise imply.

The second point is that electric mobility is a real option for sailboats.

As previously addressed by others, not for long distance cruising.

[Del Mare]

Originally Posted by Anton Tokar

Hey all!
I just for a minute considered getting a motorboat instead of a sailboat as my first boat (for liveaboard).
and I asked to chat with GPT to give me a fuel consumption comparison.
And I cannot believe my eyes,
how could a boat eat 30-100 liters an hour???
just impossible.
what would be my budget for motoring 24 somewhere???

Just like mine, I have an oil tanker to go on trips with the family, so it always refuels, very smart!
My friend, jokes aside, switch to a sailboat or continue to be scared by your diesel consumption.
In fact, GPT should be called AI, artificial ignorance, or master of statistics because it has no intelligence, it is the result of programming and follows the same. Be careful, look for community sources, then you will have correct information.
GPT is diesel with water and algae in its engine.
I love sailing, but there is no one type of vessel that is perfect for everything, or for everyone.
The limit to getting closer to perfecting what you want is knowledge and unlimited money. Then it's easy to choose, but it's not always, or almost never, like this.
I would say that it is worth it when you know little about hiring a survey if you are buying a used boat. It's not an expense, but a saving of money: it will pay off much cheaper than the endless expense surprises that a used boat hides in its gloomy basements.

[Kubcat]

We regularly get dolphins swimming around our bow on our powerboat and the whales don't seem to mind either.

Interestingly I was due for injectors and the engine was running just a little rougher than usual. We didn't see any dolphins or whales for a while, once we got the injectors replaced, they are coming back near our boat.

Originally Posted by newhaul

Mainly sound. And everything sailing brings with that relative silence.
I don't see to many dolphins or whales happily swimming within 20 ft of a power boat.
My cruising grounds here in the pnw we actually have our own breed of dolphins .
It's great to see them swimming just in front of my bow as I quietly sail along.



With driving the trawler I'm thinking about the approach to the destination and procedures to dock without any issues .
With a sailboat I'm immersed in the now what's happening on the boat the sIls and the wind.
For me it's a thought process. I think more when sailing than when motoring about what is happening around me in the moment.

There is also a certain pleasure when leaving an anchorage At daybreak under sail. Nobody k ows you are leaving.
Under power many are cursing you for waking them up that early.