Displacement vs. Semi Displacement, Plaining

[Seevee]

I'd suggest your friend is a little optimistic with his Meridians fuel figures. We have a Meridian 459 with twin 370B Cummins. When we recently did a 600nm trip I kept a detailed fuel log. Most of the way we did 7 knots at 1200RPM. If you look at the torque curve for these engines that is 98hp and the Cummins fuel burn figure if correctly proped is 14lph. I found we got slightly better than that at 12lph and our overall fuel burn came in at 2.2 nautical miles per US gallon.
I think you will find that with modern engines running at a couple of knots below hull speed the difference between a full displacement a semi displacement and for that matter a planning hull will be small. Ask people who have actually had both like the folks who own Dirona and they will tell you the same thing.
We love our Meridian. Very economical with lots of room and comfort.

I dropped my friend an email to be sure I got the info correct, 2 nmpg seems more reasonable and that's just fine with me. Got me looking seriously at the Meridian.... lots of creature comforts.

 

[Seevee]

As for fuel being an expensive cost... it all depends. On a loop trip it's probably the single most expensive thing, and a big part of the total picture. Even at the economical 2 nmpg the fuel bill with push up toward $9K for that trip, and there's no single item that would cost that much.

As for living at home with normal smaller trips, fuel is a smaller part of the picture. In general, the more you use the boat, the most fuel will be a bigger part of the picture. The fixed costs will go on if you never take the boat out of the slip... purchase price, storage, insurance.. The variables come into play when it's used..... fuel, maintenance, reserves for overhauls. So if used one hour a year, fuel is nothing. If used 500 hours a year fuel becomes a large percentage.

As far as other expenses go for a loop trip......

Food is a debatable cost on a trip, as you have to eat no matter where you are. I could argue the "additional" food cost for a trip is what the true food cost is for the trip. i.e. you can't shop as efficiently as at home and you will probably do more restaurant meals.

Restaurant meals will probably be more than staying at home.... but for me, small potatoes. Don't like restaurants.

Marine costs can be large, but that's a choice.

...... but, having never done the loop, not sure.

 

[Seevee]

Overall, VERY informative thread, thx much for the replies.

 

[psneeld]

A lot of talk not too long ago was about efficiency.....that was because many of us were worried about $5.00 a gallon fuel....not the less than $2.00/ gallon I have been paying for at least 18 months.

At $5.00/ gallon....it was going to be either the largest annual cost I had, only bested by how many transient marinas and their costs I stayed in. That was significant as I am a liveaboard.

Obviously not some people's worry, but there is a segment here that a couple thousand dollars either way in their cruising kitty is significant.

Just a note...if you stayed in nice marinas every night for a year long loop...it might easily push $36,500 for a 40 to 50 footer. That might be tough unless you searched for only 5 star places.....but certainly $75 a night including electric per marina is a realistic average and leaving out the nights you might anchor or free tie up even if that is not your style.

And that is exactly the point...no one boat or boating style fits all here.

 

[ranger58sb]

We have a Meridian 459 with twin 370B Cummins. When we recently did a 600nm trip I kept a detailed fuel log. Most of the way we did 7 knots at 1200RPM. If you look at the torque curve for these engines that is 98hp and the Cummins fuel burn figure if correctly proped is 14lph. I found we got slightly better than that at 12lph and our overall fuel burn came in at 2.2 nautical miles per US gallon.

I think you'll find that 98hp is at WOT.

Eric: Huh?

-Chris

 

[North Baltic sea]

Question that has come up.....

Regarding fuel and speed.

Is there a big difference in fuel burn with any hull when operated at hull speed, everything else equal?

I hear that the bigger the engine, the more fuel burn. I believe they can be just as efficient as a small engine, if operated at the same power, perhaps better. I've also heard that displacement hull is much more efficient than the other hull designs. Now extremes like comparing a 1300 hp engine to a 200 hp may be totally different.

But, my friend that operates a 455 Meridian gets 8.4 mph on 2.1 gph (4mpg), with twin Cummins diesels 370's. He's on his 3rd loop and a very detailed person. But sounds exceptional.

I'm using this to decide what boats to look at and seems it really doesn't make a lot of difference. It's more operator technique than design.

However, another friend who has done a half loop and a lot of boating gets 8 mph on 1.5 gal in his 32 Senator (Grand Banks lookalike), but a much smaller boat.

Gut feeling, I'll be in the 35 to 42 foot size and engines aren't significantly different.

For the technical folks, what do you say?

Hi, i look boat test site meridians 441 2x480hp cummins qsb 6,7 Zeus. You can see fuel consuptions curve. The engines are bigger, but you can see about consuptions whit twins.

 

[North Baltic sea]

And this curve are meredian 391 2x380qsb cummins

 

[North Baltic sea]

SD American tug 435 volvo D9 500hp

 

[Seevee]

North Baltic,
Thx, those curves are good info.

 

[Bay Pelican]

In several threads in the past I have made this observation. Usually each year we make one or more 85nm trips. These usually take about 11 to 12 hours. At 2 US gallons per hour that is 24 gallons. At 4 gallons per hour that doubles to 48 gallons. Caribbean fuel is frequently $3.50 US to $4.50 US per gallon. Assuming $3.50 the 24 additional gallons would be an additional $84 on a one way trip. That $84 savings using a Krogen with a single engine more than buys us dinner at a restaurant.

In perspective, if I were using 4 gallons per hour for a 24 hour round trip I would be spending $336 US to go from Rodney Bay (St. Lucia) to Bequia (St. Vincent) for the race week party.

 

[Jetstream]

Jetstream wrote;
"If you look at the torque curve for these engines that is 98hp and the Cummins fuel burn figure if correctly proped is 14lph."

I think you'll find that 98hp is at WOT. No wonder you burned less fuel. And of course there's the no wake zones, engine warmup and coming and going from harbors where you're burning far less fuel but the hour meter is marching right along.

Re the SD FD question opinions have been posted. My opinion is that a typical SD trawler will have about 1.5 to 1.8 times as much resistance as a FD trawler. A 40' Willard requires 23hp to run 7 knots.

Jetstream is that the Meridian 459 in your avatar? Looks like fun!

Hi Eric, no that's not our 459 in the avatar. That was a 34 Randell we had many years ago. They are a great looking and very good sea boat that used to be built in Western Australia.

This is our 459

Our engines are the 6BTA Cummins rated at 355hp at 3000rpm so at 1200rpm they aren't working hard at all. At WOT she gets 3050rpm and 24kts,

Brett

 

[Nomad Willy]

Nomad,
Good points. That's what I thought with twins, however one does double the maintenance. And with twins at the SAME hp as one single, I'd expect speed to be close to the same. I don't imagine that one would gain more speed with either, using the same HP... but don't know.

Thank you Seevee,
Not nearly double the maintenance though. Twice as many things to do yes but changing oil on two 60hp engines is about the same cost as changing oil on one 120 hp engine. Most things are half the size. Re the typical trawler though it is actually twice as much because the engines in a twin are the same engine as a single. But if you were to say "a twin engine trawler" all other things being equal it's about the same. But things aren't equal on the typical trawler as most twins have twice as much power as the single. And twice the power is twice the maintenance.

 

[dhays]

Dave wrote;
"A single will be more efficient than twins, all else being equal."

"all else" should be total power.
Sure if you compare a 120hp single to a 240hp twin. As most do. But if you compare a 120hp single to a 120 hp twin (obviously w two 60hp engines) the burn rate difference will be hard to detect and if detectable the twin may often be more efficient. The OP needs to be aware of that IMO.

A GB36 w two 55hp Yanmars would probably be slightly faster and burn less fuel due mostly to the much more modern engines and lighter weight. Re a GB36 single.

One of the boats that I found very interesting was the Great Harbor, 37 I believe. It had twin Yanmar 54hp engines, the same engines that are in my sailboat. It would make for a very efficient power package and those engines are easy and cheap to maintain.

 

[Nomad Willy]

Dave,
Indeed that's one thing I like about the Great Harbors. One of the few boats reasonably powered. There actually was a GB36 w twin 55hp Yanmars a few years ago. It didn't stay on YW very long. A woodie from the east coast.

Jetstream,
Holy cow that's a big go faster. Very impressive. Looks good too but I'll bet the Randell was more fun. That's a Meridian huh ... didn't know they made them that big. Made in the US?

 

[eyschulman]

I don't know if the issue of two props vs one has been considered. To match the blade area of a twin you need a fairly large prop in a single some boats can do that others (most) not so. Prop size and blade area do affect efficiency.

 

[Seevee]

Another thing worth mentioning....

The cost of gas really amounts to the dollars spend for the given trip. If one is getting 2 mpg and they are able to double that economy for even a loop trip is not HUGE dollars. Going from ~$9k to $4.5K. Yes $4500 is a lot of dollars. But if you look at it the other way... going from 2 mpg to 1 mpg the dollars double, to $9K ADDITIONAL, now getting into some serious dollars. And with a big boat, balls to the wall for a lot of the trip, that could double again.

Just guessing, a good loop trip with what a lot of us have in the 35 to 50ft boats will probably run in the range of $20K to $40K more than staying at home..... Depending. So adding $4.5K isn't a back breaker, but adding $9K or a bunch more could be.

I'll let the real loopers refine the numbers.

 

[psneeld]

Real loopers can't define the cost of a loop more than any other serious cruiser or boater in the know....pretty easy to do the math if interested enough.

It all depends on too many things.

Some loopers do the loop in literally five to ten thousand dollars, and others have reported in the upper 70s to $100,000 dollar range.

So many variables in boating, generalizing almost anything is not necessarily applicable.

 

[Seevee]

Real loopers can't define the cost of a loop more than any other serious cruiser or boater in the know....pretty easy to do the math if interested enough.

It all depends on too many things.

Some loopers do the loop in literally five to ten thousand dollars, and others have reported in the upper 70s to $100,000 dollar range.

So many variables in boating, generalizing almost anything is not necessarily applicable.

Psneeld,

Agreed, there's probably a WIDE range, but from my reading, a $30K budget is certainly doable with a lot of comforts, without scrounging. Thanks going to be my budget. My goal is to enjoy it, and to dock without hitting the neighboring boat.

At the bottom end of the range, seems like it's hard to get good creature comforts like AC, freezer space, etc. Saw a neat presentation by a 21 yr old gal and her friend that did the loop and Bahamas run on a really cheap 25 ft sailboat. When they ran out of money, they went to work... took two years. Certainly a fine adventure for 21 yo kids, but not for me.

On the other end, to spend $70 to $100K you either need a really expensive boat or really high end entertainment or both. Not my style, and there is such a thing as too big of a boat. (unlike garages).

 

[Donsan]

Just guessing, a good loop trip with what a lot of us have in the 35 to 50ft boats will probably run in the range of $20K to $40K more than staying at home..... Depending. So adding $4.5K isn't a back breaker, but adding $9K or a bunch more could be.

Some loopers have sold the fort and don't incur the home costs. I have seen all kinds of numbers on what doing the loop will cost. There are a lot of costs and a few offsets. For example, you will have marina overnight fees but you can offset that by not keeping your slip at home port. I just don't think you generalize like that. Your costs will be determined by your situation, your boat, your style and the creature comforts you demand.

 

[Great Laker]

Real loopers can't define the cost of a loop more than any other serious cruiser or boater in the know....

As a "real looper", I can tell you exactly what it cost us, including fuel, locking fees, marinas, food, alcohol, restaurants, entertainment, rental cars, museums, laundry, and more. Of course this is based on our boat and our traveling lifestyle. But this data can be extremely useful for others to adjust to their circumstances. Also the Americas' Great Loop Cruisers Association (AGLCA) has a Great Loop Cost estimator that can be useful as well.

Getting back to the thread, for us, the fuel cost was smaller than marina costs, and small relative to the total cost of the trip.

 

[Ski in NC]

I have done several 1month or so trips on my 38, some solo, some with the girl. But always south, never the loop. Most miles at slow speed, 4nmpg, about $3-4/gal. Some at high speed, 1.8nmpg, about $2-3/gal. Pretty much every expense went on the credit card.

Amazingly consistent, about $3k per month. Some anchoring, some marinas, very few restaurants, lots of beans, rice, fish, steaks, fried egg sammiches, all cooked on the boat.

In some ways you save money. Not as many opportunities to buy stupid stuff like while living the dirt life.

 

[Bay Pelican]

At approximately 3.5 nmpg we used over 1700 gallons to get to Trinidad from Chicago via the St. Lawrence. At the time the price of diesel in the US was $5 per gallon, but varied by location and country. But the cost must have been over $8,000. For the most part we anchored out and ate out no more than when at home. Thus a doubling of the fuel cost would have been significant in the cost of the over all trip.

I have followed the Great Loopers for years. The price of gasoline has varied significantly over that time but I have seen cost reports in the $20,000 range for twin engine gasoline boats in the upper thirty-or forty foot range.

I note that the immediately previous posts appear to be by single engine boats.

 

[Seevee]

After doing a bit more research on the 70/70 "rule", it seems the biggest consideration is the operating temperature of the engine. At low rpm's there is incomplete fuel combustion and soot and carbon are formed, as well as some corrosive compounds.

That said, I mostly motor at just above idle speed since I troll for fish a lot and the slower I troll the more fish I catch. I run the engine up to pretty close to max rpm's at intervals and watch the oil burn off in my wake. If I am damaging my engine, it's just a part of why I own a boat, I fish.

Every marine diesel information source I have ever encountered recommends adhering to the 70/70 "rule" from Nigel Calder on down...

What is the 70/70 rule?

 

[BandB]

You frequently hear the comment that fuel costs are a minor factor in boat ownership. Probably true overall unless you are doing a multi-thousand mile trip e.g. the Great Loop. Or a trip to the Caribbean.

However, in my experience fuel costs are frequently cited in why someone does not want to make a trip. I think of a friend who sold a Carver after it cost him $800 one way Michigan City Indiana to Leland Michigan. Our yacht club use to have a Michigan City to Chicago trip. A number of boaters used the fuel costs as the excuse for not going.

Fuel costs and out of homeport marina fees are one of the few expenses which are discretionary in boat ownership.

I think people just underestimate all the costs of boating. That includes fuel costs but then as you say it's discretionary. However, then you're not boating, just owning a boat. A lot of times they bought the wrong boat for their budget and that's sad to see because it sours them on boating. It's difficult to do a boating budget if you don't have a lot of experience, but one needs to do so or plan for the worst case.

 

[AKDoug]

Fuel costs when I retired and moved to a fixed income quickly convinced me that I couldn't afford to run my 24' Bayliner at $400 per four day outing. So I got a boat that costs me less with the financing and fuel than I paid just for fuel with my previous boat.

Fuel costs are now the least of my concerns, moorage fees quickly top fuel costs if I am tied to the dock. I spend way more on food than fuel now, especially when you factor in beer

The 70/70 rule is 70% rpm's 70% of the time...

 

[eyschulman]

SD American tug 435 volvo D9 500hp

the fuel burn here is very similar to my 48 ft SD with twin JD 6068 engines at 330HP each. A good example of where twins don't burn more fuel at a given speed. Fleming Yachts also use twins and did a lot of research on this issue because many of their boats go long range. the conclusion was no significant difference in fuel burn and the safety of a spare engine made twins the only way you can buy a Fleming.

 

[BruceK]

Hi Eric, no that's not our 459 in the avatar. That was a 34 Randell we had many years ago. They are a great looking and very good sea boat that used to be built in Western Australia.
Our engines are the 6BTA Cummins rated at 355hp at 3000rpm so at 1200rpm they aren't working hard at all. At WOT she gets 3050rpm and 24kts,

Brett

Brett,agree,Randells are great boats,though many had outdrive/sterndrive Volvos.
With the Meridian, what speed does 1200rpm bring up? I see our marina mechanic chasing lowest idle speeds because even at idle, Rivs and similar do 6 knots. Too fast for parking, so otherwise swapping, often, in/out of gear.
If you normally run around 1200rpm, is that an ok use of the engines, or is there a downside. I ask because I see some otherwise desirable boats with heaps more hp than I want or need.

 

[Jetstream]

Brett,agree,Randells are great boats,though many had outdrive/sterndrive Volvos.
With the Meridian, what speed does 1200rpm bring up? I see our marina mechanic chasing lowest idle speeds because even at idle, Rivs and similar do 6 knots. Too fast for parking, so otherwise swapping, often, in/out of gear.
If you normally run around 1200rpm, is that an ok use of the engines, or is there a downside. I ask because I see some otherwise desirable boats with heaps more hp than I want or need.

Hi Bruce, yes we had the Volvo AQAD40 stern drives in the Randell. Only blew up one of the stern drive legs in about 2000 hours of boating in her but I was meticulous on maintenance of them.

In the Meridian 1200rpm gives us 7kts and at idle of 600 rpm we do 4kts with both engines in gear and she is very easy to manuver at that idle power setting. I know what you mean about some of these Riv's etc going quite fast at idle. I've driven a few game boats and it takes a little while to get used to it.

As far as running the Cummins at low power I researched this before we bought her and the experts we talked to said the having to run them at high loads is a mith these days. As long as the engines are run in correctly under a reasonably high load initially they can be run at low load without detriment. There is a good article on the Seaboard web site about it.

We bought her up to the Gold Coast from Sydney at 1200rpm for 95% of the time but do up her up on the plane occasionally and cruise for a while at 20 knots just for the fun of it. Fuel burn goes up to about 110lph at 20knts and 2800rpm.

Eric, yes they are made in the US and ours was actually made in Washington state,

Brett

 

[North Baltic sea]

the fuel burn here is very similar to my 48 ft SD with twin JD 6068 engines at 330HP each. A good example of where twins don't burn more fuel at a given speed. Fleming Yachts also use twins and did a lot of research on this issue because many of their boats go long range. the conclusion was no significant difference in fuel burn and the safety of a spare engine made twins the only way you can buy a Fleming.

he you are Fleming 55 curves

 

[sunchaser]

For those of us boating in the waters between Tacoma and Glacier Bay the NMPG discussions tend to play second fiddle to other cruising variables. These being destinations, currents and weather windows.

Within reason our vessel has a sensible variable speed between 5.5 and 9 knots. Optimum is 7.8 knots. Mother Nature dictates much of our travel planning and times. Getting to "that pass" at slack with a close eye on currents for the day's travel involves considering throttle setting, departure time and arrival time.

Then comes the weather meaning wind and waves. To balance these 5 or 6 variables when doing a 3,000 nm trip, RPM becomes a variable as well. And paying scanty attention to whether tomorrow's travels are at a fuel burn of 1.2 or 2.1 nmpg. Getting there safely, relaxed and on time trumps fuel burn every time.

The relaxed part also involves a big dug in anchor, genset, inverter, tankage, cheap AK fuel --- oops, another thread or two.