Displacement vs. Semi Displacement, Plaining

[sunchaser]

150 hp is the EPA cut off for naturally aspirated diesel engines.

My point exactly. That said, Mark can you by your engine new today without a turbo?

For those of us that have had heavy duty equipment experience a turbo charged diesel is a necessary fact of life and has been for nearly 3/4 of a century. Millions of engines are made each year with turbos and very long warranties.

But, with a bad wet exhaust system turbos cost money to repair. An improperly designed and maintained raw water system with turbo and after cooler is indeed problematic. There are however NA engines that have suffered due to salt water intrusion through the exhaust system.

 

[O C Diver]

It has little to do with whether or not it has a turbo, and more to do with how you use or abuse, and frequency of oil changes. The marine turbo is a simple component that likes clean oil. The marine turbo diesel will live a long life running below 70% of WOT.

Ted

 

[RCook]

Our trailerable cruiser (26 feet, 11,000 lb loaded, planing hull) has a medium-sized diesel (Volvo KAD44P) with lots of bells and whistles. A straight six with 24 valves, turbo, aftercooler, supercharger, electronic engine control, fly-by-wire shift and throttle at three helm stations. 260hp from 3.6 liters, or 72hp/liter. 3800-3900 RPM at WOT. After 18 years and 6,502 engine hours, it's still running well. I don't think the turbo is a significant vulnerability.

It allows us to run a heavily-loaded boat with an efficient diesel that's happy to travel at 6 knots, or at 18, when we wish to go faster. A non-turbo diesel with enough power to do that would not fit physically in our boat, and would be too heavy for planing in our boat even if it could fit. A gas engine would use far more fuel, limiting our range on a tank, and forcing us to change our routes to have more frequent access to fuel.

One reason it's still in good shape is consistent regular maintenance. Another is that we have run most of the time at 6 knots for the past 4,500 hours - less wear and tear. Electronic engine controls help make running at lower power levels OK - just enough to keep the engine up to a proper temp, and there's no smoke. Fuel efficiency at 6 knots is nice - 4nmpg, but certainly not as good as it would be with an FD hull. Good compromise for us.

Our new boat, a 37-foot Nordic Tug, gets nearly the same nmpg at 7 knots, with an SD hull and single Cummins 330hp inboard. And it can cruise at 12 knots, thanks in part to its turbo.

 

[Seevee]

Perhaps the turbo argument belongs in a different, and I could argue it has nothing t do with the efficiencies of different hull designs. However, I'm still going to comment......

First, I'm not a fan of turbos, especially for non flying machines like boats or cars. In aviation they do offer some significant advantages in altitude capability and speed.... but there's always a price.

I've owned/operates turbos in boats, cars and planes. Now, with a boat that really has little altitude capability, the only reason I can see for a turbo is to get more power and torque from a smaller engine. So weight is reduced and the cost of the engine is probably less.

The disadvantage is that it's just one more thing to fail. And they are very critical to operate....absolutely need clean oil and free from any debris. Spinning upward of 100,000 rpm, the slightest loss of oil or a really small piece of debris can destroy the blades or bearings in a heartbeat.

Some say a turbo is more fuel efficient. I don't know, but would doubt it.

I'd like to get my knowledge level up a bit on Marine diesels with turbos. They seem like less troublesome than with cars or planes. My only marine experience was with a 450 Sundancer, Cats, and it wasn't too bad.

 

[sunchaser]

It allows us to run a heavily-loaded boat with an efficient diesel that's happy to travel at 6 knots, or at 18, when we wish to go faster. A non-turbo diesel with enough power to do that would not fit physically in our boat, and would be too heavy for planing in our boat even if it could fit
One reason it's still in good shape is consistent regular maintenance.
Our new boat, a 37-foot Nordic Tug, gets nearly the same nmpg at 7 knots, with an SD hull and single Cummins 330hp inboard. And it can cruise at 12 knots.

Great response Richard from someone who has been there and done that from the marine side.

 

[boatpoker]

The disadvantage is that it's just one more thing to fail. And they are very critical to operate....absolutely need clean oil and free from any debris. Spinning upward of 100,000 rpm, the slightest loss of oil or a really small piece of debris can destroy the blades or bearings in a heartbeat.

Some say a turbo is more fuel efficient. I don't know, but would doubt it.

I'd like to get my knowledge level up a bit on Marine diesels with turbos. They seem like less troublesome than with cars or planes. My only marine experience was with a 450 Sundancer, Cats, and it wasn't too bad.

1971 Perkins HT6-354 20,000hrs on it before I rebuilt it. The turbo was fine but as I was rebuilding the rest of the engine it seemed wise to rebuild the turbo too.

 

[North Baltic sea]

One reason it's still in good shape is consistent regular maintenance. Another is that we have run most of the time at 6 knots for the past 4,500 hours - less wear and tear. Electronic engine controls help make running at lower power levels OK - just enough to keep the engine up to a proper temp, and there's no smoke. Fuel efficiency at 6 knots is nice - 4nmpg, but certainly not as good as it would be with an FD hull. Good compromise for us.


Hey, what kind of oil change interval you have used your Cummins?

 

[CPseudonym]

Wow! Talk about thread drift.

Over 30 years experience owning and operating off road diesels 11 HP through well over 800 HP. Gensets from 10Kw through 1,000Kw and never had a turbo failure. The outright "bovine excrement" and "dock talk" on this thread is ludicrous.

 

[Nomad Willy]

Not so, Eric. Many of us Double Guys like the redundancy of twins, and are willing pay a premium for the weight, complexity and cost of twins. I always chuckle when I hear single engine owners talk about the inherent reliability of diesels, and how they don't need a spare. That doesn't jive with the years I spent on salmon seiners out of Juneau years ago. Several times we were towed home when that one engine or drive train failed. At the wrong time, having a single-engine could be catastrophic. But, this is an argument much akin to politics and religion. I'm certainly not going to convince you about twins, or visa versa me on singles.

Not so Ken,
The post you refer to was not about twins v/s singles. Nothing to do w it. Was just about appropriate power. I'm all for twins. Not the highest priority for me (obviously as I own a single) but I'd rather have a twin. I'm not anti-twin at all.
I am against the go slow go fast philosophy. But only if it involves underloading diesel engines.

 

[Seevee]

The "Twin vs Single" debate....

This is one that will never be solved. I belong to an aviation forum (similar issues) and the single twin debate has gone on forever, with thousands of posts.

It won't ever be solved in boating, either. I've had both, and could strongly argue the merits of either.

But in the end, either has little to do with hulls, the original topic.

Now, as for efficiency discussion, I'd bet that for pure efficiency a single engine that operates at ~70% power to get up to hull speed with a DH would be hard to beat for pure efficiency.

However, for most of us hear that want reasonable efficiency, if we operate at hull speed, the number of engines or type of hull is not going to make enough of a difference to stop us from making the trip. The size of the vessel and the speed will certainly make a lot more difference.

 

[eyschulman]

Back to hull type: Most on this site will own or buy a used or new production boat. Few will need extreme long range and open ocean ability.That being the case I think when boat shopping it is more important to find a boat that will fit your use needs best at the price you wish to pay. I see little point in getting too hung up on hull type or # of motors. At low or moderate speeds there is a significant overlap in practical( not theoretical) performance and ride characteristics. If you are going to go custom build then you can indulge in the game of what's better if that appeals to you.

 

[eyschulman]

Turbo needs a different long thread. Much info and likely lots of different opinions.

 

[kmacdonald]

^^^^^^^^^Yes, opinions will be all over the place and what's best in one situation may not be best in another.
Even with quotes from the engine manufacturers reps, a few anecdotal arguments to the contrary have been offered as "proof". The waters are murky at best and no consensus is likely. Pick your own poison.

 

[RCook]

Hey, what kind of oil change interval you have used your Cummins?

Hi NBS,

The Cummins manual calls for every 300 hours. I've done it at 250-300.

The Volvo manual calls for every 100. I've done that, or sometimes even sooner, when my cruising schedule made it more convenient to do so.

Very little oil consumption in either engine.

 

[Bay Pelican]

Back to hull type: Most on this site will own or buy a used or new production boat. Few will need extreme long range and open ocean ability.That being the case I think when boat shopping it is more important to find a boat that will fit your use needs best at the price you wish to pay. .

True in so many ways in boating.

 

[ksanders]

But in the end, either has little to do with hulls, the original topic.

Now, as for efficiency discussion, I'd bet that for pure efficiency a single engine that operates at ~70% power to get up to hull speed with a DH would be hard to beat for pure efficiency.

However, for most of us hear that want reasonable efficiency, if we operate at hull speed, the number of engines or type of hull is not going to make enough of a difference to stop us from making the trip. The size of the vessel and the speed will certainly make a lot more difference.

Thats it in a nutshell.

 

[Nomad Willy]

A 40' Willard makes 7knots on 24hp .. 6 knots on 15hp.
That's what it says in the widely respected book Voyaging Under Power by Robert Beebe. A real FD hull cannot be beat for long range and low fuel consumption.

 

[eyschulman]

A 40' Willard makes 7knots on 24hp .. 6 knots on 15hp.
That's what it says in the widely respected book Voyaging Under Power by Robert Beebe. A real FD hull cannot be beat for long range and low fuel consumption.

I owned a 40 ft FD that made one K less than hull speed at about the same HP. Good boats but many boaters look to other attributes of boats which are not always in the FD hull available at the time or target price range. Many want to go faster than hull speed on occasion. The bottom line match the boat hull interior looks and performance to your personal needs or desires and the hull type may and often does end up playing second fiddle. I have no argument with the fuel efficiency of a well set up FD boat but in that area we should all be aware of the long light SD boats that get great fuel burn #s and sail and motor sailors that put FD pure power to shame when it comes to long distance fuel burn values. When I owned sail I argued its virtues. When I owned FD power I argued its virtues. I did the same with multihulls, planning and semi displacement boats. Now that I am an old man and look back well they are all good boats it just depends on how you use them and feel about them.

 

[dhays]

A 40' Willard makes 7knots on 24hp .. 6 knots on 15hp.
That's what it says in the widely respected book Voyaging Under Power by Robert Beebe. A real FD hull cannot be beat for long range and low fuel consumption.

I would have preferred a FD hull form. However, I couldn't find a FD boat that ticked all the boxes of features, layout, location, price and availability. So I have a SD hull that I drive slow with an engine much bigger than I really need.

 

[psneeld]

Low resistance hulls, (long skinny ones to include multihulls) can give many full displacement hulls a run for their money in effeciciency (miles per gallon), certainly in speed, but limited in weight carrying unless substantially bigger.

 

[Nomad Willy]

Psneeld,
That's true. I went overboard on fuel efficiency when I was shopping but not so much so that I have any inclination to sell Willy. I could easily afford double the fuel consumption (2gph) but I'd only gain one knot ... if I bought a NT32. But if I was still in Alaska I'd be better off w Willy.

Dave yes often that happens. The Willard was the perfect boat for us at the time .. all things considered.

eyshulmam I'm an old man too and a certain wisdom comes along that the younger bucks lack. And I might add we had a good time learning. I must have as many lives as a cat though.

 

[rwidman]

I think you will find throughout your ownership that fuel costs will be the least of your worries. Lets think about that: An 1100 mile run down the ICW will cost me about 550 gallons of fuel (4 gal/hour at 8.5 knots, or roughly speaking 2knots/gal. At $2.50/gal, my fuel cost will be $1375. Now, lets say I dawdle and spend four weeks underway, of which, half will be in marinas, the rest at anchor or on balls. My marina costs will be about $100/night, close to what I pay for fuel. Now figure in repairs, provisions and restaurants, rental cars... Well you get the idea. If your new boat burns twice as much fuel, it will only ad $1375 to your total cost. It seems like a lot when you pull up to the pump with empty tanks, but when calculated in to the total cost of boating does not seem terrible to me. ...........................

I tend to agree. Compared to other operating costs, maintenance, dockage and depreciation, fuel costs will be minor and the difference between similar boats is not worth worrying about.

Want something to really think about? I bought my boat in 2008 (second hand, it's a 2000 model. That's a bit more than eight years ago. The current asking price for the same model boat is $50K - $70K less than what I paid. That's over $6K per year in depreciation. Then there's the $4K per year in slip fees not counting transient fees.

Add in maintenance and the fuel costs for two or three months cruising is not worth worrying about.

That's not to say I don't travel at an economical speed and look for the most reasonable fuel and marina prices, but boating is not a hobby for someone who gets too upset about spending money.

 

[ksanders]

I would have preferred a FD hull form. However, I couldn't find a FD boat that ticked all the boxes of features, layout, location, price and availability. So I have a SD hull that I drive slow with an engine much bigger than I really need.

I wanted a FD hull form as well, and for the same reasons you pointed out above we went with a SD hull and larger engines.

With five seasons under our belts I find that we use the speed capability more than we thought we would. It's nice to have the ability to get after it and make an anchorage for example during daylight hours. We also find that we much prefer the ride in beam seas if we apply some power and push the aft down. It really reduces the roll.

8 knots is nice and comfortable, but sometimes you want to get their faster and a SD hull form allows that freedom of choice.

 

[BandB]

We also find that we much prefer the ride in beam seas if we apply some power and push the aft down. It really reduces the roll.

That's something often overlooked is the advantage of being able to vary speed in various seas and especially when going through inlets/crossing bars.

 

[Nomad Willy]

I never have understood this need for speed. But speed in itself isn't a bad thing. But w a boat I'm not willing to pay the price in money or seaworthyness. And after going 6 knots for 10 years preceeded by 6 years of going 8.5 and 7.5 knots I've gotten by just fine. One exception is/was winter cruising in Alaska. With only 3 or 4 hours of daylight there were times we just couldn't get to where we needed to be. For example going north to Petersburg we needed to transit the Wrangell Narrows on a flood tide. The flood tides were at night. Ever seen Wrangell Narrows at night?

Otherwise a slow one speed boat has been fine. A lot of things in life are not needed but you don't realize you don't need those things until for whatever reason you go forth without .. as I have done w slow boats.

 

[Bruce B]

I never have understood this need for speed. But speed in itself isn't a bad thing. But w a boat I'm not willing to pay the price in money or seaworthyness. And after going 6 knots for 10 years preceeded by 6 years of going 8.5 and 7.5 knots I've gotten by just fine. One exception is/was winter cruising in Alaska. With only 3 or 4 hours of daylight there were times we just couldn't get to where we needed to be. For example going north to Petersburg we needed to transit the Wrangell Narrows on a flood tide. The flood tides were at night. Ever seen Wrangell Narrows at night?

Otherwise a slow one speed boat has been fine. A lot of things in life are not needed but you don't realize you don't need those things until for whatever reason you go forth without .. as I have done w slow boats.

Having spent the last 20 plus years cruising on sub 7 knot boats, I sure understand the desire to be able to pick it up when you want to!
I'm sure we will spend the majority of time at 7 or 8 knots in our new boat but you can be sure we will push it up at times.
Bruce

 

[O C Diver]

Nothing wrong with going faster. Didn't want to compromise space, water capacity, and load capacity to accomplish it. So often the boats I see in the 36 to 45' range, loose too much of the comforts so that they can attain speed. A slow boat seems to be designed around the comforts first. A faster boat seems to be designed around the hull form, engine(s), and fuel tanks.

Ted

 

[Seevee]

Nothing wrong with going faster. Didn't want to compromise space, water capacity, and load capacity to accomplish it. So often the boats I see in the 36 to 45' range, loose too much of the comforts so that they can attain speed. A slow boat seems to be designed around the comforts first. A faster boat seems to be designed around the hull form, engine(s), and fuel tanks.

Ted

Ted.
That's a very good point. I've been trying to find a bit of both, and the Mainship 35, 39, 40 is high on my list because of the outdoor space, area for a kayak and space. However, in reading, seems like its top end is slow (13kts) and inefficient. When I look at the cruisers (Carver, Meridian and others) a few have nice creature comforts but little outdoor space, kayak space, etc. Go faster, however, and slow speed isn't bad either.

Seems like my idea boat would be a big back cockpit with covered aft flybridge for toys, small salon and big galley, and one good state room. But a good 7 knots economy cursing with a top end approaching 20 knots. Everything else is secondary. Can't find a boat with those characteristics.... I guess it's time to compromise.

 

[ranger58sb]

Ted.
That's a very good point. I've been trying to find a bit of both, and the Mainship 35, 39, 40 is high on my list because of the outdoor space, area for a kayak and space. However, in reading, seems like its top end is slow (13kts) and inefficient. When I look at the cruisers (Carver, Meridian and others) a few have nice creature comforts but little outdoor space, kayak space, etc. Go faster, however, and slow speed isn't bad either.

Seems like my idea boat would be a big back cockpit with covered aft flybridge for toys, small salon and big galley, and one good state room. But a good 7 knots economy cursing with a top end approaching 20 knots. Everything else is secondary. Can't find a boat with those characteristics.... I guess it's time to compromise.

Just to note, the Mainship 350/390 and the Mainship 400 are (at least) two different boats. Dunno if performance is similar or not, though... In any case, they're likely not ever going to be "fast" if you're looking for 18+ knots or so cruise...

There are boats called "sedan bridge" models, at least by a few companies... and they tend to have long, extended-aft bridges. Interior much like a sportfish or convertible; i.e., not usually an aft-cabin model. You might have a look at some of those... Formula, maybe Cruisers (not sure), some of the Sea Ray bridge boat, some of the Meridian models have that kind of extended bridge, etc. Don't think they're up to carrying a heavy dinghy/outboard, but could maybe be worth a look for kayaks.

Then too there are cockpit motor yachts... usually an aft cabin model with a cockpit stuck on the aft end. The top of the aft cabin can be either a party deck or a boat deck, depending.

-Chris

 

[Seevee]

Just to note, the Mainship 350/390 and the Mainship 400 are (at least) two different boats. Dunno if performance is similar or not, though... In any case, they're likely not ever going to be "fast" if you're looking for 18+ knots or so cruise...

There are boats called "sedan bridge" models, at least by a few companies... and they tend to have long, extended-aft bridges. Interior much like a sportfish or convertible; i.e., not usually an aft-cabin model. You might have a look at some of those... Formula, maybe Cruisers (not sure), some of the Sea Ray bridge boat, some of the Meridian models have that kind of extended bridge, etc. Don't think they're up to carrying a heavy dinghy/outboard, but could maybe be worth a look for kayaks.

Then too there are cockpit motor yachts... usually an aft cabin model with a cockpit stuck on the aft end. The top of the aft cabin can be either a party deck or a boat deck, depending.

-Chris

Chris,
Yes there are options, but the sedan bridges, MYs and the aft cabin models just don't have much aft cockpit. And none of the flybridges have and "aft flybridge" that want set up for people an furniture. And some don't have a flybridge at all, like Formula (had one, great boat, but not a good loop boat).

I don't need a lot of people space like most are set up for (salon and fly bridge) I want space for toys and the aft cockpit. Looks like sacrifices.....