heavy displacement repower dilemma

[Delfin]

Originally Posted by Salmoneyes

I am in the process of "rebuilding a new boat" for long term cruising and long passages. One of the many hurdles is choosing the best option for repower.

Originally this 40 footer steel Pilot House tipped the scales at 42,000 pounds (loaded) and had a 130hp Mercedes OM352 with 2:1 and 23 inch screw. She burned roughly 7gph.

Hull is rated to 85hp (12m and 27000 lbs dry weight)

Here are my concerns

1. WEIGHT. the whole boat is undergoing major refit and mods to get her weight down closer to 30000 lbs. The Mercedes and box runs 1500 pounds. All the running gear is heavy to handle that kind of power.

2. HEIGHT of motor. The Mercedes is 32 inch tall. A lower motor will allow lowering floor in pilot house, allowing to lower pilot house roof, which makes windows smaller all adding benefits to the overall project requirements.

3. FUEL CONSUMPTION. Being it is a motor sailer, it will motor often and lower consumption means less fuel, less weight etc. I heard an argument made that more power allows you to use a smaller percentage of the motors capacity therefore using less fuel. I think using 80 hp of a 200 hp engine will use the same fuel as a 80 hp motor..

4.SIMPLICITY. This is the one that is really causing loss of sleep. I can McGiver a naturally aspirated diesel together in an emergency. The new common rail turbos could solve all these other concerns, but at the cost of simplicity. If the motor quit, I could be in trouble.

I would love to hear what folks who cruise long term with a heavy boat think about engine choice. Fuel concerns, weight concern, available parts around the globe, ability to service and repair, etc. etc.

By way of comparison, Delfin displaces 135,000 # and is powered by a 270 hp CAT 3306. In normal cruising, we use around 65 hp, and when I am at hull speed around 110 hp. Any more than that and I am just pushing water. I believe someone suggested to you a 150 hp motor? That might work for my boat, but for one 15' shorter and 95,000 lbs lighter????

If you want simplicity, I believe you are going to have to find a used and rebuilt motor since anything new is going to be larded up with electronic controls. I wouldn't shy away from a rebuild as long as it was done to factory specs by a known and competent shop.

As noted by others, diesel power is a function of fuel consumption so you are quite right that my engine pulling 65 hp is going to use pretty much the same amount of fuel as an 85 hp rated engine using 65 hp, so your fuel consumption figure I find baffling. 7 gph should produce, even on a tier I or II engine, around 135 hp. That means WOT for your engine, which I doubt is how it has been run. In any case, for your waterline length, that amount of hp is doing nothing to increase the speed of the boat and would be going into just pushing her further and further into the water. A rule of thumb is that a displacement hull engine s/b sized for 1 hp per 500# of displacement to reach hull speed in most any conditions. If you skinnied your boat down to, say 35,000#, 70 hp should do, and you would likely cruise at half that demand making the motor very happy and burning 1/3 the fuel you say you are currently burning.

Regarding torque, no, displacement hulls don't need more torque when maneuvering. They need torque to match the gear on the boat and the size prop you are trying to spin. Too high a gear ratio for a given amount of torque at idle results in a fair amount of stress on the engine whenever the gear is engaged. Because my CAT has buckets of torque, my gear is 3:79 to 1, so the 44" wheel is only turning at 150 rpm at idle. Less torque and it would have to be a smaller prop that turned faster in order to put the same load on the engine.

All that aside, the attributes of an engine for a full displacement hull are IMO, these:

1. Heavier is better than lighter
2. Slower rated rpm is better than higher rated rpm
3. Simpler is better than complex

As I mentioned, if you are going keel cooled, the world is your oyster in terms of engine selection since an industrial motor cooled by a closed coolant loop through the keel cooler is exposed to sea water no more than a land based engine operating on the coast would be. You just have to match it to a gear that is right for the engine output.

[Salmoneyes]

My apologies for not responding to the last few replies,, a lot of good information that I need to look into...

I want to address the mystery of our fuel consumption. The information we have is from previous owners, plus input from some of the folks who lived in the marina and knew the boat well..

From them, we were told the boat had so much power that it took off like a "rocket". We could not confirm that ourselves, since the boat had so much wrong with it when we bought it.

From taking her apart, the shaft bearings were shot (sealed oil bath). The hull was covered in growth, and the hollows of the keel were full of seawater (roughly 30 cubic feet). The motor had no thermostat so it ran cold. None of that would allow for any kind of efficiency im sure.

I look at it like the perfect storm. Everything combined to create max inefficiency.
Our goal is to get it right.

I spoke with cummins about the new 2.8, and what my other options may be for our requirements and since I mentioned boat I was told only their Marine engines which are all the new compliant stuff. I was told they could not sell me anything else.

I got similar information from Beta. They required I prove that the old engine was destroyed which I found weird.

All that makes the decision to go keel cool that much easier. I know the arguments for and against, but we are trying to weigh all our options and make decisions based on everything working together as best as "possible" and thats why I am looking for input.

I prefer to learn from others mistakes (cheaper that way) and I trust someone who "has it" more than someone "selling it".

[Delfin]

Originally Posted by Salmoneyes

My apologies for not responding to the last few replies,, a lot of good information that I need to look into...

I want to address the mystery of our fuel consumption. The information we have is from previous owners, plus input from some of the folks who lived in the marina and knew the boat well..

From them, we were told the boat had so much power that it took off like a "rocket". We could not confirm that ourselves, since the boat had so much wrong with it when we bought it.

From taking her apart, the shaft bearings were shot (sealed oil bath). The hull was covered in growth, and the hollows of the keel were full of seawater (roughly 30 cubic feet). The motor had no thermostat so it ran cold. None of that would allow for any kind of efficiency im sure.

I look at it like the perfect storm. Everything combined to create max inefficiency.
Our goal is to get it right.

I spoke with cummins about the new 2.8, and what my other options may be for our requirements and since I mentioned boat I was told only their Marine engines which are all the new compliant stuff. I was told they could not sell me anything else.

I got similar information from Beta. They required I prove that the old engine was destroyed which I found weird.

All that makes the decision to go keel cool that much easier. I know the arguments for and against, but we are trying to weigh all our options and make decisions based on everything working together as best as "possible" and thats why I am looking for input.

I prefer to learn from others mistakes (cheaper that way) and I trust someone who "has it" more than someone "selling it".

You won't regret keel cooling. I would suggest you look at Walter keel coolers. They require almost no external cleaning like other designs.

[a64pilot]

Re torque.
Torque is inseparable from Horsepower, they are the same thing actually, just expressed differently.
A high torque engine is one that makes horsepower down low, nothing more.
Torque is force applied but no work has been done because nothing has moved.
Horsepower is torque applied and a weight lifted.
All torque charts will have horsepower and torque cross at 5252 RPM, which is of course the horsepower formula number.

Usually for a displacement vessel an engine that makes good power at lower RPM is more pleasant than one that has to turn higher RPM to do so, that sort of leads you to a larger, normally aspirated engine, but supercharged also works well down low.
I’ll normally cruise my high RPM Yanmar at 1800 to 2000 myself cause much higher and it sounds like a lawnmower is in the Salon and I don’t like that.

The inline 6 cyl mechanically injected non turbo Cummins would be a difficult motor to beat, although I like JD’s myself.

[Delfin]

Originally Posted by Salmoneyes

My apologies for not responding to the last few replies,, a lot of good information that I need to look into...

I want to address the mystery of our fuel consumption. The information we have is from previous owners, plus input from some of the folks who lived in the marina and knew the boat well..

From them, we were told the boat had so much power that it took off like a "rocket". We could not confirm that ourselves, since the boat had so much wrong with it when we bought it.

From taking her apart, the shaft bearings were shot (sealed oil bath). The hull was covered in growth, and the hollows of the keel were full of seawater (roughly 30 cubic feet). The motor had no thermostat so it ran cold. None of that would allow for any kind of efficiency im sure.

I look at it like the perfect storm. Everything combined to create max inefficiency.
Our goal is to get it right.

I spoke with cummins about the new 2.8, and what my other options may be for our requirements and since I mentioned boat I was told only their Marine engines which are all the new compliant stuff. I was told they could not sell me anything else.

I got similar information from Beta. They required I prove that the old engine was destroyed which I found weird.

All that makes the decision to go keel cool that much easier. I know the arguments for and against, but we are trying to weigh all our options and make decisions based on everything working together as best as "possible" and thats why I am looking for input.

I prefer to learn from others mistakes (cheaper that way) and I trust someone who "has it" more than someone "selling it".

The 2.8 would be about twice the motor you should need.....

[Salmoneyes]

Originally Posted by Delfin

The 2.8 would be about twice the motor you should need.....

That is true. I was unaware it existed. I will say, that its power to weight ratio is very impressive..

It is unfortunately the opposite end of the spectrum for what we need.

[PeterS]

Originally Posted by a64pilot

Re torque.
Torque is inseparable from Horsepower, they are the same thing actually, just expressed differently.
A high torque engine is one that makes horsepower down low, nothing more.
Torque is force applied but no work has been done because nothing has moved.
Horsepower is torque applied and a weight lifted.
All torque charts will have horsepower and torque cross at 5252 RPM, which is of course the horsepower formula number.

Usually for a displacement vessel an engine that makes good power at lower RPM is more pleasant than one that has to turn higher RPM to do so, that sort of leads you to a larger, normally aspirated engine, but supercharged also works well down low.
I’ll normally cruise my high RPM Yanmar at 1800 to 2000 myself cause much higher and it sounds like a lawnmower is in the Salon and I don’t like that.

The inline 6 cyl mechanically injected non turbo Cummins would be a difficult motor to beat, although I like JD’s myself.

My apologies, I have to jump in here to clarify a few technicalities.

“POWER or Torque is how much perpendicular Force is applied over a specified distance”.
(Definition of 1 HP = work performed over distance achieved over one minute)
This was established by James Watt in 1782 after studying the ability of a draw horse to lift a quantity of coal out of a coal mine over the course of one hour.

Derivation of the Power Equation.

HP = TORQUE x RPM/5252 conversely; Torque = HP x 5252/RPM

Why 5252? 5252 is a constant, read on!

By definition, POWER = FORCE x DISTANCE ÷ TIME (as explained at the beginning)
For example and I quote various text books, a constant tangential force of 100 pounds is applied to a 12" handle rotated at 2000 RPM, from this we know the force involved, so to calculate power we need the distance the handle travels per unit time, this is expressed as:
Power = 100 pounds x distance per minute
DISTANCE per revolution = 2 x Pi x radius
Which is = 2 x 3.1416 x 1 ft. = 6.283 ft.

How far does the crank move in one minute?
DISTANCE per min. = 6.283 ft. (per rev) x 2000 rev per min. = 12,566 feet per minute.

The power can now be fully defined as:
POWER = FORCE x DISTANCE ÷ TIME

Power = 100 lb x 12,566 ft. per minute = 1,256,600 ft-lb per minute

We are still talking Ft/Lbs or POWER as the work performed, what is this in HORSEPOWER?
One HORSEPOWER is defined as 33,000 foot-pounds of work per minute.
Therefore:
HP = POWER (ft-lb per min) ÷ 33,000.

It’s already calculated that the power being applied to the crank handle above is 1,256,600 ft-lb per minute.
Therefore
HP = (1,256,600 ÷ 33,000) = 38.1 HP.

We already know that:
TORQUE = FORCE x RADIUS,

Divide both sides of that equation by RADIUS, to get:
(a) FORCE = TORQUE ÷ RADIUS

If DISTANCE per revolution = RADIUS x 2 x Pi, then
(b) DISTANCE per minute = RADIUS x 2 x Pi x RPM

We already know:
(c) POWER = FORCE x DISTANCE per minute

Inserting the result for FORCE from equation (a) and distance per minute from equation (b) into equation (c), results in:
POWER = (TORQUE ÷ RADIUS) x (RPM x RADIUS x 2 x Pi)

Divide both sides by 33,000 to find HP

HP = (TORQUE ÷ RADIUS) x (RPM x RADIUS x 2 x Pi) ÷ 33,000

Cancelling Radius (reducing) on both sides of the equation, we get
HP = (TORQUE x RPM x 6.2832) ÷ 33,000

(So now we can prove the 5252 question from the reduction).

33,000 ÷ 6.2832 = 5252

Therefore
HP = TORQUE x RPM/5252

Note: 5252 is the Delta on the power curve where torque and HP cross.
5252 is a constant in the HP calculation for the following reason.
At any RPM below 5252, the value of torque is greater than the value of HP.
At any RPM above 5252 RPM, the value of torque is less than the value of HP.
.
From that one can see that a high torque engine does not make HP down low.

You will also see that the power or work done (torque) was established before HP was calculated and that HP had to be calculated from torque, or the actual work done, which is why HP is not a particularly valid number for powering purposes. I frequently calculate shafting diameter from a variety of power parameters during my day job, HP is not really considered an absolute necessity.
Try and beat that down and Pythagoras or Poseidon will be after you!!

[Simi 60]

Originally Posted by a64pilot

.

The inline 6 cyl mechanically injected non turbo Cummins would be a difficult motor to beat, although I like JD’s myself.

I do wish I had the T and the A missing from out NTA 855 Cummins.
As she rarely gets run above 1200rpm (100hp) I doubt the T ever comes into play.

[a64pilot]

What people call a high torque motor, like a farm tractor motor for example, is a motor that develops power usually at lower RPM.

They are mistaken of course, but that has become the vernacular.

[Salmoneyes]

I must say,, this has been a very educational post... I just went back to read my original post to see if we strayed too far from my questions..

Regarding the question of simplicity vs efficiency. We weighed all the information gathered, discussed with our NA and decided that SIMPLICITY was the best choice with more pros than cons for our project.

Weight (being the main issue) height and fuel consumption, now can be addressed with the understanding that we are focused on a naturally aspirated, direct injected and keel cooled diesel with a HP range of 75 to 100. The only reason to bump horse power above 100 would be if we can not or do not lower our LWL/D ratio.

Having a clear and factual understanding of HP and Torque, including their specific function relating to (heavy displacement motor sailers) is relevant to the conversation and helpful to making the best choice for our boat. The information provided by PeterS is easily confirmed with some quick searching, and helpful in establishing a base line for fact checking claims about the function and predictable performance of a given diesel choice.

Since there is an overwhelming amount of information available on line with differing view points, I was hoping to get feed back from folks regarding their engines and what they like and don't like, assuming we are not comparing apples to oranges.

[a64pilot]

If it were me, and if one would fit, I’d want an inline 6 cyl motor, I’d not want a turbo as one isn’t needed and I’d want a Cummins or JD.
Probably an older mechanically injected Cummins. Being that it is going to be Keel cooled, I’d suspect then that a motor from a Dodge pickup could be used, and if so then there are thousands of them available and parts are very available and for a reasonable price.

I’ve seen several Cummins from pickups fitted on Shrimp boats, for financial reasons, and that they will work hard all day long, these were turbo motors, but your not going to be dragging a net.

The reason I’d want an inline 6 is explained here, remember we are low RPM motors not high revving like the BMW and old Jag.
https://en.m.wikipedia.org/wiki/Engine_balance

[CandC42]

Originally Posted by Salmoneyes

Thank you. I too spoke with the Beta folks. Their recommendation was the Beta 85 -TM345. Power to weight is very good with this unit. After talking to a couple guys here, they told me about Kubota used for water pumps and generators that were 4 cylinder units, so after looking them up, I realized that the basic engine itself is fairly inexpensive. Beta adds all the marine gear which adds quite a bit of cost. I have not ruled anything in or out yet, but if I were to go Kubota, I think I would buy one, then marinize it with all my stuff. ( I strongly considering keel cooled anyway)..

I believe your plus one on simplicity then? over fuel efficiency from computer controlled common rail?

I highly recommend marinizing a Kubota I have done a V2203 50Hp & V2403 60Hp to date and the cost is 1/3 to ½, you can customize the mounts to minimize the install work needed on the boat.

[Salmoneyes]

Originally Posted by CandC42

I highly recommend marinizing a Kubota I have done a V2203 50Hp & V2403 60Hp to date and the cost is 1/3 to ½, you can customize the mounts to minimize the install work needed on the boat.

I sent our local Kubota Dealer a request for information last week, but thank you for reminding me,,, they were out for the Hollidays and were supposed to get back to me by now..

I am interested to get specs. I was unable to get anything from web searches, and someone mentioned, they do not advertise anything that does not meet current EPA standards.

[CandC42]

Originally Posted by Salmoneyes

I sent our local Kubota Dealer a request for information last week, but thank you for reminding me,,, they were out for the Hollidays and were supposed to get back to me by now..

I am interested to get specs. I was unable to get anything from web searches, and someone mentioned, they do not advertise anything that does not meet current EPA standards.

I was able to do much better price wise on the resale market (all Tier 4) in the mid-west farm country and found most all the needed parts on line. On the 60hp I did make up a custom bell house to transmission plate but still way cheaper. The guys at Hayes Man. were very helpful. I uses ASAP supplies in the UK for mounts and damper plate, heat exchanger. You will need to make a custom disk to mount the water pump but any machine shop can do it if you don’t have access to a lathe. If you need any more info I'll let you know what I can just let me know what part you are looking for.

John

[FlightPlan]

Originally Posted by Salmoneyes

I sent our local Kubota Dealer a request for information last week, but thank you for reminding me,,, they were out for the Hollidays and were supposed to get back to me by now..

I am interested to get specs. I was unable to get anything from web searches, and someone mentioned, they do not advertise anything that does not meet current EPA standards.

I am surprised Cummins did not suggest their Re-man program for the 6BTA5.9 210. I backed into this engine by process of elimination of Lugger, Deere, Yanmar etc. when I re-powered in 2014. I didn't even want the Turbo, but finally accepted it for a compromise because I didn't want a common rail motor. Because my boat is US documented, you could no longer get a naturally aspirated marine diesel. I missed that opportunity by 6 months. If however, I had a foreign documented boat, then the options were numerous. The manufacturers do still make the engines but not for sale in the US. Enormous fines accumulate on a daily basis and even jail time is a penalty if they sell to a US documented boat. I did discover that because I was re-powering that maybe I could get a waiver after jumping every hurdle the EPA could throw at me. Since I like to use my boat, and my Perkins 6.34 was unusable, I moved on to the Cummins.


This thread would have saved me a lot of late night research and phone calls. So many considerations to include in the selection process and most of them have been discussed here. Keep in mind that all the theories are good and valuable, but don't get hot on an engine that won't meet US EPA regulations. Dealers and many service techs are intimidated by EPA and begin to act as agents of the authority so you might wind up getting in trouble.


In my case, a 47' LWL, 45T displacement hull with a four blade prop and a 2:1 ratio Velvet Drive Transmission indicated I needed a 180 SAE HP engine to get the boat to theoretical hull speed of 9.2 Knots WOT. Since I also run a DC engine drive refrigeration compressor, and a house bank alternator, the 6BTA 210 worked out nicely. I don't really hear the turbo spool up. It's quiet, smooth and has the torque to keep the boat moving at speed in moderate 6 to 8 foot seas. I do have the calculation sheet and fuel map if your interested and I figure out how to copy it to this forum.


Bob