Dream Engines

Wow!!

 

Thanks Lew Morris. I guess I should have told you Iam from a planet called EARTH! If you could loan me your shrinking ray,you might be on to something. Untill then,I still have my engine problem here on earth. Thanks for the thought,I did have some fun with my wife when I showed her our future enignes!

 

John,

The only Grand Alaskan I've seen had two CATs for propulsion. If you're looking for reliability, you can't go wrong with the Detroit Diesel. Just keep the bolts tight and the oil wiped up and she'll run for years with proper maintenance. They're easier to work on and you can also find parts just about anywhere in the world. For a 50', however, I would go with at least a 6-92. To be sure though, you should have the horsepower requirements worked out for your boat and find the one that fits in that range.

 

Thanks Terry. I intend to have a custom boat built. I would like two engins but only one varable prop.This is not as common as I had thought. The Detroit Diesel engines mentioned were 6-71 at 238 HP and 4-71 at 160 HP. Since I will be doing a lot of slow crusing,the 4-71 was recomended because with only one engine running it was thought that running any diesel at higher RPMs was better than a larger engine at slower RPMs.The mentioning of the Alaskan was just to give a general type and size. Iam open to any similar boats that have my desired two engine one variable prop design. Any info on props,gearing,engines,or electronics to run the engines ,one, or both at the same time would be of great help.It should be said that I will use this boat on the west coast,then in europe,on both the rivers and the mediteranean.

 

John;

No, it's not common, twin engines driving a single CP prop is almost unknown in terms of typical motoryachts. Why do you want to do this? As it is so uncommon, you will be dealing with custom or certainly rare bits, which is not too comforting. I have seen some WWII surplus combiner gears, but without the CP feature, which you could add. I believe these gears were built by Falk, see falk gear

Cincinnati Gear builds big combiner gears for multiple power units, CODAG etc. I believe they are custom built.


Best of luck, Tad

 

Tad; My thinking is as follows.1 A single seems to be the least pron to trouble. 2 A single controlable prop seems to be the best choice for high, and low speed traval;also best choice for keeping engines running at top efficiency.3 Two engines seem safer than one.Two engines also seem more fuel efficient;especally if you just want to go slow on a river in europe.Then is the argument over diesel engine longevity;run the engines to high an RPM and you have reduced engine life. Run the engines at low RPM and you have a carbon proplem. For these reasons two engines give me the widest choices.I have picked the Detroit Diesel 6-71 because it is a slow turing, two cycle engine,which should give years of good service under the widest of boating conditions.I have seen a Nordhavn with two engines,but the second engine was just a side engine. Just to get home in an emergency.Lastly is the fuel efficiency discussion;my thinking is that to go slow,one engine.In open water,both engines.With the single controlable prop I should always have the right power for fuel efficiency and engine longevity.Hope this answers your question.

 

John;

Tad is right, combining gears are not common in pleasure boats. They are commonly used in large Military craft, but you would need to have a custom gear box built or cobble together something based on a truck differential. Either way it would be tough getting it serviced in remote ports. You would be better served to use a more conventional approach. Blazing new trails requires either extremely deep pocket or much iteration or both.

As for the 6-71 engine choice, are you aware that the two cycle Detroit Diesels are out of production? Although the 6-71 has a longevity advantage over the Cat 3208, the 3208 has fewer parts so the cost of an overhaul is lower, making the long term maintenance cost a push. In addition, unless you plan to circumnavigate the Earth a few times and assuming you provide proper maintenance, most diesel engines will out live you and me, so why get wrapped up looking for the ultimate in longevity?

Personally, I would not consider the 6-71 for my boat. The positive overpressure in two-cycle crack-case causes them to leak like crazy and I don’t intend to spend my vacation/retirement wiping up after my engine or smelling diesel and oil all the time. In addition the DD’s tend to be noisier than most, too tall for my engine compartment and since the cost of an overhaul is higher, the cost of “Ohshits” and “Iforgots” is higher.

Here is a good article on Diesel engines http://www.yachtsurvey.com/comparing_diesel_types.htm although, since it was written in 1999, it is a little dated. A lot has changed in diesel engines since 1999. For one thing, the larger engines have gone to computer control to meet emissions requirements. The good news is fuel economy has improved (which means better range) and, since the computers can predict preventative maintenance requirements and protect the engine from many catastrophic failures (i.e. shut it down before if blows up), the cost of repaid and maintenance is lower.

For my boat, I am planning of a single drive shaft with a large main engine and a small auxiliary engine. I’ll have variable displacement hydraulic pump/motors on the main and auxiliary, which will allow the auxiliary to drive the main shaft with the main in neutral.

Regards;
Mike Schooley

 

Thanks Portager:I had read the artical that was written on diesel engines on the web site you sugested,that was one of the resons I had speced the 6-71's in the first place.David Pascoe's articles,Comparing Diesel Types,More on Performance Diesels,and Diesel Maintenance Or Lack Therof paints a pretty scary picture of what can go wrong when the wrong engine is used. His liking of the Dettroit Diesel's had many good points. I noted that he wasnt very happy with the Cat 3208 because of its short stroke.Now that I know that the 6-71 is no longer made,Iam back to square one.I had thought that I had at least my engines picked out! So the qestion is what engine in the 230HP, if I use two,or 450HP, if I use one, is the closest to the 6-71 in service,long stroke meaing better fuel economy,a large auxiliary drive housing to drive other components,replaceable liners with a block that is not a throwaway,and a high duty rating.Iam also interested in your large main engine and small auxiliary engine set up. Any additional info you care to share would be helpful.

 

You might take a look at John Deere, the 6125AFM PowerTech 12.5L might meet your requirements. They have replaceable wet liners and gear driven auxiliary drive rated at 80 hp intermittent.

My plan will use a >160 HP main engine and a 25 HP auxiliary. Both engines will have a variable displacement pump/motor which will provide up to 22.5 HP of hydraulic power. The auxiliary will be able to provide 20 HP to the main shaft, which will provide a get home capability provided the main shaft and prop are functional. If the main shaft is non-functional, either the main or auxiliary can still provide a get home capability by providing power for an electric outboard or by driving a water pump and water jets (normally used as bow and stern thrusters).

Regards;
Mike Schooley

 

Thanks Mike. I have so many questions it's hard to know where to start! Let's begin with your side engine - is it run directly off the engine with gears or is it hydraulically driven. Can the side engine be run for long periods of time or just short durations. How large can the side engine - in terms of HP before it becomes unfeasable. The reason I ask is because if I want to just putt on the rivers of Europe - can I just use the side engine or will continued use wear it out prematurely. Next - if I use just one engine in a 53' Selene how big - in terms of HP, do you think I need. Would you have any way to calculate for this boat at 10 knots what I can expect to use in fuel per hour. I know these are a lot of questions and I know you may not have all the answers but thought I'd ask since I'm a rookie to most people on this web site. Thanks again.

 

The auxiliary, or side engine, provides power to the main shaft hydraulically.

The hydraulic drive is designed to provide continuous operation. The only down side is the hydraulic pump/motor combination is only about 85%, where as gear drive (transmissions) are 95% to 98% efficient. This means that the hydraulic drive will waste more power and fuel, so you wouldn’t want to use it for the main drive. In addition, since most of the lost energy will end up as waste heat in the hydraulic fluid, you need to provide an oil cooler to remove the waste heat.

It is really more of a cost than feasibility issue. In the 25 to 50 HP range the variable displacement pump/motors are available off-the-shelf and since they are used in construction and commercial equipment they are very durable and parts are readily available. At higher power levels the pump/motors are custom designed to your application, which makes them much higher cost, more troublesome (unless you test the heck out of them $$$) and replacement parts are a special order $$$.

On page 10 of the “PROPELLER HANDBOOK” by Dave Geer he provides an equation for full displacement and semi displacement boats as follows:

SL ratio = 10.665 / (LB/SHP)^1/3

Where:
SL ratio = speed – length ratio = Speed / WL^1/2 and
Speed is in knots,
WL = waterline length in feet
LB = Displacement in pounds
SHP = Shaft horsepower at propeller
Assumes an average propeller efficiency of 55%

Solving for SHP yields:

SHP = LB/(10.665 / (Speed / WL^1/2))^3

For the Selene fully loaded weight of 88,600 lbs and a speed of 10 knots

SL ratio = 10/ (53.25)^1/2 = 1.37

SHP = 88,600 / (10.665 / 1.37)^3 = 187.8 HP

For the maximum speed of 12.5

SL ratio = 1.71 note at SL above 1.34 the results of this equation are unreliable (i.e. your results may vary, …)

SHP = 367 HP note this is the continuous rated power.

Portsmouth Marine lists the intermittent power rating for the Selene 53’ as 430bhp @ 2,600rpm on their web site http://www.portsmouthmarine.com/portsmouthmarine/content_detail.asp?CategoryID=3&NewsID=63

If you intend to cruise the canals of Europe, the Selene 53’ Bridge Clearance (Mast Down 15’-2”) will restrict you to larger canals.

Regards;
Mike Schooley

 

John, I have thought along the same lines as you using the Falk combiner Tad was talking about. Most of those Falk units were used in LCM-8's those were the larger landing craft 110' I think. Bear in mind they are for an in-line install so a pair of 6-71's and the gear would work out to like 11-12 feet long.
if your planning a 85' tug with big draft and a big wheel maybe the way to go
if you dont mind the parts finding headache for the Falk unit! You said you were looking at an Alaskan style boat....I think those are mostly a semi-displacement style hull maybe only a little over 4 foot draft on the larger models. most of them are fitted with twin cats like 3406 or larger depending on your pockets.
Portager is right about 6-71's being leakers! My first day working on a commercial tender with twin 6-71's was spent in the bilges with a bale of sorbents cleaning up after them. I will say this tho....those engines had set for 7 years of Alaska winters and the same diesel she went dry with. new batts and a little ether and they lit right up. And you can fix a cracked leaking water jacket with Marine-tex while she's still running underway. they just go and go. I have allways thought of the newer high speed diesels as disposable units! A 3208 is one of those when she gives up haul it out of there and get another. I'm partial to the Luggers with wet liners and simple you can rebuild them in-hull if need be.
thats my 2 cents good luck
8Knots

 

The Luggers are also a good engine since they are based on the John Deere block and nearly all parts are interchangeable (and built by John Deere).

See http://www.northern-lights.com/company_info.shtml , "In 1975, development of the first Lugger propulsion engines began, based on a John Deere block.".

"Alaska Diesel Electric's position is that the Lugger is much more adaptable for stabilizers, additional alternators and other needs than a plain John Deere. That, of course, is part of the reason Luggers cost more than Deeres." Georgs Kolesnikovs. http://lists.samurai.com/pipermail/trawler-world-list/1998-December/007180.html

Regards;
Mike Schooley

 

Thanks to all who have added to this discussion, it has been very informative. Let's recap. I'm using the Selene 53 as an example. The Selene 53 calls for a 430 HP single engine - I'm assuming that the Lugger's engine recommended by 8Knots would use the same HP - would you have a model number in mind? How about recommended "duty rating" for this engine? Recommended brand and model of 40-50HP side engine? I think that I would use a Lugger just to keep things the same and keep things simple but there may be a better choice in this small HP diesel engine. Recommended brand and model hydraulic pump/motor to go with the side engine? Recommended oil cooler - brand and model to cool hydraulic fluid? Is it air or water cooled? If water cooled - is it sea water or a closed loop system. Lastly, Mike Schooley mentioned the fact that if I plan to cruise the rivers and canals of Europe, the Selene 53' bridge clearance with the mast down was 15'2". Does anyone have any idea on how I can get more information on bridge heights and lock sizes in Europe so that I know which rivers I can cruise and which I won't be able to navigate. Thanks again. While I was lying in bed last night thinking about my new boat, I remembered a few more questions so here goes. The Selene 53 has a prop 4-blade, 36-inch diameter, gear reduction 2.88:1. What brand and model of controlable pitch prop would work best?Why does the Selene 53 have such a large engine? I have seen boats about the same size use as small as a 160HP engine.Top speed with the 430HP is rated at 12 kts. Any thoughts? Thanks Again!

 

Skipping to the canal question.

The canals of Europe are categorized I through VI as described at http://www.canals.com/size.htm

I converted the beam, depth and headroom to feet in the attached excel.xls file. At 15’2” your OK for category V and VI, but not for I thru IV.

For the canals in the UK in English units go to http://www.canals.com/canaldata.htm for metric go to http://www.canals.com/canaldatmet.htm .

Regards;
Mike Schooley