Building a 21' cruiser with inboard diesel and auto

Sorry but I disagree ! The prop is held at it's rpm to achieve 30 knotts by the hp of an engine and it's torque. which is attatched by the shaft of what ever drive you use. Boat engines rely on hp not much torque gearing multiplies forces of torque or decreases the amount of torque to the driven item (prop) in a higher gear 0.8 : 1 to hold the props rpm the engine will need more torque to hold it before bogging down, diesels work purely on compression and have massive torque for their capacity compared to a petrol engine for eg a BMW 3.0 has 500 nm of torque a 3.0 petrol engine has about 275 nm of torque. Torque is real power to move resistance Hp is an engines ability to breathe and spin it's masses by throwing it self efficiently, Hp is far over rated and stated , it's torque that pushes mass hp is weaker and efficient only without load. A prop has little load a hull has great resistance, which requires torque to move it againt the water, so the torque of the diesel will hold against the waters opposing force.
If most drives are 2:1 this double the value of torque of the engine being transfered to the prop, a 150 hp outboard is basicly a motorcyle engine with buggerall torque about 80 nm, therfore 160 nm of torque is being used
A diesel with 350nm reduced to 0.8 :1 drive is reduced by 0.8 which is 280nm of torque I still have nearly double the power of a 150 outboard. which is the compensation for less hp, which to re itterate is useless in a boat because of it's constant resistance>>>>>>....!!!!!!!
To put it simply all I have to do is spin the prop at the right rpm for 30 knotts and it CAN BE DONE with TORQUE!!!!!
The point of my statement earlier in the post, is that the 'marinised world is old world thought and has little developement since it's coception. I know I work in robotics where every day I re invent the wheel 100 different ways and I'm always working with every force immaginable not by vectors and trojectories but with real life time and resistances, because all the calculations in world take far longer to input than a simple test (practical)
Gearing and resistance is very very basic. it's simply X or division by the ratio.
Now to educate you on why a marine engien has loads of hp and is driven through a reduction box.
Outboards need to be small and light, so a small engine can only produce so much torque and not enough to push a prop at 1:1 so it's run through a reduction box to increase it's torque value to the prop the hp gives it a higher rpm which equivilates to less load allowing the motor to use hp to spin more freely with less resistance. To get the same result with 1:1 drive you need twice the torque of the little outboard and half the hp (Diesel does that exactly!)
The reason not to use stanard marinised drive line is to get the same results at 10% of the price. The bonus of a gear box of at least 3 forward gears is to provide excellent prop speed control at lower speeds eg while docking.
The other benefit is to achieve fuel ecconomy at reduced rpm. I'm not saying I know exactly how the drive will behave but the fundamental equasion is correct. As far as complexity, compaired to standing a motor cylcle engine on it's end, stuffing all the plumbing into close fitting cover is complex, having more moving parts in modules is far less complex and far more reliable seeing Trust me I've built bikes with quad cams 4 carbs and gearboxes that are supurbly made but lack robustness, they have a life cycle of about 80,000 kms, A lexus V8 is the same i design but for sheer volume of internal parts they are robust, and good for 500,000 km's My lexus V8 in 900kg car sits on 8500 rpm for hours under the most strenuous conditions and speeds of 150 mph, my kawaski 900 breaks stuff every 5000kms at 11,000 rpm. The point is motorcar manufacturers design for reliability because the market demands it, noone rides their bike day in day out so they are built witha lesser duty cycle.
As with marine engines IT'S A BUSINESS AND DON'T BELIEVE WHAT THE SALES MAN TELLS YOU. because he does believe what the top guy says it's culturaly ingrained into the system.

 

Sorry I've had 2 weeks of politics and trying to work out technical areas on a new system, and I'm tired of explaining METHOD, and how to get something right the first time.
Tom, I think that you're advice is without doubt "Valuble"
I agree about the surface drive options, because props are going to be my easiest variable to change in the drive, I was thinking of having the trimmable shaft drive able to nest up into the hull in a small cavity, with the prop able to surface just outside the stern. (under a fixed duck board) just to allow beaching etc as far as rudder, that would be mounted onto the duckboard, which could be unlocked to raise the rudder, or spring loaded and curved to lift automaticly on hitting something, Maybe cylinders ????
Actually seeing that all my cylinders are slow reacting I might look at the feasabilty of using the aircon compressor to pressurise soluble oil /water in conjunction with air cylinders 100psi is heaps then I can use standard airline and fittings, all over the place.
Hydrualics is too expensive and overdone for the forces required and electrical is too fragile in a corosive enviroment.
And at the end of the day I want the best and most versatile boat that is extremely reliable, cheap to service, and affordable.
My car with the lexus V8 cost $30,000 in parts and is as well engineered as any sports car in it's class and a hell of alot better looking and without doubt AWESOME.
And all made from wrecks, Mercedes, lexus, toyota, datsun, Nissan, and alot of fabricated stuff. Unfortunatley the Auto market is constrained to cultural ingraining of ideas, I'm hoping boats are a bit more liberal, seeing that there seems to be plenty of small manufacturers making a living.
The only market constraint seems to be hull design, wright or wrong it's what most boat buyers seem to judge on. so the rest is just something that won't get serviced or will be by someone else.
How do I tell a buyer that they should take the boat to Toyota for engine service, and Festo for anything else ???LOL
I think self service manual is mandetory, when I'll market to the budget conscious man, (or woman) with a passion for boating with only 50-60K not 110 or so.
And the other concideration is weight and keeping the tow vehicle affordable also. Thats where most of the aluminium honeycomb will take place. I'd like to keep it down to 1000kg fully dressed plus trailer.
Foam core hull and multi bulkheads in honeycomb as well as floor and cabin and furn. the transmission only need to be small, so front wheel drive is the key for the donor car, or an adapter plate for an other tranny of the same motor brand.
Once I get all this set in my mind I can start work on functional ideas such as driving by lcd screen and infra red for night driving, with all the forgiveness of space in the open water there's no reason a plc couldn't drive all the available technology to set course on true auto pilot. MAYBE.
I mean you can teach a plc to recognise wave height and conditions to alter pitch and speed and direction. But there goes the budget !
I'm ordering the plans after easter, so I don't think about it while I'm on holiday with the kids in Pambula, I m taking them out on a charter to see how they go in choppy seas, and then take the innevitable plunge into wee hours of the morning creating my dreams.
Simon.

 

Lucas - just ask yourself this simple question. If it were simply a matter - regardless of speed, size, weight etc - of changing the gears and prop, then why aren't all boats powered by a little Honda 4-stroke and simply geared to the required speed?
Answer - because it wouldn't work.....
I suggest you buy a book called "The Proellor Handbook" by Dave Gerr. You will learn much

 

Sorry mate learn some physics! I already explained it plain laymans terms.

 

There is only force and resistance in moving an object, force is measured in Newton Meters, opposing forces are resistance to the force.
Torque moves against resistance.
Like I explained it an outboard needs to be small and lite to hang off the back of a boat therefore a small engine is used because of it's weight they are motor bike engines that have no torque to increase the torque value a reduction box is used 2:1 means doubling the torque effect.
to get exactly the same result with a 1:1 drive you need an engine with twice the torque the end result is exactly the same , the prop spins with the same force, the hull travels at the same speed, BUT your engine spins half as fast. like I said Horse power is using the engines innertia to mimick torque, simply by throwing mass, the result and physics is EXACTLY the same except at half the rpm.
Force,Mass,Resistance requires one value of force to move it, how you achieve it is called ENGINEERING I am a Mechanical engineer. It's what I do for a living and if I'm wrong you canhave everything I own, because it's what I get paid for, so every job out there must not be working and I'm just a conman selling boat motors. LOL

 

Building a 21` cruiser with inboard diesel

www.stepdrive.co.uk is one of the many attempts to introduce multi gears to boats.Racing cars have many gear options for the days racing.Boats can make use of many gear optioins.especially with a trimmable shaft drive.See page three of Paul Kamens N.A. article Surface Piercing Propellers.www.well.com/user/pk/SPAprofboat.

 

If you re-read my posts you will see that I've not once said that there's no value in variable-speed drives of one sort or another. I simply stated that you can't take a boat that normally requires 150hp to do 30 knots, stick a 100hp in it and still expect it to do 30 knots by changing down gears. When you get in this whiz-bang car you've built (love to see a pic...) and roar off in 1st gear, you don't do 100mph as you would if you were in 5th....
There WILL be some overlap - where the smaller motor, normally unable to get the boat onto the plane - can change down a 'gear'. Once on plane you can change up and attain a higher speed that you would otherwise have done with a non-variable system. Hence my recommendation that you look at the torque-shift props that are readily available.
But - since you're a mechanical engineer, you must already know everything about boats - cause that's what they train you about at uni - so as a lowly student of yacht design, I'll just butt out and look fwd to seeing your 30 footer come whizzing by, powered by a lawn-mower engine with a 300 speed gearbox....

 

I've always heard auto transmissions aren't built to handle thrust as generated by a propeller. Austaralia? Sam

 

Will, My intension if not clear is to source a motor with enough torque (turbo diesel). Please understand that horse power is not a usable force in equating power, it is some times and all too often used to state the overall power ability of a motor that is general terminology used to give the layman some idea of how much power an engine has.
I am assuming the quoted requirement of 180 hp for the 22 monsoon is an old engine designed around the time of the boat (about 20 years ago) in those days a 180 hp engine would have had about 275 Nm of torque, I need a modern engine with at least 375 Nm of torque, A modern turbo diesel with quoted Hp of 100 hp will have about 350 + Nm of torque.
So forgive me if I missed the step of quoting Hp in the beginning but I was relaying the info that is available for the design of boat hull I will use.
So for arguments sake or not to (preferably) Lets stick to torque figures not hp.

In regards to Sams comment, that could be a possibilty, I have already thought about, what it comes down to is what the shift was designed to react to, and what I can do to 'ideal' shift which will be a matter of ensuring shift is controlled off a TPS (throttle position sensor) and rpm point. The actual set up will take place in trial.
As far as (Thrust) spinning a prop will have less resistance to wheels on a road under full load, so that info is incorrect, what may be the case is how the trans behaves with less load and changing, it's hard to know without having run it. But there is a will and there is a way. It's just part of the challenge.
The other factor may be that the lesser but constant load may cause a problem and offer a shorter duty cycle compared to raod use, but given they are designed to handle load 50% of the time it might wear prematurley or need more regular servicing to avoid friction due to broken down oil etc.
And to both of you, keep in mind that this is a design process, and there will be problems , and that is the challenge to design with utmost thought and arrive close as possible to the concept upon completion.
And seeing that I know most people use hp as a way of describing an engines power, I used it to communicate, I hope now you understand that Hp is irrelevant for this or design process.

Regards Simon (Lucas is my son)

 

Ok got my daughter off the computer.
I really wish to elaborate on the current discussion and principals so that anyone who has the question of whether auto running gear is usable in a boat that there is enough info to inform them correctly.

Another worthy note is hp is a relevant term for quoting a cars power, because the only resistance is air,tyre friction and the weight of the car.
Horse power can be used to a fuller advantage compared to a boat because the cars mass has innertia with minimal resistance to it's force.
So hp is relevant in a cars abilities.
However a boat is under heavy resistance until it gets on the plane and that dramaticly decreases the resistance, the engines torque gets it out of the water with and the hp power keeps it there.
Remembering max torque will take effect at lower rpm and the highest hp will come in at the end of the rev range.
A diesel engine has massive amounts of torque at low revs and hardly any hp at the top end.
Which is why the only time you will hear Torque being used in an advertisement for cars is when they are selling a diesel. because if the quoted that this massive 2 ton car had only 200 hp they wouldn't sell any to say it has 500Nm of torque is POWER to sell.
The two engines, petrol and deisel behave completely differently, and diesel in far more ecconomical, which is an important factor in my design.
Acceleration is not important to me, seeing that i intend to set to 2500rpm and coast up to 30 knotts through the auto.
Will, I think we got off on the wrong foot, I agree with you that I do need more power, but I assume that everybody understands what I naturaly know about power etc.
My appologies for missunderstanding your comments.
I will dig out my old PC and copy the build photos of the car, it's a 1962 ferrari gto replica, and I've had many enthusiasts of them look at it and told me it's the best they've seen, even questions of "I know about the replicas, but this is a real one right ?"
It weighs 950 kg and has 275 hp (relevant at 8500rpm) for aceleration it has 375 Nm of torque (lexus v8)
Now if I turbo charged it I might end up with 900hp (yes that's what they put out turbo charged) I will have about 500Nm of torque so the top end power would be nothing short of deadly. the accleration to the top end of the revs would be not that much greater as it currently accelerates to 100kmh in 4 seconds.
The 900hp would simply make accelerating in higher gears like 3 to 5 very bloody frightening.
So if everybody is satisfied with my statement of power please lets move on.
I'm getting the plans after easter and want to look at the hull design to see if I can improve on it's effeciancy to plane, be stable and be good all round and predictable and safe.
The info I have is it's a double curvature hull with bulbous keel, and 18 deg deadrise from stern.
I have looked at reverse hard chine info and strake info, but have not been able to determine their scientific use on their own. What effect do they have as a unit of whatever ?
I understand that all parts make a whole, but in order to understand any hull changes I need to understand the details of principals of the modifications effect.
Simon.

 

Awesome link Tom, I need to digest it another time, but it gets me one step closer to the drive design. Thanx mate.

There's enough info there to really get the mind negotiating with the inner child and perhaps a feminine side LOL.
I wander if a model drive in 1/8 scale in something 1/8 density of salt water might be the way to go ?
It would be easy to make at least comparrisons and even fuel ecconomy etc.
I'm currently eyeing off my sons radio control speed boat.
Nup! dad use to do that to me, and I still get mad about it.
Ok looks like I'll be buying a radio control boat tomorrow and some glass for a big fish tank, YEAH !!!!! :idea:

 

What I'm referring to is the fore and aft thrust. The propeller pushes the boat forward and has to transfer that thrust through the transmission. I don't believe auto transmissions are designed to withstand a lot of fore and aft thrust. Marine transmissions are. I'm not familiar with front wheel drive auto engines and transmissions but with a rear differential any fore and aft thrust is eliminated by the splines on the driveshaft. It would seem in a boat there would have to be a thrust bearing in the system able to handle all the HP or torque the engine was capable of developing. It would have to handle the thrust in both forward and reverse. Sam

 

Like Sam said, there does need to be a thrust bearing to transfer the foreward/reverse thrusts to the hull without it riding on the small thrust bearing(s) already in the transmission. Those are intended only to keep the internal parts in place, and to absorb a little friction from the splines on the driveshaft yoke. The thrust bearing does not have to be integrated into the transmision, however, so it would be reasonably straight-forward to put one in the driveline after the transmission.

 

I have grappled with that part of the design briefly, just thinking out load. One of the main reasons to work out a way of displacing the thrust energy (force) to a wider area, but with minimal rotating mass, it to look at using a cars hub and assembly as the main thrust restriction as well as the possible trim for the surface drive , maybe even steering.
There are some very over engineered bearing setups on some hubs especialy on some earlier heavier japanese cars, one in mind is the datsun 260z, the other factor is cost, a car component is produced in much higher quantities than marine components, therefore a whole hub and bearing assembly will be around $200, the duty cylce will be less than intended, but the parts are designed to be ecconomicly (labour) replaced.
Theres nothing to stop me increasing the duty cycle by having a thrust bearing on the engine side as well, but that can be added in later.
So at this point my surface drive would have a prop, then shaft in a housing which attatches to the hub assembly, which is the trim. Then the Cv joint then a smaller thrust/seal, then transom, then another small thrust against drive shaft (opposite to first bearing) with seal. The actual drive shaft from the transmission would float on spline and universal joint inside a torque tube with basic externaly greasable bearings, supported by a mustache bar and bushed to the hulls support frames.
Although it may seem complex to work out and fit, most of the components could be donated from 1 or 2 cars, with all bearigs replaced.
It's actually better to use (used) housings etc because the stresses in the castings etc are already released from their previous lives.
The biggest and yet to be disvovered cost will be the prop.
Depending on what it might be worth, seeing that the process involved in making one would be bloody expensive as well as the cost of the material, will probably determine the rest of the driveline design.
I would prefer to go out and buy a standard mass produced prop, but with the price of fuel these days it's all a matter of balance.

 

One other note, I looked at the Arneston designed surface drive last night, and to do away with stays (side load stability) he uses a pattented pivot housing over the universal joint, the thrust bearings are on the out shaft nested in the shaft housing. The only weakness is the pivoting housing that would not stand up to any side load, not that there would be much, but in conjunction with the small thrust bearings, the life expectancy of the bearings and eventual slop that would occur from general wear, would be reasonably short. Which is another design factor I'm trying to steer away from in that marine drive componentry seems to have shorter duty cycles than one would expect for the price.