Single engine? No way. Joe is right: You need the horsepower to make top-end speed. Efficient cruise speed is a whole 'nother issue.

Damn physics :angry-smiley-038:

i meant 2 engines

You need the horsepower to run in the 50-60's, too -- but the horsepower you need is only about 1/3 that you need to run 100. If your diesel swap is more than 1/3 the horsepower of the original gas engine, then you can re-gear to run efficiently in the 50-60'2. You can't re-gear to run 100 on 1/3 the horsepower.

Lost 8 to 10 mph on top, I think I can get a couple more mph but right now it's running the biggest propellors/lowest gearing they make. cruise at 56 with one person or six, makes no difference.

Oh. Two engines, proper gearing, right props, surface drives, good hull, and you've got a real shot at 110 or better -- especially if the boat could already do 110+ with a pair of 550 hp gas engines, single speed tranny.

stainless,

Your question is will one or a pair of 2,700 rpm diesels making 550 hp push a 36' cat at 110 mph?

If you say a pair, I have to tell you damm close to it.

Real world example, the boat that Stefano was killed in was a 40'er. When she was Kappa Shoes in an earlier life with twin 600 hp Seateks she could run a little over 100 mph.

A 38' V bottom with worn out 600's could run just over 90 mph all day long.

Kappa was no where as effiecent or light as a Skater or MTI, I believe whole hearted with electronic controlled real 550 hp diesels and proper gearing 100 mph plus is easy, 110mph I just don't know?

haxbyspeed,

I bet if you can gauge the amount of hp those engines are making you'll find your not near the max. You hit that wall and need more prop speed to go faster, Once you get taller gears coming on plane will be hard and you prop down and still get any faster - that is where two speeds come in to play or some form of slipper trans.

I like the direction marine diesel technology is heading but I gotta think it's going to be a LONG time before dealer support, affordable parts, parts capable of handling 1800#s of torque, and the high initial expense will make them any more attractive then the multitude of gas options...

300-400 hp diesels are comprable to 600-800 hp gas engines,its all in the torque

dmaxx,

Not to fight but show me the math or a real application that proves that, don't just make a statement - prove me wrong!!!

No, it's not all in the torque.

Fight fight fight! :evilb:

There's no fight. There's physics. Steady state speed (e.g., top speed) is determined by the amount of power transfered to the water. Horsepower measures power and is the relevant figure, not torque. If you are interested in acceleration, not steady state speed, then torque matters; but no amount of torque will allow you to reach a speed faster than the available power will allow.

No fight, I have respect and regard for everyone on here. I also have opinions and am proved wrong from time to time.

In order for diesels to progress in this market I think it is important that we all have an understanding of the dynamics and I want someone to prove me wrong.

With that said I'll fire the first real world example of gas vs diesel.

Everyone knows what a Bertram 31 is. You take the 31 Bertram with twin 350 hp, 454 cui gas engines and top end is almost 10 mph faster than with 300 hp Cats 3116's or Cummins B's. You can go onto Yachtworld and look at used boat speeds, you can go anyone of 50 forums about that subject and see the same thing.

I will give you that the cruise mph with the diesels is far better than the gas engine but the debate is does HP = HP?

Look at a repower that has 210 B's in it, it's close to 20mph slower than the gas boat with 350's!!!!

There is definitely some tricky math involved, and a myriad of factors that scew the results. I've swapped 240hp inline fours that crushed the 330hp 7.4l's that came out. A lot of the increase could be due to the more efficient (at cruise) duo props. NJAWB is right, unless there is a way to apply the same amount of prop shaft force at the same RPM, then ya aint gonna go as fast. And "theoretically", if you could somehow harness a big torque monster with overdive transmissions to acheive this, would it be any more efficient?

You guys are way over my head so I'm just askin..:D

here's your math

http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

and this is a great article:

http://www.vettenet.org/torquehp.html

it put into simple terms why Hp out does torque.

Cheers! :D:D

How come my old gas engine builder was all about torque ? he said torque is the key thing in boating not hp ? maybe he was hittin the crack pipe ?

No crack pipe. He just realized that there is more to boating than just top-end speed in steady state conditions, and that the typical single gear ratio and prop power curve don't work well with a high-revving, high-horsepower, low-torque engine.

Damn looks like they got a lot further than I knew about. Joe what do you think of their piston supercharging?:p

I understand the Cummins turned up to 600hp that will last appr. 500 hour between rebuilds will be coupled to a NXT drive with a real tranny..Possibly by the end of the year.

Sounds interesting!:party-smiley-048:

I remember you telling us you were selling a package that would be at Miami. You also argued with another individual saying Cummins did not have a 600. You stated your package would not be the Cummins. You need to get your stories straight.

that would be impossible for him to get his stories straight, he is on his 11 screen name. This guy (Jim Darr) could have a great conversation entertaining himself with all of his personalities back and forth. There is a saying, it's bad when you talk to yourself...but when you answer yourself...watch out....loose cannon.:argue:

http://cgi.ebay.com/ebaymotors/ws/eB....cWAT.m240.lVI

excaliber with twin 500 diesel merlins could be fun....maybe I should buy it and put it's motors and gears in the Harley and sell off the hull

High Perforamnce Boating with Diesel Engines
 

I promised to post this a week of two ago, but things got busy for me. This is my take on diesel vs gasoline. Comments are welcome and encouraged.

Horsepower moves the boat. More horsepower can move a given boat faster. Gasoline or diesel, the prop and boat don’t care. The engine's job is to convert stored energy (fuel) to horsepower and the propeller's job is to convert the engine's horsepower to thrust horsepower. Different engines and different propellers do this with different efficiencies. Diesel engines run on fuel that contains more energy per pound than gasoline as well as converting more of the fuel's energy to useful horsepower.

If one were to take a gasoline powered boat and simply swap in a diesel engine that made the same amount of horsepower, the result would be unacceptable. The diesel engine will have a lower speed limit (rpm) and thus turn the prop slower, and have a much higher peak torque (which tends to break parts). In order for performance to be acceptable, other changes to the propulsion system are necessary.

With equal peak power, the diesel could push the boat to the same top speed, if the power could be transferred to the water with the same efficiency. This is difficult to actually accomplish in the real world. To make the swap to diesel successfully, I see four alternatives. To illustrate the points, an example boat with the following characteristics is used:

Gasoline engine: 500 hp @ 5500 rpm, peak torque 500 ft-lbs
Max speed: 74 mph
Propeller pitch: 26"
Sterndrive reduction ratio: 1.5:1

New Configuration:
Diesel engine: 500 hp @ 3500 rpm, peak torque 950 ft-lbs
Sterndrive ratio: ??
Propeller pitch: ??

Alternative #1 (Change propeller pitch):
The propeller needs to deliver all available power to the water to reach 74mph. Changing the engine to a diesel doesn't change those requirements*. Since the diesel engine will have less rpm range than the gasoline engine, if we just swapped the 500 hp gasoline engine for a 500 hp diesel engine and left everything else the same we'd couldn't turn the prop fast enough to reach the previous top speed. Since, at planning speed, the power that the prop transfers to the water is reduced exponentially with rpm (x^2.7) the 500 hp diesel would actually be making far less than its rated output, even at rated speed. This could be overcome by changing the pitch of the prop.

The engine speed was reduced by 36% when we changed to diesel (5500-3500=2000; 2000/5500=.363). A 36% increase in pitch would "theoretically" correct this [ignoring the impact of slip, rake, cup, etc]. So, we replace the 26" prop with a 35" prop. This may not be practical on it's own due to the other variables involved in propeller dynamics that would make a 35" pitch prop difficult to live with (idle speed, planning ability, etc). There are other changes to the propeller could be made to allow the prop to absorb all of the power made available by the engine (diameter, cup, progressive pitch), but the reality here is that this solution is not a very good one on its own.

Alternative #2 (Change drive gear ratio):

Changing the drive ratio could allow you to maintain prop speed when changing engines. In this example, the gasoline engine turns the prop 3667 rpm at rated speed (5500/1.5= 3667). The new diesel engine will only turn it 2333 rpm(3500/1.5=2333). To get the prop to turn the required 3666 rpm, the drive ratio would need to change to .95 : 1 (3500/3667=.95). This would result in no loss of top speed or propeller efficiency, but may not be possible with available drive ratios. Another challenge here is that the power curve of the engine becomes a critical factor. This gear change puts a very high demand on the engine at much lower RPM than the original gasoline engine. If the engine can't deliver this, the boat performance will suffer (difficult to get on plane, difficult to stay on plane, etc).

Alternative #3 (Multi-speed transmission):

Not unlike the 2nd alternative, a multi-speed transmission could help solve the problem of not enough engine speed and too much torque available. The transmission would allow you to trade torque for shaft speed. Multi-speed could be as few as 2 or many as practical. Two is probably adequate for most applications. Heavier boats might benefit from more. The work here is balancing the gear ratios to make it work. The ratios would be set based on the desired prop speed.

Prop speed target: 3667 rpm
Max engine rpm: 3500

Drive reduction ratio 1.5:1
Low gear ratio: 1:1 (max prop speed =2444 rpm)
High gear ratio: .64:1 (max prop speed =3667 rpm)

Drive reduction ratio 1.15:1
Low gear ratio: 1.2:1 (max prop speed = 2444 rpm)
High gear ratio: .82:1 (max prop speed =3667 rpm)

This option is likely the most expensive to implement, but perhaps with some benefits not realizable with the other options, especially with heavy boats or those that require an unusually high amount of power to get on plane.

Alternative #4 (Overdrive gearbox):

Ideally, a performance diesel engine for a boat would turn the same rpm and make the same power (or more) as its gasoline counterpart. With today's engine technology, that's not realistic or cost effective. However, with a clever overdrive gearbox design, you could fake it. The overdrive gearbox could consist of coaxial input and output shafts with an overdrive ratio between them. The output shaft would be connected to the transmission or drive just like the gasoline application For this example, the input to output ratio would need to be 1:1.57 (5500/3500=1.57), more commonly written .64:1 (1/1.57). This overdrive gear ratio would reduce the torque seen by the driveline by the same ratio. From the drive's perspective, it would appear that the engine made a peak torque of only 605 ft-lbs (950/1.57=573). Maximum power output would be mostly unaffected (small % loss is overdrive gearbox efficiency). This solution results in the best overall solution to powering a sterndrive with a diesel while maintaining performance characteristics expected from gasoline engines. Low speed maneuverability might be compromised due to a higher prop speed at idle.

In practice, this is far from a trivial task and requires an extremely robust and, ideally, nearly maintenance free gearbox. Executing this properly would improve the chances of success in a diesel repower project. In theory, this could be easier and cheaper than a multi-speed transmission and still give satisfactory results.

Conclusion

There is no perfect solution for every application. The various factors (prop selection, drive ratios, boat weight, top speed, cruising speed, acceleration, handling, etc) must be weighed and a path chosen to minimize any negative impacts. Attempts at using diesel engines in performance boats have had varying degrees of success. As more people try today, perhaps the availability of modern components will improve the success rate.

Nope. Look at your own math in Alternative #2: 2333 is still just 36% less than 3667, not 54%.

You're right, I'll edit the original. I think the point holds true, that changing the prop alone isn't a great idea.

Yup, that part is true. It is also true that changing to a more efficient prop can be a good idea, especially when using a multi-speed transmission. Unless your goal is only fuel efficiency, you probably don't want to go completely to the big, low-slip route, but you probably can afford (depending a lot on gearing) to go somewhat more in that direction than with a gasoline engine.

Essentially, each choice is a compromise in one way or another. A big low slip prop would be good for long distance cruising, but hurt responsiveness.

I think most boat builders know what prop works for a given boat. You could power with diesel, gear (or regear) appropriately, and keep basically the same driving characteristics, while picking up some economy and durability.

It won't be exactly the same, hopefully better at most operating points.

There are of course other differences in the way diesel engines are controlled. Not having a throttle changes things. Traditionally, marine diesels run a variable speed governor where the "throttle" controls the engine speed setpoint. The governor adjusts fuel to maintain that engine speed as much as possible.

Modern full-authority diesels don't have to be governed this way, but they can be. They can also be governed based on a torque demand from the operator. From the operators perspective, this would more closely resemble a throttled gasoline engine. In a performance application, maybe this is preferred.

I don't know how the Cummins QSB/QSC, Cat C7 or Yanmar 6LY3 are governed. Maybe firefox or Joe know...In fact, I don't think the Yanmar is fully electronic at all.

If you read my little Cigarette write-up (5-6 pages) that I posted on here some where? (that was dated almost 20 yrs ago) - you will see all your conclusions were validated way back when!

Things haven't changed since then except the advent of muti-speed trans and better control of the diesel through electronics.

Again your conclusions were proven by me almost 20 years ago about overdrives and what a drivelines sees (I know it's just math) and that the boat can go fast.

#4 - is the best method, with some idle problems. The compenstating factor for that is when you run the little props on the Bravo's and you put them in gear the boat doesn't usally move much until you give it a few more rpm's. The diesel can idle lower than the gas and even with OD the prop speed is still pretty slow.

The only part I have to correct you on is that those overdrive boxes don't exist or are hard to make - I have patents on such a box dating back to 1991! We built and tested the boxes on generator sets. Your way to gear and type of gears for such a box is wrong and won't give you what you need, again we have thousands of hours on ours.

The problem, the market just wasn't ready for it. Looking at it today to be honest diesel is $1 plus a gallon more than gas, there is no reason to have diesel in the US from a cost/payback standpoint. I can give many reasons as you all can for it but the dollars outweight the difference usally for the normal boating public.

How do I find what I scanned and put on here and put it back on here again (I'm not were the docs are)???

If anymore would like to re-develope the old boxes, I'm willing to make this into a project and partner up on it? (thought I would just throw that out there!)

Joe Gere

I didn't find the post you referred to, but it doesn't matter, I know this stuff is nothing new.

I didn't mean to imply that the overdrive boxes never existed, but it's not like I can just go out and buy one off the shelf today. I concede that I haven't thought much about the actual gear arrangement. I'm sure there are many ways of gearing such a device. Having the input and output shafts inline would be nice from a packaging standpoint but not absolutely necessary. I won't go so far as to say what I've suggested is outright wrong...yet.

Are you saying a gearbox couldn't be built to house inline i/o shafts with an overdrive ratio? How is this different than any transmission for built for vehicles. I just need one speed, overdrive. Maybe you're saying there's and easier or cheaper way?

I couldn't find your patent(s) on Google, can you give a reference number?

I found one old thread where you posted some scanned docs, but I don't think this is what you were referring to. http://www.offshoreonly.com/forums/s...98#post2355098

That's not the thread, I'll re-post the docs when I get home.

What we built was in-line and ratio's are infinite & nothing is cheap to build one-off's. In production with castings the $'s come down quickly.

Maybe not wrong - too strong of a choice of words, not as durable. In a generator set if the gear box doesn't run 10,000 hours it's a failure so we took a differnt approach to things.

Don't take this wrong, patent has long expired, I wouldn't go into great details on here about any of it without a non-disclosure. More importantly, to me, I would want to build them again or with somebody not just as a special project but with the purpose of bringing it to market.

I hope you can understand that, what I want is simple - a chance to go back remove and a gas engine from a boat, drop in a diesel and not have the extra expensive of new drives, re-doing transoms, etc, etc.

We set out to do that starting in 1985 and thru my own fault never got there. When we had the chance to realize that I foolishly took the path of racing instead thinking we will come back to this later. Things change, later never happens and we should have stayed focused on the pleasure boat market - wow - regrets!!!

Joe Gere

guys, I think its just a matter of time before we'll see new generations diesels;watch its around the corner.Todays technology can not be compared to the 80s or even 90s;things such as common rails etc etc...check out mercedes Benz the new 300E diesel is faster and more durable than the same 300 gas that they make;aluminum blocks and guess what they even achieved same rpms isnt that what we're all looking for?? to move those props.

One thing that hasn't changed is diesel engines still cost a lot more to build than gasoline engines of the same power. In fact, with the latest emission controls, the gap may be widening.

Michael

I agree...Ill be checking this one out closely...Nortech is now doing a 50-V with the larger 600hp cummins but in a twin application vs the trip 480 Yanmars. Although the motors are heavier as well as longer and wider they are looking for the top end to be close vs the weight diff. between a twin vs trip application. Sea trial in about a month..Looking forward to this as well. Unfortunately, these larger Cummins will not fit in my 43 engine bay without modification, thats why I have to wait for the 480hp Cummins turned up version. Hopefully the Merc Drive will complete the package.

Like I said "Easy Money"
 

If you buy those Merlins let me know. I 'm used to fast turn around overhauls on them:p

Something from the bigger toys
 

I've been toying with idea of controllable pitch props like the ones on the big stuff that I work on. Anybody have soem input?:p

Do I need to come down and wax your boat again so you can keep it a little longer?:grinser010:

I understand. It's a project you were/are clearly passionate about and it's too bad it never came to completion. It's amazing how timing can affect the success of a good idea. A lot of things have to happen just right to make it all come together.

I'll get in touch with you offline if I want to discuss the gearbox concept further. An NDA is no problem. I'd like to see the same thing you would, a drop in replacement that won't kill the outdrive. The first one to get that right will have an "in" for this market, Cummins, Yanmar, Duramax, whatever.

The gearbox may find a market on it's own, but it's probably better to come with the engine in most cases. There's always someone willing to piece stuff together, but that's the minority. Most guys don't want to deal with any of the logistics.

It is widening. It's the aftertreatment more than the engine itself...for now. DPFs, SCR, NOx traps, Urea injection, EGR, EGR cooling, etc. On the engine side, Common rail, compound turbos, electric assist turbos, variable valve timing, variable compression ratio, etc. It's ALL expensive, and riddled with compromise.

Most of that stuff doesn't help the burn more efficiently (BSFC), but cleaner. Most real progress is in the name of emissions. A small minority are left to figure out how to use it for a performance advantage. Audi is doing a great job of opening up people's minds with the R10...at least 550 hp, 5000 rpm, no smoke, fuel efficient, and durable. I'll take two...

.