Like Tree0Likes

Diesels for boats

Reply
Old 04-16-2008, 12:48 PM
  #101
Registered
 
Join Date: Aug 2006
Posts: 68
Default

Well, I hope that knowing how many gears works best is based on more than a gut feeling derived from experience. I certainly don't have that experience, nor do I have a firm grasp on the more formal engineering determinants deciding the optimal number of gears. I was kinda hoping for at least a hint of insight into the latter.
Njawb is offline  
Reply With Quote
Old 04-16-2008, 07:22 PM
  #102
Registered
 
Join Date: Jun 2004
Location: Freehold, NJ
My Boats: 32 SeaCraft
Posts: 1,381
Default

Shifter,

I remember your more gears/speeds transmissions in class 1, they were awesome. I assume that those boats were almost driven like a bull dozer with a hydostatic trans - what I mean is the engine rpm's stayed very constant and you changed gears instead of throttleing???

I don't rememeber very well, but weren't those boats more like today's racing (inshore, closed course) as opposed to the old school open ocean racing???

Again, I don't remember but would those multi-speeds work well if you had to throttle alot?

Joe Gere
HabanaJoe is offline  
Reply With Quote
Old 04-19-2008, 05:28 AM
  #103
Registered User
 
Join Date: Feb 2008
Location: West edge of the Pacific
My Boats: Beat up ole Sleekcraft
Posts: 610
V-disease

I swear every time you guys see a V type engine it's lust at first sight. The Audi V12-TDI has all those flashy euro numbers lets cut them down to real world numbers 500 PS @ 1000 Nm. Or in real world numbers 493 hp SAE (actually less because they cheat on the dyno set up)@ 738 ftlbs. Now if you take a look at their own published performance curves you will see the torque curve peters out at 3000 rpm. http://www.worldcarfans.com/2060911....2-tdi-revealed
A Cummins QSB 5.9 will out perform the Audi engine hands down. Lets take a redneck physics lesson. You have a two 53' trailers loaded with 75 lb bags of pinto beans. You have one being unloaded by a dozen 10 yr olds and the other one by a half dozen 20 yr olds. The 20 year olds can lump one bag per man per trip into the trailer. The 10 year olds can lump one bag per two children per trip into the trailer. Two kids on one bag cannot move as well as one adult on one bag. It's parasitic loss. Under 15 liters of displacement straight 6 engines out perform V engines any day of the week.
29Firefox is offline  
Reply With Quote
Old 04-19-2008, 07:18 AM
  #104
Registered
 
Join Date: Jun 2004
Location: Freehold, NJ
My Boats: 32 SeaCraft
Posts: 1,381
Default

firefox - well said, I'll have to remember the pinto beans when I go off on a tangent again - thank you!!!
HabanaJoe is offline  
Reply With Quote
Old 04-19-2008, 08:28 AM
  #105
Registered
 
Join Date: Aug 2006
Posts: 68
Default

Now compare the overall dimensions and weight of the QSB 5.9 and the Audi V12.

And to make it even more fair, let's turn the prop at the same speed for both engines -- let's say 3200 RPM at the top end (the same as a gas engine that produces top speed at 4800 crankshaft RPM using a 1.5 gear ratio drive.) That means the QSB will need a 3400/3200 = 1.0625 gear, while the Audi will need a 4000/3200 = 1.25 gear. As a result, the QSB will produce 1000 lb-ft peak propshaft torque at 2070 propshaft RPM, while the Audi will produce 922 lb-ft peak propshaft torque, and will hold that same torque from 1440 to 2400 propshaft RPM. For comparison, the QSB will produce a little under 700 lb-ft propshaft torque at 1440 propshaft RPM, and a little under 925 lb-ft propshaft torque at 2400 propshaft RPM. Significantly lighter weight, same peak horsepower, and more area under the propshaft torque curve means that the same boat with only changes in engine and gear ratio will have a better top end speed and quite a bit better low-end acceleration using the Audi V12 diesel vice the Cummins QSB.

Last edited by Njawb; 04-19-2008 at 10:56 AM.
Njawb is offline  
Reply With Quote
Old 04-19-2008, 11:15 AM
  #106
Registered
 
Join Date: Aug 2006
Posts: 68
Default

Quote:
Originally Posted by HabanaJoe View Post
firefox - well said, I'll have to remember the pinto beans when I go off on a tangent again - thank you!!!
It's a silly analogy that oversimplifies to the point of inaccuracy. Using pinto bean logic, the best engine would have a single cylinder to minimize "parasitic loss".
Njawb is offline  
Reply With Quote
Old 04-19-2008, 11:56 AM
  #107
Registered
 
Join Date: Jun 2004
Location: Freehold, NJ
My Boats: 32 SeaCraft
Posts: 1,381
Default

I meant it was funny using beans.

I think his point was a just a simple every time on here when the word diesel with Duramax or someother "V" engine comes up people tend perk up about it. The only reason people get excited about a "V" diesel is they can relate it to their American V-8, push rod gas engines that they think are so powerful when in fact the hp/cui is pretty low.

I ran those Seatek's, we could kick every Amereican gas boat out there with their V-8 engines. Take away the muti-engine advantage and use Shifter's multispeeds and the V-8's still couldn't catch them!!!

Yet, since they were in-line 6's American's in general can't grasp that they could be as powerful as the mighty V-8 engine.

That has nothing to do which is better or worse it's perception and here on OSO over 25 years later from when diesels started racing and winning the mear mention of a "V" engine get's people excited and dreaming "what if?".
HabanaJoe is offline  
Reply With Quote
Old 04-19-2008, 12:14 PM
  #108
Registered
 
Join Date: Aug 2006
Posts: 68
Default

Quote:
The only reason people get excited about a "V" diesel is they can relate it to their American V-8, push rod gas engines that they think are so powerful when in fact the hp/cui is pretty low.
There goes that presumption again, Joe.

I get more excited about the idea of a marinized Audi V12 TDI than the existing QSB 5.9 not because it is as familiar as a gas, pushrod V8 (which, in truth, it is not at all), but because such an engine would have the same or better performance than the QSB while coming in a package size between a SBC and a BBC, and weighing about the same as a BBC. Yes, the bigger, heavier Cummins may well be more durable, but the Audi in SUV trim is by no means a high-strung, high-maintenance, race-only engine. On the contrary, physically smaller and lighter, automobile-based diesels (many of them V engines) will be a better fit to many performance marine applications, even if I6's continue to dominate the trucking industry.

Last edited by Njawb; 04-19-2008 at 12:17 PM.
Njawb is offline  
Reply With Quote
Old 04-19-2008, 03:18 PM
  #109
Registered
 
Join Date: Jun 2004
Location: Freehold, NJ
My Boats: 32 SeaCraft
Posts: 1,381
Default

It's not presumption and don't want to argue about a point so silly, time will tell who is right?

What do you do for a living, are you in the marine or auto industry?

If you research what 35 plus year old males in the US like you will see I'm right about assuming it's a V-8 thing. Look at the recent car auctions over the last 3 years - American Muscle cars have exploded, is it cyclic - YES. But, the fact the people with money buying those are the 35 and ups and they remember good old American V-8 power either from their own or father's cars - that is what drives the market.

It's just a point that today not 2 years or 5 years from now that the I-6 diesel engine is superior to any V out there in production form.

I for one don't disagree that V's may rule someday, but people in general don't think I's can beat a V's based on life's lesson of growing up in the USA not the engineering facts.

That's not good nor bad and you do a little research and you'll see it to be true for yourself.
HabanaJoe is offline  
Reply With Quote
Old 04-19-2008, 03:24 PM
  #110
Registered
 
Join Date: Aug 2006
Posts: 68
Default

Joe, when you declare that you know the only reason why people get excited about diesel V engines, that is presumptuous. I am a person, and I do not get excited about diesel V engines out of some sense of nostalgia for American pushrod V8s. That many people may engage in such confused, nostalgic reasoning doesn't change the fact that it is presumptuous to declare that everyone who likes the idea of marine diesel V engines is so engaged.
Njawb is offline  
Reply With Quote
Reply

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
FROGMAN524
MTI (Marine Technologies)
31
06-02-2009 11:53 PM
45sonic
General Q & A
18
12-30-2008 08:06 AM
Fenderjack
General Boating Discussion
2
03-11-2008 09:37 AM
Quicksilver
Trucks, Trailers and Transportation
12
02-02-2008 12:21 AM
Jassman
General Boating Discussion
27
01-27-2007 10:01 PM



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 04:57 PM.


Copyright 2011 OffShoreOnly. All rights reserved.