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Michael T
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Michael T
Member Posts: 7,227 ✭✭✭✭✭
Comments
PC BYC, Holland, MI
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PC BYC, Holland, MI
Definitely an interesting thread for me as I boat with two other identicals (390s) that have diesels. Both seem to be able to stay up with my cruising speed of ~32mph. It is interesting when rafted up with them . They sit about 2 inches lower cause of their weight.
& MT, sorry, you need a better excuse for those big blocks. I'm siding with RY on the chesapeake
(PS, I love the sound of my big blocks)
Dream 'Inn III -- 2008 400 Express
& now the part I can't agree with RY on. If you're going trawler speed, might as well get a trawler. I might need to start bragging about how much gas I use.
Just guessing, but my last 35 hours probably "averaged" 25mph and used 4 tanks (300 gal ea). Now THAT is what I'm talking about!! (heck, each trip to VA beach is 2 tanks round trip)
Dream 'Inn III -- 2008 400 Express
Based on what Al shared, seems like a nice gadget would be a two speed gear box like some tunnel boats have.. no? Get her on plane and slap into higher ratio, badaboom- gassers lost in soot.. :-)
By the way.. I despise soot.. its SO not needed.. my rig qualifies for superclean diesel rating, though that costs me some ponies..
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The multi speed transmission solves a lot of the need for higher rpm issues, but $$$. You'd probably never get your money back Vs using gassers. I will say the new 'clean' diesels are nice, I don't know if they are in marine use yet? I had a dockmate with a couple of big diesels in his boat and the exhaust smell was horrible to be around stinking up the boat and the docks. My F350 7.3l is a stinky one in the winter especially, I'm hoping it will be better since I chipped it.
PC BYC, Holland, MI
ahhh....looks like winter talk is finally happening for us northerners. %-(
I'm withya MT on fuel burn. The more I burn, the better the summer!
8-XDream 'Inn III -- 2008 400 Express
Insofar as a boat, if its over 30 feet, I'm gonna use a diesel.. plain and simple.. several reasons, but speed isn't one.. for running around acting a fool, which I do, the simplicity and performance of a gasser can't be denied..
So far, idiocy hasn't reached the big diesels yet.. idiocy I speak of is the regulations on auto used diesels.. much of the allure is gone with new diesels, namely, longivity.. they are enduring what gassers went through in the seventies with smog pumps and catalytic converters that didn't flow.. gassers figured that out. Diesels will, too, but right now I wouldn't buy a new one, period. DPFs cut into service life like a steam roller, adding fuel to crankcases, as but one serious problem.. another is egr techniques and yet another is urea injection.. this too will pass, but its a real problem right now..
The fuel itself sucks.. gone for hwy use is #1 and bio.. the ulsd is 15ppm sulfer as opposed to 500ppm, and in the process of stripping the sulfur, lubricity takes a huge shot.. the lack of sulfur also allows bacteria and algae to grow.. with modern high pressure injection systems, you're damned either way.. the lack of lubricity kills fuel systems, but the wetter fuels will clog them.. a fuel system from top to bottom is about a $15k job to replace, all by itself.. plus, fuel devoid of sulfur spoils quick like.. a new engine can't burn old fuel for the algae and bacteria.. an older (pre '06-08) can burn about any kind of fuel confidently .. a pre '00 can burn about anything, including home concoctions of cooking oil or various JP's..
MT, I'd get the gassers, too.. for the time being..
Isnt normal cruising speed & GPH at those respective speeds be a much better indicator of the pros/cons of gas vs. diesel?
imagine your 18v hand dill, yan.. you have a twisty thingamahjab at the business end of that thing.. you squeeze the trigger and the speed of the twist is affected.. it doesn't turn so fast on 1,2, or 3- but has hella torque (it's harder to stop).... turn it to ten, it spins fast like, but you can stop it easy with your hand alone..
it's doing more work at 10, but at the cost of torque.. so it is with engines..
gassers have a specific range.. they start depleting torque to produce HP.. so do diesels, but diesels reach maximum RPM long before they deplete torque.. on land, either can be geared/leveraged to do what you want to do with it, with emphasis on top end or bottom end...
a gasser has a huge advantage over diesels in planning hulls.. at idle, it spins fast enough to move the boat, but slow enough to manage handling.. when you goose it, it races to the max torque range of the engine- which is what it needs to push on plane- after it planes, it can start using excess torque for translating into horsepower because resistance has been dramatically reduced.. that translation is a natural function of gassers.. it has to be leveraged/geared in diesels.
I bet you don't have much problem getting on plane, huh? it's because your tq ramps up quickly, and the range it exists lasts longer.. it can't translate it into HP before it's spinning at it's max rev... the max rev is your limit, and the wall the engine runs into.. it can be leveraged/geared to be of more use, if speed is your use, but at the cost of handling down low. handling down low is hella more important.
boats with huge gassers have ample tq to push on plane, and a lot more RPM left to translate into HP. that hp comes at the cost of tq, but since it's on plane already, it can do that.. since it's on plane and it has almost too much engine, the thing can back off and cruise under much less relative load- which equates to economy... unloaded engines, as best measured with a vacuum gauge, can easily maintain stioch ratios and sip fuel.. loaded engines will be rich, dumping more fuel than they can provide air to burn properly... hence, those big blocks save fuel over small blocks doing the same thing.
a big sport fisher, say, 55', has hella weight to push before the hull planes.. and it needs constant torque that only a diesel or an electric can provide.. the gasser would be under too much load, blow through it's tq range too quickly, and not have enough tq to produce/maintain the HP for high speeds.. so, it uses a huge diesel.. in that application, the diesel will burn tenths of what a gasser capable of pushing it will, and the gasser will wear out quick like.
you could use a really high pitch prop- but chances are your drive won't survive it.. it would be a blaze of glory, though, that would most likely appear when you're trying to dock it- as in, slow speeds... in open water it would be fun until the heat destroyed your drive..
I like diesels, a lot.. but they just aren't suited for smaller boats with planing hulls.. yours, in my opinion, is just shy in size of where a diesel would shine..
True, but you cant really compare diesel vs. gas with MPG, as thats a losing proposition for the gas engine pretty much every time.
I was saying to look at a steady "normal" cruising speed (say 30mph) and then compare the two powerplants to see which which is the better option for the short & long term.
And again, I'm a newbie, but how in the world can it be ok to run WOT for extended time period? Al was that your boat, or someone elses?
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A good diesel can hold wot so long as you've got fuel, with delivery of fuel the limit.. a gasser can induct more air, a silly high rpms, than it can fuel. It becomes unstable.. gas, properly octaned for stability, is predictable in detonation.. start starving fuel and it is not stable at all, and can ignite before spark is applied and while piston is headed north.. oops.. something has to give if the pre ignition is early enough.. diesels compress to ignite, without spark.. that limits the revs.. that limit is determined by available fuel, instead of air.. they can hold max rev as long as you want without hurting them, given, its a healthy engine..
Wow, I don't get on the website for one evening & I have so much great info to catch up on! Al, I can agree that my 400 loves to cruise around 35mph. If I slow to 30, the fuel burn isn't as good and she just wants to go a bit faster. At that speed, the best I can see for fuel burn is 0.9mi/gal. On a typical day cruising I see 0.75 - 0.8 mpg. When we first got the boat, I wasn't quite expecting the 40+gph. 8-| Not saying you get used to it, but we don't let it slow us down. I really have yet to put her at max throttle/speed. Al, do you know what type of numbers I should expect, with rpm & speed?
Such a great topic to chat about! BTW, I do think there will be a time soon where diesels will be the better choice for express cruisers both for speed and efficiency.
Dream 'Inn III -- 2008 400 Express
that expression (HP) is tossed out there to quantify something that is not near as easy to quantify..
your diesel could be fueled to provide 350hp, I'm thinking, fairly easily by machining the regulator on the pump right before the mechanical injectors.. but it wouldn't do you any good at all if speed is what you're after, because it will produce the additional power in the same RPM range... w/o spinning the shaft faster, OR w/o pushing a higher pitched prop set, you're not going to go any faster... pretty much period..
you will be able to get on and hold plane with more weight on board, though..
it's a reach to compare, but think of it like this: on LAND, if you know two of three of these factors, you can figure the other with certainty- forward speed, overall gear ratio, RPM.. the only thing that can toss the math off is if something is amiss, such as shorter tires due to inflation, slipping transmission, inaccurate RPMs.. it's somewhat the same on water, but you gotta know slippage.. you're not going to get the RPM's the gassers can.
your diesel could likely be fueled to provide more TQ per stroke, and leveraged/geared to provide more HP by swapping the screw or by using a different gear case ratio.. either adjustment could and would hurt either extreme- too high a ratio due to prop or gear case and you move too quickly at idle to manage the boat in tight situations, unless you are a master at feathering gears... but, you'd improve top end greatly.. adjusting for bottom end and making it handle reasonably, you're cutting into top end speed..
edited to add: the newer engines that can nail 6kRPM have fuel systems that can easily feed them, and are computer controlled fuel and ignition.. at WOT, you aren't going to sniff stoich 14.7:1 air to fuel ratio, but much richer instead, or likely in the area of 13:1.. the additional fuel makes the detonation REQUIRE spark to ignite, instead of firing under compression.. to further make it safe, the PCM will retard timing to accommodate as well, where as it is advancing it at cruise speeds..
4400RPM cruise, you'll likely sniff a nearing perfect stoich ratio of 14.5:1~14.9:1, and you'll see ignition advanced to likely nearing 40~45* from TDC... it can do this because it's managing the vitals easily.. whe you push to the extreme, you'll see a dramatic drop off in timing to protect the engine, and you'll see the fuel start to be added like crazy to make certain and feed it- so no leaning out.. you'll also see a drop in HP/TQ per RPM.. that is why there is a perfect range for both power and economy.
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all that will happen, is you will increase how that energy is spent, since it isn't being transferred/translated into work.. and that is heat.. heat is the #1 killer of drives, be it a gear box on a boat or a gear box on a transmission.. I can speak of the transmission with certainty as to the impact heat has, but only strongly suspect a boats gear box is in the same peril when over-powered.
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If you were in the market to buy your last boat- one that you didn't or couldn't replace for whatever reason, and you had a choice between properly powered diesel or properly powered gasser- which one would you choose and why?
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The fueling is cut at 90ish% duty cycle.. the act of compression is what fires the engine, not spark. Because of that, the engine will fire and rev slower than gas.. there is a point where max revolutions is found, and it isn't that high an rpm as you would think. A two stroke diesel finds ridiculous power because it gets a powerstroke twice as often, but even it can't rev any faster.. that engine speed is far below the balance point and the engines ability to cool itself, which is good, and the reason you can run all day at wot.
If I had your rig or one sized similar, I'd want diesel.. maybe not a yan, because theyre difficult to mod.. but a diesel none the less.. I don't care about top speed.. I want something that sips fuel, will last forever, and can open up and go at wot extended periods if needed.. tortoise and the hare, and all that.. just my opinion, though.
You've got a diesel and all the benefits of it.. others have gassers and all their advantages.. making them compare is kinda fruitless, because they aren't the same.. they talk speed, I talk load management.. they talk ethanol and combustible fumes, I talk fill it and forget it... They talk different angles than you should.. being drawn into an argument where economy and loads are dismissed for speed and hp, and being a diesel owner is about as silly as a land war in Asia.
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you could likely turn 24p at rated wot rpm.. I bet you wouldn't start to drop off until north of 25p..
the drop off is because you ARE changing the overall ratio with the screw- just like using bigger diameter tires raises overall gear ratio on a truck... you're translating torque into horsepower whether you realize it or not when you do that.
like I have been trying to express (terribly, I admit), the expression of performance is HP, but it is terribly misleading.. it is expressed at the crankshaft or at the prop shaft.. it isn't actually what you're putting to the water until you figure in pitch- which is the aqua equivalent to axle ratio and/or tire diameter...
HP is a derivative of Torque. Without Torque, HP can't be created in a twirling engine. It is a measurement based off of use of torque.. in olden times, it was a 12 foot diameter wheel that an average horse could turn 2.5 times a minute with a line attached to the circumference of the wheel.. if you could do it 5 times a minute? you were exerting 2 horse power... if you could pull and twirl that wheel 25 times a minute? you were pulling at 10 HP..
engines spin.. torque is a measurement of how difficult something is to stop spinning.. if the spin is one revolution per minute, it's spinning slowly- but if it takes you gripping it with 100 pounds on pressure per square inch to stop it, guess what it's torque rating is?
engines translate the spinning into work.. one definition is how quickly the engine will **** 50lbs of the ground, and was designed to easily equate the spin into work.. back to your 18vdc hand drill- it has settings on the snout from 1-20 or so.. the one spins slowly but is difficult to stop.. it's purpose is turning screws that don't wanna turn easily.. it uses gears to REDUCE the input shafts spin, and make it harder to stop.. the high setting, 20, say, does the opposite- it AMPLIFIES the spinning speed to make short WORK of easily turned screws.. it translates all it's torque into HP.. the setting somewhere around halfway is 1:1 ratio of input shaft to output shaft.. the burden is completely on the electric motor.
your engine produces a LOT of torque, but more importantly it is difficult to deplete the torque.. it doesn't translate the torque into HP like a gasser does at higher RPM's.. the torque doesn't deplete to the point of 'not useful' because it doesn't translate.. you can turn that screw, which pushes that boat, and not worry too much about if you're going to get on plane or not.. the HP produced is enough to get you on plane, and the TQ produced is enough to fight through whatever resistance it encounters... if you increase pitch on the props, you are in affect increasing HP at the cost of TQ.. it saps more torque to keep turning, but the overall work being performed is greater. just like your drill..
gassers lie like a **** in church.. the have a rated HP, but at what cost to TQ? An engine (I'm looking at YOU Volvo Penta) can be rated to produce 300HP, and does- ON A STAND UNDER NO LOAD... But drop it in a boat? you'll never sniff 300hp because TQ is depleted long before (and therefore 'work' is impossible) the RPM range is achieved.. you'll see engines HP rated at 5800RPM, and a maximum WOT of 4800RPM.. in a real world situation, you'd have to use gears/leverage (low prop pitch) to get the dang thing anywhere near the range needed to sniff 300hp...
focus more on max torque at the engine speed (RPM) you're at when it's pushing up on the surface.