So how can u make the comparison here? Vastly different horsepower and boats? Impossible, and no example in anyway of 2 stroke efficiencyOriginally Posted by caravellerob
FNQ, that's great info. Would like to see a pic as well, and if it's true, wouldn't the same improvement work also on a 4 stroke therefore re establishing the superiority of 4 bangers over standard type 2 bangers?
i would seriously like to see your prop as its a very interesting point you are making.
Cheers!
"let not he boast who puts his armor on, as he who takes it off"
My apologies didn't realise you were the forum moderator, the OP was asking for a comparison between a 2 stroke outboard powered cat and a single diesel cat, I cant see where you have offered anything different or constructive to the original question, at least I offered a true comparison between 4 and 2 stroke and that a boat with a 2 stroke powered properly isn't as bad a some people make out.
Except my post where I noted the difference on my own boat between a 2 and 4 stroke?
In real terms no matter what the boat, the only real comparison is differnt motors on exactly the same boat.
In regard to four strokes tho, the evidence is overwhelming of their greater fuel efficiency compared to standard 2 strokes. Im hoping that FNQ can show us some further info re his prop as it will get me even greater savings on the 4 banger. Maybe. Hopefully.
"let not he boast who puts his armor on, as he who takes it off"
Hi blokes ...sorry no pics as they will only show a more or less normal but less exaggerated elephant eared prop with no paint on the high pressure side of the blades and low pressure side and hub still painted.
Easy job to do if a bit fiddly and time consuming, identify the leading impact line of each prop blade as it would rotate in water, leave the tip alone (little more on that later) where the tip impact edge becomes nearer to and then parallel then passes to trailing edge all relative to impact as the prop circulates. So roughly say the final 15-20-25%? of propeller diameter and surface area depending on how exaggerated elephant ear the prop design is
Draw a more or less leading edge following line from just below this tip region identified above all the way to the hub, I think on that last one I took initially very close to 13mm at it's deepest of this edge away. The alum if I assume alum prop leading edge will be very thick at this point so I use a grinder with a flapper disk to thin and scallop the face of the blade back to near original (takes a little artistry and patience.
On props that spin slow like on all our fishing rigs no matter the HP unmodified the leading edge thickness (in any reasonable sense) makes far less actual on the water discernible difference to the props efficiency than most think, still I get mine back to near original and sometimes a bit thinner/sharper...the rear side (low pressure side of the modified leading edge need not be touched at all until the final finished edge line is hand sand as the high pressure face of each is the one that gets thinned and shaped back.
Or one can just drill a series of holes decreasing in size along the edge/piece that other wise would be cut away, countersunk near through from the pressures side. I have done this in the past and it works fine enough but the attention at the ramp means I then decided to cut that line away and make it look more 'normal'.
Props are really very dumb and are hard to hurt being sensible and incremental so long as the tip region remains respected until more experienced.
The tip region 2mm taken from here will make a big relative difference to the props behaviour reducing overall diameter here, it has it's place at times...but easy to ruin a prop for any boat going overboard here....4mm taken from this tip region may be pushing it...one would need to test incrementally but best left alone.
I dont advocate doing these procedures to any prop one doesn't want to just scrap anyway but it's fun and also less surface area means less grip to muscle the boat around at lower rpm as a matter of coarse...so if bar crossing for example/ Cats for another??? I dunno about cats and uber bow lift necessary boats that dont spin at modified speeds then best stick with the over surface area props I guess.
^^^ What are you on about FNQ?
Maybe I am a bit slow this morning, but following your rationale/reasoning/explanation above I liken to trying to watch a Yo-Yo being wielded by someone on crack and straight Vodka, dancing to Saturday Night Fever songs at an 80's disco night, with the disco strobe at twice normal speed... with a bit of heavy metal in between... !
Lol yeah, what's a bloke to do, it was easier for me than fighting with paint and a picture and dotted lines and stuff....just need to read it slow 10 times over,,,,after I did that it almost started to make for good sensible instructions.
But I am out now lol
So in basic terms you are taking the curve out of the leading edge of the blade ??? or is the 13mm taken off all the way from the hub to nearish the tip.??
Ha Ha Ha!! This is ascending into comedy.
Im thinking ill leave my prop alone
it gets me to WOT Recommended by Suzy.
And my fuel,eco is fine, even tho its a 4 stroke!
Ha ! Over and out.
"let not he boast who puts his armor on, as he who takes it off"
FNQ, you have got to stop drinking or smoking whatever it is before posting some stuff [emoji15] [emoji3]. I thought post #34 above was weird enough, what about this one from the other thread ...
WT?? Quadratics??? Way too much 'something' before hitting the keyboard my man... !!!
I'm pretty sure I have seen some good posts from you over the (many) years, but more recently there has been a lot of incorrect statements, especially about props & 2 smokes, and especially when you apply blanket statements like you do! You are mostly always anti-4 stroke, anti-stainless props, anti-prop cupping, anti-4 blade ... and claim you can make a better prop from a typical standard alloy prop with a grinder, file and a hammer etc!
Now you might have exceptional mechanical ability, and can fashion up a pretty good modified alloy prop "for your boat", but there could very well be several (maybe many?) off-the-shelf props that are better.
Really, I don't know what all these prop companies have been doing over the years, spending millions of dollars on science based R&D, expensive equipment and 'technology', not to mention the thousands of hours spent by designers in the labs/test tanks of Naval Architect/Marine Engineering Institutes, not to mention the better technology developed to make props better - all to make better designed & built off-the-shelf props...
Have you ever got one of your 'modified props' tested/scanned? Yes, I know this involves using new technology, but it provides very good and accurate data! You may be surprised how unbalanced/inconsistent your modified prop/blades are!
How many props have you tested on your boat, types and size? 3? 5? 10? more ...? How accurate were your data records? What parameters are you basing your statement(s) on; economy, performance, speed ...? Yes, there are many off-the-shelf props that are somewhat 'average' after a prop sacn, some manufacturers have varying quality between their prop types, and sometimes with the same type.
I take exception to a few of your comments, as follows:
Really??? Based on what? That the ideal p/d ratio and blade area for your boat should suit every other boat? If I recall correctly, you have a 6m pressed tinny centre console, maybe even with a jack plate (if I also recall). Your boat is what 4mm bottom 2mm sides (or maybe 3). Regardless, very light and easy to push. Try and get a 6m Origin, Riptide, Noble, AMM, Barcrusher … etc centre console going with a 90hp 'anything stroke' - it won't happen, full stop!
"Traditional modern"… I assume you mean a new carby 2 stroke? Can't get them in this/any developed country as far as I am aware, if they are still made.
"2.0km/L"… Really??? Regardless of rated power and boat size/weight???
A certain size and weight planing hull boat needs 'A' torque converted into 'B' thrust to get it on the plane, and 'X' HP to push it at 'Y' max speed. Add weight, and the speed will drop, as will the economy.
So you got more rpm by reducing blade area without altering pitch? Did you see increased speed at the ratio of 5500/5150 of the original 'unmodified' speed? If not you just increased your prop slip, and hard to imagine you made your prop better 'overall'. What happens when you are carrying more load?
Well hello! See my comment above re speed/weight relationship. You now need more torque/power to achieve the same cruise speed. More power generally comes at a fuel penalty… well unless you are going from a carby 2 stroke to a current gen DI 2 stroke or 4 stroke.
Happy to say mine is. Sure many others will say the same too, especially those who have gone to the trouble of testing multiple types/sizes of props under many different configurations.
WT??? No comment.
As for comparisons between outboard types and economy, try these stats, all from mine & mates boats and we all fish together regularly…
Boats; 6.85m glass cabin boats, ~2.2t on the water + gear + 3 or 4 people + eskies/ice etc…
Engines; 300HP V6 4.2L Yam 4/, 250HP V6 3.3L Yam 4/, 250HP V6 E-TEC 2/ (not HO), all with good, well suited SS props.
Typical trips from 1770 to Boult/Boult wide, same load etc… 3.3L 250 uses ~5-10L more than 4.2L 300, ETEC regularly uses 20-25L more than the 3.3L.
Same boats up to Fitzroy maybe a bit beyond, ETEC uses 25-30L more than the 3.3L 4/, i.e. 170-175L vs 195-205L. REGULARLY!
Some other data. Same boats same trips, but with a 5.8m glass cabin boat in company, with a 150HP EFI merc 2 stroke and 2POB. Plenty of power, ~40Kn boat, so engine is 'loafing' in good conditions and/or light loads. 5.8m boat probably at least 600kg lighter.
In very good conditions, 5.8m uses ~20-30L less than bigger 4/ boats. As the conditions get worse, all boats use more fuel for same trips, but the 5.8m uses more pro-rata, and when it gets nasty, 5.8m nearly uses the same amount of fuel as the much bigger, heavier boats.
How would the same 5.8m boat go with a 4/? Well that would be interesting/a proper comparison wouldn't it? I would bet that its economy would get better 'across the board'.
Cheers
Brendon
Haven't been on for a while and i just read what i've been missing out on. Holy smokes... I want some of what he's having.
Darren
Ha! cracker fella's,
I worked at a cordoned off portion of a Brisbane Hospital lots of years ago, sure we could have met inside more than once?...was some REAL actual characters vacating there
respect!.
There is a saying....
"When you wrestle with a pig, the pig gets happy and you get dirty"
Heading out soon to modify the genuine 17p I bought to push at 5600 wot rpm a 6.2m and near max tow-able width, 3cyl, 90hp rig...looking for a 46 or 47km/h slow cruise at nearer to 2.1km/l this time and in full 160km day trip trim, shouldn't be too hard.
possible? or impossible?....
Amateurs.
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