Fuel consumption

[bachoau]

I am looking at 5.6m sharkcat with twin 1999 150 oil injected motors would like a ball park figure of lts/km at 22 to 25 knots compared to a 140 turbo diesel 5.6 m sharkcat. Thanks

[robothefisho]

The best i can get out of my 200 carby yamaha is 1.7 km per litre. The worst around 1.2km per litre. You have two motors which basically use the same consumption maybe a bit less because they're twins. So at best you might get 0.9 km per litre. At worst around 0.6 km per litre. Probably a bit worse again if they're Johnson not Yammy. If trolling the economy is worse again.

[Noelm]

Not exactly sure I would be too thrilled about a diesel in an 18' Sharkcat?

[ranga7]

save a tad more and get a cat with 4strokes, the one your looking at would chew a sh@t load of fuel, the extra money spent on fuel after a few years you could buy four strokes.

[koastal]

The best i can get out of my 200 carby yamaha is 1.7 km per litre. The worst around 1.2km per litre. You have two motors which basically use the same consumption maybe a bit less because they're twins. So at best you might get 0.9 km per litre. At worst around 0.6 km per litre. Probably a bit worse again if they're Johnson not Yammy. If trolling the economy is worse again.

That is great consumption for a carbed 2 stroke

[Crunchy]

That is great consumption for a carbed 2 stroke
Shyte yeh, for a 200 espeically

[scottar]

Depending on the hull, I suspect a typo or a slight flaw in the calculation. Most 4 stroke 200's and DI 2 strokes only return around that sort of economy (or worse) at around 22-25 knots. A 200HO Etec on a Victory is 1-1.3 km/l at those sort of speeds depending on load and trim and from discussion with owners the 200 Suzuki is about the same. What sort of hull is it robothefisho and how is the calculation/measurement done - just interested as if those are accurate figures they are indeed exceptional for a carbed 2 stroke engine.

[robothefisho]

Hi all,
No mis calculation. I do it using the fuel into the tank from full (filled direct into an in floor tank I can see the level in) and distance travelled from the GPS. The 1.7km/l is more a figure from cruising on a calmish Moreton bay anywhere from 25 -40 knots with 4-6 people. The 1.2 is more my offshore running around 13-20 knots with 4 people and gear etc. On a 5.9m seafarer runabout. 23 pitch prop. Capable of around 50 knots. Its trolling and slow running which kills the consumption.

[scottar]

Like I said astonishing numbers for a carbed two stroke.

[stevej]

do you stop the gps every time you anchor drift or move ?
if not your figures cant be accurate those figures are 4 stroke territory
most gps dont differentiate when a motors running or not in the distance travel log i could go to the fads 40km trip but do 60-80 with the drifts included

[bachoau]

Thanks for the info but probably right 4 s would be the go. So does anyone out there have a cat with twin 115 4 stroke. And can these 5.6 m cats hand,e the rough.

[scottar]

Thanks for the info but probably right 4 s would be the go. So does anyone out there have a cat with twin 115 4 stroke. And can these 5.6 m cats hand,e the rough.

Ultimately 4 stroke or new gen 2 stroke (depending on your persuasion) is the go unless the purchase price reflects the fact the hull has old motors. If the price difference is the best part of a repower and is the difference between a boat now and having to wait while you save a considerable sum extra, I know what I would do. It depends on your use pattern as well. If range is important, then new engines are important and will pay for themselves with regular use over big distances. If you never intend running big distances they won't and if the other attributes of newer engines (less/no smoke, quieter, can troll all day without oiling up) aren't so important then the cost savings that should be reflected in the purchase price are something to consider.

[Flex]

Are you sure it's a 5.6 sharkcat? Not often you see them with anything above 115/130hp on them. 150's would be rather impressive. I have seen one with twin 200's but that was a rare boat.

i own a 560 sc with 115 yamahas. Goes great, fuel economy is roughly 0.7-0.8l per km. I sold my 5.2kc to buy this boat. It's a better riding boat than the KC.

[robothefisho]

Spoke with a mate who runs a 7m sharkcat cuddy cab with twin 150 fourstrokes. Cruising at 27 knots it gets around 1.1km per litre.

[robothefisho]

Steve,
No I don't stop the gps. However all of my fishing is done at anchor (where I have never seen distance travelled increase while there shortish periods) most of my bay running is to a beach. They're averages from the last 3 or so years. The only reason its economical is because of how fast it is. It still uses a heap of fuel per hour. Ie at 3000rpm its doing approximately 32 mph.

[Bremic]

Spoke with a mate who runs a 7m sharkcat cuddy cab with twin 150 fourstrokes. Cruising at 27 knots it gets around 1.1km per litre.

Is that the combined/both sides usage? Bloody good going, would have to be happy with that.

[Lancair]

I agree with others questioning the accuracy of your records Robo.

Your old school 200 carby motor is equal to or slightly better than my 115Etec ? ?

I fished aboard a V17L with a 200hp carby mariner and it sucked fuel down really quick and went really quick, like you're quoted rpm and speeds.

[FNQCairns]

often the urban marketed disparity between old school 2 stroke and modern 4 stroke fuel cons makes me want to puke...well not really that's overacting...possibly just a half hearted dry reach :).

marketing works to create belief systems that almost never die, yes 4st are more efficient but really not that much to warrant the extra cost on rec craft but still also that is also personal thing.

I got a 90 yam smoker on a 6m tinny I got 2.1km/L in offshore trim in the past at 42km/h but today I get just 1.8/km because of the front casting deck and the largish aux on the back and a few other things......this 3cyl ob is small cc and low torq so not really well up to the job of the craft it pushes anymore......all outboards will use more or less the same moving average throughout their HP/CC and torque figures...all specific types of engines do.

If I went to a 115/130 yam smoker I expect at least 2.2/3 from that HP grade. The pitch of the prop that can be swung is the key and the only key ie off the shelf diameter and surface area is most often just good money thrown overboard every km travelled.

all medium and above 2 stoke ob if set up well at cruise speed and suited to size boat should see near/around 2.0km/l on average.

[koastal]

Steve,
No I don't stop the gps. However all of my fishing is done at anchor (where I have never seen distance travelled increase while there shortish periods) most of my bay running is to a beach. They're averages from the last 3 or so years. The only reason its economical is because of how fast it is. It still uses a heap of fuel per hour. Ie at 3000rpm its doing approximately 32 mph.

That makes sense

[robothefisho]

Is that the combined/both sides usage? Bloody good going, would have to be happy with that.

Yes mate that's the boats fuel economy. Ie distance/fuel use for both motors.

[robothefisho]

Lancair you're perfectly entitled to aswell. It's all so variable between boats. Ie this boat uses far less fuel than a 580sf with 140 rude I owned. I've found out of carby 2 strokes that the yamahas are generally the most economical. This is personal experience with merc/johnson/yamaha.

[Crunchy]

Best figures I get are 1.8km per litre with 90HP 2stk on a long boat which is supposed to be an economical hull so your doing well mate.

[Mark Andrews]

My Dad has a 7m x 2.6m wide Bruce Harris shark cat weighs 3ton with 2 x 175hp mercury black max carby jobs tops out @ 45nm/hour if your not holding on while you put the boot into it you will be out the back quicker then you can say jack rabbit.Best economy is @ 25nm/h cruise 1km/litre any less speed it chews juice any more speed you can double if not triple the fuel.Trolling and looking around for fish on the sounder forget it it just pumps the fuel straight out the exhaust pipe.best part of the trip is when coming home and someone trys to drag us off then we say #### the fuel bill see you later sucker.

[feral cat]

I had a 560 sportsman podded bruce harris cat with twin 90 yammy 2 stks.
1.2ltr per km loaded.
I find it hard to believe any bigger cats with bigger 2 stks would get any better.

[odes20]

often the urban marketed disparity between old school 2 stroke and modern 4 stroke fuel cons makes me want to puke...well not really that's overacting...possibly just a half hearted dry reach :).

marketing works to create belief systems that almost never die, yes 4st are more efficient but really not that much to warrant the extra cost on rec craft but still also that is also personal thing.

I got a 90 yam smoker on a 6m tinny I got 2.1km/L in offshore trim in the past at 42km/h but today I get just 1.8/km because of the front casting deck and the largish aux on the back and a few other things......this 3cyl ob is small cc and low torq so not really well up to the job of the craft it pushes anymore......all outboards will use more or less the same moving average throughout their HP/CC and torque figures...all specific types of engines do.

If I went to a 115/130 yam smoker I expect at least 2.2/3 from that HP grade. The pitch of the prop that can be swung is the key and the only key ie off the shelf diameter and surface area is most often just good money thrown overboard every km travelled.

all medium and above 2 stoke ob if set up well at cruise speed and suited to size boat should see near/around 2.0km/l on average.
Mmm i think that this last sentence a bit of an exaggeration bud. Just about all boaties i know with 150-175 2 strokes get about 1 km per litre, and i had a yammy 150 on my Yalta 20 footer and thats what it yielded. Went to a Suzy 175 4 stroke and now consistantly average 1.7 - 1.8 km per litre

[airlock]

I can't comment on the shark cats but new ally hulled cat gets around 1.8km/l from 2 yam 60's apparently it will do better but i'm not convinced.

In contrast my 5 meter cruise craft with a 135 blackmax was sitting somewhere around the 1.1km-1.3 per L. Fuel bill was high but dear god did that thing move!

[FNQCairns]

Hi odes 20.

Sorry just checked in and forgot totally I posted here, no not really an exaggeration, dumb props the standard ones we buy off the shelf for straight-line fishing rigs are awesomely over surface area for pitch...if a 4 blade add near 20% to that again. Any traditional modern 2 stroke properly matched to a hull shape and weight should see 2.0KM/L at their most efficient cruise.

People just dont know, I bought a new prop for my smoker a couple months ago when a new to boating decky couldn't judge the shallowness of a bommie when nudging up to a beach on the GBR. My boat should run a standard 13 pitch yam 3 blade to reach it's stated max RPM with load 5500, the prop that was bumped was an old 15p Yam 3 blade (redesigned by me) and could reach 5550rpm in identical situation so I replaced it with same off the shelf.......... a prop that if genuine and unmodified will hold a max wot rpm of 5150 on my boat at best in identical situations.

So the first thing I had to is have at it and redesign the surface area, I now run that brand new prop (now modified) at 5500 wot rpm identical situation from the very first test drive. My consumption with the 13p is about 1.3km/l and at a sloooowwww cruise, with my modified 15p it's 1.6km/l but at a typical 15p faster cruise speed but still the fuel consumption signifies I didn't take enough surface area from it even though cruise speed for RPM is near identical to any brand new identical unmodified genuine yam alum15p.

The weight my boat has grown so the motor is now actually too small....2.0km/l is the correct target but i will be happy enough with 1.7-8 now when propped well (when I get the surface area to best suit the boat/motor/hull/weight combo) and with next to no discernible impact upon typical cruising speeds...no boat with an off the shelf dumb elephant ear'd prop is well propped...none of them they are all dogs...I mean that in a nice way, lots of dogs out there way better than my boat.

Off the shelf props are designed to operate well enough pushing a full oyster barge at displacement speeds, why would any prop with an identical same profile also suit any relatively uber light straight line planing hull fishing rig?...quite simply it cannot, it cannot like a car with square wheels.

cheers

[Chris Tucker]

The data is old but an interesting comparison on Roger Hill's website on the Arrowcat (http://www.powercatsnz.com/public/index.cfm?fuseaction=app.showdesign&ID=168).
Almost Identical boats using the same tooling (from memory Diesel boat had more/heavier fitout). One running 2x 150HP optimax the other 2x120HP Mercruiser diesel. Optimax used slightly less fuel across the board.

[caravellerob]

my last reef trip off Whitsunday's 221 kms for 180 litres with 98 model 175 EFI merc on 19ft fibreglass, no drift, anchor every time. was going to upgrade to 4 stroke but not until this old girl dies. I used the same fuel as my mates 6.5 platey with 225 4 stroke Suzuki, go figure..

[scottar]

Any pics of the modded prop FNQ ??

[odes20]

my last reef trip off Whitsunday's 221 kms for 180 litres with 98 model 175 EFI merc on 19ft fibreglass, no drift, anchor every time. was going to upgrade to 4 stroke but not until this old girl dies. I used the same fuel as my mates 6.5 platey with 225 4 stroke Suzuki, go figure..So how can u make the comparison here? Vastly different horsepower and boats? Impossible, and no example in anyway of 2 stroke efficiency
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!

[caravellerob]

So how can u make the comparison here? Vastly different horsepower and boats? Impossible, and no example in anyway of 2 stroke efficiency
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!

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.

[odes20]

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.

[FNQCairns]

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.

[gofishin]

^^^ 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... !

[FNQCairns]

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

[scottar]

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.??

[odes20]

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.

[gofishin]

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 ...


Yeah 11 will do fine...finer than what you have i dont know if diameter...... if different consider also the 9 or 10....if what you say is not that dramatic then the 10 will do all you need without the any fuss forever...still you can fuss if you want to...sometimes I do...9 might be a bit much less but off the shelf props are crap for incremental size...10 will probably be boss if possible.......11 a no good choice compromise but acceptable as is the way with props...assuming common or near common diameter as you already provided.

get it gooder enough and some numbers then consult the mathematicians to do the quadratic equations for better still if possible...they will still sell you a bad prop if it's closest their brand has for sale.

good luck.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:


...no not really an exaggeration, dumb props the standard ones we buy off the shelf for straight-line fishing rigs are awesomely over surface area for pitch...if a 4 blade add near 20% to that again… 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!



... Any traditional modern 2 stroke properly matched to a hull shape and weight should see 2.0KM/L at their most efficient cruise… "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 I replaced it with same off the shelf.......... a prop that if genuine and unmodified will hold a max wot rpm of 5150 on my boat at best in identical situations.

So the first thing I had to is have at it and redesign the surface area, I now run that brand new prop (now modified) at 5500 wot rpm identical situation from the very first test drive… 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?



... The weight my boat has grown so the motor is now actually too small....2.0km/l is the correct target but i will be happy enough with 1.7-8 now when propped well…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.




...no boat with an off the shelf dumb elephant ear'd prop is well propped... 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.



...Off the shelf props are designed to operate well enough pushing a full oyster barge at displacement speeds… 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

[Darren Mc]

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.

[FNQCairns]

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.