Sharkcat 18ft Fuel Economy

[FINKNN]

Good morning everyone. Curious if anyone with a 18ft Sharkcat can let me know what sort of fuel economy they are getting and what engines etc.

I have a 5600 Sportsman circa 1986 with 2008 115 etecs, counter rotating stainless Viper props and Permatrims. I made my first run to the shelf off Newcastle last weekend, approx. 33nm in a calm sea at 23Kn around 4,100rpm, then trawled for apprx 30nm at around 1,200rpm before steaming home for another 33nm at 23Kn 4,100rpm. Full tanks 230l combined, 3 on board, 80l extra fuel in jerry cans and the usual fishing gear, eskies etc. Boat felt great, plenty of power on demand.
Total distance 96nm
Fuel used 204L
.47nm/L both engines
.94nm/L each engine
At 4,100rpm gauges showed 23 - 24 L/ph

Curious if other Sharkcat owners or owners of 115hp etecs can offer their experience/opions?

Good news is we hooked a blue marlin, fought it for an hour, got it to the boat. Bad news is the hook pulled loose and lost it at the boat.

[scottar]

Can't comment on a cat but on a heavy mono running a V6, the Viper from my experience is a great prop for speed. The downside is that it is about the worst prop for midrange economy. By changing to a Rebel propeller at some rev ranges my economy has improved by 15%. Not sure they will fit the 115's - depends on shaft length possibly as I think. Have you done WOT RPM checks and looked at engine heights.

[FINKNN]

Thanks scottar, I can't remember the WOT RPM but I think it was good from memory and my service mechanic has driven the boat and seems to think engine height is good too. I haven't considered re propping but will do some research now.

[Flex]

Hey mate.
I owned a 560 sharkcat with f115 yamahas.

To be honest your economy seems a bit on the high scale.



So your getting 46litres for 42km?

I’d run 52-54km/h for the same fuel usage.

With ok weather I’d get 1.2km per litre.
That was for big offshore runs aswell.
On average I’d run 120km out from mackay and 120km back and use 200l of fuel. Last trip I can remember was 242km for 196l of fuel.

I’d sit on 4500rpm the whole time doing 52-54km/h.

You sound under propped I rekon.
With that HP you should be getting a lot more speed at that rev range.


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[Lovey80]

That’s a dramatically different fuel burn between the two. Surely there’s something bigger going on than just props. Aren’t erects supposed to be as good as 4st on fuel?

[Noelm]

I have 90 Suzuki's on mine and I get much better economy than that, especially around 4-4,500 RPM for very similar speeds.

[Flex]

I rekon it’s have to be props. Seems to be slow for 115 etecs.


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[gazza2006au]

177km's that's a mish!!

[Noelm]

Not to some people in QLD, here in NSW it's only minutes to deep water, and a big trip to the shelf is only 40k or so, but in QLD that distance gets you to a Snapper spot!

[gazza2006au]

Never knew that Noel so i was quiet surprized the see someone in Newcastle area travel 177km's thats like half way to Indonesia from Darwin

[Flex]

180km run to the outer reef off mackay. Not uncommon to see 5m tinny’s 80-100km out.

Reef does protect from the massive ocean swell though


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[Noelm]

Yeah, it's a whole different boating world up there that's for sure, we can do big miles, but, it's mostly hours trolling along the shelf.

[scottar]

I rekon it’s have to be props. Seems to be slow for 115 etecs.


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That would be the first thing to check at any rate. I'd be also looking over the back to see if the foils are on or above the surface or ploughing water as well. Vipers are not a prop that typically likes to run high so potentially there are gains to be had in both engine height and propeller choice.

[FINKNN]

Thanks for everyone’s advice. I think I’ll be talking to my service tech about props and engine height. The boat doesn’t have pods and seems quite bum heavy with the engines sitting low in the water.
I’d love to get some better economy out of her as running at .9 km/l gets a bit expensive on long runs.
Cheers all

[Lovey80]

Are you able to check if you have water in your hulls? Is it possible a compartment may have filled up?

[FINKNN]

Yes I've checked the hulls and there's no water in there. I also have an auto bilge pump in each hull that very rarely pumps a small amount of water out. The self draining scupper/flap at the back sits just above the water line so when anchored and waves coming to stern a small amount of water enters the deck.
the boat was originally built to survey for TAS CSIRO and I have heard this this may mean more glass was used in the build which may make her slightly heavier than others, but I;m not sure if this is true?

[Noelm]

Contrary to popular belief, I don't think there was any extra glass used to comply with survey requirements, but there was a lot of "stuff" that was different, things like inspection ports, bulkheads, some had flowcoat under the floor (depending on the state) and the way fuel tanks were fitted and so on.

[Flex]

Rebuilt my 560 fairly heavy. It was survey aswell and I wasn’t impressed what I saw below the deck.
Survey doesn’t really add any extra weight as Noel said.

My 560 was podded and rebuilt with extra cross members using heavy layup and epoxy resin. Add in 450l of fuel and it have performance I stated above. I highly doubt your boat would be heavier.

What pitch prop you running?


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[FINKNN]

That's a lot of fuel mate and good performance too. I may be missing something here but all I see on the props is "viper" so not sure of pitch??

[scottar]

Look on the hub. Sometimes its stamped near where nut will be seated. Sometimes there is a part number that can be referenced as well.