Fuel Flow and Economy Figures

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Post Options Post Options   Likes (0) Likes(0)   Quote fushandchips Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 9:26am
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Works boring today so here are some figures for ya
5.5 Mclay with a 90HP 2stroke Merc (18" prop)
Stanmore Bay to Motuora and return , light westerlies 
Additional weight 
2 x adults 160KG
Bait and ice - 10KG
3 x totes at 23l - 70KG
fishing gear ~ 10KG

WoT  (~ 27knt's there and back @ 16nm) pretty much 18 litres of gas

So whats that work out to be fellas?
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 11:26am
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Your engine should be somewhere around 18lph @ 4000rpm. Being a Merc maybe a touch more but close enough. Anyway if you work the figures you are running around 30lph at WOT so that doesn't seem too far off what you should expect. What WOT rpms do you get to?
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Post Options Post Options   Likes (0) Likes(0)   Quote fushandchips Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 11:41am
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thanks Tagit ,around the 5500 mark
30lph makes sense if you think about the commute time. (40 mins round trip being 2/3 rd's of an hour = 20litres
I wonder what an equivalent sized 4S version would be using?
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 8:01pm
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Originally posted by fushandchips fushandchips wrote:

thanks Tagit ,around the 5500 mark
30lph makes sense if you think about the commute time. (40 mins round trip being 2/3 rd's of an hour = 20litres
I wonder what an equivalent sized 4S version would be using?

yeah about a mile a litre when cruising for a 2stroke 90 - merc are large capacity so might be a bit more

5500rpm is plenty for a 2stroke
No disintegrations!
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 30 Nov 2017 at 11:59pm
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Originally posted by fushandchips fushandchips wrote:

thanks Tagit ,around the 5500 mark
30lph makes sense if you think about the commute time. (40 mins round trip being 2/3 rd's of an hour = 20litres
I wonder what an equivalent sized 4S version would be using?
Sounds like it is pretty well set up. Was wondering if it might have been a little under propped but turning 5500 at WOT sounds pretty close.
1st gen 4 strokes would typically knock around 25% off your fuel burn at say 4000rpm cruise, but maybe not quite as much at WOT. Later lean burn 4 strokes can be 33%+ more efficient.
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Post Options Post Options   Likes (0) Likes(0)   Quote JustAnotherSpearo Quote  Post ReplyReply Direct Link To This Post Posted: 01 Dec 2017 at 6:35am
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DF90 on the 520 lazer chews 28.4L an hour WOT doing between 36.5mph to 40.5mph (trim makes a huge difference) weight would be similar to your mclay as we are always 3 POB + dive gear. Swings a 3 blade 13.75x19" pitch.
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Post Options Post Options   Likes (0) Likes(0)   Quote Bigfishbob Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2017 at 3:51pm
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So this was interesting, I have a Mercury Revolution 4 Prop that went really well on this boat when I had the ETEC. So decided to give it a try today on the merc 115 4s Pro XS CT.

Going down inch in pitch from the 16" Enertia that I posted a while back, thought that would compensate for the extra blade. Strangely enough this 4 blade prop over revved the engine, hitting 6400+ revs! 

Performance was very similar to the Enertia, just lower top end speed, and very fast hole shot. The boat handling changed alot,though the boat needed to be trimmed down harder than usual, which was surprising.

Conclusion, I'll be staying with the Enertia!

Blades 4 Prop Slip
Prop Pitch 15
Gear Ratio 2.38
RPMs Knots L/H NM/L Slip
600
1000
1500
2000 6 5.1 1.18 42.16%
2500 6.5 7.6 0.86 49.87%
3000 8 10 0.80 48.58%
3500 11 12.5 0.88 39.40%
4000 17 16.6 1.02 18.05%
4500 20 20.5 0.98 14.30%
5000 23 24.83 0.93 11.30%
5500 26 27.5 0.95 8.85%
6000 28 40.7 0.69 10.02%
6250 30 42.75 0.70 7.45%
www.waikatosportfishing.co.nz
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2017 at 7:46pm
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The etech a 2S ? Could have any one of 4 gearbox ratios from 1.85:1 to 2.25 :1 and the merc is 2.38:1
 That will make significant difference to the prop performance even if the hps happen to be similar or same.
 Also going from a 2S to 4S (if that is the case) A 2S tends to have more power / toque at the low rpm range.
 Having to be timed down harder would also be because the higher merc gear ratio.

 There is something wrong with the 5500 to WoT data, in particular the 6000 rpm data

Strangely enough this 4 blade prop over revved the engine, hitting 6400+ revs!
 
Is this the boat that was on fresh water?.. are the numbers still on fresh water or salt.. and is the boat loaded exactly the same as last time?
 Is the prop the same diameter?

Also this boat is rather under powered, from memory.. you have nil or near nil reserve power right thru the planing power range.. because of that you will be basically changing slip for speed and visa versa in general working range..
 in effect
 just checked the old data says a 15" prop  and this is also a 15" prop , just more grip???
 Sry bit confused on that data numbers (???)


 


 
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Post Options Post Options   Likes (0) Likes(0)   Quote Bigfishbob Quote  Post ReplyReply Direct Link To This Post Posted: 17 Dec 2017 at 8:17pm
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Hi Steps, The Enertia is 14.7 inches (decimalised) and the Rev 4 is 14 5/8" which calculates to 14.63". Same Freshwater lake, fuel and people load. Although my mate maybe 10kg lighter than my father inlaw. The ETEC was 2.25:1, versus the 2.38:1 of the Merc 4s.

I don't know why Slip increases at 6000 rpm. Does seem strange, but I went through the range twice in the same direction on the same section of the lake, so just accept that as an anomaly. ...for now.

This 4 blade prop is 15P, the previously Tested 3 blade prop is 16P.
www.waikatosportfishing.co.nz
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Post Options Post Options   Likes (0) Likes(0)   Quote Mr Moritz Quote  Post ReplyReply Direct Link To This Post Posted: 31 Dec 2017 at 8:40pm
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A not very good photo from my 565 billfisher
at 4400 rpm doing 52 km and getting 2.3 km per litre  .
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Post Options Post Options   Likes (0) Likes(0)   Quote tiras Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 6:37pm
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Just wondering what you guys would consider acceptable fuel consumption on a SF535 with a 2 stroke Yammy 115 salt water series. 
Currently I'm burning close to 120lt on a trip to the barrier and back with some moving around the broken island's when launching from Omaha. 
RPM is sitting around 4000-4500 so is on the high side and the total trip each way takes 1hr or less in good conditions. 
with the price of fuel getting up there this make for an expensive day on the water. 
thoughts??
RiCK JaMeS B1TcH
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Post Options Post Options   Likes (0) Likes(0)   Quote Bounty Hunter Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 6:50pm
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yeah thats fursty

a 60-odd mile day for twice the litre count

yammie 115s have always loved drinking fuel but yours does seem a bit over the top

considered going a bit slower if its hurting your wallet?
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 6:56pm
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Originally posted by tiras tiras wrote:

Just wondering what you guys would consider acceptable fuel consumption on a SF535 with a 2 stroke Yammy 115 salt water series. 
Currently I'm burning close to 120lt on a trip to the barrier and back with some moving around the broken island's when launching from Omaha. 
RPM is sitting around 4000-4500 so is on the high side and the total trip each way takes 1hr or less in good conditions. 
with the price of fuel getting up there this make for an expensive day on the water. 
thoughts??
If that is say 3 hours running(?) then that is horrible even for a SWS Yammie 115hp which for some strange reason are horribly hungry anyway. If it is 3 hours and 120l then that is more like the fuel burn of a 175 SWS 2 stroke.
Time to check engine height and prop loading/slip to see if you might have it set up a bit wrong.
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Post Options Post Options   Likes (0) Likes(0)   Quote tiras Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 7:11pm
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Originally posted by Tagit Tagit wrote:

Originally posted by tiras tiras wrote:

Just wondering what you guys would consider acceptable fuel consumption on a SF535 with a 2 stroke Yammy 115 salt water series. 
Currently I'm burning close to 120lt on a trip to the barrier and back with some moving around the broken island's when launching from Omaha. 
RPM is sitting around 4000-4500 so is on the high side and the total trip each way takes 1hr or less in good conditions. 
with the price of fuel getting up there this make for an expensive day on the water. 
thoughts??
If that is say 3 hours running(?) then that is horrible even for a SWS Yammie 115hp which for some strange reason are horribly hungry anyway. If it is 3 hours and 120l then that is more like the fuel burn of a 175 SWS 2 stroke.
Time to check engine height and prop loading/slip to see if you might have it set up a bit wrong.

17k prop, standard engine mounting height from factory and no prop slip that I can feel or hear. Have the engine trim up to the cav plate then drop it a couple of clicks. Engine has never fouled plugs and seems to run fine so isn't over fuelling from what I can tel just thirsty!!
Next trip I will drop the engine rpm to 3600rpm and see what the difference is but man it feels slow. 
RiCK JaMeS B1TcH
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Post Options Post Options   Likes (0) Likes(0)   Quote tiras Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 7:12pm
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Originally posted by Bounty Hunter Bounty Hunter wrote:

yeah thats fursty

a 60-odd mile day for twice the litre count

yammie 115s have always loved drinking fuel but yours does seem a bit over the top

considered going a bit slower if its hurting your wallet?

Go slower? not in my vocab. Maybe I just need more paying punters on the boat next time, you still diving?? 
RiCK JaMeS B1TcH
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 7:59pm
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You won't know how much the prop is slipping without doing some calculations. Do you know your speed at say 4000 or 4500 rpms? What rpms and speed can you reach at WOT?
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Post Options Post Options   Likes (0) Likes(0)   Quote tiras Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 8:18pm
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Originally posted by Tagit Tagit wrote:

You won't know how much the prop is slipping without doing some calculations. Do you know your speed at say 4000 or 4500 rpms? What rpms and speed can you reach at WOT?

WOT 5400-5500 is roughly 63-65km an hour 
4000-4500 is around 45-47km an hour

cheers for your input. 
RiCK JaMeS B1TcH
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 8:37pm
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Is it max'd out at 5500 or will it rev a little higher? First look say that the prop slip may be a little high at ~10% (WOT) but not enough to explain the excess fuel burn. Were those figures taken with your normal load onboard?
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Post Options Post Options   Likes (0) Likes(0)   Quote tiras Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 8:39pm
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5500 is max. It might hit 5600 but not often. Yes standard load on board. Full tank, three people with gear in good conditions. 
RiCK JaMeS B1TcH
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Post Options Post Options   Likes (0) Likes(0)   Quote Tagit Quote  Post ReplyReply Direct Link To This Post Posted: 02 Dec 2018 at 9:39pm
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Next time you head out make some reasonably accurate notes on your hours at the different rpms.Your fuel figures are pretty ugly even for a SWS115, but people can underestimate the time they spend at different throttle settings so some accuracy on that will tell you a bit more. I used to have a mid 90's heavy 6m tiny with a Merc 115 on it and it cruised at 25lph at 4000rpm. You seem to be in the 35lph+ range and that seems too high.
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