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Post by thehammer on Aug 10, 2021 18:13:47 GMT
Hi all,
I have a 895 Sport Offshore with 2 x F(L)225 FETX (4,2l,v6).
When I got the boat they had fitted 15 3/4 x 21 propellers (saltwater series 2).
Full throtle 44knots at 4600rpm. So they were not the right ones. Called the dealer, and quickly understood that they had put on the wrong ones.
Fitted same type propellers with 15 pitch and got 39knots at 5800rpm. So these should then be the correct propellers. Only issue is that they use 30% more fuel per mile now than with the first pair.
So, short story long; what do you guys have? What speed and consumption are you seeing? (with load and full tanks)
I need to order some new ones, because I cant live with the consumption I have now.
We use L/nm, and my best number is 3.3 liters per Nautical mile at 28kn. If I have done the math, that should equal to 1.3 Mpg.
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Post by thehammer on Aug 11, 2021 12:00:08 GMT
I forget to mention that the outboards are Yamaha.
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Post by nc on Aug 11, 2021 15:52:20 GMT
First approximate with your numbers
44kts/4600rpm×5800rpm/21"×15"= 39.6kts and you got 39kts, so it looks OK.
F225 operating range is 5000 to 6000 si 4600 is under but possible as you noticed at
44kts.
The best specific fuel consumption is a complex subject, but to go simple just take a prop selector program and you will find that for best fuel economy is calculated at a lower rpm in the range and acceleration at the top range. From that a thing can be concluded, a f225 will be at is top with a wot at 5000rpm for fuel efficiency and 6000rpm for the best hole shot.
So it is normal to get a better fuel consumption at wot = 4600 vs a wot at 5800.
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Post by thehammer on Aug 11, 2021 16:30:32 GMT
Thanks NC.
So should I go up to eg. 17 pitch to get wot back down towards 5000? Will that reduce fule burn?
Is there any prop type that are bether for economy than the saltwater series 2? I dont know to much about the subject.
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Post by Gio on Aug 11, 2021 21:24:27 GMT
I agree with NC, as starting point use a propeller selector tool, you can use Mercury propeller selector online tool (Google it).
You can insert your engine data and select the targeted use and you get certain recommended props.
With your config, running the tool, it looks like you can go to 17" pitch in order to optimize fuel consumption.
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Post by nc on Aug 12, 2021 4:17:48 GMT
I got data for 895sport with f225 from a dealer
15" salt water, 40kts at 6000 at 176 l/hr and 25.8kts at 4000 at 85.6 l/hr for a loading of 5814kg.
17" is for f250
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Post by nc on Aug 13, 2021 11:13:31 GMT
I forgot to ask how did you get your numbers?
28kts, 3.3l/Nm ( 92.4l/hr)
GPS or speed on water from Yamaha display? Speed average from up and downstream or one way speed ? 3.3l/Nm calculate by Yamaha display? RPM?
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Post by thehammer on Aug 14, 2021 13:25:13 GMT
I forgot to ask how did you get your numbers? 28kts, 3.3l/Nm ( 92.4l/hr) GPS or speed on water from Yamaha display? Speed average from up and downstream or one way speed ? 3.3l/Nm calculate by Yamaha display? RPM? Good question. I use the Garmin display linked with the yamaha system. The garmin showes both gps speed and water speed, but uses the gps speed for calculations. For the 3.3l/nm i have not done a trip both ways to average the numbers. I will test a bit more next week and write down all numbers from 1000rpm to wot. The meassurments are from the last 800nm, where i write down all data before and after the trip, and also constantly look at the consumtion during the trip, and trying to ajust the trim, tilt and speed to reduce fuleburn. At the end of the day almost all trips ends around 3.3l/nm. I have contacted a few prop spesialists here in norway and waiting for response. I also read on a few web-pages that mentioned 4 blade prop's would have higher speed / lower consumption in the midrange (but lower speed in the top). If that is true, this could be what Im aiming for. However, awaiting feedback. |
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Post by nc on Aug 14, 2021 19:20:20 GMT
I suggest you to get "standard test numbers" before trying props.
Average speed over up and down stream
Steady RPM for each range at the best trim boat and engine, it takes time and a none crowded open water,it is not important to do it from 1000, 1500, 2000, 2500....but at what it look to be your cruising speed, ex.if the boat stands easily at 3300, start from that until 4500 and WOT
Fuel consumption, before the test add fuel like 2x50 liters for 60 minutes of test, check the fuel level, after the test, add 2x50 liters, according to the boat computer test fuel burned it will give you a fuel check accuracy.
Boat pitch angle.
With those numbers it will be easier to diagnose.
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Post by nc on Aug 14, 2021 19:26:15 GMT
About adding fuel
If the computer tells 88 liters test burned fuel, when adding stop at 2x44 liters and check if you level readout is the same, this takes times because it is 2 tanks and an accurate reading method, it is easier to fill with 2x50 and approximate the level.
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Post by lynnardm on Aug 14, 2021 21:26:50 GMT
I forgot to ask how did you get your numbers? 28kts, 3.3l/Nm ( 92.4l/hr) GPS or speed on water from Yamaha display? Speed average from up and downstream or one way speed ? 3.3l/Nm calculate by Yamaha display? RPM? Good question. I use the Garmin display linked with the yamaha system. The garmin showes both gps speed and water speed, but uses the gps speed for calculations. For the 3.3l/nm i have not done a trip both ways to average the numbers. I will test a bit more next week and write down all numbers from 1000rpm to wot. The meassurments are from the last 800nm, where i write down all data before and after the trip, and also constantly look at the consumtion during the trip, and trying to ajust the trim, tilt and speed to reduce fuleburn. At the end of the day almost all trips ends around 3.3l/nm. I have contacted a few prop spesialists here in norway and waiting for response. I also read on a few web-pages that mentioned 4 blade prop's would have higher speed / lower consumption in the midrange (but lower speed in the top). If that is true, this could be what Im aiming for. However, awaiting feedback. You are correct in your comments about a 4 blade prop. I had to go to a 4 blade on my non sport 895 with an f300. A 3 blade just didn’t have enough surface area at the lower speeds under 25 and performance was terrible due to too Much slip even though the engine had enough power. But at the higher speeds over 25 the 3 blade prop was fine. I lost a couple MPH at WOT with the 4 blade but I didn’t buy this for a race boat. With twins and the blade surface area of 2 props I don’t think there would be any advantage with 4 blade props. But with a single and a heavy boy there is. Capt’n Lynn |
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idefixsc
Full Member
Posts: 34
Jeanneau Model: NC 895 Sport
Yacht Name: IDEFIX
Home Port: Georgetown, SC
Country: USA
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Post by idefixsc on Aug 24, 2021 23:49:51 GMT
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Post by Gio on Aug 25, 2021 5:15:02 GMT
Thanks for the link- It is surprising the difference in performances of Yamaha Vs Mercury, they are substantial. I wonder if a 17" prop in the Yamaha would improve them. |
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Post by charlieb on Aug 13, 2023 5:54:41 GMT
I agree with NC, as starting point use a propeller selector tool, you can use Mercury propeller selector online tool (Google it). You can insert your engine data and select the targeted use and you get certain recommended props. With your config, running the tool, it looks like you can go to 17" pitch in order to optimize fuel consumption. |
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Post by charlieb on Aug 13, 2023 5:57:54 GMT
Hi all, I have a 895 Sport Offshore with 2 x F(L)225 FETX (4,2l,v6). When I got the boat they had fitted 15 3/4 x 21 propellers (saltwater series 2). Full throtle 44knots at 4600rpm. So they were not the right ones. Called the dealer, and quickly understood that they had put on the wrong ones. Fitted same type propellers with 15 pitch and got 39knots at 5800rpm. So these should then be the correct propellers. Only issue is that they use 30% more fuel per mile now than with the first pair. So, short story long; what do you guys have? What speed and consumption are you seeing? (with load and full tanks) I need to order some new ones, because I cant live with the consumption I have now. We use L/nm, and my best number is 3.3 liters per Nautical mile at 28kn. If I have done the math, that should equal to 1.3 Mpg. |
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Post by charlieb on Aug 13, 2023 6:54:38 GMT
Hi All,
just completing prop trials on 2022/3 895 Sport offshore with twin Merc 225hp V6 3.4ltr DTS.
Boat delivered with 14.6 X 15 inch pitch which cavitated noteably trying to get out of the hole, but WOT revs were in the 5900 to 6000 range, as recomended, giving 37 knots.
Went to 14.6 X 17 inch Enertia and cavitation notably better but still there, popped onto a plane with a 4000 to 4200 throtle ( nowhere near maximum throttle possible). Still noticeable cavitation in a seaway ( I am fussy ). WOT came down to 5500 revs giving 35 knots with fully loaded boat ( carrying full instrumentation including radar, spare anchor and warp in the front cabin, full bedding in both cabins, barbeque below, spares and tools, solar panels and inverter, hot water tank and microwave, half watertank and half full fuel, antifouled bottom). Also have been out with 4 adults and three kiddies with this set up and I would imagine this could suffice for many.
Dealer tried fourbladed 14.6 X 19 pitch Revolution4 which killed WOT revs down to 4900 giving 35 knots, but engines power struggled at full thottle to get the revs up enough so noticeably slower onto a plane.
Merc Prop selector then consulted and certainly indicated the 14.6 X 17 "3 blader" as an option, but also suggested the 14.6 X 15 "4 bladed" Revolution 4 props. Trying late this week. Aim is to get promptly out of the hole with a little more than 4200 revs then good economy running at around 3700 revs around 23 knots(Closing in on this already), minimal cavitation. Much more speed than this in our bumpy offshore area is just uncomfortable.
By the way, while most seem to go for the 250hp, am happy with the V6 3.4L 225 Mercs power for the job, just getting correct props on to get good grip but maintain recomended rev range, and we are close.
About to complete the mechanical checks from the initial 20hr service.
Numerous on elsewhere forums have mentioned that new motors can naturally increase their revs during the first year of use, is there anyone that can enlighten more on this suggestion?
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