reducing fuel consumption

[wayneoro]

5.5 caribbean with a 115hp saltwater series merc . i hav 2 alum pods [55ltr] 4 blade s/s prop plus full canopy heaps gear = bit under 2ltr nm. to go from walkers pt to roonies pt fraser is, and move a few times and back 140-150 ltrs =75nm trip . av speed is 20kts at 3500 revs . financially changing motors is not an option =it would take many many yrs to recover setup cost. so wot other options r there ? how about side pods to lift boat out of water more when steaming like a tri hull ?

[Mindi]

well when you look at american boat/motor test reports with detailed consumption figures the most economical (ie...highest MPG ) figure is at 3000-3500 rpm so given decent conditions you are probably already running at the most efficient consumption engine setting.

[wayneoro]

3500-4000 is closer to wot i do so will drop back to 3250 cheers

[Wahoo]

how about side pods to lift boat out of water more when steaming like a tri hull ?

Scott from bluewater boats made something like your saying, but owner and builder wont allow me to put the pics up, and i would say Mindi is on the money, dont know what the WOT is, but i would think 5500-6000rpm, maybe your not proped right


Daz

[FNQCairns]

yeah you should be able to shave 30% of that fuel bill if you prop it well, didn't you have this same problem with the V4? I gave the new owner a hand through PM to prop it correctly for his tinny and now it's a speedboat and very economical as a result at cruise.

Just take very good notice of the prop you are using as it will make all of the difference I am assuming the WOT you mentioned is correct.

cheers fnq

[arvor]

id be very carefull fitting any addition to any hull.let alone your carribeen .international marine employed some very good marine archictects to build there boats .and did a very good job at that time.so bolting on anything that was not designed would be not adviseable .and could be dangerous.id be going with all the others .prop wise.good luck anyway.gary.

[wayneoro]

cheers fnq the prop on my motor is a s/s 4 blade merc trophy plus 48-825930a46 17p and 5000 revs is max i can pull . ty for helping out with the 90hp johno, as it turned out i had bought the correct prop off ebay just before selling it so steve repaid me for the prop and must be happy with the result. cheers

[FNQCairns]

Thanks Wayne I wondered at the time how he sourced that prop so fast. Usually unless prepared to spend big dollars fast good proping is an evolution over time when the opportunity presents. I am still looking for a particular but rare second-hand as new prop, been over a year now.

If 5000 is your wot can you raise the engine any? What is the relationship between the bottom of the hull and the vent plate?

That engine is fairly powerful for the 115hp I think and the 4 blade can give the option of raising a little higher than 3 blades.

Still if you are after fuel economy on any hull that is not a barge a well chosen 3 blade is the way to go. I suspect have not far to go, if raising doesn't help then you need to re-prop, it will pay you back over time.

IMO find out what what is the most reliable WOT rpm for that engine -from someone who is not a manufacturer stooge but uses the volume of aftermarket/real world knowledge learnt since it's introduction and set that as the safest WOT to prop toward...it could be as high as 5600??

cheers fnq

[BrenMac]

If 5000 is your wot can you raise the engine any? What is the relationship between the bottom of the hull and the vent plate?

cheers fnq

Certainly sounds like that motor is buried way too low.

Cheers
BMac

[wayneoro]

ok saw a merc ad for a new 125 -135 hp = rev 5000-5250 max ? plus my motor height looks fine and it was installed by a pro shop . then i added floation pods that have lifted stern . which reminds me the guy i bought boat off asked if i found steering was very heavy which i didnt as i put pods on stright up . cnq the top of vent is level with bottom of hull [approx]

[MarkDiver]

Wayneoro
I'm still not sure exactly what your boat looks like but my 5c worth may be fitting a hydrofoil onto the leg as this can reduce consumption for a list of reasons. I actually bought one this weekend for $100 and intend regaining that pretty quick over time on reduced fuel consumption. I did not buy it for that reason, rather for cavitation reasons. Back to your question, full canopies? Can you zip open the clears or drop the canopy down to reduce wind resistance while steaming? It may sound stupid but I found a performance difference on a larger boat I owned, especially against a solid headwind of course! Are you carrying extra perhaps unnecessary weight? Do you really need all the anchors or chain you have on board? Just have a look at what you can leave at home. A few simple things like a whole dedicated tackle box full of lead sinkers you may not need to cart around. I have found I used to cart too much crap around sometimes. Good luck

[FNQCairns]

ok saw a merc ad for a new 125 -135 hp = rev 5000-5250 max ? plus my motor height looks fine and it was installed by a pro shop . then i added floation pods that have lifted stern . which reminds me the guy i bought boat off asked if i found steering was very heavy which i didnt as i put pods on stright up . cnq the top of vent is level with bottom of hull [approx]


Ok thats good info Wayne, you have up to 2 holes higher you can go, either 2 holes and suck it to see or 1 hole which will probably return a little extra of everything you need and will keep good grip when in the rough stuff - depends on what your normal boating trip is all about. Getting to where you want to go is stepwise.

Do you have a foil fitted??.....:-[:P

cheers fnq

[wayneoro]

cheers no foil . i went to mercury props on line put my info in they came back with a 21p in the same type 17p prop i have now ? it all seems to hard lol i put my boat in as a 20ft fishing glass for midrange cruising with the classic merc 115 o/b =s/s 13.750 -p21 or alum 12.7- p21 thats less revs surely. with my pods the ptt is never used except in shallow water . i can send pics to a email add but cant figure how with the forum

[FNQCairns]

cheers no foil . i went to mercury props on line put my info in they came back with a 21p in the same type 17p prop i have now ? it all seems to hard lol i put my boat in as a 20ft fishing glass for midrange cruising with the classic merc 115 o/b =s/s 13.750 -p21 or alum 12.7- p21 thats less revs surely. with my pods the ptt is never used except in shallow water . i can send pics to a email add but cant figure how with the forum

I have seen your pods, you posted a pic a few years ago, nothing wrong with them (if they are the same ones) not something to focus on trying when trying to get your prop right in your instance anyway.

I have never got a good recommendation from that site either but it understandable when you understand what 'off the shelf' props are really all about esp when only one line of props.

Still before anything further you need to raise the engine take your new test numbers accurately then move onto the next step.

Skipping this step and just placing another prop on can work in an average sense with a dolop of luck but usually is just a waste of money and time.

From your point of view what are your options, the ones you are personally open to??

cheersfnq

[Pelagic 660]

wayneoro, I have a 150 efi merc on a 660 trailcraft and had similar queries some months ago, I took advice from FNQ and have not looked back, I went from a 17p prop to a 19p also lifted my motor 2 holes, it was originally fitted by a merc dealer and vent plate was about 5mm above the keel. Lifting in stages is the go, I was surprised by the difference. the prop I bought from the US and was about 50% cheaper than what you can get here FYI I went from cruise 4000rpm 24kn to cruise 3600 24kn, WOT 6100...36.5kn to 5700....38kn. Smiles all round.

Hey Scott got any tips on how to improve my catch rate?

Good luck with it mate, Trevor

[FNQCairns]

Sorry Trevor if it were from my experience I would say the cure is to go fishing every now and then:)

Glad to hear the end result is still working for you, hope your economy has improved too.

cheers fnq

[wayneoro]

ok 1st up i will take the boat down river and get exact figures as it is now . the merc trophy plus prop is for digging out of a hole, hard turning quick on to the plane etc etc . i need none of that . though when crabbing etc the prop gives you great control . with the long trips needed now to find fish ,less fuel consumption is my only goal , cheers

[wayneoro]

gee fnq u are so right . took a closer look and yes my motor is way to deep . there are 3 holes left hope its anough . the boat sits deeper then u would expect judging by the water line. plus i have a extra long shaft [by the looks of it ] they had rebuilt the trans; to raise it for the extra long shaft . it must have been a pig to steer before my pods went on .

[FNQCairns]

That's no good Wayne, I didn't pick that, without a crystal ball or good accurate speed and rpm numbers it's just not possible.

Still the leg height has nothing to do with the static height of the hull on the water, in setup it's entirely the relationship between the bottom of the hull and the amount of leg sticking below it.

What is the measurement of the bottom of the hull to the vent plate?

cheers fnq

[wayneoro]

ok to get it exact will put it in the water as i cant trim the leg right down when its on the trailer as its two long but its at least 1-2ins . will raise it 3 holes cheers

[FNQCairns]

That's lots! you will notice a big difference, time to go ask why they fitted it in the first place?????????????????????? sounds like it will still be too low without re-mounting the engine to the hull at the proper height.

cheers fnq

[wayneoro]

ok just jacked hull up . its exactly 1in . but as the hull sits deep in the water the [prop is 4-6in under water. aprox] why stuff like that happens in bundaberg ::) we have been wondering that for years . lucky for me i discovered Boats Galore a top marine and outboard shop they do it right 1st time . a unique experience in this part of the world .;D having said all of that the boat runs great as it is . its just to reduce petrol useage :(

[Angla]

Sounds like you are on the right track with the motor height.

Did I read right when you wrote that you do not trim the motor up while travelling at speed. I think you should try travelling at say 3800 rpm and then trim the motor up until it starts to cavitate then drop it just a smidgen until it grips again.

Tell us what happens when you do this. It should speed up dramatically as the friction of the hull reduces and you will see the RPM increase as well towards the WOT (wide open throttle)

The two photos show the distance that the leg is away from the transom firstly at full trim in ( about 5 inches)and secondly at trimmed position when travelling at 36 Knotts and WOT (more than 14 inches) It may seem to be a long way out bat it's sweet and returns great economy.

Last thing to mention is that I have found that if you rest your hand on the throttle and make constant adjustments then that is not good. I now set the throttle and leave it alone until the water conditions demand a change. Could go 20 nm before I make an adjustment now and I have found that the economy is much better

Good luck
Chris

[Wahoo]

Wayneo

best test is, when you take it for a run, half loaded will do, at about 3/4 power on the plane, check the cav plate, for my liking it should be just above the water, if it is under then you will be getting to much motor drag, this will give you the best result on where the motor should be sitting

Daz

[wayneoro]

[quote=Angla;902107]Sounds like you are on the right track with the motor height.

Did I read right when you wrote that you do not trim the motor up while travelling at speed. I think you should try travelling at say 3800 rpm and then trim the motor up until it starts to cavitate then drop it just a smidgen until it grips again.

ty mate but i have floatation pods ec side of motor so i dont think my t&t is any help . i have tested it. will do so again once i raise the motor cheers

[wayneoro]

wow ! wot a difference ty fnq and everyone who helped. yesterday wife and i raised the 115 three holes went from 1in under to 1in above . results of this mornings test run was 25% wot speed increase . 40mph the old girl put her ears back and went for it . never touched t&t :o , will play with that option .at 3200 was 20mph . steering was light . hope this translates into less fuel cheers

[FNQCairns]

That's great news, amazing the difference a better setup makes, if all of your testing was on flat water you might find when it gets lumpy the prop will aerate, if you can handle it thats ok, if not you might need to go down a hole.

What sort off WOT rpm are you now getting?

cheers fnq

[wayneoro]

5000 rpm with the leg stright down . will be fine in heavy weather . still plenty water over prop. cheers

[whiteman]

Mate, doesn't sound like you've got a fuel gauge to tell you the "instant" flow. My Navman has payed for itself many times over as I tune the revs to get the best economy and this tends to be around 4200 for my Yammie 115 2s.