Do you believe this?

[FNQCairns]

Trolling the net about motors I came across this in a review, it stood out to me, does anyone believe it? I dunno but if correct it certainly is appealing fuel economy for the cruise speed. Can anyone confirm?

Yamaha 90hp 3cyl standard 2 stroke.

"Mounted on a 5.5m aluminium cuddy cabin and spinning a 17-inch stainless steel prop, the test 90 averaged 43kmh on 4000 revs consuming 13lt/hr. #The WOT average was 64kmh on 5500 revs using only 30lt/hr, marginally more than a Johnson 70!"

cheers fnq

[Spaniard_King]

FNQ,

finnier things have happened ;) I serviced a 5.6 quinny legened yesterday with a 90 merc swinging an 18 vengeance and the owner boasted about similar fuel consumption so yer... maybe

cheers

Garry

[FNQCairns]

Thanks Garry, certainly is impressive for a traditional 2 stroke with that amount of HP although since I have found out the Tohatsu 90 may have around the same :o

Anyone got an 18 foot or bigger boat with an old style 2 stroke 90hp on it and knows how much fuel they use?

Cheers fnq

[TonyOW31]

My 525 stacer had a 90 merc carby two stroke and used to average 12l/hr, I thought this was about normal?

[Kendall249]

7m longboat with 2.2 beam (1000kg hull I think) running 150 jonno carby 2s, at 5100rpm it gives 32knts @ 42L/h. #I though this was too low, though the fuel meter has been within +/-2% of actual usage. Swinging 14.1/8 x 23in 4 blade ss prop.

[Black_Rat]

Feesable ! I get 67 klms WOT at about 5700 - 5900 RPM (GPS Speed) (throttle down to the hammer) swinging a 18P Merc Vengence prop on a 90 2stk Merc on a Formosa 5.4m aluminiun centre console
with 2 onboard in the right conditions #;)

[FNQCairns]

Thanks for the reply's these big bore 3 cyl 90s sure are cheap to run, my past experiences with 90s were V4s and they were closer to 20L/H mostly. 12L/h certainly is cheap fishing that could mean around $30 barrier reef fishing trips for us.

Blackrat do you know what economy at cruise you get? around the same as Tony? If you do then my rev-head dreams of owning a V4 115 is well and truly down the drain, wife is also reading reply's over my shoulder and she has done all the sums and unhappily I think she is right - as always ;).

Kendal I have been there before, I had to shake the piggy bank real hard for a days fishing back then, today just the thought of 42L/h ($50/h)gives me heart palpitations, but there is nothing like a big engine hanging of the back the boat everywhere else.

thanks fnq

[krazyfisher]

most of these figures are not on heavy boats. my 5.4 mtr glassy uses no more fuel now with the 140hp than it did running a 90hp. now I am sure I could get it to use more but at the same speed when I come back same dollars to fill up.

[Kopey]

I use to have a 2 stroke carburreted 125 Mariner pushing a 19 1/2 foot hand laid glass hull that used to return 1.1 - 0.9 nautical miles a litre just cruising around which I found hard to believe going by the Navman fuel flow sender but at the petrol pump it was soon verified correct.

Going by the carbed 2 strk 90 Yamie figures that equates to approx 1.78 nautical miles a litre at cruise, very impressive indeed, seems like the good old simple carburreted 2 stroke in this range will still be alive and kickin' for a long while yet. ;)

Cheers Ads

[Black_Rat]

Blackrat do you know what economy at cruise you get? around the same as Tony? If you do then my rev-head dreams of owning a V4 115 is well and truly down the drain, wife is also reading reply's over my shoulder and she has done all the sums and unhappily I think she is right - as always ;).

thanks fnq

Not sure what I get at cruising speed but when your paying $1.10/ltr (at the moment), #why worry about something you'll use once a month ( I know I do #::) ). Unless your using it day in day out or week to week fuel consumption dosen,t really come into calculations IMHO #;)

Damo

[FNQCairns]

;) :)....valiant try Black-Rat but there is no more room to move, I used this new boat and the economy over time as justification to buy, opposed to continuing the project I have atm stopped building.

My backflip is planned in time 8-) probably after female sore bones and salt soaked hair after a 20km trip home from the reef in 20kt winds. "but dear in the glass boat you wouldn't have even got wet or bumped!" :D

cheers fnq

PS. she is not reading this thread anymore I suspect my decision has been made :-[

[Kendall249]

FNQ, I thought 42L/h at WOT was reasonable, as I have been told max consumption should be around 65L/h for a 150 2s and particularly impressive when compared to your quote that 90hp using 30L at WOT . #At around 3500rpm the 150 is using 27L/h for a speed of 22-24knts. That also carrying 2 people, large eskies and fishing gear.

Should I also add that its pushing a 24ft fibreglass hull.

[Noelm]

that figure is pretty close to spot on, I had a pair of Yamaha 90,s once and I thing the description of "big bore 90,s" does not apply to a yamaha as they are a very small 3 cylinder, but very reliable motro and do indeed just 'sip" fuel.

[FNQCairns]

Yeah Kopey it is impressive IMO also, over say 12- 20 years there is no more economical option when all factors are weighted up than a known reliable and common traditional 2 stroke of the midrange and below sizes.

cheers fnq

[FNQCairns]

Hi Kendal, yes you are doing Ok, BUT! and I know this unsolitited but you are getting that economy at a very real cost because of the degree that engine is lugging it will self destruct with still half or more of it's life to live, this is a guarantee not a guess. Not quite as imortant as if it were a V4 but important none the less.
5100 is way way too low for wot operation esp on that engine if propped at closer to 5700 heavy it will go forever but you will then use the rated amount of fuel at max rpm.

cheers fnq

[Kendall249]

FNQ, WOT rev range 4500-5500 rpm, though I might make a call to prop rite to see what they can do.

Cheers kendall

[FNQCairns]

Good job Kendal, if you are going back to the dealer who propped it give him a 'thwack' across the back of his head as for his care and knowledge he makes a great spare parts sales person for his organisation. Your piston crown temps are ATM way too high at all RPMs.

As an advantage the boat will come alive on the water. ATM it is doughy like a 4 stroke (not that there is anything wrong with that).

Consider a 4 blade (with WOT marginally above 5600rpm heavy as a minimum) if you would like to keep near the best cruise speed for economy.

cheers fnq

[Kendall249]

FNQ your advice today has put me on a very positive course. I made a few calls and was directed to a bloke at one of the more reputable dealers here in t'ville. Who seems to have more expertise than the dealer I got the boat from (In brisbane)(better not name names might be breaking ausfish rules) and in particular much more experience in setting up traditional style longboats (very shallow transom deadrise). After inspecting he would like to experiment with the motor height, before touching the prop. He believes that its too low and that finding 500rpm is more than realistic propersition, as well as improving some of the handling and ride caracteristics through reducing drag. He also stated there is a lip on the last 8-12in of the hull and in respect to this the original dealer has the motor 50mm to low in his opinion. He too thinks the four blade is the way too go.

Once again cheers kendall

[FNQCairns]

Hope the plan works for you, if you liked your boat before you are going to love it when it is setup properly. IMO you probably will not see 500 rpm from the raise alone but I hope you do, it would make a nice cheap fix,without all the bother of testing props later.

cheers fnq