best fuel ecomony with this prop ?

[rocket ron]

1996 2 stroke 175 hp outboard on a streaker 5.85 tournament series 2 wieght 1.7 t 20 degree deadrise 3 blade 25 pitch prop which runs @ 40 mph wot & 5100 rpm , is this prop suited for fishing trips of about 100 mile ive got a 170 litre fuel tank. Is this a good result or can something be changed to get better fuel ecomony

 

[Bondo]

Re: best fuel ecomony with this prop ?

1996 2 stroke 175 hp outboard on a streaker 5.85 tournament series 2 wieght 1.7 t 20 degree deadrise 3 blade 25 pitch prop which runs @ 40 mph wot & 5100 rpm , is this prop suited for fishing trips of about 100 mile ive got a 170 litre fuel tank. Is this a good result or can something be changed to get better fuel ecomony

Ayuh,... What's the recommended rpm range for yer motor,..??

If ya prop it to run below that range, you might think yer saving gas, but in reality, yer burning holes in yer pistons from lugging induced detonation...

 

[rocket ron]

Re: best fuel ecomony with this prop ?

thanks for the heads up.

 

[steelespike]

Re: best fuel ecomony with this prop ?

Without your motor brand and if injected or carbed its difficult to know if your setup is working. Assuming a carbed Merc it appears you have a lot of slip.
Any 175 hp motor will burn about 17.5 US gallons per hour @ wot.
About 43- 44 US gallons one way. The right cruising speed will could use signifigantly less.

 

[rocket ron]

Re: best fuel ecomony with this prop ?

yeah its a 3 barrel carb yamaha 2 stroke 175 hp outboard 2 stroke 1996 model, i went out on what i think was low grade of fuel , which burnt way to quickly, & the last time it was 98 octane fuel with much better results.

 

[steelespike]

Re: best fuel ecomony with this prop ?

Based on your figures it doesn't add up quite right.
I believe motors similar to yours on a 3000 lb plus boat run something like a 17" pitch
at about 5400 rpm and 40+ mph.
Your slip numbers seem really high at 38% I would suspect either my figures are wrong
or your speed is faster than indicated or rpm lower than indicated.With a 25" prop I would suspect the rpm should be lower.

 

[rocket ron]

Re: best fuel ecomony with this prop ?

ok when the weather perpits i will double check with my new gps that santa bought himself for christmas this year [ ill check the new gps figures against the old gps figures & the rpm @ wot]does putting on a 4 blade prop make any sense when it comes to fuel ecemony ?

 

[steelespike]

Re: best fuel ecomony with this prop ?

You will need to varify your tach reading as well.
When you talk about fuel economy with a boat your trying to get the most speed for a given throttle setting. Usually the best practical outboard cruising speed is just on plane to about 1000 rpm higher.If a person was working with a boat with a good(not perfect) setup they would probably need a flow meter to measure any improvement.A 4 blade prop usually will get on plane quicker and allow the boat to stay on plane easier at reduced throttle settings.If you plan to operate at wot the 4 blade isn't likely to produce the best results. Have you confirmed your prop is actually a 25" Its highly unlikely it would be right for that boat.Prop numbers usually are under the prop nut.

 

[rocket ron]

Re: best fuel ecomony with this prop ?

ok i emailed yamaha with the details ive put up on this site & they recommend that i start with a 19 inch prop, thats without any further tests as thats what they start with to achive the 5200 rpm , but as we know ,i will arrange for a yamaha dealer to come out with me & do the required test to achive the best fuel ecemony & i will post the results on this site , maybe some one might find it useful

 

[rocket ron]

Re: best fuel ecomony with this prop ?

ok yamaha just sent another email informing me that maybe there is room to go down a size in the prop, but ill get the test done before handing over my hard earnt cash

 

[Silvertip]

Re: best fuel ecomony with this prop ?

Your sevice guy will not be able to confirm with any certainty that ANY prop is best for fuel economy because it can't be done without a fuel flow monitor and even then it will only be correct unless you ALWAYS carry the same load and operate at the same speed. That won't happen. The key to economy is to install a prop that allows the engine to operate at or very near the top end of the manufacturers recommended WOT rpm band. That engine should rev about 5500 at WOT with an average load. Trying to slow the engine down with the idea that you save fuel is simply wishful thinking and in fact it lugs the engine so you need more throttle rather than less. The Yamaha web site has a PEERFORMANCE BULLETINS section. You can select your boat (or one similiar), your engine, and the performance tests presented will inidicate which prop is optimum for that combination. Prop it for WOT and fuel economy and speed will be whatever that combo provides. It doesn't get better than that.

 

[rocket ron]

Re: best fuel ecomony with this prop ?

thats what ive been looking for since my first post thank you

 

[steelespike]

Re: best fuel ecomony with this prop ?

As suggested earlier without confirming your present rpm and speed and confirm the prop size
you still can't be sure of your present results or the results with a prop change.