how mucth thrashing can a 15hp take

[steptoe1111]

hi guys how are you i bought a 12ft savage tinny a coulple of years ago its got a 2005 modle 15 hp 2 stroke mariner out board this is a exelent little motor i have had no troble with at all my question is i clock up alot of miles in this tinny its not rare for me to cover around 20-35 kilometers on most trips ,one trip i thought i would take it easy and only go at half speed instead of a plane and what i found is i used twice as mucth fuel ,is the motor working harder maintaining half speed than a plane? the other thing is when the nose of the tinny starts to drop into a plane the motor is doing verry close to 4and a half to 5 thou rpm i think the motor revs out at 6 is it considerd safe operation to run it between 5 to 5and and a half thou planeing for periods in excess of 45 mins? the motor is a little more smokey at startup than when i bought it but still starts first pull allways any imfo you could give would be great ive only been on the water for a couple of years now and im still getting sea legs thanks heaps shaun

 

[5150abf]

Re: how mucth thrashing can a 15hp take

Welcome to iboats.

I don't know the exact rpm of that motor but it sounds like you are in the ballpark at 5500, outboards are designed to run a certain rpm, too little is bad and too much is bad but I think you are right on.

On a long run I have mine at WOT (wide open throttle) for a half hour, 45 minutes, I presonnaly don't think it hurts them at all as long as you are running the right oil mixxed correctly, I go 50:1 and then just a bit extra for good measure.

The best way to tell the health of a motor is a compression check, once you have a base line reading you can check it now and then to see where you are at, best to check it hot to get a true reading but cold is fine to, just do it the same each time.

100 or better is good and the cylinders should be within 10% of each other.

And on plane you are going on top the a water, at less than plane you are pushing through the water, for best mileage you want somewhere between full throttle and when you come off plane

If taken care of the 9.9s are pretty indestructable.

 

[tashasdaddy]

Re: how mucth thrashing can a 15hp take

i have a 2004 50 on a pontoon, have ran it 6 hours, at just off wot. they are built to run fast.

 

[JB]

Re: how mucth thrashing can a 15hp take

Your boat has the least drag when on plane. That is why you burned so much fuel running at half speed but not on plane.

Your posts would be much easier to read if you included punctuation and capitalization. We can get into very bad habits texting.

You will get the best mileage and longest life from your outboard if you keep it on plane at whatever throttle setting is needed to keep her there.

 

[Silvertip]

Re: how mucth thrashing can a 15hp take

The main reason you burned more fuel at slower speed than when on plane is that is taking you twice as long or longer to get to your destination. That's why I always tell people to be sure they understand fuel economy numbers when they look at the charts published by manufacturers. If your engine burns half as much fuel at half the speed you would be going when on plane, the net result is a push since you have to run twice as long so the fuel consumption can end up the same or worse than if you got on-plane and then trottled back just a tad.

 

[jasper60103]

Re: how mucth thrashing can a 15hp take

15hp sounds like a lot of motor on a 12' tinny.
It shouldn't have any problem.

 

[steelespike]

Re: how mucth thrashing can a 15hp take

I believe the rpm range for your motor is 5,000 to 6,000 rpm.
Contrary to popular belief the best mileage for many motors is in the 5 to 6 mph.range.Not a very practical speed.The best practical speed is between just on plane and about 2,000 more rpm.Experimentation or a flow meter is about the only way to figure the best mileage.
If you raise the motor on the transom to a point just before venting(cavitation)becomes a problem and carefully adjust trim and weight distribution you will be able to get the best speed and mileage.
Just be sure it pumps water.