# 15hp yamaha top speed



## scoobeb (Dec 6, 2011)

Well i went out and broke in my new 15hp 2stroke yamaha.The best i could do was 20mph in windy conditions as i can't seem to catch a break from this wind.I had me at 270lbs,my friend at 245lbs and my daughter at 40lbs,plus the weight of the motor79lbs and all the rest of the stuff was around say 100lbs.I would say it was darn near 750 to 800lbs total with everything,the motor moved us like i said 20mph gps.Is that about what this motor should do with that amount of weight?

I am also using the standard 9pitch prop,i'm gonna move up to a 10.5pitch prop i bought.I figured it would give up a few mph on the top end.It has more then enough power to get us out of the hole.I would guess a pitch and a half should get us up to at least 23mph or better.I really need to get a 25hp 2stroke.That is just the right motor for this boat.

There is a place in my area who is selling in the box 2011 25hp and 30hp 2stroke sea pro mercs which is exactly the same as a tohatsu/nissan 25hp 2strokes.They are the same but different decals thats it.He has had them for sale for 3yrs now is the only place i have ever found were you can still get a 2stroke unless you find a left over yamaha and pay out the ying yang for it.I have seen a few leftover 25hp yamahas for close to $4k,the dealers are nuts.The mercs this guy sells are only $2600.I think that 25 would make my boat a bullet with just me on it but with all that weight it would be perfect.

Is this about the right speed with a 15hp 2stroke(20mph)?I have a 1442 jon boat that is around 200lbs.I would think the 25 would get us like 25 to 30mph which is were i want to be.I'm either gonna sell the 15hp or put it on a small 12ft jon boat made for just me to go out on because this yamaha is a really sweet running motor and i may never find another one like it again.Even with the 25:1 oil ratio on the breakin it works awesome,i bet it will run way better on the right ratio of oil after the little bit of breakin gas i have left.Ok hope someone can chime in on what speeds they get with the same kind of setup.Thanks

I have one more question.What is the best tilt position on a small outboard like that to get my top speed?It has 5 tilt positions on the motor.The pin is set on the second one up from the bottom not the top.So from bottom to top you have postion 12345,maybe it would be easier if i put a pic of it up.I want to acomplish the highest top speed possible with this little 15.I have not gone out by myself yet so i bet i would gain a few to maybe 5mph with just me in the boat on the top end.Ok any help on the tilt position would be great to thanks for any help.


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## Canoeman (Dec 6, 2011)

With that kind of weight and a 15hp, your speed sounds about rite on. Be careful running to much pitch or not enough, you want to keep that motor running in its optimum rpm range.

As for the pin placement for the tilt.. its depends a lot on the boat and the amount of weight you have, Best thing to do is to adjust it while your running your normal load and go from there. If you do adjust it on the water make sure you either do it in shallow water or bring an extra pin with you because the odd's of it being dropped are good.. even better in deeper water 

The 25 hp would make that boat skip rite along.


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## fool4fish1226 (Dec 6, 2011)

+1


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## scoobeb (Dec 6, 2011)

Iv'e adjusted the pin a few times with a load and i know what your saying about loosing it as it's spring loaded.I am very careful with that.I have adjusted it a few times but never really felt a difference except the boat would pull one way really hard when the pin was all the way to the bottom or the boat would ride with the bow higher or lower.Speed wise not really much of a difference.I am going to go out myself here hopefully soon to see what my top end is with just me and no gear or people.Someone just totaled my truck so now i'm stuck waiting for a check to get a new one.I can't go out till i find a new ride.Anyway thanks for the info.


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## bcbouy (Dec 6, 2011)

i run the same motor and close to the same weight,and i get 20 mph with a 14.5' g3 v bottom. however,a tank of gas lets me run all day and still have a bit left over,which is why i didn't get a higher hp motor. i fish small/medium size lakes. i did install a stingray xr 3 hydrofoil,but haven't tested it yet.


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## earl60446 (Dec 6, 2011)

Wow, I would have never guessed that combination would go that fast. Seems like you are doing very well to me. My old 14ft lund with about the same weight and a old 1977 15hp mariner would only push us 13 mph as measured by gps.
Tim


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## scoobeb (Dec 7, 2011)

The motor i bought was actually a 9.9 which is exactly the same motor as yamaha's 15.The are i mean the exact same motor except for one part,the reed valve that sits behind the carb.When i ran the 9.9 before i installed the new reed valve it would have problems getting the same weight on plane,once i installed the new reed valve my gps speed went from 16.7mph to 20.8mph.That was also taken on a really windy day.I bet with just me and all the equipment i can get near 25mph.

I have other plans for this outboard though.There is a place down the street that has some brand new leftover 2010 12ft alumacrafts that were $850 and now their blowing them out for $675.That is a unreal deal for a brand new jon boat.Plus it's rated for a 15hp outboard.That was the first boat i ever owned[12ft alumacraft] about 15yrs ago and i tell ya it was built like a tank.I went through some nasty water with that boat i mean it took a beaten for 10yrs or so and it never leaked a drop of water.I use to have a 8hp on the back of it and it would fly,i bet with a 15 it would down right get it.That is the plan for this little 15 to put it on a 12ft jon boat as a one man rig for me.

I'm going to get a new 25hp motor for this 1442 jon boat as that is what it's rated for,for now i will just use the 15 till i get the money up for the 25.I'm either gonna go with the 25etec or a new 25hp 2stroke merc,big difference in weight and technology.Can't beat those good old 25hp merc/tohatsu carbed motors.The biggest factor is the sea pro merc is a commercial outboard and all the parts on the sea pro are ss which makes this merc/tohatsu a tougher outboard and it's made for hard long hrs of use.So i have a decision to make when the time comes.

I can't wait to get this new 10.5 pitch prop on it.I bet it will fly with it.


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## bcbouy (Dec 7, 2011)

earl60446 said:


> Wow, I would have never guessed that combination would go that fast. Seems like you are doing very well to me. My old 14ft lund with about the same weight and a old 1977 15hp mariner would only push us 13 mph as measured by gps.
> Tim


i credit the g3 hull. my old 12' beater boat with a 15 johnny and no mods wasn't as fast as my g3


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## FuzzyGrub (Dec 8, 2011)

scoobeb said:


> I can't wait to get this new 10.5 pitch prop on it.I bet it will fly with it.



Unless there is a rev limiter you are hitting (unlikely), you probably won't gain much, if any speed. You may notice it takes longer to plane, though. 

As others have said, you are doing well for a 15hp, and boat/load you are running.

The 25hp is the right answer.


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## aeviaanah (Dec 8, 2011)

I just bought a brand new 15hp 4 stroke with a 12ft mod v and 2 people I get up to 23mph


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