15hp 2stroke yamaha speed

[boater1234]

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.

 

[5150abf]

Re: 15hp 2stroke yamaha speed

I think that is about all you are gonna get out of that, with that hull and weight 20 is pretty darn good.

Obviously the 25 or 30 would be alot faster but they weight more so the transom would drop a bit and it sound slike you already have the hull pretty well loaded so take that inot consideration and of coarse make sure the hull is rated for that power.

*** to trim p[osition, without power tt it is always going to be a compromise, a given trim positon is ideal for a certain speed an condition so just play with and find a good median spot.

I had a tinny year s ago and I would put it on the 3rd pin when I was going to run then bump it down once I got on my spot but I never did find one spot that worked everywhere.

 

[boater1234]

Re: 15hp 2stroke yamaha speed

The boat is rated for a 25 but the 15 seems like it's doing a good job from what people are saying.Also the 25 is only gonna be 35 more lbs in weight.I have found brand new 2011 25hp sea pro 2strokes in the box i can get which is rebaged 25hp tohatsu's/nissans.I'm gonna sell my 15 or put it on a smaller boat and get a new 25 for this boat.From what i have been told all you have to do to the 25hp sea pros to make it a full 30hp is remove the restricter plate that sits behind the carb and thats it.So that is my plan.I bet with just me and equipment in the boat i can get prob a few mph faster,plus i'm gonna put a new prop on it 10.5pitch instead of a 9pitch.That will gain me even a few mph more.


I wonder if i were to get a new 20hp 4stroke how much better would it push my boat?I know it's only 5hp but i read a ton of threads were people are running a 20hp 4stroke merc or yamaha on the same type of boat and they get like in the mid to upper 20's with no problem and near or more weight in their boats.From a 20hp 4stroke i would gain 5hp and over 100cc's of motor,i wonder what kind of performance i would get instead of a 25hp 2stroke.I know the 2stroke would be a power house but i also would like to have a cleaner engine if i can help it.Any opinions on a 20hp.Thanks for the message.

 

[steelespike]

Re: 15hp 2stroke yamaha speed

Imo a 4 stroke is a much more complicated motor with more service intervals that are also more complicated. Your 2 stroke will likely go for years with simple seasonal service.
Sometimes a 4 stroke will struggle with a load and may require very careful prop selection.
Your 15 weighs about 80lbs the 4st 20 about 120.
You shouldn't change props without knowing your present rpm. Also your speed with the rpm tells a lot more about your setup.An induction tach like a Tinytach or an optical tach will serve you well. I'm guessing a 1 1/2" pitch increase could lower your rpm by 300 to 400.It will also will slow hole shot. Lower rpm could put the motor below the rated wot rpm not good for the motor. Your 15 likely won't plane with your typical load.

 

[Sea Rider]

Re: 15hp 2stroke yamaha speed

Don't play with prop pitch unless you have a induction tach mounted on engine and know factory mix, max parameters to be in the safe side, make a wot test and check if rpm are near or around max rpm stated for that engine, then decide proper next pitch if needed. 20 Knots is the most you will get and that's a good speed. Perhaps 1-2 knots more boating solo ? Most standard factory props are delivered with medium pitch props, good hole shot with slight less top speed. If placing a prop that gives more speed, will lose best hole shot. Can't have both at same time.

Mercury prices are tempting, buy a 25 and pass it to 30 HP for peanuts. Both models weights the same 52 kilos, go for it if your boat is rated for 25/30 HP engine.

Best trim position is around 2-3 hole out from transom, distribute passengers well inside boat, wot to plane fast and check you have your cav plate paralell to water surface with a 90? engine at transom's back.

Happy Boating

 

[boater1234]

Re: 15hp 2stroke yamaha speed

If i put the 10.5 pitch on the motor it will be on the back of a smaller boat like the 12ft alumacraft i want.Also the motor is rated for 4500-5500 rpm i'm sure with the 9pitch it's closer to the upper rpm range so a 10.5 should still be in the 4500 to 5500 range with no problems.Your right though i need to get a tiny tach anyway.I'm just going to try the 10.5.The 9pitch has a ton of hole shot actually way more then i need so i think a 1.5 pitch increase wouldn't hurt it.I have done this with a 15hp merc which is close to the same specs a hair different as far as rpm range and it worked out just fine.I am going to try it on my bigger boat one time with a load and with just me on it.If it doesn't feel right then i will just go back to the 9pitch till i get the smaller one man boat i want.


I want a 12ft boat so i can just throw it in the water and go with just me on it,a very light load will be in it plus me so it won't go over 500lbs total in the boat.I'm getting the 12ft for just a small fishing machine so i can get in some really tight places by myself.

 

[JimS123]

Re: 15hp 2stroke yamaha speed

I have a 13 foot v-hull aluminum that does a tad shy of that with its original 9.5 Rude. With my newer 9.9 it just about equals your 15. That's with me, the wife and both teenage boys aboard.

Seems like you have a lot more weight than you imagine, or your 15 isn't living up to its full potential.

The 9" prop is what you should be running. A higher pitch will not do the job. You need a tach to confirm rpm.

 

[pecheux]

Re: 15hp 2stroke yamaha speed

On my 14 footer at 280 lbs + me @ 195 lbs + motor @ 80 lbs + full tank @ 50 lbs + misc gear I get 20 mph with either a Force 15 hp or a Johnson 9.9 ... so you be the juge. I think you are doing real good with that much more weight.

Cheers.

 

[steelespike]

Re: 15hp 2stroke yamaha speed

If i put the 10.5 pitch on the motor it will be on the back of a smaller boat like the 12ft alumacraft i want.Also the motor is rated for 4500-5500 rpm i'm sure with the 9pitch it's closer to the upper rpm range so a 10.5 should still be in the 4500 to 5500 range with no problems.Your right though i need to get a tiny tach anyway.I'm just going to try the 10.5.The 9pitch has a ton of hole shot actually way more then i need so i think a 1.5 pitch increase wouldn't hurt it.I have done this with a 15hp merc which is close to the same specs a hair different as far as rpm range and it worked out just fine.I am going to try it on my bigger boat one time with a load and with just me on it.If it doesn't feel right then i will just go back to the 9pitch till i get the smaller one man boat i want.


I want a 12ft boat so i can just throw it in the water and go with just me on it,a very light load will be in it plus me so it won't go over 500lbs total in the boat.I'm getting the 12ft for just a small fishing machine so i can get in some really tight places by myself.

A 12 ft may struggle to plane with your 280 in the stern and the 10 1/2" prop won't help that.
I'm guessing a 1 1/2" increase will lower rpm quite a bit more than the 200 rpm per inch rule of thumb.
You may need a tiller extension so you can be in the middle seat.

 

[RonJon24]

Re: 15hp 2stroke yamaha speed

I have a 14' Aluminum Vhull, with a total of about 700-800 pounds of total load with the same 2 Cycle Yamaha 15hp... it is a 2003 model. Today, I got about 21-22 mph with a 9 pitch aluminum prop. Like you, I was really hoping for the upper twenties, pushing 30, but I will settle for the 22mph. It seems reasonable.

I was researching here, thinking I wanted to change pitvhes, but that seems more complicated than I first thought. Maybe I need to get a tiny tach to check things out. I need to learn how tachs and prop pitches work. I heard a four blade would do me well too. Ideas?

 

[CudaKillinSOFLO]

Re: 15hp 2stroke yamaha speed

I have a 14' Aluminum Vhull, with a total of about 700-800 pounds of total load with the same 2 Cycle Yamaha 15hp... it is a 2003 model. Today, I got about 21-22 mph with a 9 pitch aluminum prop. Like you, I was really hoping for the upper twenties, pushing 30, but I will settle for the 22mph. It seems reasonable.

I was researching here, thinking I wanted to change pitvhes, but that seems more complicated than I first thought. Maybe I need to get a tiny tach to check things out. I need to learn how tachs and prop pitches work. I heard a four blade would do me well too. Ideas?

It's not complicated... if you're at 5500 wot with a 9 pitch for instance and wanna be at let's say 5300 wot. You can go up 1 inch of pitch. Every inc up in pitch is about a 150-200 rpm drop. Every inch down is a 150-200 rpm raise. I run a 14 footalumacraft flat jon with a 2006 15 hp mercury 4 stroke with 9x10.5 and do 25mph (gps) with me, my dad, and gear (about 900 lbs total)