86 15hp evinrude RPM problem

[imported_Warren]

I am having some R.P.M. problems. I have my 15hp outboard on a 12 foot Western Aluminum X-tra wide (almost 6 feet wide) boat. It really hauls some serious *** with only me in it but when I put another person in my boat WOT RPM's drop<br /> <br />quite a bit. By myself I go 22-25mph with a <br /><br />passenger 10-13mph. I know my boat is wider so <br /><br />its going to have more drag but do I have to <br /><br />consider my boat a 1 person job? Or can I re-<br /><br />prop? Can't handle the weight of getting a <br /><br />bigger outboard. If I re-prop i'll have to keep<br /><br /> changing it back and forth everytime I go. Is <br /><br />there even a prop for me to re-prop with for <br /><br />this little motor??...Thanks in advance, I don't<br /><br /> want to damage my motor by stressing it with <br /><br />too much weight..........

 

[rickdb1boat]

Re: 86 15hp evinrude RPM problem

What pitch prop are you running now? Many people change their props back and forth when larger loads are in the boat. Also, many do the same thing while pulling a skier. Then change back to the regular prop when done. Better to have the engine in the proper RPM range, than to lug it when you have a load on it. They do make a 10 X 7" pitch that may help, if you are now running the standard 9-1/2 X 10" pitch.

 

[R.Johnson]

Re: 86 15hp evinrude RPM problem

The main factor you are dealing with here is weight, and how it is distributed.Are you running a trolling motor with it's own battery. How many anchor's. Try to balance any of this equipment, and play with the trim angle on the motor. These small motor's react quickly to any weight they have to push, and sometimes work best with the engine tucked all the way under. If your passenger is a large person, have them set close to the front. As stated before you probably are going to need a smaller prop. I have seen a lot of these jon boats where people add sub flooring, and carpet, that really puts the weight on.

 

[cobra 3.0]

Re: 86 15hp evinrude RPM problem

You must have a heavy 12 ft boat! My 14 ft boat goes 25 mph with one adult and two young teenagers on board. Alone I will go 30 mph..that's verified on my GPS. My boat only weighs 140 lbs.(Princecraft Cartopper)<br /><br />I have the standard prop that came with my 1997 15 hp Evinrude two stroke...a 9 x 11. Is your hub shot or blades banged up? This prop should take care of all your needs. There's no reason to drop half your speed if you have the standard prop.

 

[imported_Warren]

Re: 86 15hp evinrude RPM problem

Yep, my boat is wide and heavy. I have a bow mount trolling motor. 1 big battery and I built a custom deck for it with pedestal seat. I put my motor on my buddys 14footer and it moved really good. His boat is a foot and a half slimmer than mine. It moves good but is really unstable. I'm pretty sure my prop is stock. Where do I look to find out what the pitch is? I have been lookin at props for sale and they seem really steep. Mine is in mint condition(never hit anything yet). I'll go check it out and get back with a prop size......Thanks for the help...Warren

 

[OBJ]

Re: 86 15hp evinrude RPM problem

Warren...you can also improve performance by raising the motor up on the transom so the anti-cavitation plate is equal to or just an inch above the keel of the boat.<br /><br />Good Luck!

 

[cobra 3.0]

Re: 86 15hp evinrude RPM problem

Warren, mine was stamped on the outside body of the prop. It can be stamped anywhere...sometimes inside the exhaust end of the prop.

 

[waterinthefuel]

Re: 86 15hp evinrude RPM problem

I believe some of us are fudging just a little on their top speed estimates. I have a very sleek and "thin" 13 foot fiberglass boat with a 28 and a Stingray on it. It does 27.5mph with just me. This is twice the power you guys are describing and less boat. However, it is fiberglass, but if you load down your light boat with an adult and two teenagers, you have the same weight as mine with just me. I don't know of any 14 foot boat that goes 30mph with 3 adults in it, and only has 15 ponies out back. <br /><br />Sounds a bit unrealistic. I haven't seen a 15 in our 180,000 acre lake that I couldn't run circles around, small light aluminum boat, or not.<br /><br />No need to fudge guys. You all have great craft.

 

[oldboat1]

Re: 86 15hp evinrude RPM problem

If you have tiller steering, try moving to the middle seat -- might be amazed at the speed. I use a tiller extension in my 12' aluminum, and can plane with a 7 1/2. A 10 is really fast (use my 12 footer to test out motors I'm working on). A 15 would be overpowered on my stock 12' Starcraft. I would guess your issue is weight distribution.

 

[imported_Warren]

Re: 86 15hp evinrude RPM problem

Hey guys, just checked and the prop on the motor is a 9 1/2 x 10 is this prop stock? Whatcha think, do I need to re-prop to get the RPM's up?..Did a search here on the site and found a 5 x 10 and 7 x 10, would one of these suit me better with such a heavy small boat. I forgot to mention that I also have a heavy bait tank on it that I use 50% of the time.......Thanks in advance for the replys....Warren

 

[imported_Warren]

Re: 86 15hp evinrude RPM problem

Just purchased a michigan 10 X 7 here at iboats for $75 with shipping....Did I make the right choice????? The lady on the phone said that it will boost up my rpm's by 600. Will this be enough? The only other choice was a 10 X 5 and that seemed to be too much of a change in pitch....We'll see....Warren

 

[cobra 3.0]

Re: 86 15hp evinrude RPM problem

Waterinthefuel, if you read my post correctly I say 30 mph ALONE and 25mph with adult and two young teenagers(400lbs load). Your fiberglass boat weighs probably twice as much as mine. Can you pick it up and put it on the roof of your car? I can. I had a similar set up to yours..a 15ft aluminum(weight probably similar to yours) and a 30 hp Johnny. So, we used to compare speeds. Under load the 30 hp went slightly faster. One guy only with the 15, would go past the 30 with three people.<br /><br />Warren, that's the next pitch down and it'll help quite a bit. I too think the 5 x 10 is too much. It's probably designed for sale boat kicker use or pontoon-type boat use.

 

[OBJ]

Re: 86 15hp evinrude RPM problem

Just a word of caution.<br /><br />Warren....be very careful if you have no way of knowing exactly what the rpms are doing. A tach is a must for proping out an engine. Adding 600rpms may take you over the engines rated rpms.

 

[imported_Warren]

Re: 86 15hp evinrude RPM problem

Is there a way for me to put on a Temporary tach, run in one day WOT under all loads to make sure i'm not over revving. Then take the tach off?......I am using a tiller and don't have a console to put the Tach on......Warren

 

[cobra 3.0]

Re: 86 15hp evinrude RPM problem

It's called a tiny tach.<br /><br /> http://www.tinytach.com/

 

[imported_Warren]

Re: 86 15hp evinrude RPM problem

Got my prop 10X7 and my tiny tach, hooked it up and ran it. I'm overevving, went up to 6800rpm's, WOT is 6200. The stock prop is a 10X9 1/2 and is too much prop. Does anyone make a 10X8? This is a bummer. By the time I get it running right i'm going to own every prop made for an evinrude 15hp outboard I have heard of people getting there props worked over. Is this possible to get mine bent into a 10X8 or 8 1/2?......Thanks in advance for any help......Warren

 

[OBJ]

Re: 86 15hp evinrude RPM problem

Warren....Bomby offers a 9 1/4 X 8 in aluminum and a 9 3/8 X 9 in SS. The SS costs about $240.<br /><br />Your throttle range, if I recall from the service manual, is 5000 to 5500 rpm.<br /><br />Did you look at the engine set up on the boat as was posted earlier? This will make a difference in performance.<br /><br />Keep us posted...thanks.