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Guys, Maybe you can help. I have a 19cc Polar that I purchased last year. It has a Yamaha 115 4-stroke. I am having a real big problem getting it on plane. I believe it is a prop problem. At WOT 6400RPM, I'm running 32MPH with full tank and minimum weight. I don't think my RPM's should be that high. I think the problem is all related. No hole shot, and bad top speed, RPM ration. My prop is 13x19 aluminum, Factory Prop?? ANY SUGGESTIONS????? If not, maybe you know a place that I can try one before purchasing it. Thanks...
 

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First I'd say get the tach checked. A F115 isn't strong enough to twist a 19" wheel to 6400 on a 19ft boat. If it was 1000rpms off that would explain it. Although if the alum prop was worn in dia it would do it and cause all the other problems. It should also be checked for size, bent blades and hub slip.
 

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Discussion Starter · #3 ·
The tach seems to be working fine. Idles anywhere from 700 to 900. Don't see any eratic or jumping movement from tach or anything. Is there another way of checking tach? Is there any way to check the prop for improper wearing. No evident damage to blades or anything. Didn't really notice play or anything like that while mounted on engine. Definitely resembles a prop that's not grabbing water while driving. That's why i figured maybe wrong size prop.
 

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6400rpms is a little high at WOT. I would try a slightly larger prop like a 13.5x19. Is the motor trimmed all the way down when you take off? Maybe the tilt pin needs to be moved to trim the motor further down? We have a few different sizes if you want to test them out.:thumbsup:
 

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Check to make sure there is nothing on the hull in front of the prop causing disturbance to the water flow...like transducers, water intakes or whatever could have been added that may cause a little cavitation. I see this all the time on small flat bottom boats especially. I am assuming the motor was installed at the correct height?
 

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I am running a 13x19 on a 115 2-stroke Merc on my 17 Mako, which is significantly smaller boat then a 19 Polar, which I think are relatively heavy boats for their size. My 115 hp engine on a shallow deadrise 1250# hull twists up to 5500 rpms running 40-41 mph and she pops out of the water...my thoughts are that the engine is too high and is not getting a good bite on the water due to turbulance....check to see if the anticavitation plate on the engine (fins on sides of lower unit above prop if you dont already know??) with it trimmed down is pretty much even with the bottom of the hull....if it is 1 to 2 inches higher, then the engine is too high and needs to be lowered a bolt hole or 2..
 

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What's the general condition of the prop? How old, hours, etc? Do you often churn through sand or mud? Aluminum props are known to flex and lose pitch under heavy load - especially when they wear thin, but I doubt that is your only issue.

As Dunk mentioned, a slipping hub can be at fault, but when they go they usually let go completely or don't last too much longer before they do let go - especially at 6400 RPM.

Did this boat ever run correctly since you bought her last year? That could make a big difference in potential diagnosis.
 

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Diferent props can realy change the way a boat performs. If the boat is over 2000 pounds your speed doesnt sound all to bad. To check for hub slipage simply draw a line across all componenets of the prop with a marker then after running the boat around hard check to see if everything is still on the same line.
 

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I am the owner of the Polar in question. My brother posted it here for help. Here's a little back ground.
When I sea trialed the boat in August. It was myself, the seller, and his wife on board. The tank was 1/4 full. She was sitting right up in front of the console. The bow went up, came down and off it went, Top speed @ 30 GPS registered as well as tach and fish finder.
He brought the boat to a mechanic to have it serviced. While it was at the mechanic, I called the mechanic and asked him questions. He said knew this boat (less than 150 hrs) and said the engine was in excellent condition, etc..
The first time i filled the boat with gas (75 gallons later), I noticed the planing issue. If someone is in front, the bow comes down.
I originally thought the engine should be lowered to getter a better bite but was informed that if the cavitition plate was at or just below the surface while on plane I was fine, which it is. Still thinking to lower the engine but noticed if i do i would not be able to tilt up all the way because the ram for the power steering would hit).
If anyone is still reading :thumbsup:, the prop white aluminum 13 x 19 does have a few nicks on the blade so i am not sure if it is a tru 13 x 19 prop.
I was looking to find out if anyone knows who may offer demo props so i can get this dialed in correctly.
 

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I am running a 13x19 on a 115 2-stroke Merc on my 17 Mako, which is significantly smaller boat then a 19 Polar, which I think are relatively heavy boats for their size. My 115 hp engine on a shallow deadrise 1250# hull twists up to 5500 rpms running 40-41 mph and she pops out of the water...my thoughts are that the engine is too high and is not getting a good bite on the water due to turbulance....check to see if the anticavitation plate on the engine (fins on sides of lower unit above prop if you dont already know??) with it trimmed down is pretty much even with the bottom of the hull....if it is 1 to 2 inches higher, then the engine is too high and needs to be lowered a bolt hole or 2..


No expert, but this is what I thought when I read your post. I did not post as the owner of a single boat, but now that the idea has been posted I'll chime in. I'd put my money on this suggestion. I have a 21' with a #14 prop on a F150 and it planes without a problem, although is very stern heavy. The lower unit sits quite low.
 

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Check engine specs, what ever mfg. says, you are propped correctly, if you run the high mark light. e.g. 2 people 1/4 tank, if you run the boat with 4-5 all the time, and never light prop to mid way between "max operating range.
The wife up front is indicative of the standard practice of dealers to sell boats underpowered. Generally you will seatrial a new boat with your son, and 1/4 tank of fuel.
Now fill up 70 gallons at 7/lbs. per gallon, and your 3 big buddies and you have a slug!
You will be able to correct some of the characteristics you are experiencing with trim tabs, notice the Seahunt "offers" not standard, a minimal tab, even on their 23, when powered by a 200 four stroke. The mfg, will generally make sure their boat performs, but each and every owner is different,
The budget dealers, will underpowerer and under options to sell to the un-suspecting a lower performing unit.
Also be aware the Yam perf. reports are ideal as well.
Compare similar weight and length CC utilizing this resource


http://www.yamahaoutboards.com/owner-resources/performance-bulletins

You are welcome to call, and we can discuss options to HELP correct.
Thx Capt. Rich
 

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In reply to atlantis's comment, I will need to check the diffuser ring. Is the diffuser ring a seperate part that can be added to a prop? I know the seller (private guy not a dealer) mentioned he used to beach the boat so I am leaning towards my prop may not be a true 13 x19. I may have it checked so i know where to start. I may start with a stainless 13 x 19 (some form of a stern lifter prop) and get numbers from there. Thinking the stainless will drop some rpm's and give a better hole shot. Worse case is, I get my boat within range and add trim tabs i guess.

In reply to Barrel's recommendation on checking hub slippage, the prop comes off as an entire unit. I did not see a seperate hub though i will check.


Thanks for the information guys. The season is fast approaching (though i am unsure if it ever stopped) Good luck


As for Mrfrits44, believe what you want, and you are correct, I am no expert.
 

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Since the condition probably existed before you purchased the boat and you know for sure that the boat was frequently beached, the cause could be any number of things. I don't think anyone here can provide an accurate diagnosis without seeing or testing things first-hand.

I think you're on the right track by switching to a stainless prop of the expected same size. All things being equal between the old and new prop, I believe stainless alone could drop the RPM by 50 (maybe Ray - Atlantis can confirm).

Another option (if you have a micrometer or caliper handy) is to measure the thickness of the blades. Better yet, just pull the prop off and bring it to Atlantis for measurement. Ray can tell you right there whether size, cup or flex due to wear is the issue. He can also tell you if it is burned due to cavitation at high RPM. If the prop checks good in all aspects, then you may need to consider other possibilities like engine suitability, height, hub slip (I'm doubtful of that), etc.

BTW, the hub is pressed into the center of the prop with a plastic damper between the shaft spline and outer metal hub of the prop itself. It is designed to break away if the prop strikes something, so not to damage the lower unit and shaft. Over time these hubs tend to break free on their own, allowing the shaft to spin within the prop. It's all part of the actual prop - nothing separate.
 

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All the componenets may seem to be one but there are actualy seperate parts with rubber seperating them. Last spring I had trouble going on plane yet when wide open my top speed was normal. There was no sign on the prop of torn rubber or anything visible that would make you beieve the prop was slipping on the hub. But the majic marker didnt lie. When I drew a line across all the componenets and ran the boat hard a quik inspection revealed that the line was now all broken up as the parts were slipping. I had it rehubbed in Marmora with a heavy duty hub at a cost of $70. I would not waist $70 on an aluminum prop if slipage is a problem then buy a stainless and carry the aluminum as a spare.
 

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There is a selector switch on the back of the Tachometer. Make sure it is set to "6". If it is on 5, the tach will read higher than actual rpm.
 

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Aluminum props are great, they protect you from the added expense of popping a lower, should you have an altercation with an underwater object.
S/S will need to be adjusted, an S/S prop identical pitch and Dia. is not, and will not perform the same.
Get your self a benchmark, work forward, and you will get her right!
Again,
you are welcome to call and discuss
 

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Aluminum props are great, they protect you from the added expense of popping a lower, should you have an altercation with an underwater object.
S/S will need to be adjusted, an S/S prop identical pitch and Dia. is not, and will not perform the same.
Get your self a benchmark, work forward, and you will get her right!
Again,
you are welcome to call and discuss
See I don't see any reason not to go to a stainless prop in NJ waters. 99.99% of what you'll hit here will be sand or mud. That thing about Stainless wheels being dangerous to lower units really don't wash here. If the alum prop pushes the boat at all like it does here I would not waste another dime on it. This problem could be as simple as the blades being out of balance. One blade could have 20" pitch, another at 18" and one at 19". Still averages out to 19" and I've seen more than one factory prop like this. But it's still an alum prop and is not worth wasting any money on it.

F115 Yams run a 2.15 to 1 gear ratio. Kind of a slow prop twister with plenty of powerhead RPM's. My recommendation would be to go with a 13.25" x 17" Turbo made by Precision Propeller. Even these props I recommend sending out to good prop shop to be checked.

http://www.boatownersworld.com/Props/turbo/turbo_1.htm

Any stainless wheel has lots thinner blades than an alum wheel. They bite harder and cleaner right off the bat. Buy this wheel and run it for a day recording speeds at different rpms, try different loads. Then send it out to a propshop and tell them the numbers. When you can speak to a propshop intellgently you'll always get better results. It's easy for a propshop to add pitch and cup. You never want to come down from a higher pitch wheel to lessor pitch and cup. The only part of an outboard prop that can be bent are basically the blade tips. Too much of each blade it attached to the hub to bend it there.

The right prop for that boat is going to between 17 and 19" pitch running her with a medium load and getting the engine to turn 6000rpms. You'll never hurt that engine if she turns 62-6300 with real light load on fuel and people. But that engine has a tendency to get buried if she's proped to turn less than 56-5800 rpms with a load.
 

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Thanks for all this information Guys.
Once i finish prepping the boat for my needs I am going to get on this prop situation. Every one provided many avenues to check and like SSawed made mention, I should have the prop checked to see what it actually is and go from there. I did notice one thing that remained consistent, I was thinking going to a 21 pitch vs the 19 but it seems most are recommending 19 or 17 which is leading me to believe my props may be out of line.
Once figured out, I will let you know the results :)!

Good luck guys!
 

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Hello guys
My prop / planing issue has been resolved.
Unfortunately when I / my brother posted the question we were basing it on the information we knew, which all my original figures we not correct.
Due to many fuel related issues discovered this year, I was forced to take it to a certified dealer. I went to gateway marina, and I can't say enough good things about them.
Long story short, they changed my sierra filter to a racor, replaced my inline filter, replaced a fuel line which a different mechanic put on of smaller diameter, vst filter replaced or cleaned, injectors cleaned, etc...
Then they took it out for a run. Apparently my rpm gauge is way off, once they opened up my fuel system and my engine was able to breathe again the rpms said 7000. When hooked up to their laptop, I was topping out at 5500.
I purchased a Yamaha aluminium 13 x 17, and the boat took off nicely with the tech, myself, and my brother. No one had to stand in front to get the bow down and we were seeing speeds in excess of 30 mph.
Now the boat is safer to drive since I am finally in control of it, with out having to ask people to move to the front to bring the bow down, and it is enjoyable.

Thanks to all replied
Have a safe season
 
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