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All,

I've read many posts here over the years and thankfully have been helped indirectly by many of your experiences. I come to you now with a problem of my own.

I have a 1983 Outrage 18, with a 2003 Yamaha 115 four stroke. In a nutshell, we have lost speed but have not lost RPM's. I will provide as much information as possible in hopes you may be able to help.

We put a T-Top on her last summer, and aside from water in the fuel two years ago, haven't had any issues in four years owning the boat. A few weeks ago we hit a rock in the shallows and dinged the prop pretty good. It was already on it's last leg, and needed to be replaced, so it gave us a good excuse to do so. We bought the same exact prop and I'm sure you are going to ask what's the make/model, so I'll get that, but after putting it on, the boat was flying. We don't have GPS or a speedometer on the boat, but you could tell it was running good. I guessed we picked up at least 3-4 mph with the new prop.

After a few weeks, it's declined in speed drastically, and also isn't as quiet as it used to be. I can't tell for sure if it's been a gradual decline, or if it happened one day. The boat is used by a couple other family members, so while it's used regularly, it's not regularly used by me. We also have been wakeboarding and kneeboarding quite a bit lately. Anyway, RPM's haven't declined, however speed seems to have been cut in half. To the point where with two in the boat I've gotta get the other guy to go to the front to get the boat up on plane, and that's a WOT. I used the gps on my phone and clocked it at a whopping 22mph at WOT, running about 5500rpm. I swear she used to do at least 35mph. But after noticing the difference, I took the keys so no one else can use it until I diagnose and fix the problem. Oh and the boat isn't sitting abnormally low in the water, so I'm ruling out water in the hull as an issue.

One other point, about 6 weeks ago we had to replace the fuel line running from the tank to the filter/motor. The line had become frayed and deteriorated causing a leak. It cut off on us coming back from a fishing trip and after determining pressure in the bubble had been lost, we manually pumped the bubble for two miles to get gas to the engine while we putted back to the dock. Reason I divulge this is a friend said it could be dirty carburetor, which could be caused by breakdown in the old fuel line and debris getting sucked into the motor. I thought the motor would run rough, or I'd lose RPM if this was the case, also thought the fuel filter would catch any debris(maybe not).

Had another friend say it could be the prop, so changed back to the old and took it for a spin. Same problem, same RPM no speed. The new prop is in great shape and no dings. Maybe both props are spun??? Another buddy said lower unit, so was gonna sample some oil to inspect for shavings/chunks of metal. Also thought about checking spark plugs or getting the compression checked.

Based on my long story, is there someone out there that might be able to help? Thanks in advance for your time and advice.

Phil

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Phil, I am guessing you initially damaged the lower unit when you hit the rock, and then it has gotten worse over time. Sounds like a clutch slipping to me - I'm not exactly sure how O/B clutches work, and didn't even know they could slip, but that's what it sounds like. Draining the lower unit oil and checking for chunks would be the next step I'd take.

Tim

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How hard did you hit the rock and how badly was the prop damaged?

You said others use the boat, what did they do, cruise, tube etc? Did they notice anything?

With the boat out of the water, motor off and in gear, can you turn the prop with your hands?

When you got a new prop, did you replace the hub insert too or reuse the old one? You may have a partially damaged hub. While the hub is designed to reduce the shock and damage to the lower unit, it can't protect it from everything.

I second the concern above of possible lower unit damage.

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There may be lower unit damage but that does not comport with what is reported. He's getting the same RPM but much less boat speed. There is no way lower unit damage can account for that.

There is no "clutch" in the lower unit of an outboard in the automotive sense. The gearcase is either in gear, or not. There is nothing to "slip".

The propeller hub, however, can slip. That condition is known as a spun hub and can be caused by a prop strike. The hub is designed to be sacrificial and protect the propeller itself in the event of a prop strike. I recommend the propeller be removed and the hub examined.

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Thanks to all for the replies.

We hit the rock pretty hard, but I'm not exactly sure if the motor hit first or the prop. The engine didn't shut off, and the motor was kicked up in the air. There was also a little ding on the front side of the lower unit, so I'm assuming it hit the motor first then the prop.

No tubing, just wake and kneeboarding.

I'm going to take the prop back and have the dealer check it, but again I put both on and had the same results. Prior to pulling the old prop off it was running fine, which led me to assume it was an engine issue.

Gonna also test some oil in the lower unit, just to rule it out.

Should I check the spark plugs, compression, or the carbs?

Thanks again

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Wait, I don't understand something.

- You replaced the old propeller because the old propeller was in bad shape. "...we hit a rock in the shallows and dinged the prop pretty good. It was already on it's last leg, and needed to be replaced," is what you wrote.

- You now have a new prop that is visually undamaged.

So how is putting the old prop back on, and getting the same results, not a powerful indication that something is terribly wrong with the new prop?

For now, forget the spark plugs, compression, and the carbs. Forget the lower unit. Let's not confuse things here. Examine the propeller and tell us what you find. No need to take it to a dealer. Pull the hub and see if it is buggered.

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Tom, ahhhhhh I'm with you now.

Yeah the old prop was cosmetically damaged, but it still ran fine before we took it off, at least I think so. But I can't recall how long we ran it before taking it off.

I'm heading to check the new prop today and will report back. Thanks.

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Check the HUB insert.

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Ok guys, checked both props and hubs are good. Even ran the new prop back to the place I got it and had them check. Looks ike its noT the prop.

Pulled the boat this morning and checked oil in lower unit. Looks good, clean and no real shavings to speak of stuck to the plug or in the oil.
Then again, doesn't rule out the fact that something is wrong there.

Since I was curious, pulled the plugs and gaps are good, and they don't seem burned. Started raining so cut my inspection short.

Thoughts?

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Again I ask: What propeller are you using? Brand, model, part number?

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Prop is

BS. PRO KDK
Y 13-1/2 x 15

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I have never herd of any such part description of a propeller. I have no idea what that is.

I have the entire yamaha propeller catalog in front of me and the only 13-1/2" x 15" prop they offer is they aluminum three blade, part # 6E5-45947-00-EL

Can you tell us something about it? Color? Is it painted or polished? Is it stainless steel or aluminum? It has three blades, right? Does it use a press-in rubber hub or field-replaceable hub like the Flo-Torq or Guardian SQ-Lok?

I'm just trying to figure out what you have and I beginning to grow weary of playing twenty questions. Maybe a photo would help.

Or maybe it doesn't matter what you have now; it's not working. I suspect you have some overseas made aluminum aftermarket prop and it's probably just crap.

Lets just try to figure out what a good prop for you boat would actually be.

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Lets' take this ab initio. An Outrage 18 with a Yamaha F115 is normally good for close to 40 MPH. The F115 has a 2:1 gear ratio and a 6000 RPM reline which is what the WOT engine speed should be close to.

With a T-top maybe the boat is only good for 37-38 MPH. There is just no way a 15" pitch prop can get to 6000 RPM without a tremendous amount of propeller slip and that I what is suspect it going on here; the motor is simply "blowing out" the crappy prop which looses grip and the engine races. That explains the low speed and high RPM.

You want a good stainless steel propeller that will grip. The F115 uses the intermediate size gearcase (4-1/4") is relatively powerful for the propellers available in that class.

To gain more blade area and improve grip for that intermediate gearcase motor you might consider a propeller model with more diameter. The Yamaha Pontoon Series is a good example and I think would be a good fit. I would select their 14" x 13" size, part #MAR-PNTN3-V4-13 http://www.boats.net/parts/detail/pro...V4-13.html

The exact same propeller can be had in the Stiletto brand. It is the Star 4.25. The 14" x 13" Stiletto Star is part #D804013 and it will cost a LOT less.

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Getting back to the old prop, I did a little sleuthing for fun. It seems you have a propeller from BaekSan Propeller Co., Ltd. . Here is some company information:

http://www.boatshowdubai.com/page.cfm...xhibID=254

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It appears that you have some pretty good sleuthing skills!

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BaekSan Propeller Co., Ltd. makes aluminum propeller that are knock-offs of all the outboard manufactures' props. Their motto is, and no, I am NOT making this up:

"BaekSan Propeller! 1% Different!"

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Propellers are like car tires in that people always seem to want to fit the cheapest ones possible, ignoring the fact that it is the prop/tires that is one of the most critical parts contributing to vehicle performance. If there's anywhere you should buy the best it's at the prop.

John K.

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Sorry, for not responding sooner, been traveling....

So the prop is painted, prob powder coated, white is the color but that probably makes no difference.

There is a rubber insert between the prop and hub.

Since I'm out of town, I had my brother take it to the shop to get looked at, the boat that is.. Gonna be a couple days till they can look at it, and I don't get back till Friday, so it's gonna have to wait.

Let's assume it's not the prop. Anyone care to speculate?

Thanks again, especially to Tom.

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Your problem is not your motor, it's your prop and we already figured out what the prop is.

What you'll pay the shop to search for a problem that does not exist would pay for a new stainless steel prop.

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They really could have throught up a better brand name than "BS PRO" for their line or props...

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Ok, so getting a new prop, but the shop pointed out something we didn't realize, and something I thought wasn't a huge deal. Barnacles!

We keep the boat in the water most of the summer,and last year barnacles weren't an issue. After pulling the boat last week we saw that they have definitely started to cover the bottom.

My question now is, could barnacles cause such a loss in speed, and could they have taken over in a week or two? Again to the point where it's hard to get on plane, and I get no noticeable increase in speed from 4400rpm to 5600rpm?

The shop seems to think so. It is running a bit louder, where as before you couldn't tell it was on at idle. Might have em clean the fuel injectors before I pick it up.

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I am going to guess you don't have bottom paint? It's a must where you are if you leave the boat in the water. Last year there was a lot of rain, so the fresh water kept the barnacles down, this year we have had very little rain. Where I am, we have had rays and jellyfish since mid June, usually they don't show this far up river until mid-late July

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It's painted, but was painted the beginning of last summer. We kept it on the lift all winter, and no noticeable barnacles before putting in this summer. Definitely had some coverage when we pulled it out.

Probably going to scrape sand and repaint before putting it back in.

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DO NOT waste any more time or $ on this until you clean and repaint the bottom. Barnacles are devastating to the performance of your boat.

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I totally agree with Dave. If there are barnacles, all bets are off.

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Update for you....got the boat back, scraped, sanded and repainted the bottom. Put her in today and she's running good. Speed back up and no issues.

Though, I do think the motor's running a bit rough. She used to purr at idle to the point where you couldnt tell it was on. Now it's a bit louder.

Gonna get it serviced in the winter, but for now we're back in business.

Thanks to all for your help and advice.