Motor over wevving -Watch-

[jtexas]

Re: Motor over wevving -Watch-

getting kinda warm in here?

if water is blocked from flowing through the blades, it sets up a low pressure area in front. When the prop gets to spinning fast enough, it can pull the pressure down low enough to boil the water...just like water under pressure boils at higher than 212?, when water pressure drops, so does its boiling point.

You get bubbles coming into the prop, now it's pushing air instead of water, and air is lots easier to push. Unloaded, the motor races while the boat slows down.

What's more, when those bubbles collapse against the blades, they erode the metal. Take a look, you may already have pitting, and what might look like scorch marks on your prop blades.

Google "cavitation" for more info.

You made your case for propeller protection in your application...just need to tweak your design a little, that's all.

 

[Machino]

Re: Motor over wevving -Watch-

I have heard of the pitting caused by cavitation, but haven't seen any yet. Everyone here makes a good argument against the skeg guard. You have to understand, I'm broke and so is my buddy. We have put a lot into this boat and keeping it working was and is first priority. Rolling over gravel bars at 5 in the morning with one 500,000 candle spotlight that will last for 30 minutes chasing ducks will soon be here, so there is another reason I thought this would be a good addition. The advise has swayed me and maybe we will give it a try without the guard, perhaps within the week. I will post my results and let you know how it goes. I also think moving the motor down a hair could be a move in the right direction. Thanks

 

[bigpoppakdog]

Re: Motor over wevving -Watch-

Hey man, don't take offense to the skeg comments. It is an odd looking device to say the least. Appears it will disrupt the water flow thus causing some problems with the prop. Especially the faster you go. Honestly, with the Missouri River right next door, I've never seen anybody with that on their skeg. Anyway, judging from the video, it appears your motor is fine, but as your speed tops out you have cavitation/air issues in my opinion.

By the way FR you are still the man!! Never seen a single person question your decades of outboard mechanic experience. Don't want to lose your insight...especially when many people have questions on these older motors.

Oh by the way, FR has worked on more boat motors in his life than the amount of fish you will catch in your life. Hell, I bet he's helped more people in his retirement stage of life on this site than the number of fish you will catch. If you don't want answers, then don't ask questions. If FR answers your question do one thing......LISTEN. He is more than 12,000 post guy. He is a retired EVINRUDE MECHANIC. You have an older evinrude. What more could a guy ask for? He just called it a stupid skeg thing and to lower the motor. Grand total of $0 to fix. Take it to an outboard shop and see what it would have cost you when they figured it out. That is, if they even would have looked at it, since many places don't work on older evinrudes.

Now that I have vented and watched your video again, it appears clear that you have cavitation issues. Just before you throttle down when the rpm's go up you can see in your prop wake clear signs of cavitation. I truely hope that helps. You can lower the motor like everyone else has said or possibly add more weight to the rear end, but not sure if a guy really would want to do that.

By the way it really helps when a video is posted with issues. A guy could have gone round and round on this issue, when it appears your motor is fine.

Another question....is that a home made skeg guard or was this bought somewhere?

 

[swannytheswan]

Re: Motor over wevving -Watch-

Even if you don't believe the skeg guard is the problem try it without it in open water where you know you won't hit anything, if the problem is gone or even improved then you know that the guard was part or the cause of the problem...once you have it running properly then you can figure out a way to protect the prop/lower unit and you will have a base line where you know it runs right and you can work from there knowing that you can always go back to what was working until you get it where you want it (protected and running good)

 

[Lion hunter]

Re: Motor over wevving -Watch-

That skeg thing does nothing to protect the skeg. They just keep the skeg from digging in soft bottom if you hit and lift the boat instead. In reality the catch pins and motor clamps are not strong enough to lift the boat and if the skeg cant dig in somethings got to give. Usually the motor. Ifyou hit someting hard with that thing on it will do the same damage to the skeg as if it wasn't there. It may protect the prop if the motor isn't locked down but it's best to just unlock the motor until you need reverse. The circular guards are good debris traps that tear up props if a stick or rock gets stuck in them. All those gadgets are an attempt to make the motor work where it wasn't intended to (less than a few feet of water) and none work very well. Best to just go slow and leave the motor unlocked. It will jump up if you drag bottom. And yes I do run rivers.

 

[Machino]

Re: Motor over wevving -Watch-

Thanks for all the good information and advice. I mean no offense to FR or anyone else. Its just hard to look for answers and get half-hearted answers that make me seem like an idiot. I was just looking for something that would extend the life of the motor. Seems I made a mistake, but haven't completely ruled out the height either. Both seem obvious NOW. Again, really happy on the information given and how did I miss the wevving?

 

[1946Zephyr]

Re: Motor over wevving -Watch-

For the heck of it too, try the "spun prop" check. Take your prop off and take a magic marker and draw a straight line fron the center to the outer perimeter. Take it for a run and see if the motor acts up like it has in the video. If it does, remove the prop and see if there is a break in the ink line you drew. This is a good way to check if your prop is spun and if you do a search on this site for spun props, you'll find several postings.

I think Lion hunter has some good insight here in his previous post. Sometimes the aftermarket accessories can cause more problems than good. Unfortunately, there are too many nig-nogs designing things that simply don't offer, what they were said to offer. Good luck, I hope this helps you out a bit. I totally understand what you are saying about money being tight in this economy. Many others, like you are in the same boat. (no pun intended)

Hopefully, the heated disussions in this thread won't keep you from coming back to get helpful advice. There are a lot of good guys here who are willing to help.

 

[cougar1985]

Re: Motor over wevving -Watch-

You would be best served with one of these ,either buy, or if your handy make one ,this is a proper sheg guard.http://www.iboats.com/Keelguard-Ske...7606276--**********.734497922--view_id.259073

 

[Lion hunter]

Re: Motor over wevving -Watch-

Completely understand that what you have is what you got. A lot of us are or have been there. I know that a jet is best but if you don't have one you have to deal with what you have. That said there will be some comprimise. I have run prop motors dang near out of the water in shallows where they shouldn't be run. The comprimise is that I know it's not an effecient set up and I can't go very fast or turn very good, but the boat will still move which is my objective. I think that all anyone was suggesting is to set the motor up the way it was intended and then as you change things you can determine the comprimises and whether you can live with them or not. If you feel that the guard is vital, that's fine but you can't expect to have a good setup when you use it.

As far as people's suggestions on this site. The great thing about it is most don't know each other from Adam. There's no need for kid gloves and saving feelings. Nobody tries to be rude but you get straight answers without pussyfooting around and get back on the water as soon as possible. Also the answers will at times be obvious things that will make you feel like an idiot for someone even suggesting you wouldn't know that. We don't know what you know. Everyone tries to point out every possible solution because it is immpossible to determine whether we are talking to a mechanic who knows their way around motors or someone who hasn't ever checked their own oil.

Anyhow good luck and welcome to iBoats and we hope to keep you around. And good luck with the boat.

 

[boobie]

Re: Motor over wevving -Watch-

I still have a question. Did you ever take the skeg guard off and give it a water test ? Also did you lower the mtr and test again ? If you do either don't do them at the time. Point is you want to find out if either was the prob. Keep us posted as to what happens and best of luck.

 

[bigpoppakdog]

Re: Motor over wevving -Watch-

I don't think you got half hearted answers. You got full hearted answers that were all the same from quite a few people. It just appears that you didn't want to hear those answers. I think we all want to know if removing that skeg hydrofoil thing makes a difference. Keep us posted. Good luck.

 

[Craig-]

Re: Motor over wevving -Watch-

Take off the guard and don't lock it down. Should improve.

 

[bigpoppakdog]

Re: Motor over wevving -Watch-

http://www.hydro-shield.com/

Found some info on that skeg guard set up. The website indicates that it helps "lift" the boat on plane higher.

It sure seems real clear with the higher transom mount of your motor and this feature on the skeg produces the results you see in the video at the high speed. I would guess with the smaller boat it doesn't take much to effect the performance the motor will have.

 

[ChrisAG]

Re: Motor over wevving -Watch-

As others have pointed out that skeg guard is of dubious value and will create a vacuum ahead of the prop once you reach a high enough speed. Perhaps if it were mounted on a 6hp engine the prop would not ventilate but obviously for higher horsepowers such as yours it does.

I think what got people going was the delay in full disclosure - nobody knew you had that attachment on there until after several answers to your original post, and yes, it is the obvious cause of the problem. In fact, I'm the guy that posted the prop slipping theory on your video - before knowing about the skeg guard, of course.

 

[Scottycat]

Re: Motor over wevving -Watch-

If you are running rivers and worried about hitting, then just slow down and you are safe.
If you don't go into the shallows, then lose the jewelry and lower that motor.

-Scotty

 

[Machino]

Re: Motor over wevving -Watch-

Sorry about the delayed response, I had to go back home for a week for my bro's wedding. Regarding the skeg, it is off and there is minimal cavitation. I say minimally because it did still over rev with the motor higher on the transom. It is now set all the way down, and though I think it is still too low, the performance is great. 15-18mph upstream and up to 24 downstream versus 7 upstream and up to 17 downstream with the skeg. When running at WOT there seems to be a lot of splash from the pivot tube housing, but again the performance seems good. Thanks for all the responses and help again.

 

[bigpoppakdog]

Re: Motor over wevving -Watch-

I had that problem on my boat when I had two trolling motors stored up towards the front of my boat. A pretty big rooster tail and splashing towards the boat. I moved the batteries to the back and it made a huge difference in solving the problem. Good to hear your problem is solved.