New to Pontoon Boats - Having Issues

[jafo9]

I'll preface this with "I'm no expert", but I think the missing piece is just for counter steer. I would agree that you won't get much lift with a 50 on a 21. It might be worth a trip to a local Bass Pro or Tracker dealer to see how their new inventory is set up, i.e., prop size and height.

[Jake_Daddy]

A couple more comments for you to ponder...

I think you may be battleing a couple issues. From the pics I would imagine you could raise that motor up a good bit for a little better preformance. I can't imagine why your cavitating at that depth though unless your getting exhaust mixed in the stream. I will throw out there that on another boat I had with a 90hp merc that when the stator was going bad it would mess with the timing advance and I could only go WOT for a very short time then it would knock me back about 1k rpms or so. I would say try an 11p prop but it sounds like you already have, I will also suggest getting motor height tuned in first would be best. I bought a 13p this summer before I raised my motor and now I'm in the market for a 15p as adjusting the height put me about 200-300 rpm out of my high rpm range.

End of the day I wouldn't expect a lot out of the boat/engine combo but you should be set up to run through the rpm range without issue.

[aaarneson]

[quote="Jake_Daddy"]A couple more comments for you to ponder...

I think you may be battleing a couple issues. From the pics I would imagine you could raise that motor up a good bit for a little better preformance. I can't imagine why your cavitating at that depth though unless your getting exhaust mixed in the stream. I will throw out there that on another boat I had with a 90hp merc that when the stator was going bad it would mess with the timing advance and I could only go WOT for a very short time then it would knock me back about 1k rpms or so. I would say try an 11p prop but it sounds like you already have, I will also suggest getting motor height tuned in first would be best. I bought a 13p this summer before I raised my motor and now I'm in the market for a 15p as adjusting the height put me about 200-300 rpm out of my high rpm range.

End of the day I wouldn't expect a lot out of the boat/engine combo but you should be set up to run through the rpm range without issue.[/quote]

Geez...Seems like so many variables. I wish there was a way to know for sure.

What do I look for in regards to the motor height? How do I know I have it correct and can move on to the next variable, if it does not fix it completely.

[Jake_Daddy]

I agree it's tough when you get a new to you boat where you don't have a good baseline to go off of. I'm on my second toon and have gone through a similar process. My older boat had same motor as what I have now and when I first got new (to me) boat it ran 7mph slower than the old one, new boat is shorter but lighter and I figured they should be close. Anyway I'm not quite where I want to be but it's getting closer. My first battle was not getting up to rpm which was a combo of engine and prop, I had to adjust the linkages first then I got a smaller prop but still wasn't happy and I was shooting up a ton of water up at the transom which is where info from this site persuaded me to lift my motor up. After that I'm closer to what I want and am now hopefully a prop switch away from being happy with my setup. Bottom line is there may not be a silver bullet!

[Jake_Daddy]

As far as motor height I believe you want the cavitation plate within an inch or so off the bottom of the transom pod, not the pontoons, and when your running wide open you should just be able to see it. My dead give away was that when I was running I was deflecting a bunch of water off the shaft and up over the back of the transom.

This is a video of when mine was too low. You can see how the water was washing up all over the place.
https://m.youtube.com/watch?v=AdmBOUXzroM

After I picked motor up two holes, all I could, and the preformance improved noticeably. My cavitation plate is now probably 1" below the bottom of transom.

[BobL]

[quote="aaarneson"]RPM's drop and everything[/quote]

This has me scratching my bald head. I am not questioning your RPM drop but when your blades lose grip the engine RPMs go up and the forward speed of the boat is reduced.

There is a difference between cavitation and ventilation but with your motor so low, I don't see how it is ventilating (sucking air into the prop). From Mercury:

"CAVITATION: Even slightly chipped or bent blade edges can cause surrounding water to BOIL ("cavitate"). Gas bubbles then condense elsewhere on the blade, releasing energy that causes metal erosion or "cavitation burn"."

"VENTILATION: Air from the water surface or exhaust gases from exhaust outlet being drawn into the prop blades causes ventilation. This reduces normal water load, causing the prop to over-rev and lose a lot of thrust. Ventilation is most common with high transom mounting, extreme trim-out and sharp turns. Mercury props are designed to minimize ventilation."

In short, cavitation is from damaged blades, and ventilation is mostly from high mounting.

I am leaning toward unbalanced load (Bryden) but with the RPM drop, then Jake may be on to something.

[aaarneson]

[quote="BobL"][quote="aaarneson"]RPM's drop and everything[/quote]

This has me scratching my bald head. I am not questioning your RPM drop but when your blades lose grip the engine RPMs go up and the forward speed of the boat is reduced.

There is a difference between cavitation and ventilation but with your motor so low, I don't see how it is ventilating (sucking air into the prop). From Mercury:

"CAVITATION: Even slightly chipped or bent blade edges can cause surrounding water to BOIL ("cavitate"). Gas bubbles then condense elsewhere on the blade, releasing energy that causes metal erosion or "cavitation burn"."

"VENTILATION: Air from the water surface or exhaust gases from exhaust outlet being drawn into the prop blades causes ventilation. This reduces normal water load, causing the prop to over-rev and lose a lot of thrust. Ventilation is most common with high transom mounting, extreme trim-out and sharp turns. Mercury props are designed to minimize ventilation."

In short, cavitation is from damaged blades, and ventilation is mostly from high mounting.

I am leaning toward unbalanced load (Bryden) but with the RPM drop, then Jake may be on to something.[/quote]

Yes...sounds more like ventilation. And I am positive my RPM's drop about 800rpms.

[Jake_Daddy]

If we assumed ventilation I agree that your motor is low enough that shouldn't be a problem. Unless your getting exhaust in the mix, all I can think of there is if it is an aftermarket prop like a turning point that has to have a "ring" installed on the forward edge of the prop to keep the exhaust flowing out the gearbox thru the prop, maybe not installed?

Another thought is a guy at work got a 2014-2015 fishing barge and had all kinds of problems with his prop cutting loose and on a trip back to the dealership they cut a piece of metal off his transom pod and the problem was solved. Can't remember and won't see him until after new year but maybe someone else knows what this was about.

[aaarneson]

Ok...I was able to make it out today and I was wrong about the rpm's dropping. I was totally mistaken or it was another issue.

Anyway, with the trim up it runs at about 6000 rpm's and about 10 mph maybe. Then with it trimmed all the way down it ran at about 5500-5600 rpm's going about 16.8 mph. Then trimmed up again and back to 6000 rpm's running 10-12 mph. Trimmed it down a little and about 5600 max speed I got was about 17.4 or so.

Also this was with just me and a half tank of gas. The steering was a lot better as well. So maybe the issue is the loading...maybe just need to have everyone with me to sit as far back as possible? Or do you try to spread the weight evenly as possible?

https://www.youtube.com/watch?v=1DS-6lZFlpI
https://www.youtube.com/watch?v=oHVs60RVFds
https://www.youtube.com/watch?v=FPuxhfdSE1o
https://www.youtube.com/watch?v=JYjYcetipCw

[ron nh]

I think you're going to be right there around 5,600 at 17mph or so with that set up, maybe a little better dicking around with props but maybe not. I've never owned a 50hp but 6,000 rpms sounds high, unless it's a 2 stroke I guess.

[Jake_Daddy]

If I assume a 2.3 gear ratio 8" prop at the speed and rpms your getting you would have about a 5.7% slip which I imagine is to good to be true. If you had an 11.5-12" prop you would be in the 35% range which is probably closer to reality. If you are sure on the 5700 rpm at 17.4 mph (gps) double check your prop pitch, if you had an 8" on there I would keep it!

[aaarneson]

This is the prop i have on it now.

[Jake_Daddy]

Looks like an 8" to me.

I would guess that your 50hp has the 1.83 gear ratio, maybe someone else could confirm that the tracker outboard is not the same lower end as a Bigfoot with the 2.33 ratio.

If that's the case your right where you wanna be RPM wise with a light load and about 25% slip which I would say is in the zone of where you should be. You could probably play with the next size larger prop in the 9-10" range to gain a little top end.

Your in the zone now of where you should be. But if you wanted to mess with it I wouldn't buy a prop until I played with motor height. If you tinker with it and get a few more rpms then you could have a better idea of what prop to look at.

[mpilot]

That diameter seems a little small. Is it a standard or Bigfoot? I think most 50 bigfoots I have seen are turning around a 13 pitch and around a 14 diameter.

[aaarneson]

[quote="mpilot"]That diameter seems a little small. Is it a standard or Bigfoot? I think most 50 bigfoots I have seen are turning around a 13 pitch and around a 14 diameter.[/quote]
No it is not a bigfoot