New pontoon owner!

[jspice]

Hey guys I just wanted to start by saying I have learned so much by reading some of these posts and I appreciate all the greatest information i have gotten from y'all! But I still have a few questions about my new to me 2008 Fisher liberty 200 w/ a 2008 mercury 90hp 4stroke... first question is have any of y'all ever experienced having a limit set on your trim on a pontoon? Second I am questioning the speed I am getting out of my boat which is about 20mph on GPS... seems kinda slow for a 20 foot boat with a 90hp motor! Also I am questioning my prop and motor height.... I am running a 19p prop and am still over revving my motor at wot! I am including some pictures for you all to look at! Also any help or advice as to why my boat sits so low in the water in the back would be greatly appreciated! I am sorry this post is so long I guess I am just a little paranoid something might be wrong! And thank you again for any help/advice I might can get!

 

[jspice]

i am trying to uplolad pictures but it wont let me so any help there would also be appreciated

 

[Cat nip]

Congrats on the new toon. Your speed sounds about rite. Sounds like way too much pitch on the prop and possibly sucking air and thats why the rpm is so high? Most toons sit low in the back but pictures will help of you can get them uploaded.

 

[jbcurt00]

Pix posting help
http://forums.iboats.com/forum/forum-rules-and-guidelines/9938375-photo-upload-tutorial

 

[Scott Danforth]

your speed is right on a pontoon. in fact it would go the same speed with a 50hp as it does with a 90hp. until you get enough hp to get the boat up on plane, your at displacement hull speed.

its a pontoon, not a speed boat.

 

[ahicks]

Thinking 20mph is a bit beyond normal displacement hull speed, but whatever. Agree it's not that far out of line. High/max RPM with that kind of pitch doesn't sound right here either. Certainly worth checking out, if for no other reason than confirming all is right and that's just the way it's going to be. It's possible that prop has been cut down, which would be obvious when compared to a similar prop.

Regarding trim, it's just not that effective on a 'toon. Prop shaft parallel with the bottom of the lake (or maybe just a hair either side of that) is about the best you're going to do.

 

[jspice]

Thank you guys! I'm not as worried about the trim as much as I am that I can't tilt my motor up enough to beach my boat in shallow water! Also when I got the boat it had a 13p prop which allowed my motor to rev over 7000 rpm so that's why I pitched up my prop with the recommendation of my local marina!

 

[HotTommy]

I'm no expert on these matters, but the Mercury Prop Selector website suggests props in the 13-13.75" diameter range with 15-16" pitch. If you are over-reving with a 19P prop, I have to suspect something else is contributing to the problem. The first thing I'd check is for a slipping hub. Put a mark on the prop and hub and see if they are still aligned after one of your over-rev moments. As was mentioned earlier, also check that the prop is deep enough to not draw air in from the surface. And check that the prop is below the bottom of the engine pod so the flow of water to it is not inhibited.

 

[jspice]

I am positive the hub is not slipping and I am beginning to wonder if my motor is not too deep in the water BC when I am sitting idle my relief hole and my water pump relief stream are only about 1 inch above the waterline! I'm still trying to get pictures to upload BC I know a picture is worth a thousand words when it comes to describing this stuff!

 

[jspice]

No Title

Here are some pictures of my current set up!

 

[bruceb58]

The pontoon in my signature can do a little over 20MPH at sea level with a 14 x 13 prop. Same HP engine as your pontoon but I am slightly longer.

No way I would be using a 19" pitch prop.

 

[ahicks]

Is that a "V" in the metal below the transom? If so, hard to tell from the pic whether or not it might be allowing air below the cavitation plate. If no V, the pics look fine.

Re: the trim, not familiar with your setup, but some setups distinguish between trim and tilt. They move the tilt to a second detent in the switch (separate from the trim), or different button all together, to distinguish between them when the boat is at speed - so you can't lift the motor beyond whatever they deem safe using the tilt switch alone.

 

[jspice]

Is that a "V" in the metal below the transom? If so, hard to tell from the pic whether or not it might be allowing air below the cavitation plate. If no V, the pics look fine.

Re: the trim, not familiar with your setup, but some setups distinguish between trim and tilt. They move the tilt to a second detent in the switch (separate from the trim), or different button all together, to distinguish between them when the boat is at speed - so you can't lift the motor beyond whatever they deem safe using the tilt switch alone.

Yes it does have a slight V in the transom pod!

 

[HotTommy]

If the water line on the log is about where the water is when under way, then your prop looks plenty deep. In fact, it may be slowing you up just a little. ... Your speed sounds about on target to me. The only mysteries are your apparent high RPM at WOT with both 13P and 19P props. If the water flow to your prop is not clean, that could be the problem. If the V in your engine pod is not excessive, then I'd have someone check the tachometer to be sure you are getting accurate info. I'd also find out if the engine came with a rev limiter. If it did, you didn't likely hit 7000 RPM.

 

[jspice]

If the water line on the log is about where the water is when under way, then your prop looks plenty deep. In fact, it may be slowing you up just a little. ... Your speed sounds about on target to me. The only mysteries are your apparent high RPM at WOT with both 13P and 19P props. If the water flow to your prop is not clean, that could be the problem. If the V in your engine pod is not excessive, then I'd have someone check the tachometer to be sure you are getting accurate info. I'd also find out if the engine came with a rev limiter. If it did, you didn't likely hit 7000 RPM.

Do you think I could be too deep with the motor? And also I just talked to my local boat shop and they said my motor should be limited on rpms so I do think I'm gonna go in and have it checked out!

 

[ahicks]

Too deep is not very likely going to cause high revs. What it will do is hold your top speed down.

The high rpm thing is likely affecting performance the most. That needs to be figured out.

 

[bruceb58]

You are using the correct prop for your motor right? No exhaust leaking out over the prop blades when running?

 

[jspice]

I haven't noticed any exhaust leaking and that is the prop they sold me at a local marina... Is there any way to check my tach without taking it to a dealer? Sorry I have so many questions I just don't want to mess anything up?..

 

[HotTommy]

You can find tachometer/hour meters like this for sale on the big online sites for less than $10.
They are self powered an use the induced signal from one spark plug wire to calculate the RPM. I cannot attest to the accuracy of this thing, but it is fairly cheap. And if it indicates the same RPM as your tach, then maybe it would be worthwhile to eliminate your tach as the potential problem. .... In the mean time, if you can reach 20 MPH without exceeding the RPM limit for your engine (as shown on your tach), then I wouldn't be in a big hurry to make more changes. That's about as fast as you can expect from your boat/motor combination. .... One more thought. Your marina may have done everything right in selling you the new prop. After all, you can expect to see a 400-600 RPM drop from each pitch increase of two inches. So if your original prop was actually hitting 7000 RPM at WOT, then going 6 inches higher should have dropped your RPM to around 5500. But if they knew your engine was rev limited to something like 6000 RPM, they should have questioned your claim of 7000 RPM before selling you that prop.

 

[WaterDR]

Something is not adding up. No way in hell would a 19P prop even get turned over by that motor much above 4,000