What sized prop? Tube size?

[RatherBFishing]

I have a '91 Mariner 200v on a Fiberglass Procraft 200pro bass boat. The prop on it is a 24pitch Lazer II. (3 blade stainless prop) I have been having problems cavitating getting out of the hole and does not like to stay on plane at lower speeds. I can get about 60mph per gps but have to back off the throttle once I start to trim it up for speed or will over rev. I got talking about it to a guy at a boat launch that works at a Marina. He looked at the prop and instantly said the cavitation problem is that the tube size is too small. After discussing further, he suggested a 4 blade prop with a larger tube. He thought he could get me a new 4 blade for about $600 but he happened to have a used 21pitch for $200. I assume that will not be enough prop and I would be over reving. <br /><br />I would like anyone's thoughts on a 24 or 25 pitch 4 or 5 blade so I can stay on plane and get out of the hole. I have a line on a used 24p Mercury high five. Also, what will the extra blade(s) do to my speed?<br /><br />Thanks!<br />Mike

 

[LubeDude]

Re: What sized prop? Tube size?

We would like to know your RPM with that Prop you have at WOT before you start to trim out. Do you have a jack plate, sounds like your engine might be too high. A four blade might help with the hole shot and give you better bite while trimmed out. You also might concider a set of Smart Tabs.

 

[KCLOST]

Re: What sized prop? Tube size?

Tube too small?????<br /><br />What is the tube diameter of the prop right now.?<br /><br />That Lazer II should be a standard size and the correct one for your motor. <br />When you say "cavitation", do you actually mean "ventilation"? Meaning the prop is losing bite with the water, coming out of the water? If so, your engine is probably too high like Lube mentioned. Also, are you sure that the hub has not spun on the prop?<br /><br />Do you have a water pressure guage? You want to make sure you are not raisin ghe engine too high to lose water pressure? <br />Let us know...

 

[RatherBFishing]

Re: What sized prop? Tube size?

I don't have a water pressure guage but I do keep a good eye on the water stream coming out of the back. Especially since I just replaced the impeller and I am always nervous of my own work until I have run it a while.<br /><br />Ventilation could be what I am experiencing. The prop seems to lose its bite and I have to back off the throttle.<br /><br />The tube diameter appears to be about 3 5/8". (hard to measure on the boat with the flare at the end) There is 1/2" from the outside of the lower unit casing to the outside of the tube.<br /><br />Thanks,<br />Mike

 

[Jdeagro]

Re: What sized prop? Tube size?

RatherBfishing;<br /><br />Are you running anything on the motor? What is the Max Speed and RPMs.<br /><br />Your minimum speed to stay on plane is about 25 to 26 MPH! At 60MPH when you trim the motor up and the RPMS begin to over Rev it seems that you are Over Trimed. <br /><br />What is the bow rise when you take off from a stop ( hole shot)? How long does it take to get on plane?

 

[KCLOST]

Re: What sized prop? Tube size?

Well. 3-5/8" is too small, was that the outer diameter or inner? It should be 4" minimum (outer diameter)... Maybe the small diameter is causing a pocket of air/exhaust around the prop housing (being that small). <br /><br />Check out ebay... on some used props....<br />I would consider staying with a 24pitch, possibly trying a 25... Four blades will get you the best bite... But they are more costly...

 

[RatherBFishing]

Re: What sized prop? Tube size?

The bow rise seems extremely high. I don't know how to measure but it seems extreme. It seems to take forever to get on plane. I never really timed it. In a tournament though, the boat starting 10 seconds behind me blew by me while I was just coming up on plane. I was able to catch him once I got up there though.<br /><br />The measurment of the tube was the outside diameter. The air/exhaust thing is what the marina guy said too.<br /><br />Thanks for the suggestion on ebay. I see a 24p 5 blade "high five" out there. Does anyone know what the tube size would be on that?

 

[LubeDude]

Re: What sized prop? Tube size?

Untill you give us an RPM figure we are not going to be able to give you any more help. The High Five prop is a great Bass Boat prop and will have the right size hub, Im running one on mine now. You will get a better hole shot and it will hold better at WOT and allow you to trim out more. However I think you need smart tabs on your boat. I know that you do not see them on Bass Boats much at all, but read this post. As to the pitch, we need RPMs at WOT.<br /><br /> Smart Tabs, Bass Boat

 

[RatherBFishing]

Re: What sized prop? Tube size?

I believe the RPMs were running about 5600-5800 prior to trimming. I was thinking last year it was around 6000 but that may have been after trimming up a bit. It could also have to do with the fact that I am still running on last year's gas.<br /><br />That definitely sounds interesting about the smart tabs. What does a set of those cost? I had been thinking of a hydorfoil but wanted to wait till I got the prop issue resolved. My wife also has issues with speed so I would like to stay on plane at lower speeds.<br /><br />I believe I saw a post on another thread that you need to drop down a pitch to go up with 4 or 5 blade props. Is that true?<br /><br />Thanks,<br />Mike

 

[KCLOST]

Re: What sized prop? Tube size?

Dude, your at the max rpm's for that motor right now.... Stay with a 24P with the correct tube diameter...<br /><br />My best bet would be to go the a 4-blade 24P Trophy (what I have). You'll be in good shape with that and stay within the proper WOT rpm range 5600-5800.

 

[LubeDude]

Re: What sized prop? Tube size?

KCLOST Probably has you dialed in, but if the figures are before you trim out, you might even need a 26. Im actually able to spin a 14.25 X 27P on my 18' Bass Boat w/ 150 Merc as you saw posted. But I am going down to a 25 High five. Havnt tested it yet but will post results.

 

[KCLOST]

Re: What sized prop? Tube size?

Allright Lube, you did it again!!!!! Messing up my perfectly good answer... <br /><br />Seriously, the only way to confirm what is your best set-up is to test, test, test.... Lube's been doing it for a while now, and he's getting it perfected.... The drawback is, trying out different props, smart tabs, etc, they aren't easy to come by and aren't cheap... But Figure on a 200rpm drop for every inch of pitch INCREASE whether you are at moderate rpms to WOT... 3 to 4 to 5 blades of the same pitch may cause you to loose 100 to 200 or so but not that signifigant considering benifit of stability, bite and out of the hole performance...<br /><br />My concern for you is your slowness getting up on plane. Increasing pitch on the prop won't help this... So adjusting the motor height, making sure that your motor is trimmed all the way down at throttle up (using your tilt & trim), with the proper size prop is the best way to start. <br /><br />If you were closer I'd let you try out a 24P four and three blade prop, also a 23P four blade, all that I know will fit your motor and has the proper hub diameter...<br /><br />On another note, is it possible that you have an extreme amount of weight on the back of the boat? Also check your trim/tilt angle at the lowest position. At it's lowest, is the motor straight up, tilted somewhat away from the transom or trimmed more towards it?<br /><br />Let us know....

 

[robnik1]

Re: What sized prop? Tube size?

RBF<br /> If your current prop is allowing exhuast to pass over blades nothing about your current pitch and RPM can be used as a baseline for any future changes, you should try correct size prop of same pitch, you will find it bites better and will lower rpms. Prop needs good water (no exhuast).<br />Good luck

 

[RatherBFishing]

Re: What sized prop? Tube size?

KCLost, I see you have a bid in eBay on a Laser II 25P prop. It is a 24P Laser II that I have with the wrong tube size. I don't see anybody listing tube sizes or anything. How do you tell what size they are?<br /><br />There is a lot of weight in the back of my boat. The 3 batteries are there. There are two 24 gallon gas tanks, one under the seats and the others behind that. <br /><br />That seems like robnik1 has a good point on the RPM info being invalid with the tube being smaller. It seems like I would not only have the exhaust gasses passing over but also a half inch of each of the blades would be shielded from water flow by the lower unit. Sounds like I will be starting from scratch.

 

[LubeDude]

Re: What sized prop? Tube size?

I wonder what prop he has, did the smaller mercs have the same size shaft but different housings. Im wondering if it might be a smaller overall diamiter also?

 

[KCLOST]

Re: What sized prop? Tube size?

RatherB,<br /><br />I guess I just assume they are the right size. Most all Mercury grade props have the same tube diameter. Except, when you get to the lower horsepower grade.. The only way to confirm it's correct I guess is to ask the seller, measure yourself, or call Mercury with the prop part# and confirm it will work on your motor.

 

[RatherBFishing]

Re: What sized prop? Tube size?

I picked up a 24p 4 blade trophy and it seems to have solved my ventilation issue. Actually, I suspect the issue was more the thrust washer that was on the old one. The one that came with the new prop is a lot less diameter. I suspect the old one may have restricted my exhaust a lot. Anyway, the thing jumps up on plane with no problem and I am getting almost 60mph fully loaded with fishing gear and 2 people.<br /><br />Thanks to all for your advice!