Prop Selection

[bm258]

I am ready to upgrade from an AL. prop to SS. I have an 18' bass boat with a 1990 Johnson 100 HP. I am running a 14 Dia. x 17 Pitch now. Does anyone have any recomendations on prop selection? I am more interested in top end speed that hole shot. Thanks in advance for any advice.

 

[WillyBWright]

Re: Prop Selection

Generally you should stay close to what the aluminum is. You'll probably get a few more RPMs and a few more MPH. If holeshot isn't an issue, go a little steeper. But in the end, the only way to know exactly what pitch you need is to run the prop and see what it does. At some point you get too steep and start losing MPH.

 

[walleyehed]

Re: Prop Selection

What RPM are you getting with the 14X17 OMC alum prop???

 

[bm258]

Re: Prop Selection

I do not have a tach on the boat. it is a 1982 booat that i bought used a while back. I am not sure if this is going to be any help. Someone told me if I increase the pitch i will have to raise the motor up. Why is that? I had to lower the motor to the lowest position because under load i was getting air pockets b/w hull & water. The mech. told me this, and when I lowered the motor I had no more problems with that. When I was having that problem i did try a SS prop to see if the prop was spun. Once i lowered the motor the boat picked up about 7 MPH with the SS prop. I think it was a 21 pitch, but I am not sure. It was an old prop and did not have the pitch on the prop. I know all of this is probably confusing. I will try and respond to your questions to the best of my knowledge. Thanks again for your replies.

 

[walleyehed]

Re: Prop Selection

Without a tach, I won't make any recommendation for props, SS or other-wise because we have no Idea what you are turning now.<br />A tachometer is the most important instrument you can have in your boat.....the speedo is a just a result of the works efficiency-not needed for this case.<br />If your mech. told you to lower your engine, I'd like to know what prop you have now (P/N, 214?), where the cav. plate is in refference to the bottom of boat.<br />I find it almost unbelievable to pick up 7MPH by lowering the engine, unless it was being over-reved EXTREMELY before lowering the engine...it wasn't the SS prop the gained the speed, which brings me to the question of speedo type??

 

[bm258]

Re: Prop Selection

I thought I may have been a little confusing on the last post. The MPH gain was from the 17 pitch AL prop to the 21 pitch SS prop after the motor had already been lowered. Sorry for the confusion! There is a tach on the boat that is not hooked up. I am going to try and hool it up today. It may not even work. I will post as soon as I do that. Thanks again for the replies.

 

[bm258]

Re: Prop Selection

I have just hooked up the old tach. it works somewhat. It works and then goes out especially at higher RPM's and sometimes it works fine. I am guessing it is because it is so old. (23 yrs.) I may have to order another one. I am going to take it to the lake tomorrow and see how it does. I will post back then in regards to the Prop recomendation. Any ideas, other than age, why the tach may be doing this?

 

[bm258]

Re: Prop Selection

Does anyone know what my WOT shuold be? 1990 Johnson GT 100.

 

[bm258]

Re: Prop Selection

Walleyhed,<br /> to answer your questions. The speedo. is the style that a water intake is mounted on the transom and a line is run to the speedo. The part # for the prop is 176214. Forom what i can tell it is a OMC Prop.

 

[walleyehed]

Re: Prop Selection

I knew what the prop was by the size you gave above.....notice I said "OMC 14X17"????<br />That type speedo with a pitot tube is not real accurate, but for comparison it will work.<br />Max RPM you'll want 5800-5900 with just you in the boat...5700 would be acceptable for the cross-flow.<br />The 176214 is not a good prop when compared to the older 391199 (13-1/4X17) I've ran both and I don't like the 14X17...it pulls a bit harder, but no gain in speed.<br />See what ya get with the tach if it works and post back.

 

[bm258]

Re: Prop Selection

Ok. I hat to order a new Tach. got it in and hooked up yesterday. at WOT I was running @ 5300 RPM's. Sorry it took so long to get back. Thanks for the replies so far Walleyhead & WillyBWright.

 

[walleyehed]

Re: Prop Selection

First, we need to figure out why you're blowing out with the prop you have now. If the prop is in decent shape, we should be able to go to the second hole wothout a problem, and a well-cupped prop will handle the third hole.<br />Can you run the engine higher (mounting height, not trim level) with the 21????

 

[bm258]

Re: Prop Selection

I had the motor mounted on the third set of holes before. Under load I was gaining RPM's and loosing speed. I took it to the mech. and he let me try another prop (the 21) and I had the same problem. He said the hull was getting weak because of age (1982) and air pockets were forming b/w the hull and water causing RPM's to jump. He suggested lowering the motor. I lowered it to the lowest position and it has not given me any problems since. I suppose i could try it on the middle set of holes since i have not done this yet. I hope this answered your question. Thanks again<br /><br />EDIT:by third set of holes i mean the motor was at the highest mounting position. Now it is at the lowest mounting position (1st set).

 

[walleyehed]

Re: Prop Selection

Let's try it one hole at a time and see what happens with the 21.<br />Is the 21 the prop you got the 5300 with??

 

[bm258]

Re: Prop Selection

no, the 21 was a prop that i previously borrowed form a shop. the 14 x 17 was the 5300. Sorry for all of the confusion!

 

[walleyehed]

Re: Prop Selection

No problem...I am concerned as to the possible wear on the cup area of this 17.<br />If the bottom of the boat is bad enough it causes ventilation, we need to take a good look at the hull. <br />A 6ft straight-edge works good, or even a slightly shorter level will work too.<br />Do we have any pieces of gel-coat missing in the center area?? If it's the hull causing the problem, it will be located within 12-14" of either side of the keel area up to about half-way fwd. If you don't find any obvious problems in those areas, it's got to be a cup issue with your 17.<br />Any way you can barrow a "Known" 17-19" from anyone nearby??

 

[bm258]

Re: Prop Selection

Kenny... Thanks for all of the quick replies. In reguards to the hull. I had the same problems with RPM/Speed loss with the 17 prop, and also when I tried the 21. I know there are several large knicks and gouges that area of the hull. I will check more thoroughly this weekend. I also know that the outter edges/tips of the blades have been worn down from hitting sandy bottoms etc... but no major bending. I have ordered a SS Rapture 13 1/4 x 19 that should be here this weekend. I know that this not a top of the line prop, but I got a great price.... Let's face it, my boat and motor is not top of the line either. I am pretty confident that the SS prop will perform better than Al. prop though. If you have any more questions please ask. If not I will post again when I get the new prop on. Thanks again. Brad

 

[walleyehed]

Re: Prop Selection

Check the bottom of the hull good...all it takes is a very small area to disrupt the flow and cause problems.<br />As for the tips on your 17, the cup area around the tip is very important, as this is where alot of the holding capacity is for good bite...if it's worn on the tips, it's half useless......did that make sense???

 

[bm258]

Re: Prop Selection

That made sense to me. Thanks. The prop is probably half useless. I will check the hull more closely this weekend and post back. I may even post a few pics if i can figure out how. The new prop should be in today. I will post back when I get ti to the water. Thanks again. Brad

 

[Jdeagro]

Re: Prop Selection

Kenny;<br /><br />Call me regarding a "test Tach". It seems that many people do not have accurate functioning Tach and they need this to choose the correct prop. We have a Tach which will work on 1 through 12 Cyl. two or four cycle. Positive and negative leads with an inductive pick up of the Ignition pulse, and a Memory for the Max RPMs achieved during the test. What do you think? (800-233-0194)