props for my 90hp Johnson V4

[Dave_Noffsinger]

This is the first time I've ever had to replace a prop and I'm feeling a bit lost and confused with it. I did read the FAQ's on props but I'm still not sure what I need to get.

I've got a 1985 Johnson V4 90hp on a 1985 15' Glasstream Hydroski. It has an aluminum prop on it now which needs to be replaced. My buddy was driving it this past weekend and clipped a stump which took a chunk out of one of the blades. I'm assuming it's a stock prop and that would be fine as far as replacing it goes. I mostly use the boat for fishing and some tubing/skiing. I'm not sure what the recomended wide open RPM range for this motor is.

If anyone could give me some advice and direction I should go with it that would much appreciated. Also, I've been looking for some places that sell used props if anyone knows a good place to check.

Thanks,
Dave

 

[lexkyboater]

Re: props for my 90hp Johnson V4

Hey Dave - welcome to iboats! The site boatmartusa.com/marinemall/propPage.php is the best page I've seen that lets you calculate prop size for pulling/acceleration or top speed. It calculates prop based on motor, boat type, number of people, amount of gas, altitude and a few other things. It looks like it may only go back to 1991 on the motor. I didn't see a Hydroski so I used the 1500 f/s. With 2 people, 10 gallons of gas, at 3,000 ft altitude, it suggested a 13 1/4 x 17 for watersports, or a 13 1/4 x 19 for speed.

That said, what is your current prop and what did you or did you not like about it? Would you want more acceleration/pull or more top speed? Having a test prop or starting point is extremely helpful.

 

[Dave_Noffsinger]

Re: props for my 90hp Johnson V4

Hey man, thanks for the info I'll check that site out here in a few minutes. I'm not totally sure what is on there now but I would like to get something pretty much the same. I guess I would like to have a little more pulling power for water sports but I don't really want to loose my top end though. I'm planning on picking up a set of hydro fins to help plane the boat out when I'm pulling a skier but otherwise the prop I have/had did pretty well. It had a nice top end to it and was still able to pull a tube fairly well. Mainly I want the fins to help keep the bow down a little better at lower speeds for the water sports stuff.

As far as gas goes, it's only got a 10 gallon tank on it though I do plan on stuffing an aluminum 20 gallon in there over the winter that I got my hands on. The 10 gallons go fairly quick when your towing tubes and skis around all day. The boat has a shallow V hull like a bass boat and I have noticed that it does feel a little uncomfortable making sharp turns @ high speeds but I figure that is just the nature of the design really. I live in NC and mainly run the boat in local lakes though I have had it out in a couple of sounds @ the Outer Banks when it wasn't windy.

I'm going to go out and measure the diameter of the prop I have now but I'm not sure how I need to measure it for the pitch and cup of the blades.

Thanks again for helping me out here. I've pretty much been on boats the biggest part of my life but like I was saying before, this is the first time I've ever busted a prop and had to figure out what I need to replace it with. So, I can use any advice I can get right now

 

[Dave_Noffsinger]

Re: props for my 90hp Johnson V4

Here is a pic of the boat and motor just to give ya an idea of what I'm working with.

 

[Dave_Noffsinger]

Re: props for my 90hp Johnson V4

Ok, I just went out there to measure it and I saw the the hub was imprinted with 14x19, just to the outside of the shaft and nut. Does that sound like the right size to you guys for the size of the boat?

Dave

 

[Cricket Too]

Re: props for my 90hp Johnson V4

Dave....In order to tell if that's the correct prop you need to know what the WOT(Wide Open Throttle) RPM is/was, with a normal/average load.

Generally your gonna want to get the WOT RPM up around 5800 so your not lugging the engine. If the 14X19 was getting you there the replace with the same prop.

 

[Dave_Noffsinger]

Re: props for my 90hp Johnson V4

When I would run wide open it normally topped out around 5000 to 5200 RPM's. I haven't found out for sure yet but I was thinking that 5500 was supposed to the the max limit on that motor? Not sure on that though. I'm thinking now that the prop that is on there now may have been pulled off a 140hp Johnson at some point in the past. I'm guessing that I should maybe go to a smaller diameter like a 17 maybe?

 

[Cricket Too]

Re: props for my 90hp Johnson V4

Well the 14X19 means a 14" diameter and a 19" pitch, your probably OK on the diameter of 14", but if your only getting 5-5200 WOT RPM, then you should change something, there are a couple of different things to try as many guys here will tell you before dropping pitch.

Make sure your setup is correct, engine height etc.. If all that is OK, or you can't move it anymore than it is, then consider dropping pitch.

I understand you don't really have a good prop right now to even play around with. If I was in your situation I would drop to the 17" pitch and see wherfe I was at with everything else.

 

[Dave_Noffsinger]

Re: props for my 90hp Johnson V4

I was just checking out some props on ebay and ran across a guy who has 2 13x19's in fair shape for 20 bucks. I thought about picking them up just to try it out since it's cheap. I didn't really find anything for a 14x17 though. Seems like most of the ones I found a size down from the 14x19's were going to a 13" diameter. I did find a bunch of 14x19's like I have on there now, so that's always an option too.

Now as far as adjusting the motor, I don't think I have anything to adjust as far as the height goes but I do know there is an adjustment for the pitch of the motor. I believe I can go down another notch or two towards the transom. Would it be possible that I have too much angle on it now that would keep it from reaching a higher RPM?

Thanks,
Dave

 

[Dave_Noffsinger]

Re: props for my 90hp Johnson V4

I just had another thought too. At times my tach tends to jump a little bit so I'm not so sure how accurate it's reading. I suppose I should figure that out too since it's obviously going to make a difference here.

Dave

 

[Monkaroo]

Re: props for my 90hp Johnson V4

Try this link , maybe it will help you out .



http://www.marinedepo.com/proschool101.html

 

[darrklim2]

Re: props for my 90hp Johnson V4

I was just checking out some props on ebay and ran across a guy who has 2 13x19's in fair shape for 20 bucks. I thought about picking them up just to try it out since it's cheap.

This sounds like a plan to me. It would give you something to use to test with since your current prop is kinda out of commission. Then you could also test to see how accurate your tach really is.