Ate my prop, suggestions for replacement?

[RavenTBK]

Hello gurus. On a recent outing, something unknown took a decent chunk out of one of my aluminum prop blades. Its not that huge of a loss, as performance was in my opinion, poor, and I needed to look at getting something more suited for the boat anyways.

Here's my current specs:
Hull: 1987 Flare Marine 17'6" center console (awful similar to this one on this site)
Powerplant: 1994 Johnson 90HP v4
Current prop: OMC aluminum 13.25 x 17
Current WOT: 5000rpm at 32mph
Proposed use: Pleasure. Load up the kids (two adults / 3 kids) for joyrides.

I'm not sure whether its just underpowered, or under/over propped. The boat is seriously heavy, and strains to get up on plane, even with just me on board. I can raise the bow and get it to plow through the water on command, but it takes some major trim work to get the nose to roll over and the stern to rise up. There is no usable cruise... only wide open and idle.

My regular outing involves no gear, and only a 6gal red can of fuel.

I would very much like to be able throttle back and cruise on plane to save fuel to make for longer outings, which is impossible currently.

It has been suggested I move to a 15p prop to improve the holeshot, however that would slow it down even more on the top end. Local folks much wiser than me swear that my lil 90 horse should move this boat at least 45mph at WOT with this 17p.

Basically, I picked up the boat originally with a dead E110, and repowered it with a J90. So the motor/prop combo wasnt originally on this boat, but was assured it would be great.

From all my reading, I'm leaning more towards a 4 blade, 14x15 or thereabouts. Slightly larger diameter to give more raw thrust over the band, the extra blade for a real lower rpm cruise, and less pitch to bump WOT back up into the sweet spot.

What do you all think?

 

[Dhadley]

Re: Ate my prop, suggestions for replacement?

While we're establishing a baseline we need to know a couple of things -

1- Are we positive the motor is running at 100%? Really positve?
2- Where is the AV plate in relation to the keel when parallel?

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

While we're establishing a baseline we need to know a couple of things -

1- Are we positive the motor is running at 100%? Really positve?
2- Where is the AV plate in relation to the keel when parallel?

1. Yes, and yes. Motor was recently rigged up to the boat, carbs cleaned, ignition parts replaced, and test ran by a very reputable local shop.

2. I will have to go out and look. I would assume the height would be done right when it was rigged...but I honestly dont know. Will edit this post shortly.
EDIT: The AV plate appears to be about one quarter to a half an inch above the bottom of the keel when trimmed to be parallel to the keel.

 

[steelespike]

Re: Ate my prop, suggestions for replacement?

Reason we question your setup is a 17" prop is pretty typical.
Your height seems about right Does the boat respond to up trim
or does it seem to lay down like its glued to the water?
Don't assume because it is recently rigged that the throttle opens all the way.
If you have trouble staying on plane its possible the flotation under the floor has absorbed water making it tail heavy.Do you have both gas, batteries and maybe an anchor in the stern?
There is no doubt a 4 blade will improve hole shot and ability to stay on plane at reduced throttle.It will also likely improve handling on plane and at the dock.
I think a 15" 4 blade close to your present rpm should do well.The Solas Amita props have been predictable and reasonable.
I don't think you want an extreme diameter as I feel they are intended for heavier hard to push boats like a pontoon

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

Ah, well the butterflies do open up all the way. Thats one of the first things I checked first time out on the water when it didnt want to hop up on plane.

As for the foam being wet, I couldnt tell you. The floor was replaced shortly before I picked up the boat. One would hope it would be checked/taken care of before it was put back together...right? I dont really want to say the boat is tail heavy, its just heavy all around. I've actually had to slide the axle of the trailer about 16" forward to pull maybe 300# off the tongue. Made for some nice rear-end sagging before I did that.

It floats level, not really too different than any other boat I've seen of similar construction. Its just solid as a rock, cuts through chops like a sharp knife, and rides smooth as a baby's butt -- once you get it to climb up on plane.

Once up on plane, I'm not really too sure how this particular boat should respond to trim up. I can trim up all the way till the prop ventilates, and there is no appreciable difference. No bow rise at all. So I guess I should say it acts like its glued to the water.

Upon your suggestion, I did some more looking into the Amita 4 series of props, and I found a reasonably priced source for them. I was leaning towards getting a Piranha, and playing musical blades till I found something good, but now I'm strongly considering the Amita 4, in a 13x15 configuration.

 

[steelespike]

Re: Ate my prop, suggestions for replacement?

Lets assume its just bulk that holds it down.Otherwise there may be a hook in the bottom.Maybe when they did the floor they missed that there was a hook in the bottom?The 4 blade should allow more up trim.

 

[sasto]

Re: Ate my prop, suggestions for replacement?

Can't help on the prop.... you will find some experts here..........but I worked briefly building Flare and Rally Sport boats in Auberndale, FL around that time.

 

[Silvertip]

Re: Ate my prop, suggestions for replacement?

Your engine should be reving higher than 5000. It can safely run at 5600 - 5800 rpm so dropping to a 15 would not slow you down. In fact with less slip you might pick about 2 -3 MPH and have better hole shot and cruise performance in the process. Reaction to trim may also be improved.

 

[trendsetter240]

Re: Ate my prop, suggestions for replacement?

If you can only reach 5k RPM with that prop then you will need a 13p solas amita 4 blade, not a 15p.

I have two of those early nineties omc 17p props, one is 13.25 diameter and the other is 14 diameter. Both are very inefficient compared to todays props.

Though I have a different motor (70hp) and gear ratio (min is 2.41:1 vs yours at 2:1) I have experience running both your prop and the 13p 4 blade amita.

The 13.25x17p OMC prop would reach 5600RPM at WOT on my boat. The 13p amita will reach 6300-6400RPM on the same setup.

The 13p amita will reduce your slip and allow a great hole shot, cruise on plane around 4500RPM and WOT of about 5800RPM. Of course this is just an educated guess, you're results may vary.

Whatever you decide go with a 4 blade and less than 17`of pitch. And remember it`s better to be slightly underpropped and watch the RPMs then to be overpropped and lug the engine.

Cheers.

 

[Fed]

Re: Ate my prop, suggestions for replacement?

I'm running a old V4 90HP with a 13&3/8" x 17" SS prop on a 17' cuddy cab that I bet is heavier than your CC.

5300rpm @ 40mph and a very respectable hole shot.

A 17" prop should be perfect for you.
Waterlogged? Sick motor? Damaged prop?
That's my story & I'm sticking to it.

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

I managed to secure a 13.25 x 19 just for reference. Took absolutely forever (and moving my wife/son up front) to get up on plane. I didnt have the GPS with me this time to verify speed, but I tached out at 4200, cowling off, butterflies at 90*.

Can't help on the prop.... you will find some experts here..........but I worked briefly building Flare and Rally Sport boats in Auberndale, FL around that time.

Very cool to know. Seems like flare was only around for a couple years... for whatever reason.

 

[Dhadley]

Re: Ate my prop, suggestions for replacement?

We look at things a little differently at our shop when it comes to prop set up. Instead of simply going to less pitch to gain rpm we try to reduce drag and tweek the set up first. In most cases with outboards we find we can gain rpm, which improves holeshot, top speed and cruising rpm, without going to a lower pitch. Sometimes not but in most cases it's possible. Just from what you've told us we'd say there is room for improvement without going to less pitch.

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

Dodging the scattered showers this afternoon I dropped it in the river again for a quick run, this time with the GPS.

Also, a correction from my previous post, the borrowed prop is a 13x19, not 13.25.

No wind, river smooth as glass. No passengers, and only 2gal in the can. Played with trim quite a bit this time, listening for ventilation, watching closer for bow rise/fall, and trying different approaches to plane it out faster. I learned that she doesnt like 100% trim in to get up on plane... about 80%. That provided the best holeshot. Now granted, it took a bit longer than my 17p prop to get up, it still got up in a reasonable about of time. So pretty much I learned something there about this particular boat I didnt know before. I feel as though my gripes about slow planing have diminished slightly.

I did three runs, down, up, down the river.

First, after punching up on plane, and incrementally trimming up just till I hear the different sounds of ventilation, then back down slightly, I managed a peak speed of 34.2mph, at about 4200-4300rpm.

Second, up river, to past my entry point, 32.7mph at 4200rpm. On the uptake, I also attempted a part throttle cruise, and after failing a couple times, I found a trim setting that managed to keep me on plane at 23.8mph at 3200rpm. The slowest I could go before settling down is 22mph.

Third, back down, 33.6mph at 4200rpm.

So the short version of it is I wasnt fully aware of what my boat likes, and basically *I* was doing it wrong. I am stupid, I am not afraid to admit it. I know what to do better next time, however, I still need to get a replacement prop.

Am I on the right track here? I'm still wanting to lean towards the more lower-speed efficiency of the Amita 4 for a better more fuel efficient part throttle cruise.....?

 

[trendsetter240]

Re: Ate my prop, suggestions for replacement?

you are definitely on the right track in learning how to trim your motor for optimum perforance. However, with prop pitch you are going in the wrong direction.

Increasing pitch will DECREASE your rpm at WOT. One essential basic rule for prop selection is choosing a prop that allows you motor to run in the manufacturers recommended RPM range at WOT. So in your case you want a prop that allows your motor to reach 5500-5800RPM at WOT.

The 19p prop you have on now which only allows 4200RPM at WOT is lugging the motor badly and will cause premature engine damage/failure if run that way for an extended period.

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

I know that moving up in pitch is the wrong direction from where I need to go. All it was was a loaner off a buddy's boat so I can gather some more numbers to be used in this search.

I'm more or less sold on the Amita 4 at this point. Only snag is what pitch? The math says drop to a 15, but I lack the experience yall have to know for sure what'd be the best route.

I thoutght iboats had a deal where you could swap props if its the wrong pitch...as long as its returned undamaged. When I called in this afternoon, the lady whom I spoke with said they've never done that. I called up two other companies, and got similar replies. Which place was it where you could do that?

Otherwise, I will commit to whatever one is suggested here, given all my numbers.

 

[trendsetter240]

Re: Ate my prop, suggestions for replacement?

I'm still sticking with my original suggestion of a 13p or a 15p amita 4 blade.

The 13p would be best suited for heavier loads and pulling tubes etc. It will throw you back in your seat during holeshot and bring your RPM right to the top of the range at WOT; perhaps slightly higher.

The 15p will be a very good all around prop that will work best when it's just yourself on the boat with no gear. You will maintain a higher top speed with this prop and compared to the original 17p provide better hole shot, better low speed plane and mid range cruise speed. I'd expect about a 1mph gain in top speed over the original 17p because the amita has a better design.

The only issue I think with the 15p is you likely still wont reach the ideal RPM range at WOT.

Hope that helps, I'm not a prop guru like some on here but do have experience with these props.

Cheers

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

I'm still sticking with my original suggestion of a 13p or a 15p amita 4 blade.

The 13p would be best suited for heavier loads and pulling tubes etc. It will throw you back in your seat during holeshot and bring your RPM right to the top of the range at WOT; perhaps slightly higher.

The 15p will be a very good all around prop that will work best when it's just yourself on the boat with no gear. You will maintain a higher top speed with this prop and compared to the original 17p provide better hole shot, better low speed plane and mid range cruise speed. I'd expect about a 1mph gain in top speed over the original 17p because the amita has a better design.

The only issue I think with the 15p is you likely still wont reach the ideal RPM range at WOT.

Hope that helps, I'm not a prop guru like some on here but do have experience with these props.

Cheers

Thanks. I would have to say about 85% of the time its just me on the boat by myself, which lends me to just doing the 13x15p Amita 4 and being done with it. However, doing some of a crude math I've read about, it seems like the 13p would put me right at my max WOT rpm.

3-4 conversion: ~ -400rpm
4" pitch drop: ~ +800rpm

So, 5000rpm with the 13x17, would change to:
5000 - 400 + 800 = 5400. Right under my peak of 4500-5500. Of course, give or take a bit. If it performs well, I could always raise the motor just a wee bit to spin things a little faster and get more top end out of her, since I'm only at +1/4" at this point.

I wish the guru's would give some more thoughts on this rather than asking for baseline numbers and then leaving.

Like I said above, my primary use for this would be cruise. I'd like to be able to stay up on plane, at a part throttle cruise... yielding better fuel economy, and a more relaxed ride. I guess eventually I'll get a tube for the kids when they get a little older, but even then, it would be pulled at idle/low speeds up the Wakulla river, where having perfect holeshot pitch wouldnt really matter.

As there are no places I can find that will let me swap props, the small bit of money I have saved up has to go to the right part the first time. I guess if I had to make a decision right now, I guess I'd go 13p. So whats the consensus? 13p or 15p?

 

[Dhadley]

Re: Ate my prop, suggestions for replacement?

If we were to make a suggestion it'd be to not change props at all - for the time being. It seems that there may be rpm left in your set up. If we were doing your set up we'd start with checking out the motor height or X dimension. We'd do all we could to pull more rpm with the 17 you have. Then look at a different prop. Again, we're assuming the motor is running properly.

We went thru this same scenario not too long ago. Different hull but they guy had a 19 and needed more top rpm. He was convinced he would buy a 17. Yes, that would have gained rpm but lost speed. We changed the set up and actually gained enough rpm that he ended up with a 21. The top rpm was where it should be and the top speed was more obviously. The holeshot was actually stronger. His 19, which was kinda doggy in the begining, then became his ski prop.

 

[RavenTBK]

Re: Ate my prop, suggestions for replacement?

That's kinda my issue. I need to purchase another prop regardless, as the original one got ate up, and is missing a chunk out of one blade. The question is what direction should I go? 13p or 15p on an Amita 4?

What do I need to do to check X? I already measured the AV plate approximately 1/4" above the keel. What steps would I need to take? Im not afraid of doing the work, just have no clue what I need to be looking at.

 

[trendsetter240]

Re: Ate my prop, suggestions for replacement?

I think the main issue you are having here is the 90 is a bit underpowered for your boat. What is the max HP rating for the boat? You say you replaced a 110hp so I assume it's max is at least 110.

If you go with the 15p amita then you have room RPM wise to work with if you can improve your setup to increase speed/RPM.