Four blades or Three for control and vibration

[mrallen007]

Hey all,

I recently bought a Tracker Pro 165 with a 40 EFI four stroke. It's a nice boat but somewhat small and it has a lot of vibration and cavitation issues at slow speeds. If I'm trolling around a cove with the outboard or putting the boat back on the trailer the console shakes so bad I'm worried the fish finder's gonna fall off. It isn't a terrible problem, but I'd prefer if it didn't happen.

I have a stock aluminum three blade Black Max on the motor now. I understand putting a four blade prop on is better for control at slow speeds and can help reduce cavitation. Does anyone have any thoughts on that? Also, should I replace the stock prop with the same pitch? Mercury recommends a 13 or 14 for this setup. Does anyone know which would be better for reducing vibration? Or will it even matter? One way or another I need a new prop for the new season as a rock took a nice chunk out of mine last year...

Also, I'm thinking of adding a hydrofoil. I have back issues and I'm not concerned with high speeds. High speeds in any chop equals lots of ibuprofen later... Would you agree that would help with cavitation?

I appreciate anyone's thoughts. Thanks!

 

[Georgesalmon]

Re: Four blades or Three for control and vibration

For pitch we need information! WOT rpm is a big one needed to determine proper pitch. I'm not sure a 4 blade would have less vibration. I put one on my boat and the slow speed control was much better for me anyway and so was hole shot. Top speed was maybe a little less. When running about half throttle is heavy seas I feel like I got four wheel drive compared to my three blade. No expert here, JMHO.

 

[mrallen007]

Re: Four blades or Three for control and vibration

Thanks for the reply! I'm hoping for some sort of reduction in vibration. That will be the icing on the cake. The main issue really is control at slow speeds. It's a small aluminum bass boat made for slow trolling and fishing. For that matter, I'm made for slow trolling and fishing. I won't be opening it up too often except to get from cove to cove and even then I prefer modest speeds. I can deal with vibration but I'm hoping to kill two birds here.

The motor came equipped with a Black Max 13" pitch from Bass Pro. The engine runs close to 6000 RPM WOT and gets me to about 34 or 35 MPH on calm water. The Mercury Marine Prop Selector recommends a 13" or 14" pitch. I actually have a 15" pitch 3 blade Mercury Vengeance on my old motor. When I put it on the new motor it bogged it down and lowered my top speed. I took that to mean it was a bit too much for my motor and I pulled it off. It's ok as a spare. But I don't want to damage my motor.

So I guess the question here is whether to replace the stock prop with the same pitch or upgrade a bit keeping in mind my focus is on low speed control, vibration, and cavitation and not on top speed. Any thoughts?

 

[MH Hawker]

Re: Four blades or Three for control and vibration

It sounds like you may have several problems.

Their should be no vibration at all regardless of a 2, 3 or 4 blade`s. I would suspect a bad prop or a bent prop shaft to start off. The vibration will cause LU damage eventually.

Cavitation is normal a sign the motor is set to high on the transom, and a whale tail inst really a cure for much of any thing at all.

A 3 blade will take a bit longer to plane out but has better top end. A 4 blade has a lot better hole shot and quicker on plane but often loses some top end speed.

When you tried the 15 p did you have the vibration problem.

 

[blackhawk180]

Re: Four blades or Three for control and vibration

I'm not sure a 4 blade would have less vibration. I put one on my boat and the slow speed control was much better for me anyway and so was hole shot. Top speed was maybe a little less. When running about half throttle is heavy seas I feel like I got four wheel drive compared to my three blade. No expert here, JMHO.

Same 4WD experience on my boat when I went from a three to a four (stainless). Buddy really noted a vibration reduction on his Honda when he did the same thing but a properly balanced three shouldn't produce any noticeable vibration if the shaft is true.
Also agree on checking the mounting height of the motor. Have someone steer while on plane, go back and look where the anti-ventilation plate is relative to the water. If it's out of the water, your motor is set too high on the transom. If it's buried, you're too low.
If everything is balanced and trimmed and you're still needing ibuprofen, consider purchasing some air or hydraulic seats. I've got them on my boat and love them.

 

[steelespike]

Re: Four blades or Three for control and vibration

Don't adjust the height until your have your new prop.
It's usually suggested to drop one inch in pitch when going to a 4 blade.
With the 4 blade and a drop in pitch you probably wont need a foil.Hole shot will be better,it will stay on plane better at reduced throttle,
and handling should be better.
While you have the prop off check the runout on the prop shaft.Just hold some sort of pointer close to the shaft and rotate the shaft.
If its bent it will be obvious.

 

[jestor68]

Re: Four blades or Three for control and vibration

Hey all,

I recently bought a Tracker Pro 165 with a 40 EFI four stroke. One way or another I need a new prop for the new season as a rock took a nice chunk out of mine last year.
Thanks!

The nice chunk out of the prop is your problem. That would cause it to vibrate; the amount of vibration dependent upon the size of the chunk. I suspect it didn't vibrate until you hit that rock.

Replace it with a same size 3 blade or a 4 blade of one inch less pitch. The Merc prop selector comes up with a 12 pitch Spitfire(4 blade). Solas makes a 4 blade just as good, but doesn't cost as much.

If allowed to continue, the vibration will damage the lower unit at a minimum.

Motor height should be with the AV plate even with the bottom. Most Tracker boats are rigged correctly from the factory. The previous owner might have messed with the motor height in an effort to go faster.

 

[mrallen007]

Re: Four blades or Three for control and vibration

Definitely going to look into a way to cushion the seats! My back will like me for that...

Though the boat is a 2012, it is second hand. Long story short, I got it for a steal when the guy who just bought it new found out he was having a baby and dumped it off fast and cheap. It's a Tracker. So I have assumed the motor was at or about the correct height from the factory and that the prop shaft would not be bent. But, it is second hand, so I guess I shouldn't assume so much. That also means the prop could have been bent from misuse before I got it. I didn't notice the same vibration with the 15" pitch prop. So here's hoping the shaft is true and maybe the prop was just bent or warped before I got it. I didn't notice any problems, but my eye is not so experienced that I would pick up on something like that unless it was obvious.

The chunk the rock took out of it was obvious!

It sounds to me like the best option is to drop the pitch by an inch, get a new four blade prop, make sure the prop shaft is not bent when I go to change the prop, throw the old prop in the boat for a spare, and sort out later if I need to adjust the engine or get a hydrofoil.

 

[jestor68]

Re: Four blades or Three for control and vibration

I wouldn't even keep the messed up prop at all. A prop you can't run isn't much good as a spare. Every minute you run it is another minute of abuse to the lower unit. And that vibration is being transmitted up the drive train into the motor.

The 4 blade prop will make a noticeable difference. I am hearing good things about Mercury's Spitfire aluminum props. Everybody I know that has one swears by it. :joyous:

I wonder if it's made for Mercury by Solas; as Solas is reputed to make some prop(s) for Mercury. That may explain why the Spitfire works so well. :faint2:

 

[mrallen007]

Re: Four blades or Three for control and vibration

I've looked at those and the Trophy Sports as well. I have to admit it would be nice to have a stainless steel prop again. But the cost of the Trophy Sport makes that a little hard to swallow at the moment. The Solas is on sale here at iBoats for about $95 shipped. I think for now I'll go with the four blade aluminum and upgrade to SS later.

You make a good point about the other prop. I guess I should just trash it and use my old 15" SS as a spare... It may be a little big, but at least it isn't damaged. And it'll get me back to shore in case of a problem. I want to protect my investment as much as I can. And if goofy things are going to happen on a boat, they either have or will happen to me!

 

[rallyart]

Re: Four blades or Three for control and vibration

A stainless prop is heavier and has more flywheel affect that smooths out the vibration some. There should be no difference in 3 and 4 blades as far as vibration, unless one is bigger diameter (less vibration but more if it is damaged) or one is heavier than the other. At 12" pitch a three blade should give you lots of bite.