Hail DHadley!! Yamaha 115

[ssime]

I have a '89 Mirrocraft 16 foot bass boat (aluminum, flat bottom) with a '89 Yamaha 115hp 2-stroke.

It currently has a 21 pitch prop.

We've been less than pleased with the performance, specifically:

1) The boat planes very, very quickly, but top-end seems lacking - around 35mph at 5500. Should it not be going faster?

2) We cannot trim the motor very far up at all. Sometimes cruising at near (not even at) WOT is not possible as the prop loses bite at the highest level we can trim, but still isn't lifting the bow enough

3) The prop seems to wash out in corners unless it's trimmed almost all the way down

We got a small fin, and that seems to have helped in corners, and to a lesser extent, trim level.

I am fairly certain that I can't open the throttle all the way with it, I always back off the moment it seems to start going past 5500 rpm

We tried a 19 pitch stainless prop last night (pictured). The hole shot was almost silly, on plane in less than 3 seconds it seemed. But it seemed that it wasn't really possible to go past 3/4 throttle. If we touched it past around 3/4 (or 2/3, somewhere around there) , the rpm instantly jumped up to almost 6000 with very little change in boat speed.

Here's what I know:

- motor is set on the lowest possible mounting hole (deepest in the water)

- hull is flat bottomed

- bottom of hull to center line of prop is about 7.5"

- the motor has excellent compression and otherwise runs superb

Any advice would be VERY much appreciated

Thanks

 

[Bob_VT]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

Wow how big is the transom? It almost appears as if you need a longshaft motor set up high.

You don't have enough prop in the water when you are trimmed up. I would also be concerned about the water pressure for the water pump.

Other alternatives -
Get a long shaft
Cut the transom down
Mount a jack plate but lower the motor.

Hail DHadley!!! He is a pro

Youi should be seeing closer to 45 mph and IMO I would set it up right and dump that wing away.

 

[ssime]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

I guess I should have measured the transom to begin with.. it's 20.75" inches top to bottom.

Now I'm worrying

 

[Bob_VT]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

Mine is the same height as yours for a short shaft. What is the measurement from the transom top to your "hydrofoil" ? That motor looks short to me could it be a 15" ??

Edit your post title to "HAILING DHADLEY"

 

[Dhadley]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

Hi guys!

I think the height is OK (20 3/4" is a standard "20" transom), looks like we just need a prop with some bite in it. I'm guessing the cup, what little there is, ends at the tip. Lets see if we can borrow something with some bite in it to try and see what happens. I would think that a 21 would be close. Maybe a 23.

Don't get scared at 5500, try for 6000. It'll be fine.

 

[ssime]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

Hi,

"hailing Dehadly"... cool!

Thanks... I've measured from top of the transom to the top of the hyrdofoil (cavitation plate). It measures almost identical to the transom measurement... 20.75". If I drew an imaginary line continuing back off the transom, it would seem to run almost directly in line with the cavitation plate.

The current prop is 21 - we tried a 19 last night though.

The motor model number is CV115ETLD, would the "L" mean long shaft - or how do you tell a long shaft from a short version?

I meant to add earlier that I can trim nowhere near high enough to acheive a rooster tail.

Thanks again

 

[walleyehed]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

Flat-bottom boats don't like a lifting (bow) type prop..
The faster you go, the more the flat bottom lifts and pushes the nose down. It's like a 4X8 sheet of plywood going across the water...it'll be pretty flat at speed.
I have a 17ft flat-bottom Tracker with a 70 on it, and it likes a pretty much straight thrust-line. much more trim than level makes it porpoise and I have to trim down in corners as well...it's just one of the traits of a flat-bottom boat.
I'm with Dhadley on the 6000....let it run like it should!

 

[ssime]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

Thanks guys. I just want to make sure, since it's been brought up.... does the transom to cavitation measurement make sense? Do I have a short shaft motor on a long shaft transom?

And if not, would my best course of action be to look for a prop with better cupping - or up a few notches to 23p?

Thanks much

 

[walleyehed]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

You have a long transom with the correct "long shaft" engine...
15" is short, 20" is long, 25" is Xlong and 30" is XXlong.

 

[Crownie2]

Re: Yamaha 115 - need prop help - pictures

Re: Yamaha 115 - need prop help - pictures

I see where you are coming from - top speed should be over 40, but you feel the need to back off at about 5,500 rpm's. So you don't really know the top speed.

It could be that the 21" pitch is the right prop. Is it in good condition. The cupped SS wheel will give added bow lift as stated above, which you really don't need because of the hull design.

IMO I'd suggest trying a good aluminium prop of 21"-22" pitch.

 

[ssime]

Re: Hail DHadley!! Yamaha 115

Thanks much for the input.

From what I gather, I need either a change up in pitch, or a better gripping prop.

So that leads me (I hope) my last questions. I've done quite a bit of calling around to local shops today, and looking on the internet.

I haven't really received any clear information on what sort of prop has better rake or cup characteristics though. The local Yamaha dealer has an OEM 23 pitch propeller in stock (13x23), but they have no idea if it's got high-rake or cupping or whatever.

A Solas / Piranha dealer in town here told me that Solas Alcup3 and there other Aluminum props have a higher rake than stock, and that their props are generally the same as a comparable OEM prop one pitch higher (i.e. 21p Solas = 23p Yamaha).

Still another shop told me that my prop just slips too much, and a 4 blade 20 pitch would likely solve the problem.

So, lots of choices, little clarification, plenty of confusion.

1) Is there a way to asses the amount of "rake" or "cupping" a prop offers?
2) Based on discussions here, should I take a shot at a OEM 23p?
3) Should I be looking aftermarket for a prop, and if so, is there a specific model (preferably in aluminum)

Thanks again

 

[walleyehed]

Re: Hail DHadley!! Yamaha 115

Most important question.....Are you dead-set on aluminum?
Between DHadley and myself, there aren't too many props we don't have a general Idea of how they work...
If you're willing to go SS, I think in the long-run, that will be your best bet...as for which one, well, tell us if that's an option or not.

 

[Crownie2]

Re: Hail DHadley!! Yamaha 115

1) Is there a way to asses the amount of "rake" or "cupping" a prop offers?
2) Based on discussions here, should I take a shot at a OEM 23p?
3) Should I be looking aftermarket for a prop, and if so, is there a specific model (preferably in aluminum)

Thanks again

1) Not really - you have only the Mfg'rs word on how the prop is designed and what it should do.
2) Only if you can return it if it doesn't work - you may have to do some experimenting here.
3) Again you need to find a dealer who work with you. From the looks of your skeg you have hit bottom before and that is where aluminum is good - easy to repair.

Good luck!

 

[Dhadley]

Re: Hail DHadley!! Yamaha 115

Are you dead set on aluminum? If not I know where there's a 13 1/2 x 21 Yamaha ss prop. And a 13 1/4 x 22 ss Stiletto.

Kenny, do you think either of those would work OK on the flat bottom?

 

[ssime]

Re: Hail DHadley!! Yamaha 115

I'm not dead-set on aluminum, but stainless might be cost-prohibitive.

I would be interested in those SS props you mentioned, if they would provide noticeably better grip over a stock prop.

What about the Hustler series aluminum prop - do they offer a noticable advantage over an OEM?

Thanks

S

 

[Dhadley]

Re: Hail DHadley!! Yamaha 115

I'd bet either of those 2 ss props could be bought at a pretty good deal. Lets see what Kenny thinks they would do on a flat bottom. Either will have more bite and much more life than an aluminum prop.

 

[walleyehed]

Re: Hail DHadley!! Yamaha 115

I think either would be a good choice...of course you know those 2 better than I, I'm wondering if the Stiletto might have the edge in holding abilities....???

 

[Bob_VT]

Re: Hail DHadley!! Yamaha 115

Dhadley you have a PM

Bob

 

[ssime]

Re: Hail DHadley!! Yamaha 115

Alright, so I picked up a Hustler 23p prop and tried it out this weekend.

The difference is dramatic, to say the least. I went from a top end of 35mph at 5500rpm (with slipping and not wide open) to 44mph at 4500 wide open. Both with two of us in the boat.

It's fairly sluggish from a stop - maybe 6 seconds to on plane - and that's even with that stupid fin on.

I can not make this prop lose bite, I could turn it hard enough at WOT to roll us out of the boat.

But, now I can't get the motor past 4500rpm. And, although I can trim higher now, it seems that the prop has so much bite the motor reaches a certain point of trim and then stops, it can't lift anymore unless I get off the throttle.

I imagine that this all means that I should likely move down to a 21p hustler?

 

[walleyehed]

Re: Hail DHadley!! Yamaha 115

You need 1300-1500RPM...2" pitch ain't gonna do that...