Help with prop selection (with numbers!)

[DaRy0362]

Hey guys,

Purchased a Triton v186 Magnum (aluminum hull) with a 4 stroke Suzuki 140 hp, had it out for the first time today. It has a top speed of 43 MPH, which seems a bit slow to me, based on information online some of these boats hit 60 MPH with 150 hp's. Here are the specs:

-5700 RPM WOT
-operating range is 5600-6200 RPM
-Marine Trophy Plus stainless steel prop, 24" pitch, 13 7/8" diameter, 4 blades
-Engine mounted in the second hole from bottom
-Appears to be a lot of water "spraying" when at WOT

Anyone have any prop recommendations for a faster top end speed? Thanks! Dan

 

[ondarvr]

Before you do anything with the prop, post a pic of the motor and how it lines up with the bottom of the transom, frequently spray means the motor is mounted too low.

 

[Maclin]

Does the tach seem accurate? Was the speed from GPS?

 

[DaRy0362]

ondarvr-I'll take a pic this evening and post it. If anything though I'd say the motor is mounted too high, but maybe the picture will help sort that out!

Maclin- The speed was from GPS, a Humminbird Helix 7. The tach reading was from a digital Tiny Tach and verified by the analog tachometer in the dash that came with the boat.

 

[DaRy0362]

Ok so I was able to get measurements . Looks like the anit-ventilation plate is approximately 1.5" above the bottom of the hull. The Triton has a sort of built in jack-plate, that is the transom isn't just straight across, you may be able to see that in the pictures. I've included a few pictures.

Would be happy to hear what everyone's thoughts on the engine setup. Is it correct? Any prop recommendations to improve top end speed? Was thinking along the lines of a 3 blade x 14 x 23. Dropping a propeller and an inch in pitch will increase my RPMs since I'm at the bottom end of the operating range. Don't want to drop too much pitch because my top end may suffer?

 

[ondarvr]

The pics don't exactly show the height, but assuming the hull is level, and the level you're using is flat against the hull bottom so the hull bottom is correctly represented at the AV plate, then you're about 1" above the hull bottom. A stepped transom typically allows the motor to be mounted higher than without a step, so it may still be a bit low, but this can only be determined be raising the motor and using the boat how you normally would to see how it works. If the prop doesn't ventilate being mounted higher you may gain a couple hundred RPMs and a few MPH

 

[DaRy0362]

Thanks ondarvr! Yes, I leveled the boat as best I could, to use as the point of reference. The trailer interfered with my ability to old the level flat against the hull, so I attempted to just make sure the level was "level" as best I could. That's a good point about the stepped hull, I may try to raise it to the last hole and see what happens, thank you for your input!

In your opinion though, does that propeller seem to be turning at a slow RPM at WOT (with the motor fully trimmed at WOT)? Based on my WOT RPM of 5700, I still have room to increase/improve my RPMs by 5000 revolutions. Raising the motor will definitely increase the RPM's, but certainly not by 5000 revolutions, correct?

 

[ondarvr]

You're only looking for 500 more, raising the motor may get half that, but that's only a guess, and only if it can be raised, the only way to know is to try it.

If you want the last few RPM's you can start working with other props, or have the current one modified, it just depends on how important it is to you and how much time and money you want to spend on the last couple of MPH.

 

[Sea Rider]

Your post is a prime example going for the “nonsense rule” that states that AV plate must be even with lower keel/hull, the only thing that has rendered so far is a catastrophic water result. This rule says nothing, it’s only a dry installation that does not take in the least account at which lower leg height water flow at speed will pass by once combo has gone through its Hydrodimamic Lift, also referred to as Hole Shot. As you have experienced Plain Theory does not always matches Plain Practice.

Please answer these questions for clarification :

How many passengers were on board on last wot run ?
OB was trimmed at second hole from bottom which gave + or – trim ?
How many holes are left to raise OB higher ?
From what you posted, your problem seems to be as follows : check pic.



Water splashes back or over transom is produced when water flow hits the non edged square upper portion (X 1)
What needs to be done is raise OB accordingly till water flow exiting aft middle hull passes right under the protruding lip located side of upper water deflector plate (blue Line).

Don’t rise OB towards AV Plate (red line) if flow passes right over or under AV Plate will achieve excessive prop aeration on choppy windy water cond and at close tight turns at speed due to prop's thrust loss.

Raise OB fully, go for a wot run on flat calm, no wind water cond. Deck weight must be evenly distributed and OB trimmed at 90? beforehand or when combo is finally on plane. Pull head over transom and check at which lower leg height is flow passing at speed. Have a second boater follow or fly a drone next to combo to check what’s going on at back transom.

Once Tip-Top OB height is dialed, expect OB to achieve more rpm as lower leg will have less drag. From there can go for a prop maximization say, a 22 pitch 4 blade prop to pull max 5700 rpm achieved towards max wot rpm range of 6200. Prop selection is very personal, depends on your boating requirements, HP, N? of passengers along superb hole shot or best top end speed.

Check this link, duplicate it. Once OB sits Tip-Top on transom will achieve a near flat middle wake out prop.

https://www.youtube.com/watch?v=oBeZjaA76VM

Report your findings..

Let’s Make Boating More Fun….
Happy Boating

 

[DaRy0362]

No Title

Searider and ondarvar, thanks for the information! I was able to get out today and attache a GOPRO to see where the water stream is hitting the outboard. Looks like the water stream is hitting between the deflector plate (blue line) and AV plate (red plate). I've attached a pic so you or someone else more knowledgeable than myself can chime in and verify the water stream is hitting the right place! If it is in the right place I may not want to move the outboard up one hole, as already suggested. Also I've answered your questions below:

How many passengers were on board on last wot run ? Just myself, one person, 200 lbs. About 100 lbs of fishing equipment, 3 batteries (2 trolling 1 cranking), and 20 gallons of gas.
OB was trimmed at second hole from bottom which gave + or ? trim ? I'm not entirely sure what you mean here. I think you may be referencing the needle on the trim gauge as past the halfway point as "+" and below halfway as "-"? If that is the case, then positive trim when on plane. Almost seems like I can't get enough positive trim/bow lift to raise the front end of the boat out of the water to achieve a faster speed though.
How many holes are left to raise OB higher ? One

Turns out most of the "spray" looks like it is originating from the transducer I have attached to the hull, and not from the outboard, so that question is solved!

If folks think the setup looks correct, then I may be looking into buy a Mercury Tempest Plus 23 pitch in the future, since some folks have posted their results with that prop and appeared to have good success. If that is the case I'll post my results so everyone can reference (but that may take some time)!

 

[ondarvr]

I'll put it this way, there are some strange ideas presented on this site about motor set up that aren't supported anywhere else on the planet, it involves the blue line red line thing.

​If the AV plate is still under water try raising the motor, and raising until it starts to ventilate when you use the boat in the way you normally do is the only way to know if it's correct. At the extremes of raising the motor you need to lower the water pick up so it doesn't overheat, you aren't even close to that.

 

[Sea Rider]

DaRy,

So far OB height looks good, seems not opt though. the only possible way to know if OB sits at the Tip Top spot is to go for a wot spin as usually loaded on clam waters and check if prop aerates on tight close turns, if so, lower OB one hole, will better or cancel the prop aeration.

Don't understand why senior boaters likes going per the old school rule if applies, when the new school has already earned a Master Degree..

Happy Boating

 

[ondarvr]

Turns out most of the "spray" looks like it is originating from the transducer I have attached to the hull, and not from the outboard, so that question is solved!

If folks think the setup looks correct, then I may be looking into buy a Mercury Tempest Plus 23 pitch in the future, since some folks have posted their results with that prop and appeared to have good success. If that is the case I'll post my results so everyone can reference (but that may take some time)!

​Like you said, it's very difficult to tell from the pic just how low the motor is, but my guess is it's still too low. Raise it until it causes ventilation issues, then drop it slightly.

 

[Sea Rider]

If flow is passing right at middle of both plates will have good water performance at straight water courses, but prop will aerate at close tight turns, much worse under choppy, windy water cond. If wanting top water performance lower OB if possible till flow matches blue line.

If wanting going per the idiotic method of dialing Tip-Top OB/transom height by "ear method" expect to lose precious boating time as it's not that simple as to push a button and electrically rise or lower an OB. For that quest, spotter will need to sit way aft and have a musician ear to separate prop aeration from overall huge engine noise. Much faster end results is a visual check..

If you correct a prop aeration by ear method, doesn't means that flow is passing spot on where it should be passing specially if you happen to own an OB which both lower plates are taller than found on Jurassic Ob's which are shorter and easier to dial to a proper height.



BTW, these non supported color lines out of the planet motor set-up crazy ideas are all mine. Are not found on any OB Owner's Manual due to extreme conflicts between OB's and Boat's manufactures, so only state the AV Plate distance to bottom hull which on a dry installation means nothing. Seriously doubt if illuminated boater has read any OB's Owner Manual ever, aside from morning newspapers..

Happy Boating