Not Fishing - Propeller Options

[Tacklebuster]

I recently got a new 60hp 4-stroke Yamaha.

I've heard that 4-stroke motors don't perform the same as 2-stroke motors, but I didn't expect such a significant difference.

After talking to the prop manufacturer and a couple of other boat and motor retailers it seems that propeller selection is by trial and error. You would think that nowadays it would be a little more scientific or at least there would be some kind of database with info., NOPE.

Hoping that someone here might have some info to share.

The biggest issue is getting the boat on plane, especially when there are three adults and fishing gear. To try and solve this I added a hydrofoil which only moderately improved the motor's ability to get the boat on plane, but it also resulted in losing 2+mph on the top end.

My boat is a 17'Lund and motor as mentioned. The prop is a 4-blade 13 pitch.

I would really appreciate feedback from anyone with a similar size boat and motor and hearing your recommendation.

Thanks,

TB

 

[Wildfire]

You would think that nowadays it would be a little more scientific or at least there would be some kind of database with info.

Ask and you shall receive.

| Mercury Marine

Manufacturers of outboard motors and MerCruiser inboard engines, with over 4000 dealers in the United States.

www.mercurymarine.com

(Don't worry about it being Mercury. The data still applies.)

 

[Wildfire]

Are you sure yours is 13" pitch? And not 13" diameter?

13" pitch seems awfully low. Like, that would be an appropriate prop on a barge.

 

[Bandwagon]

Is your boat maxed out on HP ? Are your trimmed down all the way when attempting to get on plane? There is some real science behind it and most bass boat guys go through this.

 

[tazmania]

The guys at kawartha prop are great to talk with. I only have a 20 2 stroke on a 16.5. They gave me great infor

 

[quackers]

17' Tiller or full windshield/walkthrough with all the trimmings? Weight of the boat is the factor. Decked out 17' with 3 people would be at least 90hp to 115hp required IMO. I had an 18' Crestliner Tiller and it got up and went with a 60 HP Etec H.O.

 

[Tanker]

Unfortunately I found the process could by trial and error. To avoid that, Don Hyde Marine in Hagersville helped me choose a new prop last summer. I told them what prop i currently had (pitch and diameter), the problems I was having and based on their experience with other boats they recommended a new one.You need to know the weight of your boat and then the dealer (or yourself) can look up the guidelines of what props are recommended. For my 75 HP evinrude, the correct prop had to be within a certain RPM at WOT as per the engine manual.

From my experience, i found out that the diameter of my old prop was too big for my boat and the engine struggled and consumed more gas.

 

[Leaky]

Tacklebuster Before anyone can tell you the correct prop size you must take the boat out on the water and do a maximum rpm test with your current setup. Before going out determine the maximum recomended rpm from the manufacturer. Say they recomend max to be between 5000 and 6000 rpm by design. Take the boat out on a calm day to an area that you can run the motor wide open until it gets the boat to its maximum speed . Adjust trim or tilt to achieve this maximum speed and record the rpm. If your Rpm is within the recomended range you have the correct prop for that motor. If your recorded number is below that recomended Rpm, your prop is too large, and if the rpm goes over the recomended Rpm your prop is to small. Generally one size up or down in pitch will increase or decrease the rpm 2-300 rpm to get your motor to its perfect top rpm. Any prop shop should be able to make a good recomendation for change once you have this information.

 

[Outdorman]

you need to find a calm day and run flat out and see what your max RPM is. Should be somewhere between 5500-6000. Then talk to a prop doctor and have it re-cupped to your specific boats requirements. Trim it out until it starts to porpoise then back it down a snick and that should be your ideal set up.

I fussed with my 16' Misty Harbor with a whale tail on my 50 yamaha with a mercury 4 blade stainless and was able to run on plane at 12-13 MPH and top speed was 34MPH. It took two years of screwing around to get things all sorted.

good luck.

 

[Old Cut LongPointer]

Leaky and Outdorman are on the right track. The only thing I can think to add is the motor height on the transom correct ?

Got to love the plus side of 4 strokes for their fuel economy and quiet running but they do weigh more and don't produce that "out of the hole shot" power like a 2 stroke.

 

[Tacklebuster]

You all have been great help, thanks very much for your suggestions.

I agree about the pitch, my dad's boat was an 17.5 fiberglass, with a 120 IO merc, and it had a 19 pitch prop. I remember trying 21 pitch but the boat couldn't get on plane when I water skied, those were fun days

Regarding the current prop, it's 10.5" diameter, 13 pitch, 4-blade

According to the Yamaha prop selector web site, thanks for your suggesstions, they recommend a 13" prop, 9 pitch (which seems really low, however, my spare Merc is a 12 pitch. 3 blade, 11") I guess smaller motors require a lower pitch to get the boat out.

The Yamaha dealer is going to swap my current prop for a 11 3/8", 12 pitch, 3-blade.

Let's see, I'll I report back, thanks.

 

[Tacklebuster]

You have all been a great help and I truly appreciate it.

Today I went to Burwell, the fishing was excellent, but that's another story.

About the prop, the dealer exchanged my prop for an OEM Yamaha (your guess is as good as mine as to why they didn't put this prop on in the first place). The new prop is a 3-blade, 11 3/8 inch diameter (almost an entire inch larger than the one they originally provided) and it is a 12 pitch. This prop is very similar to the one I had on my 2-stroke 60hp Merc.

The numbers,
4 blade, 13 pitch, 10.5" diameter - max RPM 4950, max speed 27-28 mph, very poor performance (this was not an OEM prop)
3 blade, 12 pitch, 11 3/8" diameter - max RPM 5800, max speed 30 mph, excellent performance (Yamaha prop)

The new OEM prop was amazing, the boat was on plane almost immediately, maintained plane even at lower speeds, RPMs were a huge improvement, and top speed was as good or probably better than the Merc that I had because I got to 30 mph with gear and a passenger.

 

[Old Cut LongPointer]

Don't ya just love those happy endings ? Be better if the dealer picked up the tab for the B.S. you had to go through as I would assume the motors are shipped without a prop on them and it's the dealers responsibility to install the correct prop ?

You mention maintaining plane at lower speeds ? I was taught to use max throttle to get her up on plane but then throttle back to about 3/4 as it saves wear and tear on motor plus fuel and it's easier to control the boat with a smoother ride. Now that was on 2 strokes *which actually love to run full out) so I would think it would really apply to 4 strokes. I don't own any 4 stroke outboard motors so please correct me if I'm wrong.

 

[Tacklebuster]

You're so right. To have the boat and motor operating as expected and awesome.

The boat actually gets on plane as fast or faster than the 2 stroke did. I never heard about going full throttle from start to lessen engine wear, but that's what I do anyhow because I want to get on plane quickly. It makes sense about engine wear because the boat was really slogging along with the previous prop and I was full throttle and you could really feel the strain on the engine. Now it's on plane almost immediately.

I find that being able to keep the boat on plane even at a slower speeds is important, especially in choppy conditions.