Montauk 17 Yamaha F70 Propeller

Optimizing the performance of Boston Whaler boats
gman87
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Montauk 17 Yamaha F70 Propeller

Postby gman87 » Fri May 24, 2019 1:05 pm

I have a 1987 Montauk 17 that I re-powered with a 2016 Yamaha F70LA (brand new when I got it recently).
[Following advice given in a prior] discussion, I got a new Solas New Saturn 13.5 x 15-pitch. The top boat speed is 32.5-MPH, and engine speed is 5,500-RPM under calm conditions, 400-lbs crew, 10 gallons of fuel, and two batteries.

I know WOT engine speed should be closer to 6,300-RPM.

Is [5,500-RPM at full throttle instead of 6,300-RPM] a concern?

I've read older threads saying the Yamaha Performance Series MAR-GYT3B-V4-14 is optimal.

is that propeller still considered the OPTIMUM?

Are other unnamed propellers better?

Ok, I know this has been discussed before (and I took some of the advise that didn't pan out for whatever reason), so I ask about my specific case.

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Phil T
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Re: Montauk 17 Yamaha F70 Prop?

Postby Phil T » Fri May 24, 2019 1:29 pm

You are 5 mph and 800 rpm from where you could be.

The current Solas prop you have not right for your gear ratio and RPM. Why a Honda prop for a new Yamaha motor?

The prop choices members recommend include:

13 x 17 Yamaha Painted SS
13.25 x 14 Yamaha Performance Series
13-1/4” x 17” Turbo 1
13.25 x 14 PowerTech SCP

Also very important is engine mounting height. You want to be at least 2 holes up, possibly 3.
The top set of bolts should have two (or 3) open holes above the bolt. I would start at 2, test, raise it, retest with same prop and load.

Engine rigging is not always about wide open throttle (WOT) speed rather ensuring the engine is operating at the correct rpms across the entire range 0-6300.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

gman87
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Re: Montauk 17 Yamaha F70 Prop?

Postby gman87 » Fri May 24, 2019 3:39 pm

Engine mounting height is all the way up.

The Solas was per an older thread that someone had used with good results with an older F70 due to the thread age I suppose.


You gave exactly the feedback I was looking for. Thank you.

jimh
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Re: Montauk 17 Yamaha F70 Propeller

Postby jimh » Fri May 24, 2019 4:01 pm

Please give engine mounting height in units of 0.75-inch or “holes” above lowest possible mounting.

“All the way up” is ambiguous.

gman87
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Re: Montauk 17 Yamaha F70 Propeller

Postby gman87 » Fri May 24, 2019 4:13 pm

Phil, one more question, are those in the order of preference? Top being first choice?

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Phil T
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Re: Montauk 17 Yamaha F70 Propeller

Postby Phil T » Fri May 24, 2019 4:14 pm

No preference in the order.
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1992 Outrage 17, 1992 Evinrude 115

flymo
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Re: Montauk 17 Yamaha F70 Propeller

Postby flymo » Fri May 24, 2019 4:59 pm

I don't expect you'd be able to spin a 17-pitch. I would recommend starting with a PowerTech SCD-3 in a 15-pitch - I think you'll find it really makes your setup come alive. The SCD-3 has less blade area which will help your F70 spin up through the midrange to where it really makes its power. Topping out at 5500, you are missing out on a lot of acceleration and fun and also on being able to hold plane at lower speeds.

I use a 17-pitch SCD-3 on my 15 and Montauks usually drop down a couple of inches relative to a 15.

Best price I have found on PowerTech is Ken @ propgods.com. PowerTech does let you trade in within 30 days if you end up wanting a different pitch, and their props are available in 1-inch pitch increments. It's possible a 16-pitch would be best, but if it were me I'd start with a 15.

One other prop you might try is the Turbo Quest - supposedly made specifically for the F70. I have not tried it so can't advise on pitch.
Last edited by flymo on Sat May 25, 2019 6:51 am, edited 3 times in total.

gman87
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Re: Montauk 17 Yamaha F70 Propeller

Postby gman87 » Fri May 24, 2019 5:49 pm

Sorry about the "all the way up" comment. [The boat is] not where I can inspect [the engine mounting] to see exactly how many holes are free at the top. What I know is [the engine] is mounted as high as it can be, ie, lowest bolts are through the bottom holes on the mounting bracket. I think that makes it 3-holes-up—but not positive.

flymo
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Re: Montauk 17 Yamaha F70 Propeller

Postby flymo » Fri May 24, 2019 9:35 pm

Sounds like you've got the engine mounted correctly.

gman87
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Re: Montauk 17 Yamaha F70 Propeller

Postby gman87 » Mon May 27, 2019 11:02 pm

I can confirm the engine is mounted 3 holes up. So there appears to be debate over the 13 x 17 Yamaha Painted SS and 13-1/4” x 17” Turbo 1 regarding 17 pitch. Anyone else care to "pitch" in. I'd like to be a one and done the second time around.
I was able to milk a couple more mph and 200 rpm by reducing the passenger weight 100 pounds and trimming out but want to get a prop more optimal for the motor than the Solas New Saturn.

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Phil T
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Re: Montauk 17 Yamaha F70 Propeller

Postby Phil T » Tue May 28, 2019 9:33 am

The recommendations I list are not "mine" per se, rather culled from the 1000's of prop discussion/testing threads over the last 15 years from 3 whaler forums and are germaine to a classic Montauk and F70 combination.

You are welcome to call Ken at Propgods. I have recommended him for over a decade.

If you want my data, review these threads.

https://www.google.com/search?hl=en&source=hp&biw=&bih=&q=site%3Acontinuouswave.com&q=Montauk+F70+prop&btnG=Google+Search
Member since 2003
1992 Outrage 17, 1992 Evinrude 115