1964 NAUSET 16 Yamaha F70A

Optimizing the performance of Boston Whaler boats
Dave_a
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1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Tue May 16, 2023 7:19 am

I am now getting a new Yamaha F70 four-stroke-power-cycle engine rigged on my 1964 NAUSET 16.

Give me advice on propeller pitch and propeller diameter.

The hull weight is 800-lbs. A 12-gallon capacity fuel tank is mounted under the pilot seat. A battery is mounted under the console. Typically two adults will be aboard.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Tue May 16, 2023 8:52 am

A few more facts are needed.

Q1: what engine mounting height have you told the dealer to install the new engine on the NAUSET 16?

Q2: where are the existing engine mounting holes drilled in the transom?

Q3: what is the gear ratio of the Yamaha F70 engine?

Q4; what is the maximum recommended engine speed at full throttle for the Yamaha F70 engine?

Q5: what is the total weight of the boat when fully rigged and in the water?

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Tue May 16, 2023 8:57 am

Dave_a wrote:Give me advice on...propeller diameter.
The diameter of a propeller must not be larger than the propeller aperture on the engine gear case. This raises a new question:

Q6: what is the maximum propeller diameter possible in the propeller aperture of the Yamaha F70 engine?

Generally the diameter of propellers is not a parameter that can be selected separately from the propeller pitch. A propeller maker creates propellers of various combinations of pitch and diameter as are appropriate for the application to the horsepower range of outboard engines those propellers will be used with.

The propeller diameter is also related to the propeller hub diameter. The propeller hub diameter must match the engine gear case. This also raises a new questions:

Q7: what is the hub diameter of the gear case on the Yamaha F70 engine?

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Tue May 16, 2023 3:23 pm

I didn't know there was going to be a quiz, Jim. I was hoping a forum member with a similar engine and hull could chime in on what prop he had on his vessel. Prop selection at a yamaha dealer is often relegated to what the dealer has in stock, not necessarily what is optimum.
To wit:
jimh wrote:Q1: what engine mounting height have you told the dealer to install the new engine on the NAUSET 16?
Answer: cavitation plate even with hull bottom minimum.

jimh wrote:Q2: where are the existing engine mounting holes drilled in the transom?
Answer: top holes normal location as per Yam. template. Bottom holes are raised to exit into splash well as per BW Bulletin 10-84

jimh wrote:Q3: what is the gear ratio of the Yamaha F70 engine?
Answer: 2.33

jimh wrote:Q4; what is the maximum recommended engine speed at full throttle for the Yamaha F70 engine?
Answer: 6300rpm

jimh wrote:Q5: what is the total weight of the boat when fully rigged and in the water?
Answer: estimate 1,200lbs. (800-lbs hull + 253-lbs engine, 65-lbs battery, 88-lbs fuels fuel (12@6.5-lbs), and add passenger weight.

jimh wrote:Q6: what is the maximum propeller diameter possible in the propeller aperture of the Yamaha F70 engine?
No clue.

jimh wrote:Q7: what is the hub diameter of the gear case on the Yamaha F70 engine?
I don't expect propeller diameter availability to vary more than 1/2-inch, and perhaps 1/4-inch smaller, and usually for high load. I haven't investigated what is available through Yamaha or aftermarket.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Tue May 16, 2023 3:43 pm

Dave -

Dozens and dozens of 16' model (Nauset, Sakkonet, Eastport et.al) owners have selected the Yamaha F70 as their repower choice.

After many rounds of testing, these are the recommended props. Any one of these is a good selection.

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

Notes:
- Size only applies to the make and model listed and is not transferable.
- Engine mounting: Engine is mounted 2 holes up with the top engine bolt in the 3rd hole, counting down from the top.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Thu May 18, 2023 6:08 pm

Perfect Phil, your info is in the hands of the tech rigging the engine. The good news is he has a 70 on his boat.

JimH. I gave you all your requested info. Did it result in some prediction of propeller pitch? What are the results?

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Thu May 18, 2023 7:57 pm

Dave_a wrote:I didn't know there was going to be a quiz...
In order to calculate a propeller pitch I need all the information I asked you for. I don't rely on archives of anecdotal reports. I figure out the propeller pitch using algorithms that have a history of good outcomes. I don't want to waste time guessing at all the data, so that's why I asked you to tell me the data for your application.

Dave_a wrote:I gave you all your requested info. Did it result in some prediction of propeller pitch? What are the results?
Yes. Here is the predicted propeller pitch based on your input.

For 70-HP and only 1,200-lbs, a 16-foot hull should reach 46-MPH, as predicted by the Crouch Method, and the rounded bottom hull of your older 16-footer will have a hull factor of 190 when using my Crouch's Calculator to do the math.

At 6,300-RPM via a 2.33:1 reduction, with SLIP = 10 to reach 46-MPH will require a propeller pitch of 20-inches, using my Propeller Calculator.

I think the total weight value you provided is too low. It was not clear if you included weight for the crew. I will recalculate with 1,600-lbs, which could be appropriate for two adults and some of their gear, water, and ice.

Top speed will be 39-MPH. Propeller pitch will be 17-inches.

The suggestions that the propeller pitch could be as low as 14-inches seem rather odd. With a 14-pitch propeller, the expected boat speed would be about 31-MPH. That seems very slow for a 16-foot hull with 70-HP.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Thu May 18, 2023 8:23 pm

Not all 17" pitch propellors are the same. While there are a few select models from different makes that perform in a similar way in the same pitch, they are the exception to the rule.

Many Boston Whaler owners have found that you need to investigate the make and model of prop, not just pitch. It is for this reason I share all the prop identification information so there is confusion.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Fri May 19, 2023 11:48 am

Phil T wrote:It is for this reason I share all the prop identification information so there is confusion.
I think you meant to say "less confusion."

Yes, there can be differences in the effective pitch of a propeller compared to its marked pitch, and this certainly varies among the several popular brands.

The only really good way to find out what propeller is going to work is to get one and test it on the boat-engine-load configuration it will be expected to be used.

Another factor affecting engine speed and propellers is engine mounting height. Some propellers have their pitch marked for being mounted very high, and if the propeller is buried in the water it may act like a much higher pitch.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Sat May 20, 2023 12:46 pm

A 13.5-inch x 17-pitch propeller is on the Yamaha F70A engine for initial testing I'll report back results. Engine mounted in the number two hole, and [the ANNTI-VENTILATION] plate is 1/4-inch above the boat bottom.

Testing will be in [early June 2023].

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Sat May 20, 2023 1:04 pm

Dave--you have missed a very important rigging requirement:
From my prior post:

Engine mounting: Engine is mounted two-holes-up with the top engine bolt in the 3rd hole, counting down from the top.

Always include the model name and size when referring to a propeller.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Sat May 20, 2023 10:54 pm

No, I didn't miss it Phil. The tech who rigged the engine to the boat determined that [described mounting height in ambiguous manner] was too high in his opinion.

If the [anti-ventilation] plate was 0.25-inch above the hull bottom in [some other position] then in [a higher position] the cavitation plate would then be 1.25-inch above the bottom of the boat--wouldn't it?

The mechanics's opinion [was for the anti-ventilation plate to be 1.25-inches above the hull bottom] was too high.

Should [the anti-ventilation plate] be 1.25-inches above the hull bottom for best performance?

[Moderator's note: do not describe engine mounting height in terms of some vague number associated with a mounting bracket hole. Engine mounting height is ALWAYS to be described in the relation to the lowest possible position for mounting on the transom and using units of "holes" which are spaced at intervals of 0.75-inches. The common engine mounting height is to raise the engine one-hole-up from lowest position or in some cases to raise the engine by two-holes-up from lowest position.]

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Tue May 23, 2023 8:51 am

Dave_a wrote:If the [anti-ventilation] plate was 0.25-inch above the hull bottom in [at some mounting height] then in [a higher mounting height] the cavitation plate would then be 1.25-inch above the bottom of the boat--wouldn't it?
The vertical spacing interval in the pre-drilled engine mounting bracket is only 0.75-inch. Moving an engine "up one hole" only raises the engine by 0.75-inches.

Whether or not an engine works best at a particular engine mounting height is determined by on-water testing. Whether a boat and engine will work best at a higher engine mounting height often depends greatly on the type of propeller to be used and the type of boating to be done.

Another variable in the engine mounting height is the location of the existing holes in the boat transom. In the particular case of older Boston Whaler boats with shallow engine splash wells, the original engine mounting holes in the transom may no longer be useful, depending, of course, on where they were drilled.

Note that in my early reply in this discussion I asked for information on the location of the engine mounting holes as existing currently in the transom, but did not get a reply with that information.

For advice on engine mounting and location of engine mounting holes, see these articles:

Engine Mounting Height Nomenclature
https://continuouswave.com/forum/viewto ... ?f=7&t=739

Considerations in Engine Mounting Height
https://continuouswave.com/forum/viewto ... f=7&t=6618

Transom Mounting Hole Layout for Shallow Splash Well
https://continuouswave.com/forum/viewto ... f=7&t=5808

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Tue May 23, 2023 11:37 am

Many older generation outboard engine installers and those not well versed with Boston Whalers install the engines too low due to lack of knowledge or sheer laziness. "I do this all day sonny I know what I am doing," is frequently reported.

Dozens and dozens of owners have tested new engines and props on their Boston Whaler boats over the 20 years I have been on this forum and their results are in the archives.

The consensus of opinion and technical testing results recommends a minimum engine height of 1-1/2-inches above the keel of a 16/17-foot Boston Whaler boat. If you ask jimh (owner and creator of this site) if this statement is true, I am sure he would agree.

With a light load and just you, the F70 engine with one of the recommended props above should reach 6100 to 6300 RPM and boat speed will be 37 to 39-MPH in good conditions.

I would suggest you test the engine, finish break-in, and then have that same tech raise the engine on his dime.
You will gain at least 200-RPM engine engine speed and 1 to 3-MPH boat speed as a result of the reduced drag from less of the engine being in the water.

It is your boat, your $10,000 installation. Do what you think best.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Tue May 23, 2023 12:53 pm

Phil T wrote:The consensus of opinion and technical testing results recommends a minimum engine height of 1-1/2-inches above the keel of a 16/17-foot Boston Whaler boat. If you ask jimh (owner and creator of this site) if this statement is true, I am sure he would agree.
I can't answer with a simple agree/disagree option as suggested. My answer is going to longer and more involved.

The principal reason I can't agree or disagree with Phil's remarks is because I have not personally researched the data available, nor have I had the pleasure of owning a 16/17-foot hull, and I typically would not use the distance between the bottom of the hull at centerline and the engine's anti-ventilation plate as the benchmark.

In my thinking, the goal of the engine mounting height is to allow for the anti-ventilation plate to be riding just at or just above the surface of the water that is flowing over the gear case when the boat is on plane in the upper speed range of it planing speeds and with the engine trim set so the anti-ventilation plate is parallel to the water flow. When the boat is sitting on a trailer and the engine is trimmed to some position which may or may not be where it will be when on plane and trimmed as described above, exactly what the distance will be on a particular boat with a particular engine between the bottom of the hull at centerline and the anti-ventilation will be is really hard to know.

Also, there are more variations in what sets the engine's height, such as where the transom mounting holes are drilled, exactly how long the engine lower unit might be to meet the recommended "shaft height" for the particular engine model, and how far set back from the transom the engine mounting puts the gear case. All of these are variables.

A final variable is the type of use intended for the boat and what is desired. If the boat is going to be run on a lake in mostly calm water and the goal is the highest possible straight line speed, the choice of propeller will be different than if the boat is going to be run on big water in big waves with a heavy load, and the goal is to avoid propeller ventilation as much as possible.

Regarding measuring the distance the A-V plate is above the hull bottom at centerline

If there is some prior discussion in which an installation of a Yamaha F70 is described in detail and includes dimensions for all the variables, and also happens to include a measurement of the distance from the anti-ventilation plate to the hull bottom (when the engine trim is set the same as would be used when on plane), then that dimension might be useful to know. But the problem with even knowing that dimension is you first would have to install the engine at a particular mounting height, then set the trim to be correct (that is, to be the same trim that will be used when on plane), and then measure the distance from A-V plate to hull bottom at centerline. What would happen if your measurement was 3/8-inch off from 1-1/2-inches. The next engine mounting height change would be 3/4-inch, you'd then still be 3/8-inch off from the 1-1/2-inch benchmark.

Right now it seems like the dispute in the particular case of this engine installation is over a change of 3/4-inch in selecting which set of pre-drilled engine bracket holes should be used to location the top bolts. (The bottom bolts will be located by where the bottom holes in the transom happen to be drilled, unless the BIA recommended positions were strictly applied.)

By the way, a "standard" propeller for a 70-HP engine will be a 17-pitch. This is because the typical application for a 70-HP engine is on a boat whose size and weight will permit a boat speed of about 37- to 39-MPH. Assuming the engine speed range permits 6,000-RPM and the gear ratio will be 2.33:1, working out the pitch for 38-MPH gives 17.3-inches.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Tue May 23, 2023 1:05 pm

Jim -

The phrase "standard propeller" is outdated, inaccurate and not always helpful. If anything, it fosters the continuation of the past sterotyped information.

Propellers are not included by the manufacturer and are sold separately from outboards larger than 30hp.

The F70 has a WOT limit of 6300 rpm.

Just because you have not tested the boat/engine/propeller combination personally does not meant you should distance yourself from information you have read and answers to your questions on the topic over 20 years.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Tue May 23, 2023 1:44 pm

As I said earlier in my introduction to my reply:

The principal reason I can't agree or disagree with Phil's remarks is because I have not personally researched the data available, nor have I had the pleasure of owning a 16/17-foot hull, and I typically would not use the distance between the bottom of the hull at centerline and the engine's anti-ventilation plate as the benchmark.

Those are the three reasons I cannot avow that the magic number is always 1-1/2-inches above keel bottom for the A-V plate on a 16/17 footer.

Phil apparently has researched this, and when I remark that I cannot join with him and declare it so, I am not suggesting his research is in error. I just don’t have a basis to agree or disagree.

Again, the real test is where the water flow line ends up on the gear case when the boat is on plane. We could work backwards from there to discover the engine mounting height that produced that outcome, then we could measure the vertical offset for A-V plate to hull bottom on centerline.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Sat Oct 14, 2023 9:51 am

Follow up [performance] data after [engine] break-in:

First Test
Propeller is 13.25 x 17-pitch Yamaha K -series aluminum. Engine is mounted in number two hole position. Boat Speed 36-MPH at engine speed 6,100-RPM, with two adults and 12-gallons fuel aboard. There was no up-and-down oscillation of the bow other than at "extreme" trim. [The time to accelerate onto plane from a standing start using full throttle] was good; fuel economy was "good."

Second Test
All parameters as above, but engine mounting was in number three hole position. Boat speed 37-MPH to 38-MPH at engine speed 6,300-RPM. There was some bow oscillation at higher trim.

Third Test
Propeller is RAPTURE stainless steel 12 x 19-pitch. All other parameters as above.
Boat speed 32-MPH at engine speed 4,200-RPM. Engine speed increased with higher trim. Up-and-down oscillation of the bow was excessive. Acceleration onto plane was sluggish. At low speed there was "chattering" in drive.

The Yamaha dealer advices me that Yamaha guidance for optimum engine speed is 5,800 to 6,000-RPM.

Next Step
I'm looking for an aluminum Yamaha K series 13 x 19-pitch or perhaps 13.25 x 19-pitch.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Mon Oct 16, 2023 6:32 am

Dave_a wrote:Follow up data and information after break-in:

First Test...Engine is mounted in number two hole position...


Second Test...engine mounting was in number three hole position.
Your descriptions of engine mounting height are unclear. PLEASE follow the recommendations given earlier. Engine mounting height is to be described only in terms of how many units of "holes" or 0.75-inches ABOVE the normal lowest possible mounting height the engine has been mounted.

In your case, because you have drilled the lower engine mounting holes in a non-standard position to accommodate the shallow engine splash well, based on your (somewhat oblique) answer to my inquiry about where the holes were drilled, I am assuming that on your hull the lowest possible engine mounting height will no longer be resting on the transom but will now be be one-hole-up from normal lowest mounting height.

On that basis I will assume your engine mounting height in the FIRST test was one-hole-up, and the engine mounting height in the SECOND test was two-holes-up.

Please use the "holes-up-from-lowest" as the method. If you need more help in understanding how do to this, read the pinned article at the top of this forum:

Engine Mounting Height Nomenclature
https://continuouswave.com/forum/viewto ... ?f=7&t=739

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Mon Oct 16, 2023 6:40 am

Dave_a wrote:Follow up data and information after break-in...
Thanks for the follow up data on your testing of two propellers and two different engine mounting heights.

The poor outcome from using the 19-pitch propeller compared to using a 17-pitch propeller confirms my earlier recommendation to use a 17-pitch propeller, which I calculated based on the engine horsepower, engine gear ratio, hull weight, and hull speed coefficient.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Mon Oct 16, 2023 6:43 am

Dave_a wrote:Third Test
Propeller is RAPTURE stainless steel 12 x 19-pitch. ...At low speed there was "chattering" in drive.
I do not understand what you mean by "in drive." Please explain further.

Generally I would equate a noise described as "chattering" as describing propeller rattle due to loose mounting of the propeller onto the propeller shaft.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Mon Oct 16, 2023 6:44 am

Dave_a wrote:Next Step
I'm looking for an aluminum Yamaha K series 13 x 19-pitch or perhaps 13.25 x 19-pitch.


There is a rule of thumb regarding the influence of pitch change on engine speed, with the relationship that a 2-inch decrease in pitch will cause a 400 to 500-RPM increase in speed, and vice versa--but this only works if you remain in the same brand and same series of propeller.

I assume you want to decrease the engine speed at maximum throttle to be around 5,800 to 6,000-RPM to align with the engine manufacturer's recommendations. If you get another Yamaha K-series propeller at 19-pitch, you might get the desired outcome. This next test will be interesting.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Mon Oct 16, 2023 6:59 am

Regarding the occurrence of the bow oscillating up and down when on plane at higher speeds: it typically will ALWAYS be possible to employ some engine trim setting that will result in bow oscillation at higher boat speeds. The remedy for bow oscillations is to adjust the engine trim to suppress them.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Mon Oct 16, 2023 10:23 am

No point in us sharing information when you dismiss actual Whaler owners testing and decades of experience with the same model of boat and engine.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Sat Nov 04, 2023 10:11 pm

Perhaps PHIL T's local dealer will order props for him, then allow him to return them if they're not quite optimum. My local Yamaha dealer expects me to pay for them, then test them.

All four propeller PHIL T has suggested have prices are all in the $500. I'm not going to buy one without more verification. I mean no disrespect to PHIL T's knowledge and reputation, but it is my money. 'll spend it when I'm more comfortable.

None of the suggested props are available for sale used in my area--I haveBeen looking since Labor Day 2023.

I threw on an stainless steel propeller that was available--the only viable option in the marina's "prop pool". The engine obviously couldn't spin the wheel.

Also please be aware that the Yamaha dealer's tech who owns and runs a F70 advises me against stainless steel propellers. The Yamaha F70 engines will exhibit a drive line "chatter" at low throttle settings with a stainless steel propeller. He told me it might and it did.

My Craigslist/Facebook searches did turn up a like-new in a box Yamaha K 13x19 aluminum for $70.

I will give a speed report when the winds calm down here in {in Jacksonville, Florida].

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Phil T » Sun Nov 05, 2023 8:44 am

Dave --

I know all of that and am not offended. I used to provide an explanation of the prop list origins and my 15 years of experience advising Boston Whaler owners with technical advice but it gets repetitive and tiresome.

I gave you specific make, model and size props that came from actual Boston Whaler owners who repowered the boat with the Yamaha F70 and tested many props.

I created a spreadsheet of recommended props for specific engine/hull combinations specifically because props are expensive, dealers no longer allow testing/returns and there are hundreds of choices. Finding the "right" prop for a whaler hull/engine is really hard.

This list was built over 15 years of owner repowers and prop testing.

If you want to test/return, contact Ken Reeves at http://www.propgods.com. He is well respected in the community. Knows Boston Whalers and is respected for his knowledge. He sells several makes including PowerTech (on the list). He takes returns for a small restock fee.

Keep in mind that you should expect to pay $350-$800 for a good prop as it is key to delivering the power of the engine into the water. If you purchase a Ferrari, you don't go with tires from a Radio Flyer wagon.

Let us know how it turns out.
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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Sun Nov 05, 2023 8:54 am

Dave_a wrote:My local Yamaha dealer expects me to pay for [propellers], then test them.
That is the normal paradigm, unless you and your local dealer are on very good terms.

Typically a dealer selling a new engine for re-powering a customer's boat will offer the customer the chance to test a propeller or two or three, on the basis that the customer will eventually purchase one of those propellers as part of the sale of the engine and the installation of the engine. But this generally only happens if the dealer is located on a body of water where the propeller testing can be done under his supervision. I don't think a dealer would let a customer drive away with a multiple propellers for testing without buying them, but the dealer may be willing to offer a return of a propeller if it proves to be unsuitable.

Regarding the choice of aluminum or steel, at the 70-HP power level, I don't think an aluminum propeller is necessary out of the question. And a steel propeller does not have to be a polished stainless steel, it can just be a painted steel propeller.

ASIDE: once upon a time, a major engine manufacturer, Johnson/Evinrude, provided their dealers with a series of "test" propellers. These propellers were painted yellow to distinguish them from the normal retail propellers, and I presume the dealer was given some price-reduction for maintaining a nice selection of these in stock at his dealership, with the intention of getting the right propeller on the engine to enhance the customer's experience.

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Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Fri Nov 10, 2023 1:47 pm

Well gentlemen, [the 1964 NAUSET boat with a Yamaha F70 engine has] hit 40-MPH [speed over ground as measured with a GPS receiver].

LATEST TEST DATA
    Propeller = Yamaha K-series aluminum 13-inch diameter x 19-pitch
    Engine speed = 5,800-RPM
    Boat speed = 40-MPH
    Acceleration at full-throttle from a standing start = good
    The added propeller pitch may be causing acceleration onto plane to take longer.
[To get this boat speed, the engine must be trimmed] way up, and [up and down oscillation of bow] becomes uncomfortable. [A boat speed of] 39-MPH is sustainable at slightly lower trim. To get the last [3-MPH compared with the previous propeller tests--see below] requires more up-trim than I normally use. The hull gets a bit squirrelly at that point, particularly in bumpy water.

With two persons aboard and fuel tank at HALF-FULL or with one person aboard and fuel tank at FULL the results were the same. The Bimini top canvas was erected in both tests.


To recap:

PREVIOUS TEST DATA
    Propeller Yamaha K-series aluminum proepller 13.25-inch diameter x 17-pitch
    Engine speed = 6,100-ROM
    Boat speed = 37-MPH
    Acceleration at full throttle from a standing start = great
    With four persons aboard the performance was good.

ENGINE MOUNTING HEIGHT CHANGE
Raising the engine mounting height from [one-hole-up to two-holes up] resulted in an increase in boat speed of 2-MPH.

PROPELLER PITCH CHANGE
Increaseing the propeller pitch by two inches resulted in a boat speed gain of 2-MPH.

Q: how much more [boat speed] is there to gain with a quality [stainless steel] propeller from Phil's list?

MODERATOR'S NOTE: the ONLY description of engine mounting height that is acceptable on this forum is to describe the engine mounting height in terms of the the number of units of holes or 0.75-inch increments above the lowest possible position. Describing the engine mounting be designating random hole numbers is not useful. Again, you need to read the following articles to become acquainted with how to describe engine mounting height:

Engine Mounting Height Nomenclature
https://continuouswave.com/forum/viewto ... ?f=7&t=739

Considerations in Engine Mounting Height
https://continuouswave.com/forum/viewto ... f=7&t=6618

Transom Mounting Hole Layout for Shallow Splash Well
https://continuouswave.com/forum/viewto ... f=7&t=5808

Dave_a
Posts: 33
Joined: Sun Aug 07, 2022 8:55 am

Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Sun Nov 12, 2023 8:53 pm

Is there an opinion or actual data as to how much speed is left in my boat with the addition of a stainless prop from the ones suggested by Phil T?

jimh
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Location: Michigan, Lower Peninsula
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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Mon Nov 13, 2023 8:41 am

Dave_a wrote:Is there an opinion or actual data as to how much speed is left in my boat with the addition of a stainless prop from the ones suggested by Phil T?
I doubt there is any actual data that compares your set up using your aluminum propeller and compares directly with an identical set up using one of the several propellers mentioned by PHIL T.

As for speculation about further increase in the boat TOP speed by investing in a stainless steel propeller, my opinion is you are probably near the maximum already with the aluminum propeller.

Changing to a steel propeller might add some marginal boat speed. A steel propeller will be more durable; it will tolerate minor blade strikes with soft materials better than an aluminum propeller might.

Your early comment about the advice from the Yamaha dealer regarding reduction in propeller rattle by using the lower weight aluminum propeller is something to consider. You seem to have already experienced this problem when you tested the "third" propeller, as mentioned in your earlier post.

About the only useful test of possible improvement is to calculate the SLIP factor.

Use my propeller calculator at

https://continuouswave.com/calculators/propCalc.php

Enter the following data:

RPM
RATIO
PITCH
MPH

Hit the SLIP button and the calculator will deduce the SLIP factor.

Using your most recent test data, I get this result

RPM = 5800
RATIO = 2.33
PITCH = 19
MPH = 40
Computed SLIP = 10.7

A SLIP value of 10.7 is actually quite good. It indicates the propeller is working efficiently. I think you are done with your propeller testing phase.

Now you can progress to actually having fun with the boat.

ASIDE: I do admit that propeller testing in itself can be quite fun. I also confess that I own five propellers that can be fitted to my boat, and I have tested all of them, and also tested several more propellers I have had on loan for testing. What I learned from all that testing is that the propeller I use most of the time is about the best all-round propeller for my boat. But I would not pass up a chance to test a few more propellers if they become available. However, I do notice that my inclination to test more propellers is decreasing with increase in my age (now 73).

Dave_a
Posts: 33
Joined: Sun Aug 07, 2022 8:55 am

Re: 1964 NAUSET 16 Yamaha F70A

Postby Dave_a » Mon Nov 13, 2023 9:38 am

Thank you Jim.
I suspect we are nearing the point of diminishing returns. I was hoping Phil had hard data available. Assuming my tach is accurate, the 19" pitch seems optimum for boat speed. I haven't had four persons in the boat with the 19-pitch propeller. That may be its downfall.

Anecdotally, I prefer the feel of the 13.25 x 17 propeller. The boat leaps out of the water onto plane. The engine spped does over-rev with only one or two crew aboard, but works well with four in the boat.
Like everything, a compromise.

Now if I could get a 5-MPH increase with a steel propeller, that would only cost $100-per-MPH increase—almost worth it.

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: 1964 NAUSET 16 Yamaha F70A

Postby jimh » Tue Nov 14, 2023 7:08 am

The percentage of total operating time the typical outboard engine will be run at full throttle is miniscule. In testing, running at full throttle is useful as a method to assess the propeller load on the engine. In my use of my boat, total duration at full-throttle is less than one-percent of the total engine run time, and most of that occurred during propeller testing.