NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Optimizing the performance of Boston Whaler boats
Chipnice
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NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Sat Jun 06, 2020 9:38 am

[Because the topic of this thread is about boat performance optimization, the thread has been moved to the PERFORMANCE forum for discussion from another forum; the post author is notified of the move--jimh]

I have a 1970 NAUSET 16 modified [in some undescribed manner]. The boat is somewhat wet inside. The boat sits low. There are 12-gallons of fuel in the stern.

The engine is a Mercury 90 FOURSTROKE engine mounted two-holes-up.

The propeller is [later identified in back and forth discussion to be a three-blade in the express EXPRESS MACH3 series] TURNING POINT stainless steel 13.75 x 15-pitch.

Wide-open-throttle boat speed is 39-MPH at engine speed of 5,900-RPM. Cruise boat speed is 23-MPH at engine speed of 3,800-RPM. The top speed and cruising speed are great.

The [problem occurs] when the boat is traveling into an opposing current or into head winds [and head seas]. The propeller refuses to bite when the bow is up. I’m forced to [increase engine speed] to get [the propeller] to bite. [Increasing engine speed] in these conditions can be dangerous.

I am angling in a busy harbor inlet [where waves] can stack up when the tide is running. Add wind and [the sea state] can be nasty.

I need a propeller that can bite and hold at a slow speed in these conditions.

Mercury has advised me toward a four-blade propeller with the same diameter and pitch as the the current three-blade propeller.

I can’t afford to find the right setup through trial and error. Please help. Thank you --John

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby jimh » Sat Jun 06, 2020 9:58 am

Propeller selection is generally always a trial-and-error process. Generally a 90-HP engine does not need a four-bladed propeller. A three-bladed propeller will have plenty of surface area to handle 90-HP.

If the current propeller ventilates in rough seas, try reducing the trim to be more inward toward the transom; try reducing the engine mounting height.


Chipnice wrote:The [problem occurs] when the boat is traveling into an opposing current or into head winds [and head seas]. The propeller refuses to bite when the bow is up.

Your description that the propeller loses "bite" or ventilates when the bow is up seems counter-intuitive. If the bow is up due to wave action, the stern should be down. This should submerge the propeller more deeply into the water, improving its resistance to ventilate. I would expect a problem with propeller ventilation to occur when the bow is down after coming over a wave and the stern is high. That sort of pitching bow-down would tend to cause propeller ventilation.

Chipnice wrote:I’m forced to [increase engine speed] to get [the propeller] to bite.

Generally a propeller that has ventilated will not recover by increasing propeller shaft speed. Usually you have to reduce propeller shaft speed to eliminate ventilation so the propeller can return to solid water and begin to produce forward thrust.

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Phil T
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Phil T » Sat Jun 06, 2020 2:22 pm

I spent 12 years in nasty, snotty conditions, large swells, short breaking waves. Typically small craft advisory (SCA) conditions or worse, and my three-bladed propeller did a very good job. It only ventilated when going over the top of a steep swell and the lower unit was out of the water.

Your performance report is not very good. Even with a heavy hull, I would expect you to reach 43-MPH at 6,000-RPM.

Keep in mind that blade geometry is different across models and manufacturers so make, model, and size are linked. Propeller selection is 85% science and 15% art.

I think the blade design of the Turning Point model propeller you have is not appropriate for your boat and engine combination.

The Mercury FourStroke had two different gear ratios over the years so we need to know the exact production year you have to supply a precise propeller suggestion.
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Chipnice
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Sat Jun 06, 2020 3:18 pm

Would I get [more] bite [with] less pitch?

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Phil T
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Phil T » Sat Jun 06, 2020 3:56 pm

It is not necessarily all about pitch. It is the blade geometry and the pitch together.

What year and model of Mercury FourStroke do you have?
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Chipnice
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Sat Jun 06, 2020 10:26 pm

The engine is a 2017 FOURSTROKE 90 EFI. I don’t believe it is a [Command Thrust]. Ser #2b490###

The propeller is a stainless [steel] [TURNING POINT] number 31431512. 13.75 x 15 with a [FLO TORQ III] hub.

In 2019 I bought the NAUSET with this engine and propeller.

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby jimh » Sun Jun 07, 2020 7:08 am

From the "number" I think the propeller is a TURNING POINT EXPRESS MACH 3. The manufacturer describes the propeller series as follows:

Express® Mach3™ Propellers
40 to 300-HP engines with 4.25 and 4.75-inch Gearcase

...Express Mach3 series...excel at achieving maximum speed...handling...acceleration...[c]ornering....

Source: https://turningpointpropellers.com/

Apparently, the manufacturer thinks the Express Mach3 propeller does everything very well. There is nothing this propeller cannot handle according to the manufacturer. He seem very proud of this propeller.

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Sun Jun 07, 2020 8:44 am

I’m not sure how the original owner ended up with this propellor selection but I am curious to know what propellor Boston whaler would recommend for this hull-engine combination operating in these sloppy, busy harbor northeast Atlantic type conditions.

Thanks again
John

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby biggiefl » Sun Jun 07, 2020 10:31 am

A 15-pitch prop on a 16-footer with 90-HP seems about 2 to 4-inches too little.

If that FOURSTROKE 90 has a standard gear case around 1.85 or 2:1 I would assume a 17 to 19- pitch depending on load and RPM range. Two-holes-up is not too high and probably not high enough for calm waters. I would definitely try a Mercury prop that somebody here recommends like a Laser II 18-pitch.

Phil T--do you have any prop information in your database?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby jimh » Sun Jun 07, 2020 11:13 am

Chipnice wrote:....what propellor Boston [W]haler would recommend...


Boston Whaler did not rig engines on their NAUSET 16 boats. The dealer who sold the boat would rig the outboard engine of the customer's choice and fit the propeller.

The NAUSET 16 boat has not been made since c.1973, so I doubt that Boston Whaler has tested a 2017 Mercury 90-HP engine on a 47-year-old or in your case a 50-year-old NAUSET hull. Their focus is more toward testing boats they are making right now with engines that they offer pre-rigged on those boats right now.

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Phil T
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Phil T » Sun Jun 07, 2020 12:42 pm

With the OP furnishing the model year, we now know the lower unit gear ratio is 2.09:1

Owners with this engine recommend the 13.15 x 17 Mercury Vengance for the 16/17-foot hulls.

Of the 97 prop recommendations I have cataloged, Turning Point is not listed.
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby jimh » Sun Jun 07, 2020 2:32 pm

Chipnice wrote:...with a [FLO TORQ III] hub.


How did you determine the propeller hub was a Mercury FLO-TORQ III model?

There are prior discussions about problems with the FLO-TORQ III hub kit being used with certain Mercury propellers. Getting a FLO-TORQ III hub kit to work properly requires careful installation and careful tightening of the propeller nut.

For example, see

LASER II Propeller with Flo-Torq III Hub
http://continuouswave.com/ubb/Forum4/HTML/005581.html

Flo-Torq IV Hub Decreases Loud Clunk, But Has Wobble http://continuouswave.com/ubb/Forum4/HTML/005785.html


I don't know that the FLO-TORQ III hub kit is at all suited for use with a TURNING POINT propeller. And there easily could be a problem with the way the FLO-TORQ III hub kit has been installed on the TURNING POINT propeller.

It may be reasonable to order the specific TURNING POINT hub kit that they manufacture for their propellers. These are called MASTER GUARD HUB KIT Systems:

https://turningpointpropellers.com/_CON ... ystems.php

Call them to get the proper part number. Figuring out what hub kit fits what engine and propeller is about impossible on their website.

ASIDE: I find the TURNINGPOINT.COM website incredibly difficult to use and to navigate to any particular information. It keeps playing stupid videos with corny music tracks showing some sterndrive runabout, while incessently bragging about how great their products are.

If the propeller is not properly fitted onto the engine propeller shaft so there is a good fit between the gear case bullet and the propeller, exhaust gas from the engine may be leaking around the outside of the hub. This would tend to aerate the water flowing into the propeller blades. Aerated water flowing into the propeller blades would tend to create propeller ventilation. This tendency is reduced when boat speed increases. This description of your control problems at low speeds seems to fit with this explanation.

In your situation, I would call the propeller manufacturer on the telephone. Tell him about the terrible performance you are getting from the TURNING POINT EXPRESS MACH3 series propeller when trying to control the boat in rough and confused seas and accelerate. Tell the manufacturer you are using a Mercury FLO-TORQ III hub kit. Tell him your TURNINGN POINT propeller ventilates. See what the manufacturer has to say about this problem.

A telephone call is a lot cheaper than buying new propellers and testing them.

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Sun Jun 07, 2020 6:41 pm

Correction I have the [FLOR-TORQ IV] hub installed.

I will get in touch with Turning Point. I will likely get a Mercury propeller designed for this engine and classic Boston Whaler boat combo.

Thanks again. This is a great resource

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Sun Jun 07, 2020 9:26 pm

Phil T wrote:With the OP furnishing the model year, we now know the lower unit gear ratio is 2.09:1

Owners with this engine recommend the 13.15 x 17 Mercury Vengance for the 16/17-foot hulls.

Of the 97 prop recommendations I have cataloged, Turning Point is not listed.


Phil---I do t [do or don't] see a VENGEANCE propeller in this diameter and pitch.

What other propellers come to mind?

Are any four-bladed propellers recommended?

Thanks--John

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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby jimh » Mon Jun 08, 2020 7:34 am

Chipnice wrote:I will likely get a Mercury propeller designed for this engine and classic Boston Whaler boat combo.


Mercury does not make a propeller specifically designed for 50-year-old boats with modern engines. There is really nothing about the NAUSET 16 hull that would require a propeller to be specially designed for that boat.

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Phil T
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Phil T » Mon Jun 08, 2020 9:52 am

John--one source [for a Mercury VENGEANCE propeller]:

https://www.boatpropellerwarehouse.com/product/28818/vengeance-13-1-8-x-16-mercury-rh-propeller-48-16986a46

If you want other brands and blade configuration, consult a prop guru who knows props and Boston Whaler boats. One of them is Ken Reeves. He has helped a lot of Boston Whaler boat owners. Definately worth a phone call.

https://propgods.com
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Chipnice
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Chipnice » Wed Jun 10, 2020 8:22 pm

Phil T wrote:John--one source [for a Mercury VENGEANCE propeller]:

https://www.boatpropellerwarehouse.com/product/28818/vengeance-13-1-8-x-16-mercury-rh-propeller-48-16986a46

If you want other brands and blade configuration, consult a prop guru who knows props and Boston Whaler boats. One of them is Ken Reeves. He has helped a lot of Boston Whaler boat owners. Definately worth a phone call.

https://propgods.com

Thanks for the info
Ordered a stainless 4 blade 13x15 through ken.

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Phil T
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Re: NAUSET 16 with 90-HP; Propeller Ventilates in Rough Seas

Postby Phil T » Wed Jun 10, 2020 9:29 pm

Please include the make and model of the prop selected.

We would be interested in your performance results, WOT rpm and speed, handling characteristics.
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