2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Optimizing the performance of Boston Whaler boats
keithp66
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2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby keithp66 » Mon Oct 30, 2023 8:50 pm

Q1: for a 2000 VENTURA 18 with a Mercury OptiMax 135-HP engine, what will be the advantage of switching to a used Mercury MIRAGEplus 15.5 x17-pitch propeller from the current Turning Point HUSTLER aluminum 14.25 x 17-pitch propeller?

Q2: for a 2000 VENTURA 18 with a Mercury OptiMax 135-HP engine, what will be the disadvantage of switching to a used Mercury MIRAGEplus 15.5 x17-pitch propeller from the current Turning Point HUSTLER aluminum 14.25 x 17-pitch propeller?

The used MIRAGEplus propeller under consideration is in great condition.

The Turning Point aluminum propeller has small vent holes.

With the Turning Point aluminum propeller the VENTURA 18 "jumps" onto plane, with two people and half-full fuel tank. At engine speed of 4,500-RPM the boat speed is 26-MPH. At full throttle the engine speed is 5,600-RPM and boat speed is 41-MPH. With five or even six people on the VENTURA 18 the performance with the Turning Point aluminum propeller is fine.

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Phil T
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Re: Mirage Plus propeller switch

Postby Phil T » Mon Oct 30, 2023 8:56 pm

The diameter of the propeller is dictated by the gear ratio of the lower unit.

A propeller of 15.5-inch diameter is EDIT - (NOT) too large for [the Mercury OptiMax 135-HP] engine.
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jimh
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Re: 2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby jimh » Tue Oct 31, 2023 7:47 am

The decision to buy the MIRAGEplus propeller will depend on the asking price. If the price is very reasonable, say under $150, and if you want to experiment with a different propeller, the MIRAGEplus is a good choice.

The only real way to find out what the performance will be is to buy the propeller and test it on your boat.

As for predicting advantages, the stainless steel propeller will be more durable, and it may enhance performance.

As for disadvantages, the cost of the propeller may be prohibitively high, you will need to get a FLO-TORQ hub kit, there may be a tendency for shifting to FWD from NEUTRAL to produce a "CLUNK" sound because of the increased weight of the propeller, and the propeller larger diameter and larger blades may not allow the engine to accelerate at full-throttle to an engine speed in the recommend full-throttle engine speed range as listed in the manufacturer's guide because of the greater load created by the larger propeller.

Regarding the diameter of the MIRAGEplus as being unsuitable for your engine due to the engines gear ratio, I don't see that as an objection, as long as the propeller aperture on the engine is large enough to accommodate the 15.5-inch diameter. I am not familiar with the details of the Mercury OptiMax 135-HP engine, so you need to check the maximum permitted propeller diameter.

Also, clarify the number of blades on the Turning Point aluminum propeller. I believe that could be a four-bladed propeller.

PROPELLER DIAMETER

Turning Point (three-blade or perhaps four-blade) is 14.25-inches
Mercury MIRAGEplus three-blade is 15.5-inches

Typically an increase in propeller diameter will result in a higher load on the engine, reducing the engine maximum speed, but in this case, if the number of blades is reduced to three blades from four blades this should mitigate somewhat the amount of engine speed change due to diameter increase.

BLADE RAKE

On propellers with significant blade rake, the effective diameter of the propeller is reduced, but the actual length of the blades may be similar to other propellers that do not employ much blade rake. The total blade area of a smaller diameter but raked propeller might be similar to the blade area of a propeller with a greater diameter but having little blade rake. For this reason, the exact amount of load imposed on the propulsion engine by two particular propellers cannot be completely inferred just by comparing their diameter; the blade rake must also be considered.

The Mercury MIRAGEplus propeller does not have high blade rake.

keithp66
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Re: 2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby keithp66 » Wed Nov 01, 2023 7:39 pm

The Turning Point propeller is a three-blade propeller.

The manufacturer told me it has a decent amount of rake and cup. They will not give out the exact dimensions through.

I already have the MIRAGEplus. I (essentially) got it for free.

The Mercury OptiMax 135-HP engine [originally] came with a MIRAGEplus 15.5 x 15-pitch. I think the 15-pitch was the original propeller from the dealer.

Someone proposed a swap for the 17-pitch because he needed a 15-pitch.

I felt like the pitch was too [great] for our uses.

It sounds like, if I made the switch [to the 17-pitch from the 15-pitch], I would be going to a larger diameter, "flatter" propeller with the same pitch.

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Phil T
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Re: 2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby Phil T » Wed Nov 01, 2023 9:04 pm

Here is your answer from a Whaler expert and prop guru:

Tom Clark wrote:...Mercury MIRAGE (or a MIRAGEplus for that matter) is 15-1/4" x 19" and is known as a fast, low slip propeller that can handle a lot of power. It might be a little bit too much prop for an 18' Ventura with a 135 but I think it will be OK if you drop down to a 15-1/2" x 17" MIRAGEplus. You want to be able to hit 5500 RPM at WOT. I would expect top speed to be about 42 MPH.
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jimh
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Re: 2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby jimh » Thu Nov 02, 2023 11:37 am

keithp66 wrote:I already have the MIRAGEplus. I (essentially) got it for free.
What pitch is the MIRAGEplus propeller you already have?

keithp66 wrote:...The Mercury OptiMax 135-HP engine [originally] came with a MIRAGEplus 15.5 x 15-pitch. I think the 15-pitch was the original propeller from the dealer.
From your remarks I assume you already have a Mercury MIRAGEplus 15-pitch propeller. If so, then:

Q3: have you tested the MIRAGEplus 15-pitch propeller?

Q4: if you have tested the MIRAGEplus 15-pitch propeller, what was the performance? Give use some numbers if you have them.

keithp66 wrote:Someone proposed a swap for the 17-pitch because he needed a 15-pitch. I felt like the pitch was too [great] for our uses.
Here I am unclear.

Q5: are you saying you thought the 17-pitch MIRAGEplus was too much pitch?

keithp66 wrote:It sounds like, if I made the switch [to the 17-pitch from the 15-pitch], I would be going to a larger diameter, "flatter" propeller with the same pitch.
A Mercury MIRAGEplus propeller marked 17-pitch and a MIRAGEplus propeller marked 15-pitch will NOT have the same pitch.

keithp66
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Re: 2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby keithp66 » Sat Nov 04, 2023 10:17 pm

I have the MIRAGEplus 17-pitch. I got it in a swap for the MIRAGEplus 15-pitch.

I thought the 15-pitch MIRAGEplus propeller was too low-pitched for our set up. [With the MIRAGEplus 15-pitch] the [OptiMax 135-HP] engine speed would accelerate very rapidly and accelerate to an engine speed that was too high with a light load.

The propeller currently in use is Turning Point HUSTLER three-bladed aluminum 14.25 x 17-pitch.

Based on what Tom Clark wrote, the MIRAGEplus 17-pitch propeller might be a few MPH faster on the top speed than the Turning Point HUSTLER three-bladed aluminum 14.25 x 17-pitch.

But I don't know how the time to acceleration onto plane from a standing start at full-throttle will compare between the MIRAGEplus 17-pitch and the Turning Point HUSTLER three-bladed aluminum 14.25 x 17-pitch.

I will need to perform tests in the 2024 boating season.

Thanks for the replies.

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Re: 2000 VENTURA 18 with OptiMax 135: MIRAGEplus Propeller

Postby jimh » Sun Nov 05, 2023 8:39 am

I expect that you will find the MIRAGEplus 17-pitch propeller will be a greater load for the 135-HP OptiMax engine to turn, compared to the aluminum propeller you are now using. Because of the greater load, the engine speed at full throttle will be lower than it was with the 15-pitch MIRAGEplus, and the time to accelerate onto plane will be longer. Whether or not the boat speed at full throttle will be greater with the 17-pitch remains to be determined.

You should check the owner's manual for the Mercury OptiMax 135-HP engine to determine what the manufacturer recommends for the optimum engine speed range at full throttle. This will give you the best metric to determine if the propeller load is well-matched to your particular boat and your particular normal total boat weight.

Typically with two-stroke-power-cycle engines the optimum engine speed range will not be at the very upper end of the allowed engine speed range. Many two-stroke-power-cycle outboard engines actually develop the most horsepower at an engine speed below the very maximum engine speed allowed. For example, if the maximum engine speed allowed is 6,000-RPM, the engine speed for maximum power output might be in the range of 5,700 to 5,800-RPM. Usually the owner's manual will give guidance on this.