Q1: for use with a 1965 16-footer for towing a water skier, should I buy a Mercury 115-HP ProXS model with Command Thrust or without Command Thrust?
Q2: if I buy a Mercury 115-HP ProXS Command Thrust, will the maximum boat speed be lower than if I got the same engine without Command Thrust?
Q3: will buying the Command Thrust version of the Mercury 115-HP ProXS engine result in a difference in trying to pull up out of the water a 220-lbs skier?
BACKSTORY
I’m in the process of re-powering my 1965 16-footer, which I use with my family for slalom water skiing and barefoot waterskiing. I need sufficient engine power to pull up out of the water a 220-lbs-water-skier on a slalom ski and also to have a top boat speed if around 45-MPH. I may buy a Mercury 115-HP ProXS engine, but I am not sure which gear case version to get, Standard or Command Thrust.
Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
-
Nickman0017
- Posts: 3
- Joined: Mon Aug 05, 2024 8:57 pm
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
I think readers would be better informed if you mentioned the difference in the gear ratio between the two models.
115 ProXS has a 2.07:1 gear ratio.
115 ProXS CT (Command Thrust) has a 2.38:1 gear ratio.
Readers would be better informed if you also mentioned that the Command Thrust engine uses a "larger" gear case and can thus use a "larger" propeller, according to the Mercury literature. Here I would assume that the dimension that is larger is the diameter of the gear case, and thus the engine needs to use propellers with a larger hub diameter.
Mercury literature states that this combination will provide "greater" acceleration. Here I would assume that "greater" means more rapid acceleration than would occur with some other gear case, but there is no stated unit of amount of time reduction created to accelerate from one speed to another, or what the speeds were.
Mercury also says that the Command Thrust provides "better" handling. Here I would assume that "better" means faster response to input from the helm in changes to the direction of the propeller thrust, but again, there is no reference for the comparison.
Mercury also states that the Command Thrust provides creates awe-inspiring maneuverability. Here I would assume that this means nothing and is just silly advertising language that is trying to convince potential buyers of a benefit without ever really defining what the benefit will be. Generally a characteristic of a boat that is called "maneuverability" is related to the hull design of the boat, and the total weight of the boat with engine and gear and crew, and also the prevailing wind and waves. That a change in gear case could affect the maneuverability of a boat seems like a stretch.
Mercury also states that the Command Thrust provides "superior" control. Here I would again assume this means nothing because there is no reference given for the control that is to be used for comparison, and with such a standard or reference the notion of the Command Thrust being "superior" is meaningless, nor is there any specified amount of improvement.
If one were to assume that all references in which the Command Thrust version of the engine is "larger", "greater" , "better" , more "awe-inspiring", and "superior" were in comparison the ProXS without Command Thrust, then I would assume that there is no possibility that anyone would ever want the engine without Command Thrust, unless their preference was to get slower acceleration, worse handling, less awe-inspiring maneuverability, and inferior control.
One might be tempted to think that only a fool would buy the ProXS without Command Thrust, but I think there must be some reason for making the two different models, with and without Command Thrust. Now exactly what possible attribute might be gained with the non-Command Thrust engine is unknown to me, but I think if you talked to a Mercury product manager for the ProXS, you could find out if there is any attribute for the non-Command Thrust model.
Also, I am not sure exactly what the ProXS engine has going for it compared to a non-ProXS model of the same rated power and displacement, other than the ProXS model has cooler decals on the cowling.
115 ProXS has a 2.07:1 gear ratio.
115 ProXS CT (Command Thrust) has a 2.38:1 gear ratio.
Readers would be better informed if you also mentioned that the Command Thrust engine uses a "larger" gear case and can thus use a "larger" propeller, according to the Mercury literature. Here I would assume that the dimension that is larger is the diameter of the gear case, and thus the engine needs to use propellers with a larger hub diameter.
Mercury literature states that this combination will provide "greater" acceleration. Here I would assume that "greater" means more rapid acceleration than would occur with some other gear case, but there is no stated unit of amount of time reduction created to accelerate from one speed to another, or what the speeds were.
Mercury also says that the Command Thrust provides "better" handling. Here I would assume that "better" means faster response to input from the helm in changes to the direction of the propeller thrust, but again, there is no reference for the comparison.
Mercury also states that the Command Thrust provides creates awe-inspiring maneuverability. Here I would assume that this means nothing and is just silly advertising language that is trying to convince potential buyers of a benefit without ever really defining what the benefit will be. Generally a characteristic of a boat that is called "maneuverability" is related to the hull design of the boat, and the total weight of the boat with engine and gear and crew, and also the prevailing wind and waves. That a change in gear case could affect the maneuverability of a boat seems like a stretch.
Mercury also states that the Command Thrust provides "superior" control. Here I would again assume this means nothing because there is no reference given for the control that is to be used for comparison, and with such a standard or reference the notion of the Command Thrust being "superior" is meaningless, nor is there any specified amount of improvement.
If one were to assume that all references in which the Command Thrust version of the engine is "larger", "greater" , "better" , more "awe-inspiring", and "superior" were in comparison the ProXS without Command Thrust, then I would assume that there is no possibility that anyone would ever want the engine without Command Thrust, unless their preference was to get slower acceleration, worse handling, less awe-inspiring maneuverability, and inferior control.
One might be tempted to think that only a fool would buy the ProXS without Command Thrust, but I think there must be some reason for making the two different models, with and without Command Thrust. Now exactly what possible attribute might be gained with the non-Command Thrust engine is unknown to me, but I think if you talked to a Mercury product manager for the ProXS, you could find out if there is any attribute for the non-Command Thrust model.
Also, I am not sure exactly what the ProXS engine has going for it compared to a non-ProXS model of the same rated power and displacement, other than the ProXS model has cooler decals on the cowling.
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
I am still trying to weigh [the value that occurs in using] the Command Thrust instead of the regular lower unit decision for my re-power. I can't seem to get a straight answer, perhaps because there is none.
I have learned with boating is that there is always a tradeoff.
As Jim says, if the Command Thrust were better all-round with no tradeoffs, one would expect Mercury to make the Command Thrust gear case the standard equipment for all 115-HP engines and beat the competition in every category.
The only [negative] tradeoff I have read about--besides extra cost $800 cost--is that the larger lower unit causes more drag in the water at high speed and could [reduce] top speed. [A loss of top speed] might be unimportant [in some applications].
I have learned with boating is that there is always a tradeoff.
As Jim says, if the Command Thrust were better all-round with no tradeoffs, one would expect Mercury to make the Command Thrust gear case the standard equipment for all 115-HP engines and beat the competition in every category.
The only [negative] tradeoff I have read about--besides extra cost $800 cost--is that the larger lower unit causes more drag in the water at high speed and could [reduce] top speed. [A loss of top speed] might be unimportant [in some applications].
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
The Command Thrust engine gear case being somewhat larger than the standard gear case could produce more drag than the standard gear case, and that could decrease the top speed of a boat.
The best way to assess what differences might occur would be to have detailed test information on a particular boat and rig it with both engines. The testing would need to be carefully controlled for many other variables that could occur between test runs, such as weather and sea conditions. But a carefully controlled test might reveal for a particular boat what change in performance there will be between the larger and smaller gear cases and the different gear ratios. But those outcomes would be specific to the boat used in the test.
Then several different boats whose hull designs and total weight are different from the initial boat tested would need to be similarly tested and detailed measurements taken.
The measured values for speed would be the top speed attained and the time to accelerate from a standing start to various speeds. This data would resolve the question of the top speed tending to be reduced with the larger gear case.
As for all the other claimed benefits, such as handling, maneuverability, and control, there would have to be new test methods devised to allow an actual measurement of those behaviors. As it stands now, all three behaviors are only subjectively assessed. The problem with non-measured characteristics is the assessment is often influenced by other factors than the actual physical changes.
My feeling is that human nature plays a part in making subjective assessments. For example, if you just spent $800 getting the Command Thrust engine, and also spent more money to get the ProXS model, and also spend even more money to get a special propeller, you probably now have about $2,500 invested in the engine that is not the standard four-stroke-power-cycle 115-HP with a non-special propeller. It is just human nature after spending $2,500 to get improvements to assess the actual outcome as providing improvement in those behaviors that are not actually measured and are subjective assessments. Have you ever read a report in which a guy describes how he spend $2,500 trying to improve the performance of the boat and everything got worse?
The best way to assess what differences might occur would be to have detailed test information on a particular boat and rig it with both engines. The testing would need to be carefully controlled for many other variables that could occur between test runs, such as weather and sea conditions. But a carefully controlled test might reveal for a particular boat what change in performance there will be between the larger and smaller gear cases and the different gear ratios. But those outcomes would be specific to the boat used in the test.
Then several different boats whose hull designs and total weight are different from the initial boat tested would need to be similarly tested and detailed measurements taken.
The measured values for speed would be the top speed attained and the time to accelerate from a standing start to various speeds. This data would resolve the question of the top speed tending to be reduced with the larger gear case.
As for all the other claimed benefits, such as handling, maneuverability, and control, there would have to be new test methods devised to allow an actual measurement of those behaviors. As it stands now, all three behaviors are only subjectively assessed. The problem with non-measured characteristics is the assessment is often influenced by other factors than the actual physical changes.
My feeling is that human nature plays a part in making subjective assessments. For example, if you just spent $800 getting the Command Thrust engine, and also spent more money to get the ProXS model, and also spend even more money to get a special propeller, you probably now have about $2,500 invested in the engine that is not the standard four-stroke-power-cycle 115-HP with a non-special propeller. It is just human nature after spending $2,500 to get improvements to assess the actual outcome as providing improvement in those behaviors that are not actually measured and are subjective assessments. Have you ever read a report in which a guy describes how he spend $2,500 trying to improve the performance of the boat and everything got worse?
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
The initial question asks:
Somewhat lost in that question are two considerations that seem to be ignored:
In the 60-years since the boat was manufactured, the strength of the hull and particularly the transom are unlikely to have become stronger.
If the original rating was 80-HP in an era when horsepower was measured at the power head and not at the propeller shaft, the propeller shaft horsepower of an engine rated at 80-HP would have been perhaps 72-HP. On that basis, to re-power with 115-HP in 2024 with the power measured at the propeller shaft thus represents an over-powering by about 43-HP, an increase to 1.6-times the originally rated horsepower.
Q1: for use with a 1965 16-footer for towing a water skier, should I buy a Mercury 115-HP ProXS model with Command Thrust or without Command Thrust? [Emphasis added]
Somewhat lost in that question are two considerations that seem to be ignored:
- the 1965 boat is now 60-years old; and
- the maximum power rating for the 1965 boat was probably 80-HP measured at the power head, not the propeller shaft
In the 60-years since the boat was manufactured, the strength of the hull and particularly the transom are unlikely to have become stronger.
If the original rating was 80-HP in an era when horsepower was measured at the power head and not at the propeller shaft, the propeller shaft horsepower of an engine rated at 80-HP would have been perhaps 72-HP. On that basis, to re-power with 115-HP in 2024 with the power measured at the propeller shaft thus represents an over-powering by about 43-HP, an increase to 1.6-times the originally rated horsepower.
-
Nickman0017
- Posts: 3
- Joined: Mon Aug 05, 2024 8:57 pm
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
[The 1965 boat] currently has a 115-HP, and the boat had previously been re-powered. I plan to swap it with the same 115-HP.jimh wrote:If the original rating was 80-HP in an era when horsepower was measured at the power head and not at the propeller shaft, the propeller shaft horsepower of an engine rated at 80-HP would have been perhaps 72-HP. On that basis, to re-power with 115-HP in 2024 with the power measured at the propeller shaft thus represents an over-powering by about 43-HP, an increase to 1.6-times the originally rated horsepower.
-
Nickman0017
- Posts: 3
- Joined: Mon Aug 05, 2024 8:57 pm
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
Thanks for the response. As I’m sure you are aware, it is simply not an option for me to rig both and run comparisons. If I had that kind of [money] I would just buy a new boat.jimh wrote:The best way to assess what differences might occur would be to have detailed test information on a particular boat and rig it with both engines.
I was looking for experiences of individuals who had either version to help me make a more informed decision.
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
My remarks about the best method to determine which engine--standard smaller gear case or larger Command Thrust gear case--would be the best to determine the actual difference in their performance were not intended that YOU would undertake all the testing. Perhaps Boston Whaler or Mercury might perform the testing--but it would never be done on a 60-year-old boat that was powered well beyond its rated power. If there were such test data, it would be from a boat that was in production at the time of the testNickman0017 wrote: As I’m sure you are aware, it is simply not an option for me to rig both and run comparisons. If I had that kind of [money] I would just buy a new boat.
Actual testing of the two different engine gear case options on a single boat conducted in rapid succession is the only really valid way to assess the performance of each model and offer a basis for deciding which one to buy.
ASIDE: I also get a laugh from the name of the larger gear case as "Command Thrust." That is a loaded expression. Why not just the more neutral and more accurate name "High Thrust"? No, its "COMMAND" thrust--you are now in command, I guess, where without Command Thrust you are at the mercy of the winds and wave.
Being called "Command" and "Pro" and "XS" the Mercury 115-HP ProXS Command Thrust engine is just loaded with marketing-oriented names that all tend to impart a notion that this engine is better than other models--and therefore you have to pay more for it.
If one engine is a "Pro" model, does that make the almost identical engine an "amateur" model?
Also, Mercury marketing loves the "X" factor. Their propeller are made from mysterious "X7" steel.
The only missing buzzword is "Eco"--wait, you can get the "Eco Enertia" propeller.
You'd have the holy trinity: ProXS, Eco Enertia with X7 steel, and Command Thrust.
Re: Mercury ProXS: Command Thrust or Standard for Use in Water Skiing
You are certainly welcome to look, but the first problem you are going to encounter is that for your boat, 115-HP is above the manufacturer's rated power, so the number of other owners of a 60-year-old 16-footer who also happen to have a 115-HP engine on the transom is probably going to be very small.Nickman0017 wrote:I was looking for experiences of individuals who had either version to help me make a more informed decision.
The next problem among the limited number of owners of 60-year-old 16-foot hulls who have 115-HP engines on the transom, you need to find the ones who have Mercury engines.
Then next these owners must have the Mercury 115 ProXS model.
Then you need some who have the standard gear case and some who have the larger gear case.
And finally you need these owners to have collected detailed performance data about performance, such as boat speed as a function of engine speed, and times to accelerate.
And then you have to hope that all the 60-year-old boats were tested with the same total hull weight, in the same weather conditions, and with the same number of people aboard, in the same type of water, at the same water temperature, and on and on.