Hi all. I just got a pre-owned 1998 Dauntless 18 with a Mercury 135-HP engine. Intially I thought [the boat's] propeller might be wrong because [the boat] was really struggling to [accelerate onto plane from a standing start]. At wide-open throttle (WOT) the engine could only accelerate to about 4,300-RPM. The propeller that came with the boat was 19. A propeller calculator gave various pitch recommendations between 14 and 17. My dealer thinks I ought to put on either a 15 or a 17.
I'd really appreciate anyone's thoughts on the matter. I've read some of the previous discussions related to propeller pitch and made use of a propeller calculator but wanted to [seek advice from] you all.Thanks.
Dauntless 18, 135-HP
Re: Dauntless 18, 135-HP
Another factor to consider is how high your engine is mounted. Many are mounted lower than the optimum height. Consider checking the engine mounting and report back before buying a replacement propeller.
Several years ago I found it best to both raise the engine and change the propeller. I wanted the best possible hole shot and was willing to sacrifice some top speed. Tom Clark recommended a four-blade propeller of a different manufacturer and pitch which made a huge difference and achieved my performance goals. I had a 1999 Dauntless 16 with a 115-HP two-stroke-cycle engine.
Several years ago I found it best to both raise the engine and change the propeller. I wanted the best possible hole shot and was willing to sacrifice some top speed. Tom Clark recommended a four-blade propeller of a different manufacturer and pitch which made a huge difference and achieved my performance goals. I had a 1999 Dauntless 16 with a 115-HP two-stroke-cycle engine.
Butch
Re: Dauntless 18, 135-HP
Good point, thanks! I will check on that.
Re: Dauntless 18, 135-HP
According to the owner's manual of your outboard engine, what is the recommended range for the engine speed at full throttle? This is most important to know. The manufacturer, year of manufacture, model, and horsepower are not as important as the recommend full-throttle engine speed range. If you can find that information, please reply with it. Also, please give the gear ratio of the engine gear case.
If your engine can only accelerate to 4,300-RPM, that suggests the propeller is not optimum. Usually an outboard engine will permit WOT speeds of up to 5,000 and sometimes as high as 6,000-RPM. Recommended full-throttle range varies with model, and that is why we must know what engine speed is recommended by your engine maker for your model.
We also need to know the boat speed in MPH when the engine speed was 4,300-RPM. And what the weather, wave conditions, crew weight, fuel load, and amount of gear aboard were when you obtained the data. What measured the engine speed? What measured the boat speed?
As a general rule when the boat is properly set up, the engine will be able to accelerate to the upper portion of the manufacturer's recommended full-throttle engine speed range when the boat is being operated with the typical load, in the typical weather, and in the typical sea conditions you will be using with the boat.
If your engine can only accelerate to 4,300-RPM, that suggests the propeller is not optimum. Usually an outboard engine will permit WOT speeds of up to 5,000 and sometimes as high as 6,000-RPM. Recommended full-throttle range varies with model, and that is why we must know what engine speed is recommended by your engine maker for your model.
We also need to know the boat speed in MPH when the engine speed was 4,300-RPM. And what the weather, wave conditions, crew weight, fuel load, and amount of gear aboard were when you obtained the data. What measured the engine speed? What measured the boat speed?
As a general rule when the boat is properly set up, the engine will be able to accelerate to the upper portion of the manufacturer's recommended full-throttle engine speed range when the boat is being operated with the typical load, in the typical weather, and in the typical sea conditions you will be using with the boat.
Re: Dauntless 18, 135-HP
To jump ahead a bit, if your 1998 DAUNTLESS 18 has the original engine, the engine is probably a Mercury OptiMax 135. The rated engine speed range at full throttle for a Mercury OptiMax 135 should be 5,000 to 5,600-RPM. If this is true, then your present propeller has too much pitch, or there is something seriously amiss with the engine that is causing it to be unable to deliver its rated power.
If the boat was set-up by Boston Whaler with the propeller that is on the boat now, I would be suspicious of the engine not making rated power. That is because I doubt Whaler would have put a propeller on the boat that only let the 135-HP engine get to 4,300-RPM.
If the boat does not have its original propeller, contact Boston Whaler to see what propeller pitch they recommended for the boat and the 135-HP engine. Boston Whaler typically very thoroughly tests and evaluates the propeller selection when they deliver the boat to the customer with the engine pre-installed.
In c.1998, Boston Whaler boats may have still be getting fitted with an engine at the dealer selling the boat. Maybe the dealer selected the propeller. I don't recall what policy was in effect at that time.
If the boat was set-up by Boston Whaler with the propeller that is on the boat now, I would be suspicious of the engine not making rated power. That is because I doubt Whaler would have put a propeller on the boat that only let the 135-HP engine get to 4,300-RPM.
If the boat does not have its original propeller, contact Boston Whaler to see what propeller pitch they recommended for the boat and the 135-HP engine. Boston Whaler typically very thoroughly tests and evaluates the propeller selection when they deliver the boat to the customer with the engine pre-installed.
In c.1998, Boston Whaler boats may have still be getting fitted with an engine at the dealer selling the boat. Maybe the dealer selected the propeller. I don't recall what policy was in effect at that time.
Re: Dauntless 18, 135-HP
Re the dealer engine selection: as late as 1999 the Pensacola, Florida, Boston Whaler dealer would deliver a new Boston Whaler with the buyer's choice of engine. That's the year I bought a 1999 Dauntless 16 powered with a 1999 115 HP Evinrude FICHT engine from that dealer. The dealer may have first removed a Mercury engine from the boat, but I doubt it as there was no effort on the part of the salesman to sell the boat with a Mercury engine.
Butch
Re: Dauntless 18, 135-HP
I contacted Boston Whaler. {They said] the engine [in its present mounting] was mounted a little higher than where they would have set up the engine for the DAUNTLESS 18. I know [mounting the engine] too low is a problem, but is too high?
I also confirmed that Boston Whaler would have put on a 17 [pitch propeller].
I hope by adjusting [the mounting height to be lower and the propeller pitch to be lower] will help.
The change in pitch should add 400-RPM alone; the 19-pitch propeller is being swapped for a 17-pitch propeller. Thanks all
I also confirmed that Boston Whaler would have put on a 17 [pitch propeller].
I hope by adjusting [the mounting height to be lower and the propeller pitch to be lower] will help.
The change in pitch should add 400-RPM alone; the 19-pitch propeller is being swapped for a 17-pitch propeller. Thanks all
Re: Dauntless 18, 135-HP
Can you confirm the type of engine on your boat to be the Mercury OptiMax 135-HP?
What is the present mounting height?
What mounting height did Boston Whaler customer service tell you would have been used if the factory rigged the engine on the boat?
ASIDE: engine mounting height is measured in units of 0.75-inch or "holes" and measured up from the lowest position.
What is the present propeller?
How many blades does it have?
Who made the present propeller?
What model is the present propeller?
Did Boston Whaler recommend to you a particular brand, model, and pitch of propeller?
What propeller are you planning to change to?
What is the maximum boat speed with the present propeller?
What is the present mounting height?
What mounting height did Boston Whaler customer service tell you would have been used if the factory rigged the engine on the boat?
ASIDE: engine mounting height is measured in units of 0.75-inch or "holes" and measured up from the lowest position.
What is the present propeller?
How many blades does it have?
Who made the present propeller?
What model is the present propeller?
Did Boston Whaler recommend to you a particular brand, model, and pitch of propeller?
What propeller are you planning to change to?
What is the maximum boat speed with the present propeller?
Re: Dauntless 18, 135-HP
Absolutely! I’ll respond categorically:
Yes, affirmative to the engine being the Optimax 135-hp.
The present mounting height is the 4th hole from the top. BW customer service said the factory rig would have been the 3rd hole down (so I’m actually mounted higher; which should mean, I presume, that height is definitely not a problem as I’m not cavitating either).
The present propeller is a three blade, with pitch at 19, which was producing a max speed of 38 mph. No particular brand or model was recommended, but the recommended pitch was 17.
Again, I really appreciate everyone’s input on this.
Yes, affirmative to the engine being the Optimax 135-hp.
The present mounting height is the 4th hole from the top. BW customer service said the factory rig would have been the 3rd hole down (so I’m actually mounted higher; which should mean, I presume, that height is definitely not a problem as I’m not cavitating either).
The present propeller is a three blade, with pitch at 19, which was producing a max speed of 38 mph. No particular brand or model was recommended, but the recommended pitch was 17.
Again, I really appreciate everyone’s input on this.
Re: Dauntless 18, 135-HP
Stu02 wrote:The present mounting height is the 4th hole from the top. [Boston Whaler] customer service said the factory rig would have been the 3rd hole down (so I’m actually mounted higher...
You confuse me. I think you are saying the present mounting position is three-holes up. Is that right?
I think you are saying Boston whaler suggested two-holes up. Is that right?
Re: Dauntless 18, 135-HP
With the following data about your engine and propeller:
RPM = 4300
RATIO = 2.0
PITCH = 19
and using boat speed at
MPH =38
the propeller SLIP calculates to a very low 2-percent.
Generally a propeller SLIP calculated under 10-percent is a good outcome. Under 5-percent is a very good outcome.
RPM = 4300
RATIO = 2.0
PITCH = 19
and using boat speed at
MPH =38
the propeller SLIP calculates to a very low 2-percent.
Generally a propeller SLIP calculated under 10-percent is a good outcome. Under 5-percent is a very good outcome.
Re: Dauntless 18, 135-HP
The rating of propeller pitch is not a universal dimension. When changing propeller pitch and also changing the brand and model of propeller, it is not reasonable to expect that pitch will be completely uniformly measured.
My recommendation for now: put on a 17-pitch three-blade propeller and retest the for maximum engine speed and maximum boat speed. Be sure to get an arrangement to return the 17 for another pitch if it does not work out.
A good starting point for a general purpose propeller for a large gear case outboard is a Mercury MIRAGEplus or VENGEANCE propeller.
My recommendation for now: put on a 17-pitch three-blade propeller and retest the for maximum engine speed and maximum boat speed. Be sure to get an arrangement to return the 17 for another pitch if it does not work out.
A good starting point for a general purpose propeller for a large gear case outboard is a Mercury MIRAGEplus or VENGEANCE propeller.