CONTINUOUSWAVE

I really liked my 2000 Dauntless 160 but I wanted to add a 115 HP outboard to it. The 2008 Yamaha F90 gave me passable results, especially after adding trim tabs but I really wanted a little bit more power. I recently came across a 2001 Dauntless 160 with a 2015 Yamaha 115 for a price that I just couldn't pass up.

Everything was moved from the old boat to new.

Both boats have the "notch"

The 2015 is a newer generation and only weighs about 10 pounds more than the 2008.

2000 Dauntless 160 2008 F90 before adding the trim tabs but removed Doel Fin

DATE: 5/29/19
FUEL = about 30 gallons
CREW WEIGHT = 420 pounds Me, dog, son
GEAR = bow mounted trolling motor, 3 batteries in the consol (one starting, 2 trolling) 20 pounds of anchor chain/rope in anchor locker 20 pounds misc.

PROPELLER UNDER TEST = Power Tech SDC4 4 blade 13" 15 Pitch Prop
RPM = 5600 WOT Trimmed in
MPH = 31.1
RPM =6000 (Trimmed out to 6000)
MPH 34.4
Outboard mounted two holes up.

2001 Dauntless 160 with the 2015 Yamaha F115
DATE= September 15, 2019
FUEL = about 25 gallons
CREW WEIGHT = 500 pounds Me and neighbor
GEAR = bow mounted trolling motor, 3 batteries in the consol (one starting, 2 trolling) 20 pounds of anchor chain/rope in anchor locker 20 pounds misc.

PROPELLER UNDER TEST = Power Tech SDC4 4 blade 13" 15 Pitch Prop
RPM = 5800 WOT Trimmed in
MPH = 36 per auto gps that did not show tenths
RPM =6200(Trimmed out to 6200)
MPH 38 per auto gps that did not show tenths.
Outboard mounted 1 hole up.

These test were done with the same propeller, removed from the 2000. The only significant change in the test is that the F90 was mounted one hole higher.

Top speed is 4-MPH higher--I was hoping for more. The boat goes on plane much faster. It also stays on a slower plane more easily with out constant adjustment of the throttle to maintain the same speed. I may raise the F115 one hole higher.

I started a new thread for this comparison but feel free to combine it with my old thread that was strictly referring to my Yamaha F90.

http://continuouswave.com/forum/viewtopic.php?f=7&t=4257

Boat speed is generally proportional to the HP-to-weight ratio to the 0.5 exponent.

If you increase horsepower to 115 from 90, and the total weight remains the same, the boat speed would change according to a ratio of (115/90)^0.5 or 1.13:1. If the 90-HP speed was 34.4-MPH then the 115-HP speed should be 1.13 × 34.4 = 38.8-MPH.

Your test data shows the speed with the 115-HP was 38-MPH. There is no weight data, but it seems reasonable to expect the 115-HP engine weighs more than the 90-HP engine, and this added weight will reduce the speed gain.

Since the predicted speed gain and the measured speed gain are in very close agreement, differing by perhaps no more than 0.8-MPH in a range of 38.8-MPH or a variation of about two percent, I don't think there is any significant deviation in the actual results from what would be the best case predicted result.

Hello B.E. Coyote,

I have a 2001 Dauntless16 with a 2017 Yamaha F115 mounted three-holes up. It is equipped with a Solas Titan HR 4 blade 13x15 propeller. My boat also has trim tabs although they are self-leveling tabs. Your data is similar to my boat's performance. I reach a maximum speed between 38-39 mph GPS, 6100 rpm, depending on sea and wind conditions. I installed a Solas Titan HR 4 blade 13x17 propeller and reached 42 mph GPS at 5900 rpm, but put the 15 pitch propeller back on because it felt better in rougher seas. Also, 42 mph is a little to fast for my comfort zone.

Prior to installing the F115, the boat had a 2001 Yamaha F100 engine which is similar to F90 except that the F100 is carbureted. It had the Yamaha 13x17k Black steel propeller and a Doel fin. The boat did not have trim tabs mounted when I had the F100 engine. With the engine mounted one hole from the highest setting, I would achieve 39 mph GPS at 6000 rpm, while keeping and eye on the tach so that I would not exceed the max rpm. This engine served me well for 16 years and 1800 hours.

The most significant improvement in my boat's performance was achieved by the installation of trim tabs and a 4 bladed propeller. I only purchased a new engine because the old engine had salt water in the oil and after 1800 hours I felt new was better than overhaul.

Both those speeds seem a bit low. Historically 160 Dauntless owners with 90 HP engines tended to report top speeds around 38-39 MPH. With my 115 HP, I used to get 44-45 with the original stainless prop, and 42-43 MPH with the 4-blade Trophy Plus that I'm using now. It's slower but accelerates much better than the old prop.

With your Yamaha 115, if you're easily hitting 6200 RPM then I wonder if you need another 2" of pitch to make use of the engine power.

-Bob

Thanks for all the replies

Bob--engine speed tops out at 5,800-RPM. I have to trim out to get above that.

I was disappointed that I didn't cross that 40-MPH barrier, but I am sure that I could with a higher pitched propeller. My real concern though isn't top speed, it is low speed planing and snotty-water ride.

What pitch is the four-blade trophy you are using?

Which 115-HP engine was that on?

Both boats were loaded down. Just the two trolling motor batteries weigh in at 120-lbs for the pair.

I plan to raise the engine mounting height by one hole.

I won't decide about the trim tabs until I get it out on a snotty day in the bay. The test run was on smooth freshwater.

Remember that propeller characteristics are not universal across brands and models.

I think you need a different propeller.

BobL what is the make, model, and size of your four-blade?

You always match a prop with the engine trimmed out to the max. If you don't you will be under propped. I usually get another 500-RPM when the engine is trimmed out at WOT and that is where I measure my max rpm. In other words if I am running full tilt boogie and trim the engine back in, I will usually lose 500-RPM.

I am running a Mercury Trophy Plus 13-3/4x17 prop on a 2003 Mercury 115 4-stroke (the Yamaha powerhead version) with a 2.07:1 lower unit gear ratio. It's not as fast as the original Mercury Vengeance 13-1/8x16 (even though on paper the Trophy Plus has more pitch, in practice it does not) but it planes off the boat much more quickly, accelerates faster, and just generally provides better all-around performance. I am totally with you that those attributes outweigh top speed.

GoldenDaze wrote:I am running a Mercury Trophy Plus 13-3/4 x 17 prop on a 2003 Mercury 115 4-stroke (the Yamaha powerhead version) with a 2.07:1 lower unit gear ratio.

[Is the Mercury TROPHY PLUS propeller] a four-blade [propeller]?

[Gear ratio] on the 2015 Yamaha F115B is 2.15

The engine speed at full throttle recommended range is 5300 to 6300-RPM. The engine easily hits 5800-RPM when trimmed in and when trimmed out the engine accelerates to more than 6200-RPM.

I still plan to move up the engine mounting height by one hole [to a four-holes-up position].

Maybe I'll see about trying a little higher pitch. I think my buddy runs a 4 blade 13x17.

B.E.Coyote wrote:[Is the Mercury TROPHY PLUS propeller] a four-blade [propeller]?

Learn more about the Mercury TROPHY PLUS propellers at

https://www.mercurymarine.com/en/us/pro ... ophy-plus/

Previous test

Outboard mounted one-hole up.
PROPELLER UNDER TEST = Power Tech SDC4 4 blade 13" 15 Pitch Prop
RPM = 6200 (Trimmed out to 6200)
MPH = 38 per auto gps that did not show tenths.

Yesterday I moved the motor up one hole to the two hole up position.

Outboard mounted two-holes up.
PROPELLER UNDER TEST = Power Tech SDC4 4 blade 13" 15 Pitch Prop
RPM = 6300 (Trimmed out to 6300)
MPH = 39.4


[With the higher engine mounting the boat speed had a] 1.4-MPH gain and [the engine speed increased] 100-RPM. I could have continued to trim out but stopped because the WOT engine speed range of the engine is 5300 to 6300-RPM.

I may try a higher pitch propeller, such as a TROPHYplus 17-pitch or another SDC4 prop in 16-pitch or 17-pitch. But even if the higher pitch propellers seem better all around, I would keep the SCC4 13 x 15-pitch for family tubing.

[The speed differences were] 0.4-MPH trim-in and 1.4-MPH trim-out.

Admittedly, the GPS receiver used on the previous test did not show [speed over ground to a resolution of 0.1-MPH] so I do not know if trimmed out I was going 38.0 or 38.9. In any case, not much of a difference.

The boat did seem to steer more easily.

A GNSS receiver using the Air Force NAVSTAR Global Positioning System will be measuring SPEED OVER GROUND (SOG), which will generally be different that speed through the water due to effects of current in the water.

The generally accuracy of SOG by GPS is about plus-or-minus 0.5-MPH.

When making tests over a period of time in which you wish to compare test outcomes to each other, the test conditions should be held as constant as possible. The instrumentation in use to measure parameters should also be held constant. That means the device providing boat speed should not vary from one test to another if you want to compare the test outcomes.

Even with use of the same GPS receiver, there can be other variables that affect the accuracy of the SOG reading. See

Using GPS Speed Over Ground Data
http://continuouswave.com/forum/viewtopic.php?f=12&t=4973

The second boat came with only a SONAR unit. On the first test with the second boat I brought the Garmin 665 off of my motorcycle and didn't realize that it didn't show tenths until I was on the water.

I now have a Simrad Go7xsr on the boat and any further tests will be using that same unit.

I don't plan on raising the outboard any higher. Overall I am fine with the performance, but I may try a higher pitch propeller if I can borrow one or find one for a great deal.

GoldenDaze wrote:I am running a Mercury Trophy Plus 13-3/4x17 prop on a 2003 Mercury 115 4-stroke (the Yamaha powerhead version) with a 2.07:1 lower unit gear ratio. It's not as fast as the original Mercury Vengeance 13-1/8x16 (even though on paper the Trophy Plus has more pitch, in practice it does not) but it planes off the boat much more quickly, accelerates faster, and just generally provides better all-around performance. I am totally with you that those attributes outweigh top speed.

Hey Bob, what did you end up with for Vent plugs on that prop? I picked up a nice used one and but I need to order the plugs.

I finished removing all the bottom paint and found some dings and blisters. Been working on making repairs and then I am going to bottom paint in the spring with the VC Performance Epoxy. Anxious to retest the PT 13x15 also to see if the epoxy bottom paint makes a difference.

My bottom wasn't horrible, but it wasn't perfect.

I tried small vents, medium vents, and no vents. Medium was best, it didn't spin up fast enough with small vents and it ventilated too much with no plugs.

-Bob

Over the winter I stripped off the old anti-fouling bottom paint, repaired some gel coat blisters, and painted the bottom with Interlux Vc Performance Epoxy.

I also picked up a Mercury TROPHY PLUS 17-pitch propeller
Test below is with the [Mercury Performance Ventilation System (PVS) propeller hub vent holes filled] with the MEDIUM vent plugs:

2001 Dauntless 160 with 2015 Yamaha F115 mounted two-holes-up
DATE= May 20, 2020
FUEL = about 20 gallons
CREW WEIGHT = 350
GEAR = bow mounted trolling motor, three batteries in the consol (one starting and two trolling) 20-lbs of anchor chain and rode in anchor locker, 20-lbs miscellaneous gear

PROPELLER UNDER TEST = Mercury Trophy Plus 17-pitch medium vent
RPM = 5900
MPH = 42.2

B.E.--looks like you have the propeller optimized. The boat speed has increased to 42.2-MPH from about 38-MPH. That is a nice gain of 4-MPH.

I'd say you're dialed in just about right. I generally get a 41-42 MPH top speed. The original 3-blade Vengeance 16" prop was a few MPH faster but the Trophy Plus gave much better overall performance. Enjoy!