2000 Dauntless 16 engine mounting height, trim tabs, 3 to 4 blade prop

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2000 Dauntless 16 engine mounting height, trim tabs, 3 to 4 blade prop

Postby B.E.Coyote » Tue Feb 26, 2019 10:41 pm

For a 2000 Dauntless 16 with the notch cut out, a 2008 Yamaha F90TLR is currently mounted two holes from the top, 3/4" above the transom. The outboard's mounting bracket as [four sets of mounting] holes. [Please see the article at the top of this forum on how to describe engine mounting height—jimh]

The propeller is 13 x 17 pitch stainless steel [perhaps a Yamaha three-blade K 17 propeller as determined later]

Engine speed at maximum throttle (WOT) is only 5500-RPM, and the acceptable range range for WOT is 5500 to 6000-RPM.

I plan to raise the motor but not sure if I want to raise it another 3/4 inch or 1-1/2 inches.

To owners of a Yamaha F90 on a Dauntless 16: what is your engine mounting height?
Last edited by B.E.Coyote on Wed Jun 19, 2019 1:10 pm, edited 2 times in total.
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Re: 2000 Dauntless 16 engine mounting height

Postby Phil T » Wed Feb 27, 2019 8:38 am

WOT at the bottom of the WOT range is not bad, generally speaking.

To answer your questions, there are a few pieces of information missing.

What is the wide open throttle (WOT) boat speed at 5500-RPM.

Is this running light and empty?

Describe load, gear, fuel etc.

What is the brand and model of the 13x17 propeller?

Just the size means nothing.

Where is the anti-cavitation plate in relation to the bottom of the keel?

Take a builder’s level and extend it past the engine and measure. The target is 1-1/2 to 2-inches above the bottom of the keel.
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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Wed Feb 27, 2019 9:48 am

Describe the engine mounting height as explained at

viewtopic.php?f=7&t=739

From your description the mounting height is not clear.

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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Wed Feb 27, 2019 5:28 pm

The engine is mounted at the one-hole-up position.

With the boat level and the engine trimmed so the anti-ventilation plate is level, the anti-ventilation plate is 5/8-inch above the keel. This is the actual keel not the top of the notch.

The propeller brand is uncertain. I believe it is Yamaha. It has “17 K” marked on it. When I search on the internet with the term “17 K” I get results for Yamaha being the brand.

I'll need to do another sea trial before I make any changes.

When I had the boat out before, it had quite a few barnacles on it. I did realize that they effected speed but I didn't put two and two together and realize that they would also effect the RPM of the [engine].

The hull is now clean and I need to take new data.

[At the prior test reported above the boat] speed was just under 30-MPH. The crew weight was 500-lbs, and the fuel tank was half-full.
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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Wed Feb 27, 2019 6:20 pm

Yamaha makes a black painted steel propeller of 17 pitch that is marked “17 K.” Are you certain the propeller you have is stainless steel? Does it have a polished finish?

To reach an engine speed of 5,500-RPM with a hull having substantial fouling with marine life sounds like the engine will acellerate to a higher crankshaft speed when the hull is cleaned of that growth.

Boat speed is always related to engine speed.

A hull with marine growth has more resistance to moving through the water than a clean hull.

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Re: 2000 Dauntless 16 engine mounting height

Postby Phil T » Wed Feb 27, 2019 7:02 pm

The 17 is the number of inches of pitch.

The K is Yamaha's letter code for its intermediate gearcase.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Wed Feb 27, 2019 7:14 pm

I figured the drag could also cause some prop slip. Now I know.

The prop is somewhat polished. It is magnetic but way to heavy to be aluminum.

I pulled the propeller. On the outside I see 17-K. Stamped on the inside of the hub is "13x17-k2". Maybe inside the hub I see a C or O.

prop.jpg
Fig. 1. Propeller under discussion
prop.jpg (5.39 KiB) Viewed 12480 times

Seems to a Yamaha Part# 688-45930-02-00 OEM670341 (3X13"X17"-K2) Replaces 688-45930-02-98, 688-45930-01-98
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Mon Mar 04, 2019 5:53 pm

I was able to take out the boat. It now has a clean hull.

[The top speed measured over ground by GNSS receiver was] 34.7-MPH at engine speed of 6000-RPM. I may have been able to gain a little more speed with more outward trim but didn't want [the engine to accelerate] above 6000-RPM. There was less than half-tank of fuel, and crew weight was 450-lbs. There was a 170-lbs trolling motor and batteries on the bow and two 50-lbs batteries in the console.

Since the last run, I added a [anti-ventilation plate foil extension]. The boat transitioned to hydroplane much faster and easier. The A-V plate was just below the surface at full throttle/

How much [speed could be gained] by raising the engine mounting height so that the A-V late is above the surface?

If I can gain 2 to 3-MPH, I think I would [raise the engine mounting height] Any less [speed increase] and [the trouble to raise the engine mounting height] is probably not worth [the effort].

I do like having things correct, but this boat will spend most of its time in a no-wake zone and out in the bay. I doubt I'd want to run full throttle.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Mon Mar 04, 2019 8:42 pm

The gear ratio of the lower unit is 2.31
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Re: 2000 Dauntless 16 engine mounting height

Postby Phil T » Tue Mar 05, 2019 8:15 am

Note: there are extensive threads and rigging recommendations for the Dauntless hull with the notch in the archives: LINK

A theme of all the discussions is motor height and a stern lifting propeller.

I would raise up the engine one more hole, since it is a DIY and costs nothing, but you have a nagging propeller dilemma.

If you raise the engine, you will gain about 200-RPM at WOT due to less drag. This will increase WOT engine speed outside the recommended RPM range. Think of driving on a highway in third gear instead of fifth.

As it is now, you are slightly underpropped. You need more pitch on the blades to reduce the engine RPM at WOT to the acceptable range. Changing to a 19-pitch in the same make and model propeller will reduce engine speed by about 400-RPM. You will also gain speed through the engine speed RPM range.

With engine rigging, you have several variables. When testing, you want to change only one variable at a time. Given this. I would:

--first RAISE engine, and then retest boat speeds and engine speeds
--second, CHANGE propeller, then retest
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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Tue Mar 05, 2019 9:09 am

Based on the appearance of the propeller under discussion in the small image above, it does not look like a polished stainless steel propeller. It may be a steel propeller that was originally painted black, and over time or due to some intentional effort, all the black paint has been removed by abrasion, leaving just a dull finish to the steel.

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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Tue Mar 05, 2019 12:29 pm

Thank you gentlemen. I am going to raise the motor this weekend.

There is also a good propeller shop down the road. I'm going to run the propeller over to them and see if the propeller is in good tune. I'm fairly well convinced that I have to go to a 19-pitch propeller, but to know what I am dealing with right now would be good.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Tue Mar 05, 2019 5:33 pm

[It turns out that] the propeller was previously [painted] black. It is stainless steel. The propeller had some damage and needed re-work.

[A local propeller shop] had the exact same propeller in 19-pitch that had already been tuned. He swapped that out with my old propeller for $130.

He is tuning my old propeller this week. I have the option to switch back for free if I am not happy with the 19-pitch. Apparently the old propeller needed work anyway. [The propeller shop] said vibration could damage the [engine's gear case] if not taken care of.

I am going to try a tuned propeller with a higher pitch before raising the motor. Since the old propeller was damaged I figured it wouldn't be good data anyway.
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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Fri Mar 08, 2019 10:34 am

To be clear, the present engine mounting height is one-hole-up, and testing will resume with a 19-pitch propeller. The engine has a 2.3:1 gear ratio, and the recommended full-throttle speed range is 5,000 to 6,000-RPM.

We would anticipate the engine might accelerate to 5,500-RPM. With 19-PITCH and 10-percent SLIP, the boat speed should be around 38-MPH.

We now await a table of data, with ENGINE SPEED in RPM and BOAT SPEED in MPH.

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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Fri Mar 08, 2019 8:11 pm

A new 19-pitch propeller got [the 2000 DAUNTLESS 16 boat] to 36.3-MPH [and let the 2008 Yamaha F90TLR engine accelerate to] 5700-RPM [To compensate for] my son not being aboard (130-lbs), I added 20 gallons of gasoline fuel to the fuel tank which is aft of the console. [In earlier testing] my son sat in front of the console.

[There was a] difference--not for the better--in bow rise and time to plane. I did not care for the results with the 19-pitch propeller. I changed the propeller back to my original 17-pitch propeller which is now repaired and polished.
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Re: 2000 Dauntless 16 engine mounting height

Postby Phil T » Sat Mar 09, 2019 10:32 am

Ok, hang on for a sec: you increased the pitch of the Yamaha Painted stainless steel propeller to 19-pitch from 17-pitch, which increased boatspeed and lowered your WOT engine speed to fall inside of the manufacturer's recommended RPM range.

Did you use trim?

I do not see how adding weight in the stern and taking it out of the bow (son not there) has anything to do with the propeller. This scenario makes the boat harder to plane and trim out.

The first generation Dauntless 16 does experience bow rise and comments from owners on being slow to plane. Adding weight forward does help.

Is the foil still attached?

I think you should retest with son aboard and then evaluate prop.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Sun Mar 10, 2019 1:26 pm

Correct, a little faster, dropped rpm.

I did not mean to imply that the weight moving back had anything to do with the propellers. Just pointing out that there was a change.
The bow rise and time to get to top speed I think was more than just the change in balance. It was significant, and I just preferred the acceleration that the boat had before.

The foil is still on. The boat had terrible bow rise with the 17-pitch propeller before the foil; the foil made a huge difference.

I need to get out again now that I have 17-pitch propeller that is tuned. The propeller shop said the damage they repaired was significant enough to cause performance [decrease].
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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Mon Mar 11, 2019 7:07 am

It is much simpler if you can provide data in a table instead of burying it in long narratives about what you did. If I have found the correct data, your results are as follows:

BOAT = 2000 DAUNTLESS 16
ENGINE = 2008 Yamaha F90TLR
GEAR RATIO = 2.31
MOUNTING HEIGHT = one-hole up

Test 1:
FUEL = "half full"
CREW WEIGHT = 500-lbs
HULL = fouled with marine growth

PROPELLER UNDER TEST= damaged 17-pitch Yamaha three-blade K17 series propeller;
RPM = 5,500
MPH = "just under" 30-MPH

Remarks: because the propeller was damaged and the hull fouled with marine growth, this data is of little value.

Test 2:
FUEL = "less than half full"
CREW WEIGHT = 450-lbs
GEAR = 270-lbs of batteries and trolling motor
HULL = cleaned of marine growth

PROPELLER UNDER TEST= damaged 17-pitch Yamaha three-blade K17 series propeller
RPM = 6,000
MPH = 34.7
Notes: added a foil extension to the A-V Plate

Remarks: the addition of a foil extension to the A-V Plate and the cleaning of the hull are significant changes from the prior test. Still testing with a damaged propeller, so this data is of little value.

Test 3:
FUEL = added 20-gallons (about 125-lbs) to tank that was less than half full
CREW WEIGHT = (450-lbs minus 120-lbs or) 330-lbs
GEAR = (same as Test 2)
HULL = cleaned of marine growth

PROPELLER UNDER TEST = like-new 19-pitch Yamaha three-blade K17 series propeller
RPM = 5,700
MPH = 36.3
Test observations: "significant" change observed in "bow rise" and "time to plane" but no specifics given; no crew seated in bow.

Remarks: altering the location of 130-lbs of weight to aft of the console from forward of console may have influenced the boat trim, and the time to plane and bow rise during transition to plane may have been affected. We have engine speed at a proper range; boat speed is best observed so far.

Test 4. (Results not given)
FUEL =
CREW WEIGHT =
GEAR =
HULL = cleaned of marine growth

PROPELLER UNDER TEST = repaired 17-pitch Yamaha three-blade K17 series propeller
RPM =
MPH =

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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Mon Mar 11, 2019 7:42 am

Regarding your observations about "bow rise" and "time to plane" having changed "not for the better", I am presuming you meant to say that in Test 3 the time for the boat to transition to plane from a standing start increased compared to Test 2, and that in Test 3 during the transition to plane the bow rose higher than it did in Test 2.

You report you have changed the propeller to a repaired like-new 17-pitch Yamaha K17 three blade, but you did not give any engine speed or boat speed data. Did you test with the repaired 17-pitch propeller?

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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Mon Mar 11, 2019 7:46 am

Re a propeller being "tuned": the notion of "tuning" implies a change in a resonant frequency of some sort of resonating device so that its frequency of oscillation is changed. I don't think "tuned' is an appropriate word to describe a propeller that has been repaired from a damaged condition to a like-new condition. Propellers are either in a normal, like-new original condition or they are damaged. The process of repairing a propeller with damage to a like-new condition is generally not referred to as the propeller having been "tuned."

A propeller can also be modified so that the propeller blades might have greater uniformity; this process is called balancing. A propeller might also be modified from original condition to alter the shape of the blade trailing edges, giving them a slightly changed profile; this is called adding blade cup. The trailing edges can also be modified by grinding them to a sharp flat transition. It may also be possible in some instances to change the overall blade pitch, either to increase it or decrease it sightly. The outcome of making modifications to a stock propeller will depend on the skill of the person making the modifications.

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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Mon Mar 11, 2019 8:00 pm

So with test 1 and 2 done with the damaged prop it looks like test 3 and 4 are the only two that need to be compared.

Test 3:
FUEL = added 20-gallons (about 125-lbs) to tank that was less than half full
CREW WEIGHT = (450-lbs minus 120-lbs or) 330-lbs
GEAR = (same as Test 2)
HULL = cleaned of marine growth

PROPELLER UNDER TEST = like-new 19-pitch Yamaha three-blade K17 series propeller
RPM = 5,700
MPH = 36.3
Test observations: "significant" change observed in "bow rise" and "time to plane" but no specifics given; no crew seated in bow.

Remarks: altering the location of 130-lbs of weight to aft of the console from forward of console may have influenced the boat trim, and the time to plane and bow rise during transition to plane may have been affected. We have engine speed at a proper range; boat speed is best observed so far.

Test 4.
FUEL = Same as test 3 give or take the amount of fuel I used during test 3. 15-20 minutes of run time.
CREW WEIGHT = Same as test 3 (450-lbs minus 120-lbs or) 330-lbs
GEAR = same as all previous tests
HULL = cleaned of marine growth

PROPELLER UNDER TEST = repaired 17-pitch Yamaha three-blade K17 series propeller
RPM = 6000
MPH = 36 mph with tailwind 35 mph headwind

Remarks: I much prefer this set up as the boat got to speed faster, had less bow rise or at least got to plane much faster.

Since I was alone for test 3 and 4 I mounted a small video camera off the transom. It was odd that in test 3 with the 19p propeller that the doel-fin broke the surface (barely and not constantly) but that it did not with the 17p prop.

In test 3 I trimmed the motor up until it stopped improving the speed. In test 4 I stopped trimming the motor up when it reached 6000 rpm. In test 4 the motor was at 5700 rpm WOT trimmed all the way down.

Because of the video showing that the doel-fin was not above the water in test 4 I do believe that my motor could be moved up but then I would likely be outside of the proper rpm range for the outboard. I am not sure at this point if chasing down that last little of performance is worth it right now.

I'll probably revisit the engine height after I get some other work done.

I have some gelcoat repairs to do as soon as it gets warmer. :)
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Re: 2000 Dauntless 16 engine mounting height

Postby Jefecinco » Tue Mar 12, 2019 10:17 am

I may have missed it but I'm unclear as to your ultimate objective. Are you after the best possible top speed from your Dauntless or for best overall performance? For your long term satisfaction I recommend best overall performance.

Getting the notched hull Dauntless 16 on plane quickly and maintaining plane at lower speed is difficult and particularly difficult with a 90 HP engine. If cost is not a problem consider repowering with a 115 HP engine. Otherwise, I believe your most economical solution is to mount your engine three holes up, remove the fin from the anti-cavitation plate and find a four blade propeller that fits your needs. The only cost of this recommendation is for a different propeller.

Typically, a four blade propeller will provide less top speed than a three blade propeller but will provide much better acceleration for getting on plane quickly and will hold a plane at lower speed and in tight turns.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Tue Mar 12, 2019 11:20 am

I have no doubt that a 115 outboard is the better choice for this boat but it came with a 90hp 2008 Yamaha 4 stroke with only 350 hours.

The only reason I could even afford this boat was because it was neglected and needed lots of work, all new wiring, some gel coat repair etc, The motor was a big step up for me as my last boat was a 1994 Yamaha 55hp 2 stroke.

I just couldn't justify selling off this motor and having to lay out the money for a new 115 at least not any time soon. I really like the boat and plan on keeping it for a long time so maybe in a couple years.


My goals I guess are (1) to not damage the motor by running it at too high RPM, and (2) to have a functional fishing boat that can get on plane easily enough. Top speed is really not too much concern. Most of where I fish is a no wake zone. When I do head out into the bay it is only about three miles from the launch to the Chesapeake Bay Bridge tunnel where I would probably use my trolling motor and spot lock to fish around the structure.

I do appreciate all of the comments.
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Re: 2000 Dauntless 16 engine mounting height

Postby jimh » Tue Mar 12, 2019 2:01 pm

Less propeller pitch (as you have achieved by changing to 17-pitch from 19-pitch) will give faster acceleration. It will also allow the engine to accelerate into its best power range at lower boat speeds; that will let the boat stay on plane at a lower boat speed in most hulls.

More use of the boat will give you a better feeling for optimum engine trim.

To have the A-V Plate ALWAYS running above the water is good for smooth water and straight-line speed. For more diverse running conditions, you may find that the engine mounting you have now (where the A-V Plate is not completely out of the water and not running dry) will be useful, particularly when operating at slower planing speeds in rough water.

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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Tue Mar 12, 2019 8:00 pm

Thanks Jim. I think that sums it up well. After I have more hours on the boat, I may revisit this if I see any concerns that need to be addressed.
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Re: 2000 Dauntless 16 engine mounting height

Postby GoldenDaze » Wed Mar 13, 2019 2:47 pm

Regarding getting and keeping the 160 Dauntless on plane, consider putting on a set of trim tabs. I added the Lenco limited-space tabs to my 160 last year and the results were really great, much better than with a hydrofoil on the lower unit. See http://continuouswave.com/forum/viewtopic.php?f=6&t=3860 for details. The total cost was about $800. Also see http://continuouswave.com/ubb/Forum4/HTML/007963.html for an earlier (and much briefer) discussion of the same.

Similarly, going to a 4-blade stainless prop was also helpful to me. I lost about 2 MPH in top speed (where I never run anyway) but significantly improved acceleration.

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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Wed Mar 13, 2019 5:43 pm

Thanks Bob,

I had read your post previously. I also added hydraulic steering and am happy with it! When I bought my boat the teleflex cable was frozen and it was much easier to replace the cables with hoses.

I think those trim tabs look great and could be something I add down the road after everything else is sorted out.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Wed May 29, 2019 8:53 pm

Jefecinco wrote:I may have missed it but I'm unclear as to your ultimate objective. Are you after the best possible top speed from your Dauntless or for best overall performance? For your long term satisfaction I recommend best overall performance.

Getting the notched hull Dauntless 16 on plane quickly and maintaining plane at lower speed is difficult and particularly difficult with a 90 HP engine. If cost is not a problem consider repowering with a 115 HP engine. Otherwise, I believe your most economical solution is to mount your engine three holes up, remove the fin from the anti-cavitation plate and find a four blade propeller that fits your needs. The only cost of this recommendation is for a different propeller.

Typically, a four blade propeller will provide less top speed than a three blade propeller but will provide much better acceleration for getting on plane quickly and will hold a plane at lower speed and in tight turns.



My main goal is overall performance with the main hope being to get the bow down from 10-18mph

I want the boat to be able to go out to the Chesapeake Bay Bridge Tunnel on reasonably good days and that bow rise in that speed range I think would be awful in bigger water.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Wed May 29, 2019 9:06 pm

New tests, raised the outboard one hole to two-holes-up.

O
O
x
O

I ran the boat last week but just to get out. I only had a quarter tank of gas and was solo other than my dog.
5600 WOT trimmed in 32.2
6000 (trimmed out until I reached 6000) 36 even.


Today I installed a new Power Tech SDC4 4 blade 13" 15 Pitch Prop

5/29/19 Test 1 with Doel Fin

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 = 5400 WOT Trimmed in
MPH = 29.7
RPM =6000 (Trimmed out to 6000)
MPH 34.2

5/29/19 Test 2 Removed Doel-Fin

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 = 6,000 (Trimmed out to 6000)
MPH = 34.4
Last edited by B.E.Coyote on Wed May 29, 2019 9:39 pm, edited 1 time in total.
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Re: 2000 Dauntless 16 engine mounting height

Postby B.E.Coyote » Wed May 29, 2019 9:13 pm

My Dauntless 16 is becoming more functional.

I think this 4 blade prop was an improvement. Anecdotally the boat has better hole shot, less bow rise and top speed was very good maybe even better considering the boat was slightly more loaded.

It still has more bow rise than I'd like between 10-18 mph but it may just be the hull design and something I will have to live with.

I will leave the foil off and may consider trim tabs for next season.

Not sure if more HP will help this situation but the new Mercury 115 weighs 10 pounds less than my Yamaha F90. Maybe an option down the road if I decide to keep the boat long term.
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Re: 2000 Dauntless 16 engine mounting height

Postby Jefecinco » Thu May 30, 2019 11:15 am

I believe raising the engine another hole will provide the best performance. When I had a 1999 Dauntless 16 with a 115 HP OMC engine and a four blade propeller I removed the aftermarket fin from the engine and gained about 1 MPH at WOT with optimal engine trim with no loss of part throttle performance. The nice thing is it so easy to change the mounting height.
Butch

B.E.Coyote
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Re: 2000 Dauntless 16 engine mounting height - trim tabs

Postby B.E.Coyote » Fri Jun 14, 2019 8:14 am

I added 12"x4" Bennett Bolt trim tabs to the Dauntless 16

I really wish I had done this as my first modification to the boat. Huge difference, I have so much more control of the boat and can keep the bow down easily.
I installed them myself so the total cost was less than the cost of the new 4 blade prop which while helpful would probably not have been needed.

Even when the tabs are up, the bow doesn't rise as much at lower speeds. Probably because the rising bow digs the tabs deeper into the water.

I love the boat now and will start saving my pennies for a new 115 hp out board.

My only regret on the tabs was cheaping out on the switch. I bought the most basic switch. It has no lights and no auto retract. At only 4" long I wasn't worried about auto retract. I also didn't see the need for the L.E.D. indicator lights but already I have found that at times I hit the switches in an odd way and one tab moves up or down a little more than the other. You know immediately that something is off, but the indicators would be nice.
2001 Dauntless 160
Virginia Beach

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Re: 2000 Dauntless 16 engine mounting height, trim tabs, 3 to 4 blade prop

Postby B.E.Coyote » Wed Jun 19, 2019 2:11 pm

A surprise from testing three-blade and four-blade propellers. I did a back-to-back test of the Power Tech SS 4-blade SCD 13 x 15 and the original [three-blade] Yamaha 13-1/4 x 17.

I initially put on the PowerTech propeller before I added the 12 x 4 Bennett Bolts trim tabs. I thought there was more stern lift from the four-blade but didn't know how to verify it.

I downloaded an android app called angle meter. Mounted the phone on my console as flat as I could and zeroed out the meter.

Image

I measured [some data with testing of] both propellers at 10-MPH SOG by GPS.

BOAT = 2000 DAUNTLESS 16
ENGINE = 2008 Yamaha F90TLR
GEAR RATIO = 2.31
MOUNTING HEIGHT = two-holes up
FUEL = 3/4
CREW WEIGHT = 350
HULL = clean
Gear= 3 batteries, trolling motor, fishing gear

Prop Power Tech 4 Blade 13x15
Tabs up 10 mph = 11-degrees bow rise
Tabs Down 10 mph = 9-degrees bow rise
Time to plane = 5 seconds
RPM at WOT= 5,800 trimmed down; 6,000 trimmed up
BOAT SPEED at WOT MPH = 33 trimmed down' 34.6 trimmed up


Prop: Yamaha 3 blade 13 1/4 x 17
Tabs up 10 mph =10-degree bow rise
Tabs down 10 mph = 6-degree rise
Time to plance = 6 seconds
ROM at WOT = 5700 trimmed down; 6000 trimmed up
Boat SPEED at WOT = 32.6, trimmed down; 35.3 trimmed up

The tabs, even in the up position did a lot to limit the bow rise. I wish I would have used the app to measure the bow rise before the tabs.

The propellers are very similar in performance.

I will sell the four-blade to recoup the investment. The tabs were cheaper than the new PowerTech propeller and had a more significant impact.
2001 Dauntless 160
Virginia Beach

jimh
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Re: 2000 Dauntless 16 engine mounting height, trim tabs, 3 to 4 blade prop

Postby jimh » Wed Jun 19, 2019 4:12 pm

Interesting data. Thanks for providing it. Your data shows the three-bladed propeller seems to give the best all round performance—not a surprise for me.

A propeller can create stern lift, which can reduce wetted surface and wake, resulting in improved performance. Of course, stern lift tends to push down the bow.

Trim tabs can also create stern lift, and create stern lift more effectively and more selectively and with more control than any propeller. But they also create added drag, perhaps slowing the boat slightly.