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Author Topic:   Dauntless 16 with Yamaha F80
Chris CH posted 05-28-2014 05:14 AM ET (US)   Profile for Chris CH   Send Email to Chris CH  
We have a 2000 Dauntless 16 with a c.1997 to c.2002 Yamaha F80 for-stroke-power-cycle outboard engine. It obviously doesn't have the right propeller, an aluminium 12-3/4 x 21-pitch, and the motor is a little weak for this boat. We don't get over 4,600-RPM and maximum speed is 28-MPH, even not very loaded. It planes at 16-MPH. We manage to wakeboard and waterski on the lake (with a Turboswing), but it's very difficult to get an adult on skis out of the water, or getting on plane if we're more than four adults on the boat. During acceleration the rear of the boat seems to be nearly sinking, with a very high bow lift. We're looking for more power and not so much for speed.

From what I read here, maybe the Trophy Plus 13-3/4 x 17 would be an option. Or maybe a stainless steel propeller with a 15 or 16-pitch, e.g., a Stiletto Bay Pro 15 or 16, three-blade or four-blade. Any advice?

The motor is now in its lowest position possible, and the cavitation plate seems to be about level with the bottom of the boat. Should we raise it?

What about adding a hydrofoil? If so, which one?

I'm new on this site, but it has given us already very valuable information. Thank you--Christiane

Lupi posted 05-28-2014 08:14 AM ET (US)     Profile for Lupi  Send Email to Lupi     
Hi Christiane. I have the same boat but equiped with a Mercury 90-HP two-stroke, so I have more power and also a lighter engine than your Yamaha 80-HP four-stroke. My engine has been perfectly propped (thanks to Tom Clark) with a Stiletto 13-1/4 x 17.

With a 21 pitch, you are certainly too high. Your engine has a 2.27:1 gear ratio. Given you are just powered, you would not want even a 17-pitch. Perhaps s 15-pitch good stainless steel propeller would do the job, with engine mounted high on the transom, but I am not the expert here.

What is sure is that with 80-HP, you are underpowered--my light weight 90 is just OK with perfect prop, for global performance.

Many people having this boat report here that it should be powered with 115-HP, and some have added a foil for better planning speed and acceleration from a standing start. Many discussions may be found here.



jimh posted 05-28-2014 09:54 AM ET (US)     Profile for jimh  Send Email to jimh     
To improve acceleration onto plane when heavily loaded, change the propeller to a lower pitch.

The engine may not be developing full horsepower if it can only accelerate to 4,600-RPM under normal load. This also suggests a lower pitch propeller.

The engine mounting height now is likely too low for best performance. Check the relationship between the anti-ventilation plate and the water flow when the boat is on plane and in its upper speed range. The anti-ventilation plate ought to be running just at or just above the water surface. The mounting height can be raised, but typically a good propeller is needed. The propeller must be able to maintain good traction or grip with the water when running at a higher mounting. This usually means a stainless steel propeller with good blade configuration.

As for adding a foil appendage to the anti-ventilation plate, I recommend hold off on that option until you have experimented with a lower pitch propeller and better engine mounting height.

Tom W Clark posted 05-28-2014 10:34 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Christiane -- The Yamaha F80 is, by today's standards a very low power-to-weight motor and marginal for a Dauntless 16, especially if you are asking it perform for waterskiing or wakeboarding wit four adults on board.

On top of that, the motor is grossly over-propped and you are using it at 1200 feet of elevation which may add a slight power loss of around 4 percent.

With the motor mounted so far too low, I am surprised you even get the performance you do.

The Yamaha F80 has a 2.31:1 gear ratio and a 6,000 RPM redline. I would expect this boat, lightly loaded at sea level to be good for 36 MPH. Given where you are and your intended uses, the top speed may be a little less.

I recommend the following:

- Raise the motor two more sets of bolt holes. This will have a profound impact on the bow rise during acceleration and will help your top speed increase.

- Install a 13-1/4" x 13" Stiletto Advantage 4.25 with a Mercury Flo-Torq III hub kit to help alleviate the shift clunk and prop rattle this in-line four stroke will almost certainly suffer with a heavy stainless steel propeller

- Install a foil. I do not normally recommend this, but the early Dauntless models suffer from stern squat during acceleration and this will really help, especially for towing skiers and boarders with a heavy load aboard.

Chris CH posted 05-28-2014 10:54 AM ET (US)     Profile for Chris CH  Send Email to Chris CH     
Thanks. For now we're trying to get the most out of this combination with the F80, and will invest maybe later in an F115.
Which Stiletto model do you have, Luc ? Does it have 3 or 4 blades ?
And we'll do as you suggest Jimh : first step see how it works with a better prop.
But which model exactly could be the "ideal" one ?

Chris CH posted 05-28-2014 10:59 AM ET (US)     Profile for Chris CH  Send Email to Chris CH     
I just posted my reply without seeing your advice Tom.
Thank you, I was hoping for it...
Chris CH posted 05-28-2014 02:44 PM ET (US)     Profile for Chris CH  Send Email to Chris CH     
Very interesting, Tom. All those parameters we didn't think of... The guy that sold us the Dauntless 2 years ago (a professional boat renter) was obviously not very honest...
We wakeboard from time to time (+ some skiing), we also do quite some cruising around with sometimes 6 on board, sometimes 20 miles x 2 (now at very low speed...). Knowing this, wouldn't you rather take a 15" pitch ? Also it seems that even with a slip of only 10%, the boat could theoriticaly reach 29 mph with a 13P, and 34 mph with a 15P at 6000 RPM. Or is this calculation wrong ?
If I understand it right, from what you wrote elsewhere, the Flo Torq III fits on any engine and any propeller ? Does it mean there is only 1 Model ? Because on the market it is a bit confusing: sometimes it is called "Quicksilver Flo Torq III Hub Kit" sometimes "Mercury" (I suppose it's the same) but then there are sometimes 3 different models: one 835272Q09 for Yamaha 50-100 HP "Splined foward thrust washer", one 835271Q09 For Yamaha 115 HP and one for Mercury.
Do you know if the 835272Q09 For Yamaha 50-100 HP "Splined foward thrust washer" is the right one for our Yamaha F80AET(L) ? I don't know what it means.
Thanks a lot for your help.

Tom W Clark posted 05-28-2014 03:07 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Selecting the appropriate pitch depends on the desired WOT engine speed, the gear ratio of the lower unit AND the anticipated calculated propeller slip. That prop slip will be different for different models of propellers.

My 13" pitch recommendation is specific to the Stiletto Advantage 4.25 which I expect will yield a calculated propeller slip of around negative 5 percent, because that is what is typical of this propeller on small Whalers.

The hub kit you want is Quicksilver 835272Q09 which includes the splined thrust washer that your F80 uses.

Lupi posted 06-02-2014 07:42 AM ET (US)     Profile for Lupi  Send Email to Lupi     

my Stiletto is an advantage (3 blades) 13-1/4*17. It allows me to reach my redline (5500 rpm) with a top speed of 40 mph that nearly gives a negative 5% propeller slip, that is consistent with what Tom wrote about Stiletto performances

Chris CH posted 06-02-2014 07:08 PM ET (US)     Profile for Chris CH  Send Email to Chris CH     
We're looking foreward to the new power we'll get. I ordered the Stiletto and hub kit you recommended, Tom.

Now we wonder how we're going to raise the motor, since it is now directly mounted on the transom and that we have no experience with this.
Do we need to add a riser block (home made or ready made) ? Or back/jack plates ? If so, which type ? I saw it can be static/adjustable, vertical/with trim, more or less set back, 5 inch or more, etc... Or is it possible to elevate the motor without adding something ?

Tom W Clark posted 06-02-2014 07:41 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris -- The Yamaha F80 has four sets of bolt holes in the motor mounting bracket. The lower sets may be a continuous slot instead of individual hole,s but the range is the same.

The mounting bolts are currently going through the upper most set of holes so the motor is as low as it can go.

You need to unbolt the motor and raise the motor on the transom and reinstall those bolts through the lowest set of holes.

It is actually easier to lower the transom than it is to raise the motor. If the boat in on a tailer. block under the motor while it sits upright and once the motor is unbolted you can raise the tongue of the trailer and the transom will go down.

You will need helping hands and a way to stabilize the unbolted motor, but it works. Be sure the bolts are sealed where they pass through the transom with caulk upon reinstallation.

If you have access to a loft or hoist you can suspend the motor and place it where you need it while bolting it back on.

You do not need, or want, a jackplate.

Jefecinco posted 06-02-2014 07:48 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     

If your boat is on a trailer the engine mounting height adjustment is dead easy and no special tools are required. A friend to help will be useful but is not required.

First visualize your trailer as a lever. If you raise the front you lower the rear, etc. With my Dauntless 16 powered by a 115 Evinrude I lowered the engine tilt until the engine was more or less vertical. I then placed a timber below the skeg with two timbers nailed to the first on either side of the skeg to produce a slot for the skeg. I raised the trailer tongue until the skeg contacted the timber. I then removed the bolts in the bolt holes and loosened the bolts in the slots of the engine mount. By raising the front of the trailer I lowered the transom thus effectively raising the engine. When the engine was at the desired height I reinstalled the bolt in the new hole and tightened the bolts in the slots.

I was doing the job alone so it was a little less straightforward than described with me running back and forth from the transom to the trailer jack several times. In addition the engine managed to become less than vertical side to side. This was solved by banging on the timber supporting the skeg until the engine was at the attitude required to reinsert the bolts.

I used new sealant in the transom before reinstalling the bolts. I used BoarLife Caulk but 3M 4200 or 5200 may be a better choice.


Marlin posted 06-07-2014 08:18 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Christiane, the 16/160 Dauntless is a heavy boat, and in particular it's stern-heavy. Adding a hydrofoil to the engine was the best change I ever made to my 2003. Really trim tabs would be even better, but that's a lot more complicated and gets in the way of the swim ladder.

I can't offer any help on a prop for your F80, other than to say I think you will have very marginal performance with that engine. My Mercury 115 4-stroke powers the boat very well, but is still somewhat heavy in the stern. If I were to repower, I'd strongly consider an Evinrude 115 E-Tec to lighten the stern weight a little bit.


skred posted 06-10-2014 10:39 PM ET (US)     Profile for skred  Send Email to skred     
On my 2001 16 Dauntless, I had a 90 Honda, carburetor version, and had the same symptoms described here. I added a Tigershark VG hydrofoil (like a Doel-fin, but better), and performance improved radically. Not sure which propeller I had, but the performance improvement with the hydrofoil was significant.
Chris CH posted 06-12-2014 06:41 PM ET (US)     Profile for Chris CH  Send Email to Chris CH     
I apreciate very much your help. Thank you all.
Yesterday we received and tried out the prop and hub : and as you predicted Tom, we reach ~5500 RPM easily, and the acceleration is great. It is now even more obvious than before that the motor needs to be risen, because the stern seems even closer to "drowning".

About rising the motor:
There is a black plastic profil around the top edge of the transom, and since it is ~1/8" thick it is in the way of lifting the motor.
Would you recommend to cut it off, or rather to add a 1/8" thick plastic or aluminum plate between the transom and the motor to keep it all flush ? We don't feel to good cutting out an original part that we might want back on one day...

And about the caulking : do you advise to take out all the bolts and seal them again when we rise the motor ? Or should we just leave the bolts where they are and add some sealant (non-permanent) on the motor side ?
I don't think there has been any sealing or siliconing done on this boat in the last 10 years except for fixing this motor on it, maybe 5 years ago.

About the hydrofoil. Do you think the Tiger Shark would be the best one in our case ? I wonder if a longer fin (length in boat direction) wouldn't be better to hold the nose down, like for ex. the "Fast tail" ? Does anybody have experience with it, or with aluminum hydrofoils ? But there might be a space problem between the prop and the motor with a hydrofoil fixed under the cavitation plate.

Marlin posted 06-12-2014 08:26 PM ET (US)     Profile for Marlin  Send Email to Marlin     
I simply cut back the black trim at the top of the transom. I put on a Sport SE 2000 hydrofoil because that was what was easily available to me. The Tiger Shark looks okay too. All the aluminum ones I've seen look rather clunky, although at least one design (I don't remember the name) doesn't require that you drill holes in the anti-ventilation plate. Personally I think that the Doel-fin 2-piece designs are inferior because they put more stress on the anti-ventilation plate.

If you do drill holes in the plate, try to avoid the trim tab.

Tom W Clark posted 06-12-2014 09:33 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Chris -- Cut the trim piece on top of the transom. That boat should never have a motor mounted all the way down on the transom ever again so that missing piece will never be missed ;-)

As to the foil, I do not have a specific recommendation HOWEVER, I recommend a foil with greater length and less width. I am not sure if there is much difference between all the products on t he market, but if there is, get a one-piece foil that is narrower.

I recommend this because a foil can exert a tremendous amount of force on the cavitation plate (anti-ventilation plate, A/V plate) if it strikes an object at speed. This is probably not as much of a concern on Lake Geneva as where I am but nonetheless, less width means less leverage on the motor and less risk of damage in the case of a strike.

With the motor mounted in a higher position, it is my hope the foil will be mostly out of the water when the boat is moving fast, and thus less at risk of hitting any object in the water. It will also produce less drag at higher speeds.

On the other hand, a foil that extends rearward more will maintain more contact with the water at lower speeds and negative trim angles of the motor. This will be a huge aid to water sports where you are trying to pull somebody and get the boat up on plane at the same time.

Chris CH posted 08-08-2014 06:58 AM ET (US)     Profile for Chris CH  Send Email to Chris CH     
Hello Tom !
So finally we did everything you recommended and are glad we had such valuable advice.

We lifted the boat with a manual crane (120 year old!) on a 4-wheel trailer.
It was the first time since we have the Dauntless (in fact 3 years) that it got out of the lake
and I'm relieved we found a good way to do it. And we also raised the motor with the crane.
Then we waited another couple of weeks for a Permatrim aluminum foil, which you can't find in Europe,
and here are the results :

on a "medium calm" lake with a ~half full tank and

1 adult : 54 km/hour = 33 .55 MPH at 5900 RPM
2 adults : 52 km/h.
3 adults : 50 km/h. = 31.07 MPH at 5800 RPM
4 adults : 48 km/h
5 adults : 46 km/h
6 adults : 44 km/h = 27.34 MPH
On a very flat lake wiith just one person and half full tank: 56 km/h = 34.8 MPH at 6100 MPH
As you predicted...

We still have some porpoising, but much less with the Permatrim foil than without.
And considering from where we started off...
The foil is just on top of the water when the boat is planing, but the shape of the Permatrim generates 2 sprays of water behind the boat. The aluminum plate is bend down on both sides. This isn't a problem for us, but maybe it could be in your opinion (?)

One last question on this performance subject : there is a ventilation hole in the prop.
Would there be a reason to try to close it partly or fully with a vent plug or Mercury PVS plug, if they fit ?
I read some of your answers on the subject, but I can't figure out what would make sense in our case.

Thank you very much Tom for sharing your great knowledge in this step by step undertaking.

There are still some steps to be taken : while doing the anti-fouling painting, we saw that the gelcoat has an osmosis problem.
We'll try to take care of this in winter - with the help of this great website.
: )

Tom W Clark posted 08-09-2014 11:50 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Christiane -- I'm pleased to hear your boat is performing so much better.

If the spray coming off the foil is not bothering you and not spaying the motor itself, then leave it be. That's just part of having the foil.

The propeller has three 5/16" vent holes. Mercury PVS plugs will not fit those holes and I do not think you need to fill them unless you feel there is any propeller slippage during semi-planing boat speeds while wake boarding, for example.

The vent holes are there to help a four stroke motor like yours to accelerate by allowing a little partial ventilation to get the motor into a higher RPM range where more toque is generated.

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