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I repowered my 1997 Dauntless 15 with a 2013 Mercury 60 hp 4-stroke last summer. The dealer mounted the engine 2 holes up.

o
o
o <- bolts through this hole
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o

This places the anti-ventilation plate 1-1/4 inches below the bottom of the hull. Prop is a Mercury Spitfire 10.3 x 13, recommended by the dealer.

Some performance figures for this setup: Planes in about 4-5 seconds (estimated, I don't have exact measurement).

Top speed 33-34 MPH by smartphone GPS at 6000 RPM WOT with 2 passengers (350 lbs), 1 dog (65 lbs) and 6-8 gallons gas.

Boat porpoises with what seems to be minimal trim up especially into the wind. I can often see water streaming up the front of the engine into the splash well, depending on trim position.

The new engine starts easily, no smoke or smell, runs smooth and quiet and fuel economy is better, in comparison to the old 1997 Merc 75 hp 2-stroke.

My questions: Is this the best top speed that I can expect? The Mercury web site prop selector suggests about 39 MPH top speed.

Can I decrease the boats tendency to porpoise? I suspect that the engine needs to be raised at least one hole, based on many posts and threads that I've reviewed. Will raising the engine cause excessive prop ventilation or increase RPM over 6000?

I don't understand how to use calculated slip to determine prop selection. Are there other props that I should consider or test?

Thanks in advance for the experts and moderators replies. I've learned a lot from this site.

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Sadly, many, if not most, dealers are not very good at propping boats.

Your boat should not porpoise and should be considerably faster.

I recommend the motor be raised two more bolt holes and a good stainless steel propeller installed.

If you want to stay with a Mercury propeller, try the 10-1/2" x 13" Vengeance or 10-5/8" x 13" Trophy Sport

I expect the boat to be good for 39-40 MPH with just you onboard and 36-37 MPH with an extra passenger and big dog.

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Thank you, Tom. What performance differences might I see between the 2 props? I've read the Mercury web page information about both, but it's hard to distinguish any differences by reading.

I'm not committed exclusively to Mercury products. I've noticed that you often suggest Stiletto props for similar sized boats, for a variety of motors. The economic pricing of this brand is also attractive. Are there any Stiletto or other props which you would suggest that I consider?

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You'll have to test both the Vengeance and the Trophy Sport to find out the differences. Do not rely on marketing babble, that's not going to get you anywhere.

I often recommend Stiletto for two reasons:

- They are VERY good value

- They often are a better option for the mid range motors where Mercury really doesn't offer much.

For a Mercury 60 HP FourStroke, Stiletto offers two models: The Triad and the Star.

What Stiletto can't offer that Mercury can is a cushioned hub that reduces shift clunk and prop rattle. The 3.0 Mercury propellers now come with their proprietary Reflex hub kits designed to alleviate the annoying prop rattle.

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Hello gbollin and regarding the Dauntless 15 being sensative to positive trim, they are. You will need to test your set-up (with safe water conditions) for a trim setting that will afford you good performance just before the hull begins porpoising.

Good weight distribution within the boat is very ideal. Where is your battery located? Current fuel capacity? Is the fuel tank (or tanks) still located within the helm seat area?

I unfortunately cannot suggest a prop selection but Tom is very knowledgeable and will offer sound advise. If you know, what is the weight of your outboard? Ideal motor height would place your cavitation plate from 1.0 to 1-1/4 inch above the keel center-line without prop "blow-out" or cavitation as some say. For this height change you will need to consider a stainless steel prop.

Happy boating to you...
Angel M.