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Author Topic:   Prop for 18 Dauntless
TomT posted 06-19-2004 09:46 AM ET (US)   Profile for TomT   Send Email to TomT  
I am looking for advice on propping a 125 classic 2 stroke on an 18 Dauntless. Both are year 2000 and it is used in small inland lakes. I have a 17p and a 19p rapture ss to chose between (have a 17 black max as a spare) and the normal load is 3-4 fishermen. The operating range is 4750-5250 and peak hp is at 4900 and redline at 5500 as I understand it.

Tests with 2 people:

The 17 produces 27mph/4000rpm, 31@4500, 35@5000, 38@5300 and 39.6@5400 WOT.

The 19 produces 29mph/4000rpm, 4800/39.6 and 4950/41-42+ WOT.

Tests with 7 people:
17p @ wot into wind 5050-5250 rpm (rarely have that load). 19p wot4650-4700 into wind. 17 has a noticably better holeshot fully loaded but with a light load the 17 & 19 vented seem similar.

The difference I notice is in the cruising range of 4200-4400 (about 33mph) where the 19 feels better (2-3 people), is running 3+mph faster with a quieter motor. The 17 in that rpm range is 30 mph and has gotten on plane but it seems the extra 3 mph on the 19 make it skim better, steer better, etc. The ss certainly has less blowout than the aluminum and trims easily. Per Whaler customer service, the standard engine height is the 3rd hole (middle hole) and mine is up one (in the 4th hole).

Two prop shops, whaler customer service, and mercury say to run the 19 as it is at the lower to middle end of the recommended operating range and goes faster at lower rpms. It seems that most people on this chat site recommending propping all the way to redline to let the engine breathe. That motor is a lot quieter and more economical in the 4000-5000 rpm range so I do most operating there.

Any thoughts on the 17 vs the 19 regarding engine wear and tear? I am running with open vent holes and have not experimented with that. One thought is to keep both and switch to the 17 with larger loads.

Lars Simonsen posted 06-20-2004 09:52 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
If you can't reach redline with the 19p prop, it's too much prop. My understanding is that if your motor can't push the prop to redline, the prop may overload your engine and cause damage to the engine. Personally, I'd stick with the 17. I've got a 19p on my 18' Dauntless, but I have the 135 Optimax motor.

If the 17p you've got now is aluminum, you might get a bit more speed with a stainless steel prop of the same pitch.


TomT posted 06-21-2004 08:39 AM ET (US)     Profile for TomT  Send Email to TomT     
Thank you for the input. At WOT what rpms and mph does the 135 run and what is the redline?
Lars Simonsen posted 06-21-2004 07:45 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
At WOT, with the motor trimmed out completely, I reach redline (5600 rpm), and with a full tank, and two occupants (usually me and one of my sons, the oldest of whom is 13), I can get 52 mph or so (also depending on wind/wave conditions). It's very fast, but not a terribly comfortable speed to travel.

Have you checked whether your motor is mounted at the right height? If it's hanging too low on the transom, that can affect top speed as well as whether or not you can reach redline. You mentioned that you get less blow out with the 19 pitch prop, which may mean you have your motor mounted high enough (if the motor were too low, you'd probably not get much if any blow out).


Dauntless18 posted 06-21-2004 08:53 PM ET (US)     Profile for Dauntless18    
Good to see your posts. Very helpful. Had the boat on LI Sound on Saturday (ran great), but noticed a few things. 1. Excessive bow-rise on hole-shot, 2. Occasional "inability" to get on plane - usually works itself out and 3. WOT gets to about 4,900 (just me in the boat). It actually planed more easily when I had two families in the boat which kept the nose down and did not allow the bow to point skyward.

The boat came with a SS Mirage (don't know the pitch) propeller, but it has a small ding that, when worked out left a small ragged edge. Hence, I too am thinking about a new propeller.

Would like your thoughts. Also, I am still on the second from the bottom hole (of five) for the engine mount. Think I should move it up one?


Lars Simonsen posted 06-21-2004 09:38 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     

You also have the 135 Optimax, don't you? If so, I think you could raise the motor one more hole. From the "symptoms" you're reporting, it sounds like your prop has too much pitch. Raising the motor may help some. I'd try that before I shelled out the bucks for a new propellor. The "rule of thumb" (if I recall the rule correctly) is that you get an extra 200 rpm for each hole you raise the motor. So if you're only able to get to 4900 rpm, then you should get to about 5100 by raising it another hole. That's still not the redline of the optimax, but if you trim the motor out to try to squeeze out the last bit of speed, that could raise the rpms up a bit more.

From your description, I doubt that the ding in your propellor is causing your problems, but it may be a small factor. The mirage is a good prop. If it's just got a small ding, instead of replacing it, you could take it to a prop shop. For a lot less money than a new propellor, they can make it like new for you.

If you could find out what the pitch of your prop is that would also be helpful.

Also, when you're trying to get on plane, you have to trim your motor all the way down. The Dauntless hull seems to be very "sensitive" to trim adjustments. If you don't have your motor trimmed all the way down, you'll have lots of bow rise and will have a hard time getting on plane. I always trim my motor down as I'm coming off plane, so that when it's time to get going again, the motor's all the way down (now that I have trim tabs, it's less important to do that).


TomT posted 06-22-2004 09:41 AM ET (US)     Profile for TomT  Send Email to TomT     
Thanks Lars,
My engine is one hole higher than the factory setup 4th hole from top. The 17 I am testing and reported stats on is stainless and may be the way to go. It is just odd that Mercury, 2 prop shops and Whaler customer service recommend the 19 that only hits 4950-5000 yet everyone else recommends propping to be able to hit redline to save engine wear. Maybe Jimh or someone from whaler can tell us all how low, is too low for max rpms when propping. It seems that the other end of the equation is that you can cruise faster turning lower rpms by propping at the lower to mid of the operation range. Thanks & I wish I had the 135. Let's stay in touch on other D18 issues.
Lars Simonsen posted 06-22-2004 10:39 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     

Sounds to me like your motor is properly mounted. I would stick with the 17p. I have no idea whether or not the 19p would damage your engine, but it makes sense that it would, and I wouldn't want to risk it.

It's always nice to see more 18' Dauntless owners posting here!

Dauntless18 posted 06-23-2004 12:18 PM ET (US)     Profile for Dauntless18    
As always, you are a wealth of information. Thanks. Yes, you are correct, I have the Opti 135 (1998). I don't know how to check for pitch, but will see if someone at the marina knows. Is your 135 in the middle hole (3rd from bottom?) Also, my performance in 1-1.5 ft chop (plus up to 2.5ft swells from wakes etc.) was excellent with two families on board (kept the V slicing the waves). What is your experience with the tabs in that type of water? Finally, what pitch / type of prop are you running with?


Lars Simonsen posted 06-23-2004 10:23 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     

My motor is mounted in the third hole (I know it's third from the top anyway). If that's where yours is mounted you should be in good shape. I have a 19p Stainless Steel three blade Stilleto prop. I got it at Sal Mercurio's recommnedation, and I'm very satisfied. I got it from; the price was very reasonable, and they shipped very quickly. Someone recently posted a link to a place that had them even cheaper than, but I don't remember the web site address.

I remember reading your post about having 8 people aboard your boat. I thought about it last saturday because I also had a large load (6 kids and 3 adults). I didn't need to use the trim tabs at all! With all that weight it does ride very nicely. It's somewhat akin to having the trim tabs, but the tabs don't add all that weight!

The tabs definitely improve the boat's choppy water performance.

The pitch of your prop will usually be printed at the end of the "serial numbers" on the hub of the prop (somewhere between the blades). With my original aluminum prop, it had been sent to a prop shop, where it was repainted, and a new number stamped into it. It was hard to find the pitch numbers, but after scraping a little paint, I found them. That prop was a 17p, and with it, I could easily exceed redline, and when I raised the motor, I got a lot of blow out. The stilletto seems to "grip" the water better, and provides a lot of stern lift.


Dauntless18 posted 06-24-2004 11:12 AM ET (US)     Profile for Dauntless18    
Oops. I posted that as a new topic by mistake. Sorry Jimh.


Thanks. Yes, I am in the fourth hole from the top, so maybe I will try moving up one. I will also look into the Stiletto. Are there any other "lifting" props you have checked out? Also, does that mean stern lifting - I have only seen reference to bow lifting props on Mercury's site (teasing myself with thoughts of a High-five, etc. though I have no clue what they would do for me... or against me).

bkloss posted 06-29-2004 04:32 PM ET (US)     Profile for bkloss  Send Email to bkloss     
My 180 (135 optimax)came from the factory with the motor mounted all the way down and I am definitely going to raise it two holes. WOT for me is 4900-5000 with a 17 ss prop-no where near red line for this motor. It's a great ride slicing through the waves with eight people in the boat but when I want to take her out, alone, and hit the waves; I'd prefer my internal organs to stay in place.


Lars Simonsen posted 07-02-2004 10:34 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     

I would definitely not use a bow lifting prop on the Dauntless. The Dauntless already has plenty of bow lift. The reason for the rough ride in choppy water is that the bow is too high to cut through the waves. Instead the waves slap up against flatter bottom of the boat. Stern lift is what the boat needs, which is why the trim tabs make for so much of an improvement.


Raising your motor two holes will help. You may end up needing to put on a hydrofoil (or, even better, trim tabs) to give you some extra stern lift and keep the boat in a more bow-down attitude.

jimh posted 07-03-2004 10:43 AM ET (US)     Profile for jimh  Send Email to jimh     
I do not believe it is recommend to operate the Mercury 125-HP four-cylinder "classic" outboard above 5250 RPM.


bkloss posted 07-04-2004 08:25 AM ET (US)     Profile for bkloss  Send Email to bkloss     

I raised the motor up 2 holes yesterday and I am headed out to San Diego Bay in about an hour to test her out. Should prove to be interesting. I already have a dol fin so we shall see. I may experiment with the props as well to see the differences but after some hours are put on this motor with the changes already made.

bkloss posted 07-04-2004 07:56 PM ET (US)     Profile for bkloss  Send Email to bkloss     
All I have to say is awesome!!!!!

What a complete diference in the way the boat rides and handles. I was able to get an extra 500 rpm's at WOT (45 mph - GPS) and I now have the ability (most of the time) to slice through the waves or gently roll through and over rather than slamming up, over and down - like before.

I'm curious though; if it makes such a positive difference - why does the factory mount the motor all the way down?


Lars Simonsen posted 07-05-2004 09:06 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     
Glad to hear raising the motor made such a difference for you. As to why they mount the motor so low, I have no idea. I assumed it was the dealers that did that (although I know that Boston Whaler now pre-rigs their boats at the factory, but I don't know when they started doing that).


Dauntless18 posted 07-06-2004 07:45 PM ET (US)     Profile for Dauntless18    
Thanks for the trim info. Since reading your post, I have kept notice on the trim and have always started at full-down. What a difference (OK, so, I'm still learning). I also have taken to pushing the throttle a little faster forward to "jump" onto a plane and that seems to help (as opposed to babying it too much). Given your and BKloss' experience of being in the third hole, I will try to get the marina mechanic to raise the motor one more hole and see what happens.

By the way, do you fresh-water flush your engine? If so, where is the access port to put the water in? My mechanic said there isn't one (not sure I believe him).


Lars Simonsen posted 07-06-2004 09:57 PM ET (US)     Profile for Lars Simonsen  Send Email to Lars Simonsen     

See my response to your post on the flush port. I generally only flush the motor if I'm putting it up for a long time (never), or if I've been in salt or muddy water.

Yes, I personally see no reason to "gradually" get on plane. Make sure all your passengers are ready to get going, and then go ahead and jump the boat up on plane. Once you get on plane you can ease back on the throttle and start trimming the motor up. When the water is smooth, you can really feel the boat respond to the change in trim; everything suddenly smooths out, and RPMs rise, and the boat speeds up (if you go too far up, you'll start to porpoise).

Learning is most of the fun! I'm still learning, too.


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