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Author Topic:   18 Dauntless Prop
M Gould posted 11-12-2014 07:45 AM ET (US)   Profile for M Gould   Send Email to M Gould  
Repowered my 1998 Dauntless 18 late summer with Suzuki 150 four stroke. Have it 2 holes up (same as I had Optimax in the past) .

After break in, this will run WOT at 6000 RPM and hit rev limiter at between 44.5 and 46 mph by GPS. Prop is Suzuki stainless 15 1/2 by 19. It is ridiculously powerful and is perfect for pulling skiers, tubes, etc. I want a prop for the fall/winter cruising on the lake which usually is me only or with one other person.

I was thinking of going up to a 21 or 23 pitch and dropping to a 14 ish diameter.

I have purchased from Tom Clark in the past with excellent results for the Optimax. (Stiletto 19p and 17p props are for sale or trade !)

Any thoughts ? It would be fun to go over 50 on this boat and I am sure if propped correctly this motor will do it.

masbama posted 11-12-2014 02:28 PM ET (US)     Profile for masbama  Send Email to masbama     
How is the weight of the motor handled by this boat? I have a 1999 with a two stroke evinride 150 and I don't think it could handle much More stern weight.
M Gould posted 11-12-2014 03:36 PM ET (US)     Profile for M Gould  Send Email to M Gould     
It sits about the same in the water - I cannot tell any difference. I think when calculating the weight of this motor plus prop is very close to the weight of the Optimax 135 plus prop plus full oil tank (which is removed for the 4 stroke).

Resulting change in power is phenomenal, and the fuel consumption is less at cruise. I have an HDS-7 with a fuel flow sensor. It will use more fuel than the 135 at WOT. Amazing how quiet it it.

I do have Bennett trim tabs which improve the ride as well, but do not need them on calm water if only myself and one other on board.

Only improvement would be hydraulic steering as you can definitely feel the torque of the prop even with the tab adjusted all the way on the skeg.

masbama posted 11-12-2014 07:53 PM ET (US)     Profile for masbama  Send Email to masbama     
Thanks. I have been toying with getting the 140hp or 150 E TEC when my motor goes. I don't have trim tabs but have a jack plate. I have hydraulic steering but it still pulls strong when trimmed down.
Teak Oil posted 11-13-2014 07:57 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     

Dont assume you will gain 4mph by going up in pitch. You may need to raise the motor another set of holes, if you have three sets left you can certainly go up another set without issues.

You can try a Mercury Enertia prop which has good fuel economy and a good top end as well, Boston Whaler equips many new boats with this prop.

Talk to Ken the Prop God, he is pretty good at recommending sizes and better yet he allows trade ins on props.

He will probably put you in a 20 or 21", be sure NOT to get the Enertia Eco

Tom W Clark posted 11-14-2014 01:15 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
The Suzuki DF150 has a 2.5:1 gear ratio and a 6000 RPM redline. I will perform best with a larger diameter propeller like the Suzuki three blade you have now.

If the motor is hitting the rev limiter at WOT, then I agree the pitch should be increased. The fact it *is* hitting the rev limiter makes it hard to gauge just how much to increase the pitch but looking at your tops peed may give a clue.

The boat can go 45 MPH with a 19" pitch prop at 6000 RPM, that is -5 percent calculated propeller slip. That is unusual for that model of propeller Are you sure of your tachometer and boat speed readings?

At any rate, if we think this boat might be good for 50 MPH, and I do not think ter is any reason not to think it is since factory test data I have for the Dauntless 18 shows it capable of 49 MPH with a 135 HP motor, then a 21" pitch propeller would be close.

The 14-3/4" x 21" Mercury MIRAGEplus would be worth trying as well as the 15" x 21" Suzuki three blade.

M Gould posted 11-15-2014 09:30 PM ET (US)     Profile for M Gould  Send Email to M Gould     
Thanks for the help. The tach is brand new with the motor and the speed is by GPS with a Lowrance HDS-7. Tom Clark, any thought on a Stiletto 21 or 23 ?
M Gould posted 11-15-2014 09:47 PM ET (US)     Profile for M Gould  Send Email to M Gould     
Tom (or anyone) - Why would the engine with more horsepower need a larger diameter prop ? I know the gear ratio is different on the 135 Optimax to the 150 Suzuki. Any good real world analogies ? Thanks.
jimh posted 11-16-2014 02:09 PM ET (US)     Profile for jimh  Send Email to jimh     
Larger diameter propellers can have more blade area. More blade area may help produce more water being accelerated sternward. Thrust is proportional to volume of water and how much that volume of water is accelerated. Thus propeller diameter tends to increase with horsepower. Notice how the propeller on a ship with 10,000-HP is much larger than the propeller on a dinghy with 3-HP. This is a general trend.
M Gould posted 11-16-2014 05:08 PM ET (US)     Profile for M Gould  Send Email to M Gould     
Thank you, Jim.
jimh posted 11-16-2014 11:01 PM ET (US)     Profile for jimh  Send Email to jimh     
In outboard engines there is a limit to propeller diameter set by the aperture formed by the propeller shaft and the anti-ventilation plate. Lately it seems like outboard engine designers have been making the aperture larger, and propellers of diameter of 16-inches or more can be accommodated on these newer engines.

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