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Author Topic:   Dauntless 160 performance
Marlin posted 06-16-2003 02:41 PM ET (US)   Profile for Marlin   Send Email to Marlin  
I'm going to climb the Continuous Wave mountain to ask some more questions of the gurus who live here at the peak...

I have a 2003 Dauntless 160 with a Merc 115 4s. This past weekend I raised the motor from the lowest hole (ventilation plate about 1/8" below hull) up to the middle of 5 holes. The plate is now about 1 1/4" above the hull when trimmed level.

I was out yesterday to test it out. Just planed off at 3200, the plate rests on the water. Between 3500 and 4500, it's probably about 1/4" above the water surface when trimmed level, trimmed down it touches the water. As all the other messages lately have said, the ride improved significantly- much less porpoising, and just generally seemed softer. I'm not sure what makes that possible, but there it is anyway.

I'm propped with a Vengeance 16" pitch (I previously said it was a 19" pitch, proving I can't read). Before raising the motor, I couldn't sustain WOT without exceeding the 6000 RPM limit, which I've been careful not to do. I didn't have the chance to test it out yesterday, but if anything that problem will now be worse, not better.

Okay, on to my questions:

1) Back when I thought my pitch was 19, lhg suggested a 20" Laser II instead. Since I now know it's 16, would the recommendation still be a 19" or 20" Laser II?

2) I find that I now break out much more easily when trimming up or turning hard. I think the motor is probably a bit too high for the Vengeance. I've seen the Laser II described as "surface piercing" and "better holding", would it be likely to improve breakout at this motor height?

3) What kind of performance change would I expect to see by going with a High Five instead?

4) When I use the propeller calculator and plug in all the right numbers (5900 RPM, 2.07 ratio, 16 pitch, 45.5 MPH) I get -6.9% slip. What's with that? The easy answer is I'm doing something wrong, but the 5900 is right off the tack, 2.07 is from the Merc website for the 115 EFI 4s, 16P is stamped on the prop, and 45.5 is from my Garmin Map76S, in two directions.

Well, that turned out a lot longer than I expected...

-Bob

Bigshot posted 06-16-2003 02:55 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Speed is wrong. 16" pitch on a 2.07 you are in the mid-high 30's. Try a 18 or 19" prop, 16" way to small.
Marlin posted 06-17-2003 12:35 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Bigshot,

It's hard to disagree with your conclusion. However, I've measured 44+ MPH on the GPS on 3 different days. Even if the tach isn't quite accurate, I'm told the 115 EFI has a rev limiter at about 6200, so I can't be over that. I have to assume that Merc is competent enough to list their gear ratio correctly, and to stamp the prop hub correctly. Now I'm wondering whether I was wrong about being wrong about the 19" pitch. I'll get the entire part number off the prop next time I'm over to the boat.

My measurement technique for all this wasn't particularly exacting, so there's some modest margin for error in revs and observed speed, but putting conservative estimates (higher revs, lower speed) into the prop calculator still only gives me about 0% slip. Obviously, at 0% slip you have 0 degrees angle of attack, and so 0 thrust.

Well, any way you look at it, I need a taller prop. I guess the question still remains, Laser II or High Five?

-Bob

jim_usa posted 06-17-2003 02:39 PM ET (US)     Profile for jim_usa  Send Email to jim_usa     
Marlin, Is that a four stroke? Because There's a guy in NJ selling a 2002 160 Dauntless with a 90 2 stroke saying he's had it up to 54. Sounded high to me.

I'm in the market for a 160 this summer hopefully and am looking to learn more before laying out the cash.

Marlin posted 06-17-2003 03:51 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Jim, yes, it's a 4-stroke. Nice motor, very quiet. 54 sounds unreasonably high with a 90. There are a couple people with 160s and 90 2-strokes on this site, I'm sure they can provide better information. I seem to recall reports of speeds in the low 40s.
Sal DiMercurio posted 06-17-2003 07:30 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Marlin, "WOA" a second, first lets answer your 1, 2, 3, questions
Question #1, yes you should "TRY" a 19 pitch prop, but being you can't give us your max rpms with the 16 pitch we may have to change the 19 to ??? wont know until you try the 19.
I would use a performance prop being your blowing out.
Question #2, it's called blow out, not break out,.....if you go to prison, you might try & "break out", prisoners break out, props blow out.
Question #3 I really dont feel your outfit needs a High 5.
Question #4 for some reason, I dont think your gps is giving you the correct speed, thats pretty fast for twisting a 16p prop.
On your next post down, you mention 0 slip so 0 angle of attack, 0 slip will give you 100% of angle of attack, then you mention o slip equals 0 thrust,.....you have it backwards, 0 slip will give you 100% thrust with no loss at all.
Then you mention you need a taller prop, nope, taller is diameter, you need a longer prop which is the pitch.
If that were my boat, i'd put a 13.25 x 19p Stiletto on it & go from there.
Sal
Marlin posted 06-17-2003 10:19 PM ET (US)     Profile for Marlin  Send Email to Marlin     
Sal, thanks for your comments. I've been boating a long time, but I'm much more adept at trimming a genny than at picking a high-horsepower (to me, that's anything bigger than a 9.9!) prop. It's amazing how much I've learned, and am still learning, from the people on this site. I'll see if I can't try out a 19" and see where that takes me. And I'll try to avoid the need for breakouts in the future ;-)

On the 0% slip comment, let me clarify what I meant- if the prop is operating with 0% slip, then by definition it's at 0 degree AOA, where the blade is encountering the water exactly straight on. A prop blade, like a wing, needs a positive AOA to generate significant lift/thrust, at 0 degrees AOA it's just coasting.

As for the top speed I'm getting, nobody has cleared up my confusion by saying "hey dummy, you forgot to account for ...", so I think I won't comment on that further until I do some more careful testing. Hopefully that will clear things up on its own.

-Bob

cmarques posted 06-17-2003 11:00 PM ET (US)     Profile for cmarques  Send Email to cmarques     
I have 2002 Dauntless 160 with the 90 2 stroke- could top out at 41 mph with top down and large unaerodynamic body tucked behind windscreen. After installed doel fins the boat rides much better but even with diet cannot exceed 38 mph anymore.
jimh posted 06-18-2003 12:14 AM ET (US)     Profile for jimh  Send Email to jimh     
If you are confident in the GPS measurement of boat speed, then something else must be off.

Perhaps the Tachometer is not set correctly?

Or the lower unit ratio is actually something other than 2.07? Are you certain te 115-HP 4-stroke has that ratio? If you plug in 1.86 you get much better numbers.

Or the prop pitch is more like 17 or 18?

When you come up with a negative number in the SLIP column it means the boat is going faster than it ought to with the other parameters set to their instant values.

--jimh

jim_usa posted 06-18-2003 11:32 AM ET (US)     Profile for jim_usa  Send Email to jim_usa     
Is there a chance that the weight of the 115 4s on that boat is a problem?

I've heard of porpoising problems on the 2001 & 2002 ? pocketed hull 160's. But I was told this problem was fixed mid 2002 when they stopped making hulls with pockets.

Marlin posted 06-18-2003 12:10 PM ET (US)     Profile for Marlin  Send Email to Marlin     
In my opinion, the 115 4s weight is not a problem with regards to static trim. I've had 4 adults in the aft seats and helm seat with a full tank of gas, and no water in the splashwell drains. That filled-in notch has got to help; it probably adds about 2 cubic feet of displacement, or about 125 pounds of buoyancy.

Planing off with the same people required liberal application of the throttle. The lighter 90 2s might make that easier, but on the other hand you'd have 20% less power available. I'd rather have the power.

Jarhead posted 06-18-2003 04:54 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
Sal..

Not to bust your chops or anything but a tire "blows out" a prop "breaks loose". [page 5, installation manual, Mecury 115hp 4 stroke, 90-10216020 April 2001, Mercury Marine]

Sal DiMercurio posted 06-18-2003 06:16 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Yeh, but they dont break out, usually prisinors & kids faces break out.
LOL.
Sal
Jarhead posted 06-18-2003 07:07 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
And what money seems to do from my wallet...:)
fno posted 06-24-2003 12:23 PM ET (US)     Profile for fno  Send Email to fno     
Raised my motor this weekend by two holes to the fourth one from the top. Originaly it was mounted in the second hole putting the cav plate at the keel. By the way, this is a 2000 notched transom with a 90 4 stroke Merc with a Doel fin. What a difference, started with the 14 pitch and it jumped out of the water. Put the 15 on and it was more like before the lift job as for planing but now goes 40 mph compared to 37.5 pre lift. Have noticed some break out on sharp turns on the river. I have not tried it out in ocean yet to see how it performs in rougher water. I might stick with the 14 pitch prop and take off the fins next. Overall ride characteristics are much better than before.

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