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Author Topic:   Porpoising 160 Dauntless
Carolina_Whaler posted 07-03-2003 11:45 AM ET (US)   Profile for Carolina_Whaler   Send Email to Carolina_Whaler  
Just stumbled across your site and hope some of the Whaler gurus here can help me. I have a 16' 2002 Dauntless with a 100 HP 4-stroke Yamaha. This thing porpoises like crazy no matter how I trim it out. Is there something else I'm missing?? Also, I haven't fully tested this out (we haven't had the boat too long) but I've had the boat loaded with 4 kids on several occasions and I don't have a problem but get an adult in the back, someone in the front and it seems to be a major pain. I hate to install trim tabs but am not sure if this is a problem with the 16' Dauntless. I've heard some discussion about this on several other occasions but when we went for water test the boat didn't seem to produce the problem.
Jarhead posted 07-03-2003 03:07 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
I think what you're going to hear is to raise the engine on the transom a hole or two and or a hydra-lift or other fin.

I have a '03 160 Dauntless w/115 4s Merc. and have never had a problem with porposing. Engine all the way down on transom, prop that came with the engine [13.25' 16P SS] and no fin.

Guess I'm just lucky. :) Good luck..

JohnJ80 posted 07-03-2003 04:42 PM ET (US)     Profile for JohnJ80  Send Email to JohnJ80     
I have a [15 Daunltess] and went through this exact [problem] this year when I repowered from a 237lb 70HP Johnson 2 stroke to a 75HP Evinrude 324lb FICHT DFI motor.

My bet is your yamaha is on the heavy side for the boat but I'm not qualified to judge that. The fact that moving weight around has a big effect on the porpoising sort of supports the fact that you are out of adjustment. My experience with a 15 Dauntless is that once you are in the groove, it just isn't all that sensitive to weight placement as being out of the groove. (All small boats are sensitive to one degree or another).

Here is what i did:

1. Dealer mounted motor all the way down. Ride was awful, porpoised like the real thing.

2. Moved motor all the way up so the AV plate is 1.5" above the lowest point of the hull. Moving up one hole to even made a huge difference in ride, but porpoising still there. Went up one hole, added fin, then the rest of the way up. You need to experiment with this.

3. Added grand island marine Hydro Lift foil on AV plate. Major major change. Porpoising 75% eliminated trim range increased, ride improved, hole shot improved.

4. Added a stainless steel stilletto prop removing the aluminum one. Stainless prop has more cupping better 'grip' on the water. this really helped to raise the stern and make boat run much better.

At step 1, I couldn't run the boat except with motor trimmed all the way in. In any sort of chop, it was unusable unless you wanted to beat out your fillings.

Step 2 improved the ride dramatically and got a little trim back. Still had V shaped spray off the lower unit at speed.

Step 3 got me to be able to trim to 0-30% of trim range based on the gauge. Biggest single improvement overall in ride, porpoising, exhaust noise and hole shot.

Step 4 put it all together. I can now in flat water trim to 100% of trim range, speed is increased, performance is better than with old motor.

I highly recommend the Grand Island Marine Turbo Lift fin. Great product. There are performance differences between fins.

I feel the same with Stiletto props but I have little to compare to other prop mfgs. Sal recommends Stilletto and he really seems to understand props.

Do it in this order:

1. motor height
2. fin
3. prop

If you can't get it with that, you can do trim tabs. I would be really surprised if you couldn't get it with the process above. this all costs a lot less than tabs and you should do it anyhow.

Check out

for the whole process I went though in this adjustment to solve the same problem you are.


jimh posted 07-04-2003 11:09 AM ET (US)     Profile for jimh  Send Email to jimh     
The tendency for a hull to porpoise seems fairly common, particularly in smaller boats. Porpoising is an oscillating condition, and it starts when the normal hull pitching up and down in waves feeds back on itself and the magnitude of the oscillations tend to increase rapidly.

I don't think even among experts--marine hull designers, naval architects, etc.--that there is good agreement on what happens to cause this. It is a dynamic condition, where the hull and the waves interact, and it is affected by trim and weight distribution.

On most hulls you can reduce or stop the oscillations by changing the engine trim and the boat speed.

There are some reports that porpoising is accentuated by use of heavier outboards, but I don't know of any real evidence that this is true.

You can probably get any Boston Whaler hull to porpoise, it just seems some have a very wide window of conditions that will lead to these osciallations beginning and growing in amplitude, while others have only a narrow range in which the oscillations can sustain themselves and they are easy to suppress with a minor speed or trim change.

I think the suggestions you have received are good ones, and you might find that you can affect the porpoising by implementing some or all of them. I'd start with raising the motor mounting.

Dick posted 07-04-2003 07:41 PM ET (US)     Profile for Dick  Send Email to Dick     
I agree with all of the above. Start with raising the engine, Whalers rigging sheet specifies one hole up.
You need to experiment, I ended up mounting the motor with two holes above the transon on my Montauk.


Marlin posted 07-05-2003 08:24 AM ET (US)     Profile for Marlin  Send Email to Marlin     

Jarhead's nailed it. I have the same boat as him- 2003 with a Merc 115 4s, with the Vengeance 13.25 x 16. I raised the engine by 2 holes, so the anti-ventilation plate is about 1-1/8" above the transom bottom. The ride improved significantly, and the porpoising decreased as well. At this height, my prop ventilates a little too easily, so I need to tweak things a little more. With a couple of adults in the stern quarter seats, planing off is a little slow. A foil would probably help, but that's not on my immediate to-do list. With the boarding ladder and sonar transducer, I don't know that there's a lot of room left for trim tabs.

Jarhead, what kind of speed numbers are you getting, and what's your WOT RPMs?


Jarhead posted 07-05-2003 10:41 AM ET (US)     Profile for Jarhead  Send Email to Jarhead     

On a fairly large lake. Wind speed 5 to 10 MPH, light load, full tank.

42-43 MPH- GPS, both ways. WOT- 5700-5800 RPM.

That's with the engine on the first set of holes [all the way down], trimed out about half.

Your numbers?

I have no real problem with the ride or porpoising however I must say with all I've heard on the subject I'm intrigued with the idea of raising the engine one set of holes... :)

Marlin posted 07-05-2003 12:53 PM ET (US)     Profile for Marlin  Send Email to Marlin     

Sounds like your numbers match mine pretty well.

3200 RPM, 19.8 avg
3500 RPM, 24.3 avg
4000 RPM, 27.7 avg
4500 RPM, 32.2 avg
5000 RPM, 36.7 avg
5500 RPM, 40.3 avg
6000 RPM, 43.8 avg
6200-6300 WOT, 44.5 avg

I *still* can't figure out why I can't make the numbers match up on JimH's prop calculator (tried it myself in Excel, got same numbers). I need 0% slip to make these numbers work out, and that's obviously wrong. Experimentally verified the 2.07 gear ratio. That 16" Vengeance must be more than 16"...

Raise that Merc one hole, you won't regret it.


Jarhead posted 07-05-2003 01:33 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     

Well now you've gone and done it.

Guess I'll have to see what all the hub-bub's about. :) :)

Perry posted 07-05-2003 03:29 PM ET (US)     Profile for Perry  Send Email to Perry     
Carolina, does your hull have the cut-away or notch at the bottom of the hull at the transom? Whaler made a design change in the middle of the 2002 model year in which they did away with the notch. This change in design is supposed to improve the porpoising problem as well as the bow-up ride characteristic of the Dauntless 160. I also raised my 4 stroke 90 2 holes on my Dauntless 160 and saw a big improvement in performance.
Carolina_Whaler posted 07-07-2003 06:37 PM ET (US)     Profile for Carolina_Whaler  Send Email to Carolina_Whaler     
Thanks for all the great suggestions. You guys are amazing! I'm planning on stepping thru the solutions you've provided. Do you take your boat to the Whaler dealer/Yamaha dealer to move the engine or do you have capabilities in your garages to make those changes? Seems like a lot of back and forth to the dealer but certainly worth it to get this issue resolved. The problem is that the dealer I bought it from is 5+ hours away in another state. I haven't contacted the local Whaler dealer yet to ask about this. Since my engine's a 4-stroke Yamaha, I'm not sure how helpful they'll be but this boat's still under warranty.

Perry, this boat does not have the notch in the hull; its all V. I've see that the engine is already up on the second notch

lhg posted 07-07-2003 08:08 PM ET (US)     Profile for lhg    
Porpoising is ALWAYS caused by excess engine trim, even if the engine is all the way in. The Classic 1978-84 Outrage 20 suffered from this problem when equipped with an OMC 175 HP engine of the time. That engine had inadequate tuck-in trim range. The boat hull design can enhance it, so can engine weight, but engine trim, and or boat loading, can always overcome it. Passengers can't always sit where they want to. Mercury has always advertized that they have the broadest trim range, and I believe this to be true. Note that the problems mentioned here are Yamaha and OMC engines, with the Mercury engine performing well on the Dauntless 16.

Engine mounted fins (stern lifters) are not the answer to this problem, as in order for them to function at planing speeds, they must be running in the water, causing considerable extra drag and loss of top end, wasting fuel. Several manufacturers (such as CMC) make aluminum "transom wedges", thicker at the top, which allow the outboard additional "tuck-in" range, which is evidently what is needed with certain engine brands. This would be my recommendation, and it is a simple installation.

The solution for Marlin, with the ventilation problem, is to get a prop intended for surfacing operation. Since Mercury does not go this low in pitch with their performance line, a Stilleto, Michigan Wheel Rapture, or Cabela's performance, might be the answer, probably 17" pitch. Otherwise, keeping the Vengeance, the engine should come down one hole.

Marlin posted 07-07-2003 10:14 PM ET (US)     Profile for Marlin  Send Email to Marlin     

Thanks for your suggestions. I've pretty much concluded that although I tach a little high with the 16" Vengeance, a 20" Laser II is probably too much prop (unless those hub vents are magic!). Yesterday I dropped the engine one hole, leaving me about 3/4" above the hull bottom, but I haven't yet had a chance to try it out. I'll take a look into the other prop types that you've mentioned, at the moment I know nothing about them.

It's pretty clear over the course of several of your posts that you are, in general, not a fan of engine-mounted foils. However, I think a foil might help this boat with 2 specific "issues" ;-) -- lowering the speed that it'll stay on plane (currently 19 MPH at about 3200), and getting on plane faster when loaded down. I'd intend the foil to run out of water at faster planing speeds. I'm especially interested in getting the planing speed down for improved ride in chop. I think the boat has an absolutely terrific ride, but c'mon, it's still only a 16-foot boat. I'd be interested in your thoughts on this use of a foil.

Carolina, I've now moved the engine height twice on my own (second time was a lot faster), using the approach that a few others have mentioned. I back the stern just barely into my garage, tie a line from the engine lift points to a stud-mounted fitting above the garage door to give a little vertical support, then block the skeg on the floor so that the engine supports its own weight. Two more lines from engine to stern cleats steady the engine side-to-side. The bolts come out, a few cranks either way on the 3rd wheel raises or lowers the transom, and the bolts go back in with a bunch of 4200 sealant. It's not hard, but it requires a certain amount of confidence. I wouldn't want to have to pick up a 400-pound motor off the garage floor and try to put it back!


Jarhead posted 07-08-2003 08:05 AM ET (US)     Profile for Jarhead  Send Email to Jarhead     

Great tutorial on engine height adjustment.

When looking over the various methods posted previously I noticed others have used the same but I was concerned about putting the weight of the engine on the skeg.

It appears my concerns are unfounded. I do think I'll use a 4by4 under the skeg as a cushion however just for peace of mind. :)

Perry posted 07-08-2003 02:10 PM ET (US)     Profile for Perry  Send Email to Perry     
I used my chop saw to put a little cut in a piece of wood for the skeg to fit into snug. It worked well.
Jarhead posted 07-08-2003 05:24 PM ET (US)     Profile for Jarhead  Send Email to Jarhead     
Looks like I won't be needing the 4by after all.

Called my Whaler dealer today and he said they'd do it for me at no charge :) :)...

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