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Author Topic:   Roostertail
rkp posted 09-26-2003 10:12 PM ET (US)   Profile for rkp   Send Email to rkp  
About a month ago I posted that I had bought a 13 dauntless with 40 Johnson and was having a problem with porpoising. I reported that I raised the motor one hole and installed a wedge and this had corrected the problem mostly. I also mentioned that I had a pretty good roostertail and some responded that I should raise the motor more. I just raised it one more hole and got maybe 2-3 mph more but still have the rooster tail. The motor is peeing well and there is no cavitation. Should I be concerned with the roostertail? Any other comments?

Thanks,

RKP

jimh posted 09-27-2003 12:26 AM ET (US)     Profile for jimh  Send Email to jimh     
Are you talking about:

-- spray coming directly off the engine's lower unit and directed upwards, or are you talking about

--a roostertail breaking the surface and blowing out into the air in the boat's wake, 5-10 feet behind the boat?

Bigshot posted 09-27-2003 12:59 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
roostertails mean you are shooting some water......enjoy it!
adaps4 posted 09-27-2003 01:08 AM ET (US)     Profile for adaps4  Send Email to adaps4     
I have the same thing- I have a jack plate, and the cavitation plate is about 1/2 inch above the bottom of the transom. Before the jack plate, it was a lot worse. I was hoping it would go away, but it seems to be here to stay. Mine is from water hitting the lower unit. I can't see how I can get it any higher, and it doesn't seem to be affecting anything. My suggestion would be to just live with it.
rkp posted 09-27-2003 07:53 AM ET (US)     Profile for rkp  Send Email to rkp     
the roostertail is breaking the surfave about 5-10 feet behind the boat.
David Jenkins posted 09-27-2003 08:38 AM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
It sounds like you do not have your engine trimmed correctly. Why did you install the wedge and how is it oriented?
jimh posted 09-27-2003 07:50 PM ET (US)     Profile for jimh  Send Email to jimh     
There are two distinct phenomenon being mixed together in this discussion.

Excessive spray being generated directly off the lower unit will usually vary with the trim. Often on the lower unit there is a secondary foil or wing a few inches above the primary Anti-Ventilation plate (AV plate) which helps to deflect the spray coming off of the lower unit.Typically the spray coming off the water surface from the point where the lower unit enters the water will come up at a steep angle, hit this foil, and be thrown horizontally away from the boat. Depending how the engine is mounted (height) and trimmed, this spray can become excessive, missing the deflection foil, and creating a shower of spray right behind the boat.

All propellers tend to create a long, rising wave behind the boat and eventually the bubbles of the propeller thrust break the surface, but I don't think it is normal or desirable to have a prominent rooster tail.

The appearance of a rooster tail some 5-10 feet behind the boat would indicate to me that the main thrust of the engine is being directed toward the surface.

We will have to ask one of our resident naval architects or physicists if there is a loss of thrust by having it break the surface too soon.

I would guess that the main thrust stream from the engine should not be breaking through to the surface until at least one boat length behind the boat. I was just looking at some pictures I have of well trimmed and well set up Boston Whalers underway at hydroplaning speed, and they only have a slight rise, not really a roostertail, which occurs about 1.5 boat lengths behind the boat. Well, I should qualify that, as I just realized that most of these pictures are of boats with twin engines and with engine setbacks and jack plates. That probably creates a different situation than a single engine mounted on the transom.

--jimh


jimh posted 09-27-2003 08:09 PM ET (US)     Profile for jimh  Send Email to jimh     
Here is a photo:

http://continuouswave.com/whaler/images/DSCN0142-small.jpeg

This is LHG's fine OUTRAGE-18 T/T WHALE LURE going about 25-MPH. You see there is just a slight rise in the wake about 30 feet behind the boat. I would not categorize this as a rooster tail.

By the way, in this shot we are heading southeast in the Johnstone Straight, east of Vancouver Island, British Columbia. I took the photograph more for scenic reasons than technical ones, but it does show the wake on a Boston Whaler with proper set up.

Taylor posted 09-29-2003 02:37 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Sorry to be off topic, but I agree, that's one fine looking canvased Outrage. I did not realize the two of you were cruising in company.
Bigshot posted 09-30-2003 03:56 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Geez Larry.....how do you dock that thing?
lhg posted 09-30-2003 05:00 PM ET (US)     Profile for lhg    
Very simple, Nick. Just ease up to the (floating) dock, un-zip between the aft curtain and side curtain, and step out. I keep the bow line, from the cleat on the bow pulpit, run inside the bow rail back to the helm station, so I have a line on the bow. The stern line is already outside of the aft curtain, since it comes up through the hawsepipe in the teak gunwale.

This is the first photo I have seen of an Outrage running with the full Mills canvas set. Normally, the aft curtain is not needed, but this was one cool, damp, wet and rainy day. The only one out 12 beautiful days on the water. Mills canvas made the trip possible, literally. They seem to have thought of everything when this canvas was designed, including docking!

Generally, when I see a true roostertail from other than a full bore racing boat,, I assume the engine/stern drive is not trimmed properly, with the resultant inefficient loss of thrust.

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