follow up to fish and ski rooster tail problem

[wtxpatrick]

I finally got to take pics of the engine mount and height. At planing speed, I have a symmetrical V shaped rooster tail shooting up and the boat catches a little water from it. The load in the boat at the time of the test was around 400 pounds. Engine is centered on transom and seems level. Mount seems to be to spec. Engine could adjust up but not down. I get a smooth ride at planing speed, no porpoising, or bouncing. prop is 13 1/4 x 17, no tach but RPM sounds ok as does speed. there is no hydrofoil on motor, but I did purchase a Stingray on ebay for it. Cavitation plate on motor is true, no bends or distortions on the metal. Engine is a 70 HP evinrude, mounted to a 15' Magnum fish and ski type boat. Boat is rated to 90 HP maximum. 750 pound maximum load. Boat model # is 150. Fiberglass construction. Tri hull design. weight is unknown. The cavitation plate looks to be about 1 3/4 to 2 inches below the bottom of the transom,as the photos will show. The motor tilt setting was in the 2nd hole from the front, I moved it out to the 3rd hole, but it made no difference. Possibly I need to move it all the way forward ? The tilt is manual, no power tilt, I really miss that. The only thing i see is the lower engine mounting bolts stick out about 2 inches and the washers are square 1 1/2 , kinda large and possibly wrong type. I bought the rig from an electrician.

Anyone got any ideas ?
Thanx
Patrick

 

[tallcanadian]

Re: follow up to fish and ski rooster tail problem

Your cavitation plate looks to be a bit below the centreline of the hull. That to me seems to be the culprit. I have similiar spray on mine but only on one side. It's coming from my transducer. As far as that stingray goes, that may slow you down. Good Luck.

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

Your cavitation plate looks to be a bit below the centreline of the hull. That to me seems to be the culprit. I have similiar spray on mine but only on one side. It's coming from my transducer. As far as that stingray goes, that may slow you down. Good Luck.

The cavitation plate is defiantly below the centerline or lowest point, where does it need to be ? flush with the bottom ? do you see a need to raise the motor 1 or 2 inches, possibly more. These are the fine points Im trying to learn here. Thank you for the help
Patrick

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

You sure did a fine job on your rebuild there, great videos.

 

[tallcanadian]

Re: follow up to fish and ski rooster tail problem

Thanks Patrick. The cav plate should at least be level with the bottom of the boat or even a couple inches above it. Not sure if you really want to bother raising your outboard. I can't believe you don't have power trim on that 70. You must have arms the size of tree trunks. lol. I have a 45 so I know you must have a harder time pulling that puppy up. I installed a CMC power trim unit. My cav plate is about 2 inches above bottom of the boat.

 

[Snowfish]

Re: follow up to fish and ski rooster tail problem

My bet is the transducer.

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

My bet is the transducer.

thats what I thought at first, but the rooster tail is a perfect V so I don't think the right side mounted transducer would cause that.

 

[scoutabout]

Re: follow up to fish and ski rooster tail problem

I'd also say your cav plate it a couple of inches too low based on how mine is sitting anyway.

You may be catching the bottom of that widened area on the leg of your motor where the lower leg attaches to the upper part. Looks like you've got the adjustability on your motor mount put pulling the thing off to move it up a hole will be a pain.

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

I'd also say your cav plate it a couple of inches too low based on how mine is sitting anyway.

You may be catching the bottom of that widened area on the leg of your motor where the lower leg attaches to the upper part. Looks like you've got the adjustability on your motor mount put pulling the thing off to move it up a hole will be a pain.

Well, it seems I face a dilemma here. I'm not worried about the work ajusting the motor up as much as I am concerned about weakening the transom from drilling more holes. I did plan on installing a stingray hydrofoil on it, and I do have one more hole to adjust to when I take it out next time. Thanx guys for all the ideas and please keep it coming.
thanks to all again
Patrick

 

[nitsuj]

Re: follow up to fish and ski rooster tail problem

Well, it seems I face a dilemma here. I'm not worried about the work ajusting the motor up as much as I am concerned about weakening the transom from drilling more holes.

Aren't the mounts slotted so it can be moved up without drilling?

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

Aren't the mounts slotted so it can be moved up without drilling?

I finally got in early enough to check your idea in the daylight and found that I do have the holes and slots to make the adjustments up. I guess I need 1 1/2 square tubing to hold it up off of the transom, and a couple of strong backs.
Cavitation plate flush with bottom I guess?

 

[scoutabout]

Re: follow up to fish and ski rooster tail problem

Everything I've seen says the standard position is to have the cavitation plate about even with the lowest point of the hull.

As for holding the engine up off the transom -- something like you described or even a nice chunk of hard rubber would do the trick.

Believe or not, my 90 horse Yammy 4-stroke has absolutely nothing in that gap. Scout must be pretty confident of their transom cuz it gives me the willies just lookin at it.

 

[tallcanadian]

Re: follow up to fish and ski rooster tail problem

I've actually seen a lot of outboards with that gap in it. I guess you have to do what you need to get the motor adjusted right. You would think by now that boat manufacturers can get the transom the right length.

 

[grego]

Re: follow up to fish and ski rooster tail problem

To raise the motor. lower the jack, lock the engine in "down" position. block the engine skag, with lumber. remove bolts and just raise the nose untill it matches bolt patern. support engine "left and right"
hope this helps.

 

[grego]

Re: follow up to fish and ski rooster tail problem

After rereading post, seems to me that if you are cavitating, shouldn't you lower the prop? AND! if you add fins to cav plate, fix problem? Or is there a lot of weight forward? Or, is the engine "transport" lock in the UP position, holding the engine in a higher position? you said it did not have trim, those locks are not easy to see. more pics please.

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

To raise the motor. lower the jack, lock the engine in "down" position. block the engine skag, with lumber. remove bolts and just raise the nose untill it matches bolt patern. support engine "left and right"
hope this helps.

Thats a great Idea Grego, thank ya very much. And many thanx to all that contributed. Now, I'm gonna twist this thread a little bit. I think I need 1.5 inches up on the motor to be flush, the A/V plate with bottom of hull. Question is, do I raise motor first then install the wing? Seems like the thing to do, but you guys know a lot more that I do about this stuff. I had great great results on a VIP shallow V with the stingray on a Chrysler 90. I just had to try it on this one.

 

[Frank Acampora]

Re: follow up to fish and ski rooster tail problem

You are about 3-4 inches too low on the transom. See that fin above the cav plate that is even with the bottom of the notch? That fin's purpose is to stop impact water from traveling up the leg and into the splashwell. Too low, as it is, and water impacts above it rides up and sprays into the splashwell.

Now: the notch in the transom, acts like a jackplate. It sets the engine back into cleaner water. Water rises off the vee bottom so by the time it gets to the engine leg, it is about 3 inches higher than the vee. Thus for proper performance, you need to raise the engine-- I would say start with two inches and go from there

 

[grego]

Re: follow up to fish and ski rooster tail problem

GO with a medium size fin first. No need to go through raising motor if a quick fix works. What is "rpm" at throtle wide open? If you raise motor your rpms WILL! go up. making more roostertail.

 

[grego]

Re: follow up to fish and ski rooster tail problem

I really think, that those that built this boat, knew how to set the engine to get the most from what they offered. if I bought a ranger bass boat that ran 25 mph. and cost me 40,000 dollar before mods, I might not buy it. LOL! I think you are looking at a simple fix.

 

[wtxpatrick]

Re: follow up to fish and ski rooster tail problem

You are about 3-4 inches too low on the transom. See that fin above the cav plate that is even with the bottom of the notch? That fin's purpose is to stop impact water from traveling up the leg and into the splashwell. Too low, as it is, and water impacts above it rides up and sprays into the splashwell.

Now: the notch in the transom, acts like a jackplate. It sets the engine back into cleaner water. Water rises off the vee bottom so by the time it gets to the engine leg, it is about 3 inches higher than the vee. Thus for proper performance, you need to raise the engine-- I would say start with two inches and go from there

ok, that makes perfect sense. Looks like I can raise it about 2 inches max. possibly a hair more. Thank ya frank