Transom Issues

[HNTDUKS]

Transom Length

Length to AV plate

Working on and looking at a Tracker Grizzly 1448 Mod V.

Ok, I got rid of a long shaft Johnson I had, It was almost 6 inches to long for this boat. I bought a short shaft Mercury. Put it on the boat. Noticed the cavitation plate seemed to high now. Took it to the lake this morning and all it does is cavitates. What is left to do? Here are all the pics with measurements. I am pretty well fed up at this point so any input would be great.

Would adding a jack plate, installing it slightly lower on the transom and putting the motor on that be the answer? I have also seen that by moving the motor back, you can move it up. If thats the case can I put a jack plate on at the same level of the transom and be in good shape?

I tried the trim pin at all positions and even tried it out. Still had the same results.

 

[JB]

Re: Transom Issues

Hi, Duks.

Welcome to iboats.

You have a 15" transom. Height should be measured vertically from the top, not on the surface.

Pic #2 shows the anti-ventilation plate just below the bottom of the boat and pic #3 is too dark to tell.

When you get under weigh, is the AV plate above, below or on the water surface? The AV plate is the one just above the prop, not the one above that.

I think your prop is ventilating, not cavitating. The problem might be with the prop. Though your installation could be fine tuned, I don't see anything that would cause heavy ventilation.

 

[roscoe]

Re: Transom Issues

Like JB said, "I don't see anything that would cause heavy ventilation."

THe 2nd photo looks good, could possibly raise the motor and inch or two.

No reason the prop should ventilate, as it is completely below the bottom of the hull, and should therefore, be under water.

 

[lakelover]

Re: Transom Issues

Put a straightedge along the bottom of the hull to the AV plate, it's kind of hard to tell from the picture. That will let you see pretty much exactly where it is. Usually AV plate even with or one inch above is ideal, or within that range.

 

[Mel Taylor]

Re: Transom Issues

This may be a dumb question and if so I apologize in advance, but is there any possibility that you are dealing with a spun prop?

 

[MH Hawker]

Re: Transom Issues

I was wondering that too mel

 

[HNTDUKS]

Re: Transom Issues

First of all thanks for all the answers. I will add a couple more pictures with a straight edge to try to show what I am having problems saying. The pictures before may have been deceiving.

Secondly. They spun prop doesn't sound to far off. Only problem I have with that is I bought this motor used at a Marina, and they ran it in the test tank for me and I didn't notice any thing out of the ordinary.

What was happening today with the boat/motor was more or less this, as I would begin to accelerate the motor would start pushing from idle on up no problems. At the very first sign of heavy acceleration the motor would "rap" out in RPM's and loose all forward momentum. As I said before, like it was cavitating.

This is a straight edge off the bottom of the hull as requested. The distance between the cav plate and the straight edge is roughly 2.5 inches.

Here is the straight edge off the tip top of the prop. Just for reference more or less. About 3 inches to the bottom of the hull.

 

[Mel Taylor]

Re: Transom Issues

It's been a long time since I've had a spun prop but if I remember correctly that's exactly the way mine acted. I was able to get back to where I needed to be only by running at the slowest possible speed. If I tried to speed up RPM increased and the boat slowed down or stopped altogether.

 

[HNTDUKS]

Re: Transom Issues

Any way to determine if its spun other than marking it and driving it and seeing if the marks moved?

 

[Jeep Man]

Re: Transom Issues

Still sounds like a spun prop. Without the pressure of pushing a boat and/or higher RPMs, in a tank it wouldn't be obvious.

 

[brnschoneck]

Re: Transom Issues

yeah i would think this is close enough before moving motor id make sure i bet u have a spun prop ??

 

[HNTDUKS]

Re: Transom Issues

It is not a spun prop hub. Just went out and held the nut on the hub with a wrench and attempted to turn the prop with no luck. Hub looks like new.

 

[Mel Taylor]

Re: Transom Issues

It is not a spun prop hub. Just went out and held the nut on the hub with a wrench and attempted to turn the prop with no luck. Hub looks like new.

Ahh..... OK, but I had this same conversation with my father-in-law (of blessed memory) when he had a spun prop on his boat not long after I spun the prop on my boat. Strangely enough, when he replaced his prop with one of my spare props the problem went away. I don't think you can exert enough force by hand to make the hub slip.

 

[saumon]

Re: Transom Issues

Ahh..... OK, but I had this same conversation with my father-in-law (of blessed memory) when he had a spun prop on his boat not long after I spun the prop on my boat. Strangely enough, when he replaced his prop with one of my spare props the problem went away. I don't think you can exert enough force by hand to make the hub slip.

What he said! Go out and report back...

 

[HNTDUKS]

Re: Transom Issues

Ahh..... OK, but I had this same conversation with my father-in-law (of blessed memory) when he had a spun prop on his boat not long after I spun the prop on my boat. Strangely enough, when he replaced his prop with one of my spare props the problem went away. I don't think you can exert enough force by hand to make the hub slip.

I will take it to the water tomorrow after marking the hub and prop and see if it moves.

So putting the spun prop aside. Should I disregard the 2.5 inch height difference between the cav plate and the bottom of the hull?

 

[Mel Taylor]

Re: Transom Issues

I will take it to the water tomorrow after marking the hub and prop and see if it moves.

So putting the spun prop aside. Should I disregard the 2.5 inch height difference between the cav plate and the bottom of the hull?

I'll have to defer to someone else on that one. Good luck and whatever the cause I hope it's easy to find and cheap to fix.

 

[saumon]

Re: Transom Issues

What was happening today with the boat/motor was more or less this, as I would begin to accelerate the motor would start pushing from idle on up no problems. At the very first sign of heavy acceleration the motor would "rap" out in RPM's and loose all forward momentum. As I said before, like it was cavitating.

From your description, it really look like a spun hub (At the very first sign of heavy acceleration). At this precise moment, that's were the bow goes upward and, inversely, the prop goes deeper so there's absolutely no reason to have ventilation. It usually occur at WOT, while planning, if you trim too far out and the prop loose grip...

 

[lakelover]

Re: Transom Issues

It looks from this that you are pretty much right on the money for height if your left hand is holding it aginst the hull, and the ruler is flat on the plate.

 

[MH Hawker]

Re: Transom Issues

I ran into a slipping hub on my first boat and at the time I didn't know the marking trick, Mine would slip around 3/4 power if I had the family on board. Just me it was fine. Ended up messing with it all one summer until I dinged it bad and had to replace it, and the problem went away.

Your motor height is close enough to where it should be working fine, you may be able to fine tune it, but it should work just fine as is.

 

[HNTDUKS]

Re: Transom Issues

Ok, stupid question. Will I be able to just back the boat in the water, leave it strapped on the trailer and try to go forward. I can go out and mark the hub/prop now and stick it in my pond to make this happen. I can unload it into the pond as my banks are very steep. But am able to get the motor in far enough to run it.