Porpoising while trimmed down

[John_S]

Re: Porpoising while trimmed down

My guess is that it is too high from the home made jack plate. The clamps are probably in the way to lower it just an inch or two. Might have to remove it.

 

[oops!]

Re: Porpoising while trimmed down

please take a full side shot of the back of your boat......the full motor and the back section.

 

[Bounce19712]

Re: Porpoising while trimmed down

next time you test her out, watch your wake/rooster tail when trimming up. Note the point at which you start cavitating.... that'll give you a reference point with a picture in your mind of what your wake should look like in different trim positions.

I didn't look at the pics yet but you could possibily alleviate some porposing by shifting weight in the boat...

edit: looked at the pics.... I don't see the vent/cav plate being more than 2 inches higher than the keel... do you guys?

Try pulling your tilt pin and putting it a couple holes higher...maybe you can get away with adjusting just the pin instead of a motor move....I'd try it first anyways..

then get a level and hold it under the cavitation plate and mark where it matches to your transom.....that'll give everyone a true height

talk to the previous owner?

I trim this boat and bring the cav plate much higher than yours...all though it is a bit different...

 

[Maclin]

Re: Porpoising while trimmed down

You know, that is not a jackplate is it? Jack plates connect to the transom then have another plate that the engine mounts to that has more holes in it for moving it up and down. That one looks more like a reinforcing for the transom. ZOIKS

I would not try any other adjustments until the motor can be moved down. You already know you cannot trim up any without the prop catching air.

A "real" jackplate could help you though. If that is a real one on your boat then I apologize.

Here is what I think of for "jackplate" or setback plate...:

 

[Maclin]

Re: Porpoising while trimmed down

Bounce, you have one of them thar "pad" hotrod bass boats, I believe prop height is different for V-bottoms with more deadrise and no pad.

 

[Bounce19712]

Re: Porpoising while trimmed down

I'm guessing that's a rotten transom fix plate

 

[Danny C]

Re: Porpoising while trimmed down

Took some more pics. The cav plate is about an inch and a half above keel. As far as the "jack plate" goes, it is just a quarter inch thick steel plate looks like reinforcement to me. I do not see how I would be able to lower the motor any even if I take the steel plate off. Am I missing something here. And to clarify, I did cavitate when I tilted up but I believe I REALLY gave it some tilt before I cavitated. As far as moving tilt pin up, would that not just raise the cav plate up. How would that help. I'm all for doing it if it helps just don't get it. And I am game to lower motor too, but how would I do that. Sorry for the blue tarp in the pics, trying to keep the sun out of my pictures.

 

[Danny C]

Re: Porpoising while trimmed down

more...

View attachment 110332
View attachment 110333
View attachment 110334
View attachment 110335

 

[Danny C]

Re: Porpoising while trimmed down

and 2 more...

View attachment 110336
View attachment 110337

 

[Bounce19712]

Re: Porpoising while trimmed down

adjusting the tilt pin up a hole or two will change your max down trim of the motor....sorry to throw two issues at you when others are saying lower the motor...I'm saying adjust the trim of the motor.... to ensure you've tried an easy fix...compared to the heavy lifting and remounting fix

looking at your photos there, that looks like a good amount of down trim in the motors current position.... I would want to try making the vent/cav plate is on the same plane as the hull with just the trim button...but you could bump the tilt pin up a hole as well.... and still have some good down trim

 

[John_S]

Re: Porpoising while trimmed down

You know, that is not a jackplate is it? Jack plates connect to the transom then have another plate that the engine mounts to that has more holes in it for moving it up and down. That one looks more like a reinforcing for the transom. ZOIKS

I would not try any other adjustments until the motor can be moved down. You already know you cannot trim up any without the prop catching air.

A "real" jackplate could help you though. If that is a real one on your boat then I apologize.

Here is what I think of for "jackplate" or setback plate...:

View attachment 110314

Well, there are fixed jack plates and adjustable ones. commercial and home built.

Could be right that it is a patch for a rotten transom, but is also why is motor is mounted higher.

 

[John_S]

Re: Porpoising while trimmed down

I couldn't see the latest attachments, but would like to see some of the top plate/motor mounting.

 

[zagger]

Re: Porpoising while trimmed down

Looking at the picture of the back it looks like the fin would be totally under the water at planing speed. This is OK on take off and slow speed but once on the plane the fin should be out of the water or just skimming the top. What I think is happening is that the tips of the fin bite the water at higher speeds and are sucking the transom down thus cosing the bow to bounce. I would ditch the fin you have and maybe go with one that has better geometry like DoelFin. Also everyone is telling you to bring the motor down but I think in your situation if anything it should go up to get these fins out of the water once on plane. Just the way I see it, I'm sure others will disagree.

 

[Bounce19712]

Re: Porpoising while trimmed down

I remember seeing my dolphin tail on the JohnRude 140 on top of the water when on plane......fwiw

 

[ezmobee]

Re: Porpoising while trimmed down

In light of the new pictures, I retract my earlier comment.

 

[roscoe]

Re: Porpoising while trimmed down




Looks like the plate is 3-4" above the lowest point on the keel.

Lower it down so the plate is a little below the bottom of the drain hole.

Take off the foil.

Don't let up on the throttle abruptly unless you are intending to wash the splashwell.

And, you do have a light boat, so it is going to be weight sensitive.

And you don't need that pin at all, you have power trim, adjust motor to vertical when she is floating.

 

[Danny C]

Re: Porpoising while trimmed down

Also, if I don't have a jack plate, how would I lower the motor. It looks like the motor mounts that "clamp" onto the transom dont have much room to move even if I took the steel plate off. Is this gonna require some transome drilling. What am I missing here? there are some shots in the pics below. I seem to remember the guy selling me the boat saying that that plate was just extra reinforcement that was added for piece of mind. (Although, could have been hiding a rotton transom I guess).

Repost of bad link pics...

 

[Danny C]

Re: Porpoising while trimmed down

2 more...

 

[ezmobee]

Re: Porpoising while trimmed down

Looks like the plate is 3-4" above the lowest point on the keel.

I think you're looking at the wrong "plate" (as I was earlier).

 

[zagger]

Re: Porpoising while trimmed down


Still think it is the tips of your foil that cause the stern to stay down at speed and bow to bounce. I would do nothing to motor hight or trim till I changed the foil.