# porpoising



## devrep (Feb 22, 2009)

I have an 07 mitzi 17, non tunnel.  Yamaha 50 2 stroke.  I've had the boat  since new.  It has always porpoised badly but I had trim tabs on it from the get go and have just compensated with them.  I have to run the tabs halfway down to not porpoise, drives me crazy.  the bottom of the hull is straight as an arrow, I have a 6 ft level and I used it as a straight edge.

Boat set up:
stern -  50 hp Yamaha, poling platform, live well, 2 storage compartments, bilge, 2 anglers about 170lbs ea.
console - starter and trolling motor batteries.
bow - riptide 55, 12 gal fuel tank.  run anywhere from 6 to 12 gal, depending on trip.

I've had the motor mounted at 3 dif heights, doesn't make any difference.  any tips would be appreciated.


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## BugDopeforENP (May 29, 2013)

1. Buy a jack plate 

2. Buy a dulphin/ cavitation plate

3. Make sure your prop to pad is at three inches

Any one of these could be your solution. Others will chime in to.


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## [email protected] (Feb 10, 2013)

Put those tabs down a little more if that doesn't work put some bigger tabs on. They're not all that pricey. My Ipb16 would jump 20 feet in the sky if I even thought of trimming up at full speed I'm good to go now. Put a buddy on the bow and see if that helps first.


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## Brett (Jul 16, 2008)

First you have to understand the cause...

http://www.dtic.mil/dtic/tr/fulltext/u2/b240994.pdf

Then you find a solution.

The easiest are:

1 - Balance the load so the hull isn't stern heavy.
     Weight forward helps to eliminate porpoising.

2 - Adjust engine trim angle. Trimmed out too far causes porpoising,
     tucked in can cause plowing. Have to find the sweet spot, which can change
     depending on hull loading and sea conditions.

3 - Trim tabs....but you knew that

4 - Passenger location (see loading)


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## flatsmaster22 (Feb 24, 2007)

You can also run a prop with a semi-clever blade. This will create stern lift without the use of tabs. Look at the powertech SCB


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## topnative2 (Feb 22, 2009)

it is all about weight distribution and trim as brett stated

u got tabs which is the best solution-buying any thing else is a waste of money

O.K.----- if u still porp. w/ the motor completely vertical w/ no trim put a cup in the prop

after that I am at a loss


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## Creek Runner (Sep 1, 2011)

Raise the motor up its way to low, up 2 holes. Change your prop, don't know what would be the best because I'm not sure of what the boat is doing. 

What I have noticed a lot times when I have customers bring up the same situation you have is, when I go run the boat with them they simply aren't going fast enough to give the motor positive trim. 

My 25 shearwater with a F350 porpoises really bad, anything below 4500RPM or 42MPH it annoying, it doesn't go away until above 4800RPM around 51MPH. Anything below 4500RPM's and I have to reduce trim and put my tabs down about 1/3 of the way.


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## JBMitziSkiff (Nov 2, 2012)

Move your motor back to the 3rd hole form the top.  Then definitely get a 4 blade stern lift prop.  I have a 15 Mitzi and did that with the addition of tt and it stopped.  Although it was only self induced by speed, weight and motor trim, a quick pop of the TT and it will not do it.


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## devrep (Feb 22, 2009)

I had the motor raised up 2 holes with a 4 blade heavily cupped Powertech prop. I then lowered it 1 hole and then back to the setting as pictured. no difference at all as to porpoising. I have tried 3 dif heights and 3 dif props. I know the tabs fix this but using the tabs drops the speed down about 2 mph (I know that's not a big deal) and it just bugs me. What if I had this boat without tabs? crazy.

on a smooth day I am getting right around 32 mph on my gps with the 50 yammie and the 3 blade 14 pitch yammie prop at 5300 rpm.

anyone else have this same boat? would love to hear if you have the same problem.


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## devrep (Feb 22, 2009)

I didn't even know what prop-to-pad was until you posted this and I googled it. have not taken a measurement on this yet but looking at my photo it looks more like 6" than 3".

everything I've read says to put the anticavitation plate level with the keel. what if that is way off the prop-to-pad? also I read 3" ptp for 4 blade prop and 3.5" ptp for 3 blade prop?


> 1. Buy a jack plate
> 
> 2. Buy a dulphin/ cavitation plate
> 
> ...


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## mikeregas (Mar 15, 2013)

Pretty good article and a good diagram for measuring prop to pad.

http://www.bassboatmagazine.com/chi...=b8aa9fb956890e3b9318cf88126056ae&amp;t=13664


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## BugDopeforENP (May 29, 2013)

> I didn't even know what prop-to-pad was until you posted this and I googled it.  have not taken a measurement on this yet but looking at my photo it looks more like 6" than 3".
> 
> everything I've read says to put the anticavitation plate level with the keel.  what if that is way off the prop-to-pad?   also I read 3" ptp for 4 blade prop and 3.5" ptp for 3 blade prop?
> 
> ...


The anti cavitation plate will help you plane off it allows the prop to push more water. Having the anti cavitation level with the keel is for planing off and can be corrected by using the trim and tilt. As for props for ptp I didn't know about that but what I do know is that you can go to your local prop shop and have your prop re shaped with a little added cup to it and some prop shops will let you test props to find out what is best for your boat before making a purchase. 

What I would do first would be to get your ptp, level everything off and get your measurements and set the ptp to three inches. If this cant be achieved by your motor mounts buy a manual jack plate or get a hydrolic jack plate if your not worried about weight to get the right ptp. Hydrolic jack plate would be the way to go to eliminate a lot of time,labor and frustrations.

Before you go spending money try finding some one that will loan you a anti cavitation plate and see if that fixes your problem same goes for a prop. If neither of those work get a jack plate and go from there.


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## Creek Runner (Sep 1, 2011)

> I didn't even know what prop-to-pad was until you posted this and I googled it.  have not taken a measurement on this yet but looking at my photo it looks more like 6" than 3".
> 
> everything I've read says to put the anticavitation plate level with the keel.  what if that is way off the prop-to-pad?   also I read 3" ptp for 4 blade prop and 3.5" ptp for 3 blade prop?
> 
> ...



Your boat doesn’t have a pad.

Just because you read 3.5” or 4” doesn’t make it right it’s just a starting point.

Most boats with a pad will have an offset transom from the pad, yours does not.

You need to find why your porpoising before you can fix it. Have you tried calling Mitzi to see what set up they recommend?

Are you porpoising because your bow is to heavy? To Light? Because the transom is squatting? 

Your boat does not have a pad and is not going to air out.

You said you tried a 4 blade prop with heavy cup, was the cup in the trailing edge? On the leading edge? How much rake did it have? All these things will affect the way the boat runs. 

And before you go spend the money on a jack plate, it doesn't matter where my jack plate is set on my shearwater it porpoises if I'm below 4800RPM's I have to tuck the trim and give it some tab. Every boat will run different, and need different things.


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## mmurray (Jan 16, 2012)

My mitzi 16 would porpoise at any speed if I tried to trim it out to much. Jackplate and cav plate have definitely helped. 
I would raise the motor back up. move at least one if not both batteries to the bow. do you use the livewell, try it with the livewell empty. I can tell a difference on mine if it has a full or half full tank. Have someone sit in front of the console to see if that helps.


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## el9surf (Dec 23, 2008)

Where is your fuel tank mounted and how many gallons is it? How full do you keep the tank on average?


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## Barbs_deep (Jul 4, 2010)

This is kind of strange... my buddy recently bought a 17 Mitzi and it rides so flat. Not even a hint of porpoising. Boat has NO tabs on it. I was extremely surprised how well it rode. His fuel tank is up front and 2 batteries under the center console. He also has a 50hp.


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## Vertigo (Jun 3, 2012)

There are three things you can do to trim a boat out:

1. Change the center of gravity (move weight around)
2. Change thrust axis (adjust motor position)
3. Change the forces acting on the hull (use tabs, sponsons, cav plate)

To control porpoising, move weight fwd, raise and tilt the motor, fiddle with trim tabs and cav plates. A well designed and balanced hull, properly powered should not porpoise and should not require tabs once on plane.


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## devrep (Feb 22, 2009)

see my 1st post in this thread.



> Where is your fuel tank mounted and how many gallons is it? How full do you keep the tank on average?


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## devrep (Feb 22, 2009)

very interesting. was hoping to hear about another boat of the same type. thanks.



> This is kind of strange... my buddy recently bought a 17 Mitzi and it rides so flat. Not even a hint of porpoising. Boat has NO tabs on it. I was extremely surprised how well it rode.  His fuel tank is up front and 2 batteries under the center console.  He also has a 50hp.


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## devrep (Feb 22, 2009)

I cannot use my trim at all. motor always has to be in the lowest position. I might as well not have trim on my motor.



> My mitzi 16 would porpoise at any speed if I tried to trim it out to much.  Jackplate and cav plate have definitely helped.
> I would raise the motor back up.  move at least one if not both batteries to the bow.  do you use the livewell, try it with the livewell empty. I can tell a difference on mine if it has a full or half full tank.  Have someone sit in front of the console to see if that helps.


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## devrep (Feb 22, 2009)

I really appreciate all the reply's and the time everyone took to help.  after hearing about the other mitzi set up and equipped exactly like mine I will call mitzi today and see if they have any advice.  I really like this skiff, it rides super dry, is easy to pole and has great ergo's.


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## CurtisWright (May 9, 2012)

Is there any where in your skiff that could be filling up with water? A livewell in the rear or a drain comaprtment without a plug?


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## JBMitziSkiff (Nov 2, 2012)

Only thing is your year 07 and up to 2009 I believe had transom height issues from the factory.  Mine will not porpoise unless I make it.  I know for a fact some earlier models transom height was an issue.  I think it was not molded right something about the height so the motor never sat right on it.  I think Mike at Mitzi said something about it.  Not sure if that would have any affect on it but it could no matter where motor height was mounted.

15' 40 ETEC 4 blade powertech prop speed is 32-33 
aluminum stock  3 blade 36-37 mph
6 gal fuel up front 1 battery up front
1 battery under console
Like Cwright said do you plug your aft live well or leave it open?  I use a plug on mine so no water in it.


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## devrep (Feb 22, 2009)

I have run with the live well full and empty makes no difference.  

I also read about some being built with the transom too high, earlier models before they were bought out I believe (mine was built by Mitzlaff I think).  You may be barking up the right tree.  Is your transom this high?


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## devrep (Feb 22, 2009)




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## JBMitziSkiff (Nov 2, 2012)

> I have run with the live well full and empty makes no difference.
> 
> I also read about some being built with the transom too high, earlier models before they were bought out I believe (mine was built by Mitzlaff I think).  You may be barking up the right tree.  Is your transom this high?


I will measure it tonight, but I have a 15' not 17' not sure if they are the same. But just looking at it mine seems different. I think someone else on here or might have been another site had their transom repaired by Mike at Mitzi. They do build a better boat after Mitzlaff sold the molds. They engineered them a littel better.


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## JBMitziSkiff (Nov 2, 2012)

Here is a couple pics of mine. It measures 21 from outside center keel to top of transome.


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## devrep (Feb 22, 2009)

looks like mine. I got somewhere between 21 1/2 to 22", was tough to get close with the motor in the way.
Was 20 1/2 inside. thanks for taking the time to photo and post.


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## devrep (Feb 22, 2009)

If I were to move my trolling motor battery (about 85 lbs) to the bow, would there be an issue having it next to my 12 gallon portable fuel tank? Kind of makes me nervous.


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## mikeregas (Mar 15, 2013)

> If I were to move my trolling motor battery (about 85 lbs) to the bow, would there be an issue having it next to my 12 gallon portable fuel tank?   Kind of makes me nervous.


I have had TM batteries next to fuel tanks for years now, I am still hear to talk about it. Just make sure with a portable that the area is well vented...


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## JBMitziSkiff (Nov 2, 2012)

Nope no issue. Put it in a battery box like I did with mine. Been that way for 3 years no issues. It actually makes the boat sit really level on mine. 

Mine is setup 1 bat. in bow with 6 gal fuel tank
1 battery under console.


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## devrep (Feb 22, 2009)

so I'm going to try transom wedges. They come in 2 degree and 5 degree. any thoughts on the subject?


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## richg99 (Nov 28, 2009)

They cured my porpoising problem on a 150 hp Evinrude mounted on a 20 ft Gulf coast at one time. That boat had an unusually flat transom, I thought.

Ideally, you would have tucked your engine all of the way down to get up on plane, and then gradually raised the tilt while under way...and you would have stopped when the boat started to porpoise..your hull's action would be normal.

If, however, you STILL have porpoising all through out the run... then you have to find some other method to fix the issue.

Personally, I would try increasing the size of my tabs, before I tucked the engine under (which is what the wedges do). You will lose, IMHO, far more speed with additionally tucking of the engine, than you would by increasing the size of your tabs. Rich


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## flyfshrmn82 (Oct 12, 2007)

Interesting. Keep us posted...


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## JaxLaxFish (Aug 23, 2010)

my dad has an almost new 17 mitzi. it has a 50 honda and there is a big battery under the front deck and one in the bilge and a 6 gallon fuel tank under the bow deck also. its actually really tough to make it porpoise so I would strongly suggest trying to move the battery first that seems like the easiest route to me. also we have an enclosed front hatch and the battery next to the gas is the standard way the dealer rigs all of his mitzi skiffs. he told us that since the rod tubes are not the highest of quality there is enough air that gets through there to vent it.


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## devrep (Feb 22, 2009)

my bow is completely open anyway. Yes, I'm going to move the bigger battery to the bow this coming weekend and see what that does before doing anything else.


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## devrep (Feb 22, 2009)

btw, thanks for the info.



> my dad has an almost new 17 mitzi. it has a 50 honda and there is a big battery under the front deck and one in the bilge and a 6 gallon fuel tank under the bow deck also. its actually really tough to make it porpoise so I would strongly suggest trying to move the battery first that seems like the easiest route to me. also we have an enclosed front hatch and the battery next to the gas is the standard way the dealer rigs all of his mitzi skiffs. he told us that since the rod tubes are not the highest of quality there is enough air that gets through there to vent it.


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## Barbs_deep (Jul 4, 2010)

Your set up sounds similar to everybody else's. I'm curious to know if you have a hook in your hull...


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## JBMitziSkiff (Nov 2, 2012)

> Your set up sounds similar to everybody else's. I'm curious to know if you have a hook in your hull...


good point DS! Forgot about that... I read about that here a while ago
http://www.thehulltruth.com/boating-forum/54174-what-hook-hull.html


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## devrep (Feb 22, 2009)

read my 1st post in this thread.



> Your set up sounds similar to everybody else's. I'm curious to know if you have a hook in your hull...


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## devrep (Feb 22, 2009)

Moved my 85 lb trolling motor battery into the bow, no change. raised the motor 1 hole (again), no change. Thinking about having a boat shop look over my set up.
Rick with Mitzi has spent a lot of time trying to help me with this but it's probably pretty hard to diagnose without seeing the boat.


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## swaddict (Dec 19, 2009)

this is frustrating, i can't image what you are going through. have you let someone else drive the boat, not saying you're a bad driver, but maybe someone will see or feel something different. is there a chance the motor is not mounted dead center or maybe slightly tilted? keep us posted on the process


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## Dillusion (May 21, 2012)

> this is frustrating, i can't image what you are going through.  have you let someone else drive the boat, not saying you're a bad driver, but maybe someone will see or feel something different.  is there a chance the motor is not mounted dead center or maybe slightly tilted?  keep us posted on the process


Even if the motor was slightly tilted, it wouldn't cause the vessel to porpoise. it would make it lean to one side.


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## devrep (Feb 22, 2009)

the motor is mounted straight and centered. I can let go of the wheel and it tracks straight. I have noticed that if I throttle down some the porpoising pretty much stops, but that isn't a solution.


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## JBMitziSkiff (Nov 2, 2012)

Dev, does your boat porpoise if you trim down almost like its tucked under? Then after your under way move it out a little at the time till it starts to porpoise to move it back down? Or does it just do it all the time? 
My 15 I don't have to run any of the tabs and it will not porpoise until I bring th motor up to over trim it and make it do it. 
I usually put trim tabs in it and bring the motor up to almost porpoise and then it kicks my speed to 34 wot


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## AfterHours2 (Aug 2, 2010)

Only problem I have ever had like yours was once on an old fin & feather. I let my brother in law borrow it one weekend and he obviously hit a sand bar way too hard. It took several weeks for him to admit the fault but the boat always had the same issue after the fact. Come to find out, when the motor hit it caused the trim ram to be slightly bent. It threw off the camber of the trim and it was a PITA to diagnose and fix. You have pretty much been through all the logical things but I thought I would just put it out there. Good luck..


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## devrep (Feb 22, 2009)

I can't trim up at all, might as well not have trim. porpoises with the motor all the way down and gets worse if I use any trim.


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## devrep (Feb 22, 2009)

that's pretty interesting but since mine does it even with the motor all the way down I don't think that could be it. I will look closer at the ram shaft though.



> Only problem I have ever had like yours was once on an old fin & feather. I let my brother in law borrow it one weekend and he obviously hit a sand bar way too hard. It took several weeks for him to admit the fault but the boat always had the same issue after the fact. Come to find out, when the motor hit it caused the trim ram to be slightly bent. It threw off the camber of the trim and it was a PITA to diagnose and fix. You have pretty much been through all the logical things but I thought I would just put it out there. Good luck..


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## CurtisWright (May 9, 2012)

When your trim tabs are up, does the water seperate from them or is it picked up and carried to the end?

If your tabs are mounted too close to the bottom of the boat they will not seperate from the water and actually cause a reverse action.  Try disconnecting the actuatior from the tab and just letting them flop around back there.

...does that make sense?  like the rocker on a wake board picks the front of the board up

Your port tab looks to be mounted much lower than the starboard one. Lenco recomends a minimum 3/8"


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## devrep (Feb 22, 2009)

they are at the same ht. I installed these and followed instructions meticulously but hey I will check anything a this point. You can see in this pic they are not too low. I'll see if I can get some pics in motion.


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## devrep (Feb 22, 2009)

anyone have any pics of tabs installed on similar hulls? If this is the problem I'll be dancing a jig.


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## Dillusion (May 21, 2012)

Tabs being mounted too close to the bottom of the hull won't cause porpoising, porpoising is a product of too much weight in the transom and speed. If anything the tabs being too low will act like sponsons and keep the bot from chine walking.

Even if a Leno tab plate is mounted too close to the bottom of the transom, if installed correctly they should be 3/4" above the bottom of the hulls plane allowing them to be out of the water when all the way up and on plane.


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## devrep (Feb 22, 2009)

tabs are 3/8" above bottom of transom and aft edges are 1" above bottom of hull using a 4 ft straight edge.


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## TwoKids (Jan 2, 2013)

Devrep - Seems like you have exhausted all the obvious most common causes so here's thinking way outside the box here so bear with me.. I am not familiar with Mitzi boat construction but is there anyway that you can have some water sandwiched between hull layers/false floor of some sort, maybe where foam should be, that could flow to the back when accelerating causing an abnormal amount of weight in the stern leading to the porposing? Or a heavy water logged wood core transom? Maybe a stringer issue? Low probability it is any of these since you say its done this since brand new but who knows... you may just have some sort of not so obvious CG type issue.


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## topnative2 (Feb 22, 2009)

I think u may have something there


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## JBMitziSkiff (Nov 2, 2012)

> Devrep - Seems like you have exhausted all the obvious most common causes so here's thinking way outside the box here so bear with me.. I am not familiar with Mitzi boat construction but is there anyway that you can have some water sandwiched between hull layers/false floor of some sort, maybe where foam should be, that could flow to the back when accelerating causing an abnormal amount of weight in the stern leading to the porposing? Or a heavy water logged wood core transom? Maybe a stringer issue? Low probability it is any of these since you say its done this since brand new but who knows... you may just have some sort of not so obvious CG type issue.


Also get a stethoscope have someone raise the bow and you listen for water in the hull. Just another outside the box thought


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## devrep (Feb 22, 2009)

apparently you missed this discussion a while back.  I originally called this thread 2009 Mitzi but I was wrong, it's a 2007.

http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1355667479/0


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## TwoKids (Jan 2, 2013)

> apparently you missed this discussion a while back.  I originally called this thread 2009 Mitzi but I was wrong, it's a 2007.
> 
> http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1355667479/0


Yes that was before I registered to microskiff. Knowing that history now I'm led to believe you have more water in that hull somewhere or something is water logged and heavier then factory back by the stern of that boat.




> the motor is mounted straight and centered.  I can let go of the wheel and it tracks straight.  I have noticed that if I throttle down some the porpoising pretty much stops, but that isn't a solution.


When decelerating by throttling down the water could move back fwd hence moving cg fwd and eliminating porposing. Supports the trapped water theory.


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## devrep (Feb 22, 2009)

I don't think there's any more water in there or we would hear it. also, I don't think there is anything under the deck that can get water logged. This is a Mitzi 17 hull.


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## topnative2 (Feb 22, 2009)

There is not enough floatation in the picture to meet USCG requirements...

What does the manuf.say?


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## devrep (Feb 22, 2009)

There is a large area under the bow that is foam filled and most of the stern all around the storage compartments (under the poling platform) is foam filled. This is done when the hull is capped. They may add foam under the deck also, I don't know. The photo is early in the process.


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## Creek Runner (Sep 1, 2011)

If there is foam in the boat that got wet it is water logged, see my oringal post on your thread about the 11 gallons of water. 

What year is the boat?


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## BayStYat (Sep 12, 2012)

Is is closed cell foam? That would not hold water correct?


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## TwoKids (Jan 2, 2013)

Know anyone with a pinless moisture meter?  Marine surveyor or maybe a servpro tech, wood floor installer, termite guy, home inspector?

IR thermal imaging camera see through walls pretty good maybe it would work through fiberglass?

http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1325517911/15


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## mmurray (Jan 16, 2012)

Jack up the front of the boat as high as it will go. remove the lowest screw from the trim tab mounting bracket, it is probably drilled all the through the transom but have the correct size drill bit handy to clean out the hole. If there is enough water to make the hull porpoise then it should come pouring out when the screw is pulled or the hole is drilled out. if nothing comes out run a coat hanger in there to check for moisture. 
check boat sides as they are seperate compartments
I do get some water in my rear compartments (mitzi 16) if my boat is in the rain. I installed a couple of deck hatches so I can check for water in them occassionally.


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## devrep (Feb 22, 2009)

that's a good Idea and easy to do. I'll do that this coming weekend.



> Jack up the front of the boat as high as it will go.  remove the lowest screw from the trim tab mounting bracket, it is probably drilled all the through the transom but have the correct size drill bit handy to clean out the hole.  If there is enough water to make the hull porpoise then it should come pouring out when the screw is pulled or the hole is drilled out.  if nothing comes out run a coat hanger in there to check for moisture.
> check boat sides as they are seperate compartments
> I do get some water in my rear compartments (mitzi 16) if my boat is in the rain.  I installed a couple of deck hatches so I can check for water in them occassionally.


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## devrep (Feb 22, 2009)

I know the foam is closed cell type and wasn't water logged because after I got all the water out I core drilled a large hole in the foam compartments each side of the poling platform and dug the foam out all the way to the bottom, about 5" diameter. foam was dry and no water holding in the compartments. I then put in waterproof round access plates that have bags in them and I store a set of rain gear in ea one. I'll take pics and show you what I mean. Not to say there couldn't be some water in the very stern at the transom but I don't think it could be much. I don't think they use any wood in the transom or any where else that could be water logged.



You can see the port side access plate next to the stern cleat in this photo.


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## mmurray (Jan 16, 2012)

there would not be enough water in the hull to cause any problems if you have already checked the area under the access hatches. 
The last idea I have is the prop. Get the numbers off of it and compare it to see if it is the stock prop, see if you can borrow a different one. If the prop is providing too much bow lift then it could cause porpoising, I have never heard of one causing it to this extent but who knows. 
I have a se300 foil I can send you if want to try it. I put a large compression plate on my motor and bow lift is not one of my issues.


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## mmurray (Jan 16, 2012)

just wanted to add that if the prop is providing too much bow lift then running the motor on the lower holes will be adding to the problem, if it is any better running it in the top holes then the prop may be a solution. 

not an expert but I act like one occasionnally


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## Creek Runner (Sep 1, 2011)

Closed cell foam will absorb water! 

I'm not trying to start anything here but lets look at the entire post. 

Hook in the boat? Owner says nope he has checked it

Motor mounted to low? Owners says no has ran it higher with no change

Wrong prop? Owner says he has ran it with a 4 blade prop, pics also show a stock aluminum prop, (I guarantee you that stock prop doesn't create that much bow or stern lift)

Weight distribution? Owner says nope has tried nothing helps

Water in the hull? Owner found water in the hull, (I do believe 11 gallons was quoted) drained all water out

Foam water logged? Owner says no 

Additional water in the boat? Owner isn't sure but doesn't believe there to be

That just about covers every thing so either you missed something above or it's operator error. I would suggest taking it into a shop that has the expertise to handle your issue.


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## CurtisWright (May 9, 2012)

This is a good thread. I am sorry it is at your expense, but I am learning alot.


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## devrep (Feb 22, 2009)

> Closed cell foam will absorb water!
> 
> I'm not trying to start anything here but lets look at the entire post.
> 
> ...


I AM GOING TO BE TAKING THE BOAT TO ECC IN THE NEXT WEEK OR 2 TO HAVE IT MEASURED FOR A CONSOLE GRAB BAR AND I WILL SEE IF THEY WILL LOOK THE BOAT OVER.


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## devrep (Feb 22, 2009)

it wasn't raining for a change when I got home so I went out in the back yard and checked the water issue again.  no water at all, foam was completely dry.    I keep the front of the trailer cranked all the way up so any water would have been in the stern.


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## TheFrequentFlier (Feb 17, 2016)

Creek Runner said:


> Raise the motor up its way to low, up 2 holes. Change your prop, don't know what would be the best because I'm not sure of what the boat is doing.
> 
> What I have noticed a lot times when I have customers bring up the same situation you have is, when I go run the boat with them they simply aren't going fast enough to give the motor positive trim.
> 
> My 25 shearwater with a F350 porpoises really bad, anything below 4500RPM or 42MPH it annoying, it doesn't go away until above 4800RPM around 51MPH. Anything below 4500RPM's and I have to reduce trim and put my tabs down about 1/3 of the way.


yep, but every time you push the tabs down further you’re just adding drag. You’ll stop the porpoise but your SOG will also suffer.

A perfectly designed boat wouldn’t require any tabs at all in any conditions and at all but that’s just not reasonable.

I believe tabs will always be necessary, but finding that happy balance where you use them efficiently with after finding the best combination of other variables that have already been discussed above.

I always find, for any given throttle setting:

1) the engine tilt that gives me the most RPM before airing out prop or any decrease in SOG

2) the amount of tab a function of the conditions; one must always balance between ride and speed, to some extent 

3) repeat steps 1 & 2 again as necessary

And that works great until conditions change or you need to change your running speed. Then restart. 

Anyone else have a technique they use?


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## Smackdaddy53 (Dec 31, 2012)

TheFrequentFlier said:


> yep, but every time you push the tabs down further you’re just adding drag. You’ll stop the porpoise but your SOG will also suffer.
> 
> A perfectly designed boat wouldn’t require any tabs at all in any conditions and at all but that’s just not reasonable.
> 
> ...


My HPXT will run 33.5mph with tabs half down and outboard trimmed out past flat. The tabs get the stern up and bow down while the prop is pointed up a little. I call it “airing her out”. It feels fast to me. If I don’t use the tabs and run the outboard tucked under to keep it from porpoising I’m doing good to hit 30.


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## TheFrequentFlier (Feb 17, 2016)

Smackdaddy53 said:


> My HPXT will run 33.5mph with tabs half down and outboard trimmed out past flat. The tabs get the stern up and bow down while the prop is pointed up a little. I call it “airing her out”. It feels fast to me. If I don’t use the tabs and run the outboard tucked under to keep it from porpoising I’m doing good to hit 30.


Good point. Edited my above. I find I always require a little tab to “lift” the stern as you say… that seems to prevent a subtle porpoise at high speed. Still playing around with my new skiff though, so contemplating moving the motor up a hole and possibly changing prop based on some of the WOT rpms I’m seeing.


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## Smackdaddy53 (Dec 31, 2012)

TheFrequentFlier said:


> Good point. Edited my above. I find I always require a little tab to “lift” the stern as you say… that seems to prevent a subtle porpoise at high speed. Still playing around with my new skiff though, so contemplating moving the motor up a hole and possibly changing prop based on some of the WOT rpms I’m seeing.


That’s where the WOT likes to be, stays right at 5500-5600rpm with a XXXcup threr blade. My buddy has the same hull with an F70 and a single cupped shelf PowerTech and hits 37-38 but hole shot sucks.


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## devrep (Feb 22, 2009)

9 year old thread.


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## TheFrequentFlier (Feb 17, 2016)

devrep said:


> 9 year old thread.


Sure is. I’m interested in the topic. Would you rather me have started a new one?


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