14' Aluminum is Porpoising. How can I avoid this?

[Viper2872]

I have a 14' Deep V Alumacraft boat. It has 3 bench seats. I have a 25hp Merc Tiller on it. I have the battery in the back of the boat because I have a transom mounted Trolling motor. I moved the gas tank in between the middle bench and back bench. I have to have the motor angled very far down just so that I can control the boat. I can move it up a notch or 2 when my Wife is along but that still isn't correct. It should be set about 5 notches back from what it is now so the cavitation plate is almost parallel with the keel. The only thing I can think of is a Hydrofoil or Hydro stabilizer. I'm not 100% positive that it will fix the problem and I don't want to drill into the plate if I'm just going to take it off again. I really don't want to move the battery up front and probably shouldn't move the gas tank that far away from the motor. I don't think trim tabs are an option because the boat is so small anyway. Any suggestions?

 

[jjacobs007]

Re: 14' Aluminum is Porpoising. How can I avoid this?

motor might be too big n heavy.

 

[royal0014]

Re: 14' Aluminum is Porpoising. How can I avoid this?

^^ +1
Gonna have to lose some in the back, or gain some in the front.....


<<)))(((>>

 

[pootnic]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Whats the " It should be set about 5 notches back from what it is now so the cavitation plate is almost parallel with the keel" mean?
Do you have a a long shaft motor on a short transom?
Weight on small aluminums is a big issue,you may have to move some.
You could always try a foil some people have good results with them,I've never used one.

 

[ingalp01]

Re: 14' Aluminum is Porpoising. How can I avoid this?

I'd try to move the battery all the way to the front. With that short of a boat, as long as you use a decent guage wire, you can run juice back to the trolling motor. Or see if you can put some inexpensive trim tabs on it... Smart Tabs perhaps...

 

[gt]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Please, I don't want to start a hydro-foil war here, I understand they don't work on every boat...

I had a light 16' open aluminum boat (Discovery). In the back was a 25hp Johnson electric start (20"), battery, 12 gallon tank, and me (240lbs on a good day). Without ballast (wife?) in the bow, porpoised like crazy. Going into the wind in rough water was scary. I installed a set of those hydro-foil type wings ($50?) on the cavitation plate. Solved 100% of MY porpoising issues. I ran it like that for 15 years.

One thought, buy a set, and c-clamp them on to try them. You'll be out the $, but won't have holes in the cavitation plate...

 

[FunInDuhSun]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Sounds to me like you need to move some weight forward BUT before relocating the battery, I'd add some heavy 'stuff' in the bow (anchors, extra gas tank, maybe an old battery) and see if it helps.

 

[wifisher]

Re: 14' Aluminum is Porpoising. How can I avoid this?

I had the same problem. 14' aluminum tiller steer, different brands, but same situation. I moved the battery and gas tank to the bow, and added a hydrofoil. moving the weight forward helped quite a bit, and the hydrofoil helped even more. It handles like a completely different boat now.

My gas tank and battery are both in front of the front seat. Just run a longer gas line, and a couple of wires. If you want to keep the transom troller,(I like them in the bow) you just need some heavier wires. If your motor has electric start you will need heavy wire anyway.

 

[Viper2872]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Sorry to cause a little confusion. I will try to take pictures this weekend when i get the boat and trailer back together and the motor mounted again. It is a short shaft motor on a short shaft transom. I think i am just REALLY light in the bow and it doesn't have enough weight to keep it down.

 

[Viper2872]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Here are the pics. This is how I believe that this is how it is supposed to be set up.


I have to have it all the way tilted towards the transom. The pin would be in the closest hole to the transom instead of the 4th like I have it shown here.


Does this help explain things better?

 

[tx1961whaler]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Is the motor's anti-ventilation plate even or slightly higher than the bottom of the boat? It's hard to tell from pics due to angles and such...

 

[gt]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Anyone chime in if you think I'm off base here...

In my opinion, proper running attitude on a small boat (without power trim), is a compromise at best. You need some negative trim to get on plane, and once on plane, you want it somewhere between porpoising (bow too high), and plowing water.

In a boat like yours (I ran mine for 15 years), proper attitude is attained from weight distribution and/or motor trim adjustment. Don't worry about what hole you think the motor trim should be in. Put in in the hole that gives you the best performance, both out of the hole, and up on plane. Every boat is different.

My old boat was very similar. And because of the way I used it, I was not willing to put the battery or fuel tank in the front for ballast. Originally, mine porpoised real bad. I had it bouncing one day going into the wind, I almost flipped it over backwards (at least it felt that way, scared the crap out of me).

My hull only weighed in around 350 lbs. Put a 150lb motor, 60lb battery, 80lbs of fuel, and my 240lbs in the back, and the boat was a little 'light' in the front...

The difference that hydrofoil (or whaletail, or whatever it's called now) made, was unbelievable. But again, I always ran in the lowermost hole. The motor looked like it was too far down, but with just me in the boat, it ran great. No porpoising, and jumped right up on plane. If I had another body in the front, still ran fine, although, I could get away with picking up 1 hole if I wanted to.

Like I mentioned before, I know those hydrofoils are not for every boat, and I've heard the stories of those for whom they have not helped at all, but for my boat, which was very similar to yours, it worked great.

Get it tuned for the way you want it, and don't worry about which hole your pin is in....

Good luck

 

[pootnic]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Have you tried in the pin closest to the stern?
Is it possible to raise the outboard up alittle bit?
Can't really tell if the plate is even with the bottom of the hull.
If I was porpoising in a light boat I'd try the pin as close to the stern as possible,the more you tilt the motor back the more the bow will want to come up.
Like you already know weights a big factor and maybe like mentioned before a foil would be a friend.
Just thought I'd add this in.
Do you know if your outboard has the right prop(rpm)?
Proper pitch,number of blades could help/hurt your situation as well.

 

[Viper2872]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Well, I went an bought a Stabilizer Foil today and will be installing it this afternoon. Hopefully it will help. I decided to after what GT said. It really helps to have someone with a similar boat have previous experience.

POOTNIC - I have tried it in the closest hole but then It doesn't feel right. I don't know how to explain it. I don't have a TACH so I'm really not sure about the RPM. However, I put a new prop on it that was the same specs as the Factory Prop.

I will try the stabilizer and let everyone know how it works. Thanks for the advice.

 

[bonz_d]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Hi Viper,
I know which Alumacraft model you have and it should do very well with that 25 Merc on it. Another experiment you could try would be to remove the trollong motor and battery for a test drive and see how it performs. I too believe you are a bit stern heavy.

My Lund S-14 is very simular to your Alumacraft and before I got a 35hp console steering engine I ran it with an 18hp tiller on it and to be honest both performed about the same and ran flat and stable either way

 

[Mi duckdown]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Move the pin to the second hole from the transom. and test

 

[ezmobee]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Anybody else think that motor looks to me too low? Does to me.

 

[Captain Caveman]

Re: 14' Aluminum is Porpoising. How can I avoid this?

The motor does look slightly low, but I'm not sure if it's enough to cause bad porpoising. I wouldn't rule anything out though. Hopefully that Stabilizer Foil worked yesterday. I'd like to hear how it went.

If I would have gotten to this thread early enough, I would have suggested having you and your wife switch spots - you sitting in the bow with her running the motor with the pin in different positions. That would have told you pretty clearly if weight distribution was the real culprit. The Foil should help with that but it may not be the only thing that you need to do. Are you a big guy? It's worth asking.

 

[Mi duckdown]

Re: 14' Aluminum is Porpoising. How can I avoid this?

That motor does look to low. if so. that hydra foil will hurt more than help.
I think measurements are in order, or clearer/ better PIC

 

[NYBo]

Re: 14' Aluminum is Porpoising. How can I avoid this?

Anybody else think that motor looks to me too low? Does to me.

Yes, but not by much.