Boat porpoising

[DRIFTER_016]

 

 

Would trim tabs help?

 

I emailed the dealer to see what they have to say.

 

I have said before to put on a pair of Smart Tabs.

Best bang for the buck as they only $134 at Cabelas and there is a $10 mail in rebate until July 4th.

 

Smart Tabs at Cabelas

 

I would also check motor height as well as angle when tucked in.

I have been in boats that just don't handle well at all without tabs though.

[smally21]

thats no good pete. some great ideas to fix the problem but the boat should run fine the way it is solo and unwieghted...the porpoising and other should occur because you have wieghted the boat wrongly with gear or passengers..you shouldn't need to run with full live wells or pop bottles or patio stones jammed in the bow.

 

it probably wouldn't porpoise if you left the trailer attached to it either but doesn't solve it!

 

whats the dealer say? not familiar with the setup are there any settings on the outboard to adjust its angle or height for setup?

[DanD]

If it is really all the way down. Then you have problems I think you need 15deg shims. Between your motor and transom your engine may may be too low. Post photo

Change prop or trim tabs

 

dang I hate autocomplete on phones

 

I agree that if your motor is already down all the way, it needs to be shimmed down. (prop pointing on a more downward angle when trim set fully down)

The HP of the (your) motor has the ability and power to still lift the bow past plain and on to the bouncing that you’re feeling.

The whole idea of power trim is so that you can compensate for different weight distribution (one two or more people); so adding fixed weight to the front is just a bandage for the root issue.

When set up properly you should be able to take off from a dead stop with the trim all the way down; that’s to hold the bow down.

Once up to speed, you start trimming up, until you can feel and here a RPM increasing without a throttle change and the boat leveling out. Go past that trim point for the weight in the boat and it will start to porpoise.

Your motor (I think) is posibly set to close to water surface level line and you cannot drive the bow low enough under power, to stop it from bouncing.

My last boat that I had, had enough range with the power trim that if I was by my self or with four people; I could still plain the boat without porpoising and the only difference was top end speed.

 

Dan.

[sneak_e_pete]

Thanks for all of the responses. I am of the mind that I shouldnt have to add anything to make it run right. I will see what the dealer says.

[Sinker]

Your right, you shouldn't have to change anything but the trim. I still have a feeling it was those lake erie rollers, but I could be wrong. I'd take it for a run on some smaller water first, just to see.

[SRT8 smoker craft]

I run WOT on erie rollers all the time and my lund is light in the bow TM/starting batteries are in the back You should definately be adjusting the trim once you get on plane . My father in-law was told not to mess with it "it's not needed" his boats a 18'6" bowrider and it always feels like your going to speer a wave because the bow is to low and it "Falls" off of the waves and is porpoising all the time ,scares the crap outta me. I have tried to explain the trim to him but he takes his buddies advice over mine and just leaves it trimmed down all the way and put a hydrofoil on it .

[aplumma]

If you have some one close who knows how to trim out a motor and knows what to feel for it would be worth a 6 pack of brown pop to tempt them out for a blast.

 

 

Art

[Terry]

I have never seen a boat porpoising because the trim is down too far

 

to me porpoising means the bow of the boat is lifting too high {by the power ,the angle, height and prop} and continues to lift till the engine can no longer support the lift and it falls and hits the water again it starts to rise and the cycle continues over and over.

trim angle down too much and the thing should get up on plane easy but then the bow will plow through the water and will bounce somewhat on each wave if the right size the engine may not reach full rpms

[sneak_e_pete]

Ya, its hard to explain. When I was going slower (maybe 2500 rpm) the bow was high, but when I gave it gas the bow just started bouncing big time on each wave. I got nervous each time and let off the throttle. My boat before this was a 16 ft with a 40 and I would have run wide open in those waves.

[Sinker]

Ya, its hard to explain. When I was going slower (maybe 2500 rpm) the bow was high, but when I gave it gas the bow just started bouncing big time on each wave. I got nervous each time and let off the throttle. My boat before this was a 16 ft with a 40 and I would have run wide open in those waves.

 

I don't think you even got to the point of trimming up. I think if you'd have kept on the throttle, the bow would have come down, and then you could play with the trim. Sounds like you were almost at the point where you need to start trimming up, but let off the throttle.

 

Again, its hard to explain.

 

Getting someone to take it for a rip, who has more experience in a bigger boat would help.

 

Just hammer it, trimmed all the way down. There is nothing to be afraid of. Once she breaks, and the bow comes down, start trimming up a little at a time until revs come up, with no added throttle.

 

I don't think this is a porpoising issue. The best thing you can do is run the boat more, and get used to it. Every boat handles differently.

 

S.

[DRIFTER_016]

Yeah, it sounds like you had not gotten to the point of being on plane.

I gather you were running into the waves by the sounds of things.

When I used to run my boat on Erie into nasty close together waves I would drive it bow up on purpose.

If not you just took too big of a pounding. Anything over 2 1/2 or 3' I would run this way.

2 footers I would just skip across.

 

Running into waves the face of the wave is much steeper than the back of the wave and this causes the bow to bounce up. Porpoising occurs when you are riding in a swell (on some boats as small as 6") and the bow bounces up and down like a bucking bronco. Very unsettling (trim tabs get rid of this).

[sneak_e_pete]

Thanks so much to everyone for posting. I will play with it a bit more and see ( without the kids in the boat ).

[Skipper D]

Just sent you a pm .

[Harrison]

Just throwing this out, sometimes it is just a matter of finding the sweet spot between speed and trim. It is a new boat, you may just need to spend a bit more time dailing it in.

Edited June 18, 2012 by Harrison

[beagle dad]

my boat does the same thing..

i move weight back..when alone i fill the back livewell with water

took porpoise away

[Sinker]

Just throwing this out, sometimes it is just a matter of finding the sweet spot between speed and trim. It is a new boat, you may just need to spend a bit more time dailing it in.

 

This is what I'm thinking too. Don't start changing things, or adding things yet. Run it a few times and get a feel for how it works. They are all different.

 

S.

[hutch4113]

Hi all, got the new boat out yesterday. Although it was really nice to have her in the water, she was porpoising like crazy once I got over 3,000 rpm. Although there were some small rollers, I should've been able to open it up.

 

Not sure what to do. It was trimmed down all the way. For reference, its a Smokercraft Promag with a 140hp.

 

Thanks in advance.

 

 

Reading the post with interest, as I have the same boat. The other thing to look at would be the pitch of the prop. If it is wrong, it will cause some of the issues you are seeing. The dealer may have installed the wrong size, or may not know what size to put on. As an example when I bought the boat, it had a 23 Pitch on it. Since it was used, I am thinking they just threw anything on it. Horrible to plane. Also when I had 3 people in it (or the livewell full of water) it would bounce around like crazy.

 

I am testing out a new prop right now (21P) and will probably go lower (either 17 or 19 - 4 blade Spitfire from Mercury). My issue is I don't think my RPM gauge is reporting the right WOT numbers (it shows 6100 at full throttle...at which point the engine should cut out...but doesn't).

 

From what I have researched the proper pitched prop can make a world of difference (along with the motor being at the right height).

 

I think my engine is at the height so if you want to compare, let me know (I am in Barrie).

Edited June 19, 2012 by Tupelo

[corvette1]

what hole is the motor in what size prop what rpm at wot

[solopaddler]

I had a horrible problem with porpoising when I maxed out my old 16' Lund when I put a 40 on it.

 

Even in flat calm water it porpoised terribly. In addition turning and overall performance sucked.

 

And yes, I tweaked the position of the motor on the transom as well as the prop.

 

Ultimately I installed trim tabs and the problem was instantly gone as well as enjoying a very noticable improvement in performance.

 

No more porpoising, on plane twice as fast, higher top end speed and much more control making tight turns.

 

I wouldn't think twice about it. Install the correct trim tabs and be done with it.

[bigbuck]

It's a brand new package, it should run correctly from the get go, if it does not, it's the dealer's problem. The owner should not have to spend on trim tabs on a brand new boat.

[Sinker]

The boat hasn't even been on plane yet. Let him get it up on plane, and then add some in put.

 

I think he got to the point where the boat was just about to break onto plane, and he let off instead.

 

I've never seen an 18ft aluminum boat with trim tabs. I thought Mike added them to his to slow down his trolling speed......

 

S.

[mpt]

Hi all, got the new boat out yesterday. Although it was really nice to have her in the water, she was porpoising like crazy once I got over 3,000 rpm. Although there were some small rollers, I should've been able to open it up.

 

Not sure what to do. It was trimmed down all the way. For reference, its a Smokercraft Promag with a 140hp.

 

Thanks in advance.

 

 

From your original pic it looks like the motor is trimmed too far down.

You should be nose diving not porposing. Was the motor position adjusted after this pic?

[sneak_e_pete]

Nope, was fully down like that

[sneak_e_pete]

Taking it out on Saturday and will let you know how it does

[hutch4113]

Taking it out on Saturday and will let you know how it does

 

How did it go? I put a smaller prop on my Pro Mag (had a 23P on it..went down to 21). Noticed that I have quite a bit more bounce than before.

 

I am going to go to the new Merc 4 blade prop and will try again.

 

Should also note I had 4 people in the boat. Didn't seem to matter where I put them.