boat hydroplaning???

[neversinksmith]

hey gang. ive got a 16' fiberglass 85 Ozark fish and ski. v hull in the front, almost flat rear 1/3.
here is my problem:
after I get up on plane the boat feels like its "grabbing" the water and lists to the left. I steer right a little and it flattens out then it grabs and lists to the right, I steer a little left and it flattens out. It feels like its trying to balance itself but it cant. seems a little better when I have someone else in the boat with me. I cant figure it out.
boat originally had a merc 50hp 2stroke. it didn't really do it then but hardly got to full plane. then an 85hp 2 stroke. then a merc 60hp 4 stroke bigfoot really started acting up. just put a Yamaha v4 115hp 2 stroke. better but still feels a bit out of control. whats going on here ???

best way to describe the feeling on plane is that its struggling trying to balance itself then the edge of the bottom hooks up and grabs

 

[jbcurt00]

Google chine walking.....

Probably overpowered based on most 1985 Ozark 16ft specs,

50hp was probably underpowered


http://boatspecs.iboats.com/Ozark__Outboard/bp/42br1333bt3

 

[QBhoy]

I’d think the engine height is wrong or maybe you aren’t playing with the trim well enough ? Just a though.

 

[JASinIL2006]

Chine walking.

 

[MTboatguy]

Overpowered and Chine Walking. The 17 footer in that model is rated at 120 HP, but if I remember right, yours should be rated right around 90 HP, you will have to do some playing with the tilt and the trim tab on the engine.

 

[neversinksmith]

it was doing it with the 60hp four stroke. that's not overpowered is it?

 

[Scott Danforth]

it was doing it with the 60hp four stroke. that's not overpowered is it?

what does the capacity plate for your boat state is max hp capacity?

if you have a V-165, the capacity is 45hp
if you have a V-162, the capacity is 60hp
if you have a V-161, the capacity is 70hp
if you have a F-165, the capacity is 50hp
if you have a F-163 or F-161, the capacity is 110hp

these are all from the iBoats library of data and I question the 110hp of the last two.

 

[neversinksmith]

plate says 75hp max. I just did some reading on chine walk and most info says it typically happens at high speeds. mine does it at around 20mph. by the way it seems to be less noticeable w more people in the boat.

 

[neversinksmith]

also its not a vee bottom. not flat but slightly rounded

 

[ahicks]

also its not a vee bottom. not flat but slightly rounded

That's part of your problem. The boat is looking for, and having trouble finding, a surface that will carry the boat's weight hydro dynamically. In the center, it's OK, but as the boat turns, a great big gob of hull area is suddenly wetted, creating a ton of drag and turning the boat in that direction.

The 115 is way over the top in my estimation, creating it's own set of problems.

Bottom line, if I'm following what you are saying correctly, that boat has a crummy bottom design. Likely OK for a fishing boat, but maybe a bit sketchy as a ski boat.

 

[Texasmark]

Nobody mentioned "plowing" whereby the engine is high in HP but tucked into the transom too far causing the bow to dig in.

Get your engine vertical with the boat sitting horizontal or get the engine's lower unit pushed farther out from the bottom of the transom....if you have PTT it's a no brainer......push it out till it porpoises at WOT, then tuck it in till it quits. Come back with the reply.

Assuming you do as I suggested and your hole shot....coming up on plane from dead in the water, and you have PTT, just tuck in the LU close to the boat till you are on top or as you are getting on top and bump it on out till the boat floats on the water at your higher speeds.

 

[neversinksmith]

not new to boating. boating since I was 12. 35 yrs ago.
outboard is pushed back via the jack plate. planes out in about 1- 2 seconds. cant tilt back with the ptt very far before porpoising begins
I understand the concern about the overpowered 115 by like I said I had the same issues w the 60hp 4stroke merc bigfoot

 

[JimS123]

The motor is too big. The 60 was too heavy. You have an accident waiting to happen. The boat designers put those stupid plates on for a reason.

Be sure your insurance is current, but don't tell your agent that you violated the rules.

 

[roscoe]

Hmmm, question --

When the boat is at rest, is the motor perfectly perpendicular to the water?
Straight up and down, not tilted to one side or the other?

 

[southkogs]

... going with roscoe a little here ... and is it perfectly centered port to starboard?

 

[QBhoy]

Say it again haha. Sounds like an engine set up issue. Height or similar. Are you well aware of trimming etc. Not just the engine but the weight around the boat too ?

 

[Texasmark]

Back to the "plowing" question...............

 

[briangcc]

Here maybe this will help - based off what I could find on current production models....

Your original 50HP weighed in at 158 lbs
The 60HP 4Stroke weighed in at 247 lbs
The 115HP Yammie weighs in at 377 lbs


You keep adding more and more weight to the transom and it probably wasn't designed for this amount of weight. It's behaving differently between the motors as you basically have a 220lb adult now riding on your transom in addition to the weight of the original 50HP. Dump the adult on the transom. You'd more than likely be better off finding an older 60HP 2stroke.

**This assumes your transom is actually built to handle the additional weight & thrust of the larger engine - it ain't so why push it??

 

[garbageguy]

THe other thing that might help you get help is some pictures - the whole boat, then closer and closer to where you think your problem is

 

[tacx]

Just a thought. Would some type of fin added to the center of a flat bottomed boat help the side sliding problem?

just thinking about water skis having a fin on the bottom to help keep the ski straight? Skis made without the fin slide all over the place?

Just thinking out loud?