My Boat "Spins Out" when turning hard

[75-JOHNSON]

Boat is a 16 foot tri haul, with a 1976 75hp johnson. i have the motor set so the anti cavitation plate is about half an inch higher than the keel of the boat. It has a brand new 3 blade prop. the trouble is is when i turn very sharp and give it full throttle, it accelerates hard then seems to 'spin out', while the motor instantly shoots to 6000 rpm. i have to let off the throttle, then come back on it again. this also happens if i am going at WOT and turn VERY sharply. i am sure it is not the hub slipping, as it is brand new. I tried lowering the motor on the mounts, but that did not help. also trimming up or down does nothing. any ideas appreciated.

 

[Overkill82k5]

Re: My Boat "Spins Out" when turning hard

That's normal. The sharper you turn (at speed) the closer to the surface of the water your prop gets. While leaning (turning) there is more of your boats hull in the water and that gives you more lift, raising your prop closer to the surface of the water. The RPM jumping is the prop grabbing air (cavitation, or ventilating). When you add air to your props water, it spins much easier and the RPM's jump up. When you back off the throttle you are letting your boat settle back into the water and your prop goes back to pushing just water, no air, hence RPM's lowering and thrust returning. Hope that made sense, haha.

 

[26aftcab454]

Re: My Boat "Spins Out" when turning hard

boats turn like cars... you go to fast and turn to sharp a car will spin out too.

lower the motor deeper-or do not turn soo fast- or slow down.

 

[DuckHunterJon]

Re: My Boat "Spins Out" when turning hard

Yup, pretty normal. Some props are better than others, but most will ventilate when pushed hard in a turn. Beyond lowering the motor, trimming down, or trying a different prop - I'd say you learn to live with it. I back down on turns, but that may be me being too chicken to take them any more than half throttle anyway.

 

[Bob_VT]

Re: My Boat "Spins Out" when turning hard

There is allot to do with the hull design too. I would imagine your hull is pretty shallow at the stern and the lacking of the deeper V the more it happens.

 

[royal0014]

Re: My Boat "Spins Out" when turning hard

Why do you find it necessary to turn sharp at WOT? It's hard on the boat and the motor, and dangerous. Slow down, before you become a statistic!

 

[kellmike626]

Re: My Boat "Spins Out" when turning hard

Dude, slow down. If you want to make sharp turns at WOT, that's what jetskis are for

 

[INJUN]

Re: My Boat "Spins Out" when turning hard

I agree, slow down and it will not happen. Whats the need for WOT turns.

 

[Moto-Mac]

Re: My Boat "Spins Out" when turning hard

I agree, slow down and it will not happen. Whats the need for WOT turns.

especially in a tri hull boat!

 

[steddy]

Re: My Boat "Spins Out" when turning hard

Another cavitation phenomenon - it's referred to as "gearcase blowout" in some service manuals. If you have a right hand prop rotation, it is more apt to happen in a left hand turn. The opposite is true for a left hand turn prop.
Trim down & throttle back to alleviate the problem. Stay safe.

 

[75-JOHNSON]

Re: My Boat "Spins Out" when turning hard

thank you all for the replies, sorry im late getting back to you. Great advice and well appreciated. i have no problem living with this little problem, i just didnt know it was a normal occurance. Thanks again =)

 

[DaNinja]

Re: My Boat "Spins Out" when turning hard

I watched a little tri-hull flip in the channel in Grand Haven. The driver hit full throttle and full left/port with the steering and the boat pitched up and rolled over. We watched as all three teenage guys popped to the surface. The Coast Guard was on the scene in a minute since they probably heard it from the station.

So yeah, throttle back and trim down so a spin doesn't turn into a flip. Stay safe!

 

[Lyle29464]

Re: My Boat "Spins Out" when turning hard

Sounds like you have hit the perfect setup. Some people plow tons of unneeded water.

Can you raise it a 1/2 inch more were it almost gets air with a normal turn

 

[The Hammer]

Re: My Boat "Spins Out" when turning hard

I know in driving performance cars on a slalom course or skid control course you learn to listen to the tires, they actually tell you how much you can push it, so maybe this is how your boat is talking to you.

 

[DaNinja]

Re: My Boat "Spins Out" when turning hard

I know in driving performance cars on a solome coarse or skid coarse you learn to listen to the tires, they actually tell you how much you can push it, so maybe this is how your boat is talking to you.

No idea what a "solome coarse or skid coarse" is, but with the way the Starcraft is propped right now, I can hear in the turns when she wants to be trimmed down or the throttle reduced.

 

[The Hammer]

Re: My Boat "Spins Out" when turning hard

Sorry its spelled slalom. Its a driving course with orange cones. Also I should have said skid control course.

 

[DaNinja]

Re: My Boat "Spins Out" when turning hard

Sorry its spelled slalom. Its a driving coarse with orange cones. Also I should have said skid control coarse.

Sounds like a coarse course.

 

[hibbert6]

Re: My Boat "Spins Out" when turning hard

Interesting stuff. 40 years ago, my buddy's family had a 24' Thunderbird tri-hull cuddy. When his dad let me drive it, he told me to not be afraid to turn harder - "That's what these hulls do well, son" if I remember correctly. As if to compensate for the ride being so harsh.

So now, I own my own Tri Hull, and it cavitates on hard turns. All this time, I figured something was wrong, either with my boat or my driving. Thanks for restoring my self esteem!

Dave

 

[NSBCraig]

Re: My Boat "Spins Out" when turning hard

There really is never a need to turn WOT.

IN fact some hulls like flat bottom skiffs and vented performance hulls are way worse then your tri hull.

Problem- operator error
Fix- figure out how to handle your boat.

 

[Gary H NC]

Re: My Boat "Spins Out" when turning hard

Hull design is a major factor as already said.
Mine will turn hard at WOT but it needs trimmed in a bit.
Not a practice i usually do though.