What speed does my boat become unsafe?

[Skyhead22]

I have a 93 rinker captiva 186. It's 2500 pounds give or take dry. 18ft. Largest engine from rinker was 4.3 but is fitted with a 5.0/lx. I thinknow rated at 230 horse.

It currently tops at 55gps and still feels really stable. I'm having a serious thought of swapping it with a 350 mag mpi 300 horse. Proper setup should be in the upper 60mph area.

My main concern though, with this hull design at what speed does it really become unsafe? It was built to handle well and be a 50mph boat tops it's not an 80mph powerboat from the factory.

If you ask why? Why the need for speed, that's pointless. It's in my blood! I've been a horsepower and speed fanatic my entire life. I've raced dirt track, have a 700 horse mud bogger, I'm very knowledgeable with the working mechanics of drivetrains. I respect power and speed and use it responsibly, that's mainly why I'm concerned with the hull shape and designs limitations when it comes to top end.

 

[dingbat]

The problem isn't the boat or the driver. The problem is the unpredictability of the water.

I've been airborne a couple of times from rouge waves coming out of no where. Same HP, but twice the weight of your boat.

 

[Scott Danforth]

I have been in a hydrostream where we had to slow down from 90 to 50 to turn. Same boat and its owner flipped end over end 2 weeks later as the boat hit a small wake and became airborne then caught some wind.

As dingbat stated, its the unpredictability of the water.

I would expect your boat to still be stable at 60, however as the boat gets faster, less and less of the boat is in the water. does your hull have a bit of a pad?

 

[Bondo]

My main concern though, with this hull design at what speed does it really become unsafe? It was built to handle well and be a 50mph boat tops it's not an 80mph powerboat from the factory.

Ayuh,.... The line yer lookin' for, can't be found, til ya cross it,......

If yer Lucky, as I've been, you survive it,....

Back in the day, Hydro-Stream speed boats were one of my dreams,...
Ended up with a Glastron Jet-Flite, a 14' hull rated for 60hp,....
1st motor I put on it was a Merc I-4 80hp outboard,.....
After a couple of those, I slapped a Tower of Power, 135hp on it,....

Donno what the speeds were, no Gps in those days,...
With the 135hp, the line was pretty easy to find if the water conditions were anything but a 4" chop,...
A couple of times there were butt clenching moments, but I lucked out, 'n landed wet side down every time,....

The joke on the lake I boated at was, Nobody knew what the top of my boat looked like, because all you could ever see was the bottom of the boat,....

That was launchin' with the ole 80hp, no power trim,....
With the 135hp, it would do that 3 times before it landed runnin' on-plane,....

'course, power trim fixed that part of the equation,...

Even with Horsepower, a 50 mph hull ain't gonna be a 70 mph hull,....
If ya wanta go Fast, find yerself an off-shore style speed boat,... it safer, 'n needs less horsepower to do it,....

 

[thumpar]

I think you would probably be OK up to 60 or maybe a tad more but you will need to be careful. That is a light boat and could chinewalk on you quick.

 

[fhhuber]

Max safe speed depends on waves/weather and how your boat is loaded.

There is no fixed answer for all conditions
(unless you want us to assume worst case for everything and tell you not to exceed 20 mph, meaning never get on plane.)

Glassy smooth water and the boat loaded for best balance, you could potentially be safe at very high speed.... until you turn the steering wheel.

Note that crossing someone's wake on that glassy smooth water running top speed might be as good as launching the boat off a ski ramp.

https://www.youtube.com/watch?v=1UEETjztLqI

See where the boat starts "tipping" side to side at appx 1:00... He's unsafe right there, but getting away with it.

1:24 he's in that unstable condition and then purposefully crosses another boats wake... GAME OVER

You need to learn to FEEL how the boat is running and adjust the boat or the speed to NOT be unstable..

 

[alldodge]

Don't know what speed that will be. If your going to push it, suggest changing to full hydraulic steering.

 

[Skyhead22]

We shot this video last night. Kind of scary now I watch the video, it felt like I had a lot more boat in the water than that. At the beginning I look like the guy in bass boat crash. I did throttle out for the wake I crossed.

https://youtu.be/EO4BRP50bfo

 

[thumpar]

It looks like it is just porpousing. Trim in a tad.

 

[HT32BSX115]

We shot this video last night. Kind of scary now I watch the video, it felt like I had a lot more boat in the water than that. At the beginning I look like the guy in bass boat crash. I did throttle out for the wake I crossed.

https://youtu.be/EO4BRP50bfo

That video looked pretty "normal"

I have hit a small wake at approx 55 mph with my 21ft FourWinns 211 Liberator. It wasn't fun at all. 80mph would be very bad.

The following Youtube video is just that....Just bad...... Seven people in a Fountain 38, going at a pretty high rate of speed. They hit a wave/wake at an oblique angle. but in the video, it doesn't appear that the wave is all that big. the driver didn't seem to alter the course to hit the wave at a better angle

The boat is looks to be "chine-walking" a little but doesn't seem excessive... Everybody looks to be holding on.... but couldn't. .

If you ask why? Why the need for speed, that's pointless. It's in my blood!

https://www.youtube.com/watch?v=Kp50CSUKBbc

Above, the driver is literally thrown from his seat, and looks like he hit his head on something and you can see some of that "blood"

The "accident" happens at 2 min 20sec

I am not trying to "beat you up for asking about going fast. It's a good question.

But, if you look at most of the "go-fast" boats, they're heavy and they're mostly "cat" type boats, hydroplane or flat bottom. Not Deep-Vee. Deep V boats tend to "chine-walk" as additional speed gets them higher and higher in the water reducing the whetted surface in the water.

Just taking a "run-A-Bout" type deep vee boat and putting a LOT of HP (way over the placard hp) in it to go fast is potentially dangerous.

Regards,


Rick

 

[jumpjets]

I'm kinda like you. I want to see how fast I can go, but I don't have the ability to buy a high performance cigarette, fountain, or formula at the moment. As such, I just experiment in my current family boat a bit. I currently have a Rinker that does 55+, but it feels a bit wonky at that speed. I modified my old Wellcraft to get from a 38mph top speed to 53mph by changing a couple props, retuning the carb, ignition timing, and using better fuel.

Here are my personal rules of speed for a regular boat:
1. Go out and do top speed runs by yourself. Less chance of hurting passengers should you royally screw up. Also, less weight.
2. Go out early in the morning. Water is generally smoother, fewer other boats out producing wakes, and the air is cooler so you'll get a few extra HP out of the engine.
3. Unload all unnecessary gear. Less debris to fly around the cabin should I screw up, and less weight, thus higher speed.
4. Only make high speed runs on familiar waters, that you know are deep enough and free of debris. Do a low speed pass and watch your depth sounder prior to making a top speed run.
5. Be light on fuel. Less risk of fire, less pollution if you wreck, and less weight, thus higher speed.
6. Ease into the throttle, don't just go flat out from a stop. I get on plane and then increase in 500rpm increments, so I can assess the handling and throttle back if the boat gets squirrelly.
7. Go top speed for short bursts. It saves wear and tear on your drivetrain to only go WOT for short time periods. It also minimizes your risk of things going south. I'll get up to WOT, trim it, assess my top speed, and throttle back. It takes 30 seconds or less.
8. Go straight. No hard turns.
9. All other basic boat safety rules apply. Tell someone where you're going. Wear a life jacket. Have a radio available. Have a tow plan. Have a fire extinguisher. Don't go out unless it's warm enough that you'd survive being in the water for a bit. If the water is rough that day, forget it.

I like the bragging rights of having a 55+MPH boat. My family could care less. By following these rules, I get to be a speed demon, and my family doesn't have to deal with getting wind blown as I chase personal speed records for my own satisfaction.

 

[HT32BSX115]

It sounds like you have thought it out and have a plan.

I won't say it's not "fun" to go fast.... I have gone 450 knots at 400'........ It was pretty cool......pretty scary, but pretty cool.......it's amazing how comfortable one can get at those speeds........one slight mistake though, and.................

That's out of my system now .

Cheers,


Rick

 

[fhhuber]

It looks like it is just porpousing. Trim in a tad.

Definitely..

Bow is bouncing = you need bow weight and/or adjust the thrust angle to push the bow down until it quits bouncing.
Or you're going too fast if it can't be trimmed to stop the bow bouncing on basically smooth water.

And that video was pretty smooth water, so the boat should be rock steady when properly trimmed.

********************

Not saying to go slow...
Just make sure the boat is stable at whatever speed you will go.

 

[redneck joe]

Swapping a motor for an extra 5 mph sounds like a lot of work.

 

[H20Rat]

You are highly optimistic about your expected speed... No way no how it is going to hit upper 60's with that engine. It will take another150-200 hp in addition to what you are doing to get that hull to upper 60's. I'd expect no more than 60 even on a good day.

 

[Skyhead22]

I have gotten some great responses! Very appreciated.