Overpowered Boat ?
 

I grew up water skiing behind your typical family production boat. I also have several seasons at Havasu on a friend’s 21’ Shockwave. My wife and I recently purchased our first boat a 2004 25’ shockwave with a 500efi.

Is there a top speed/engine power for a boat like mine? As I understand from my boater safety course most production boats have a max recommended engine size.

As I learn more I have heard/read of guys supercharging there engines or putting massive 1000hp motors in boats like mine or even smaller boat.

The reason I ask is, at 78mph (indicated on my speedometer) my boat was starting to get a little “floaty” for lack of a better term. I was wondering how a boat can handle such a jump in power without just becoming a youtube crash video.

Sounds like chine walking. When you're running with very little wetted surface, your boat is probably riding on just a small pad, and can "slip" from side to side as it falls off the "pad", which is the the lowest/flattest part of your hull.

that is what I figured,

Can this be corrected? I am guessing it is a trimming issue?

How would a boat with more power not just make the problem worse?

your trim would have nothing to do with it your trim control up and down motion theres really nothing u could do about it

Bad advice, Does it have hydraulic steering? if it does not that will be the first thing to do above 75 mph. A different prop etc. There are lots of place out that way that have experience with that hull and they can probably calm it down.

All boats get a litte "floaty" at speed. Thats when the hull lifts up and starts to release. Chine walk is a definite oscillation from side to side, almost a wham, wham, wham when really bad. You may just be experiencing the wetted surface releasing. Do you have tabs? A performance boaters course will give you the Non "internet opinions" to identify your issue. It may be nothing, it may be something

It has hydraulic steering and Dana trim tabs. I am not really worried about my boat. I am happy with the performance and handling. The floatyness I described is what I expected when running at top speed, and was only felt the last mph or two gained. At 75 the boat felt solid. My question is, with more HP's, different prop ect, the boat will go faster. Please correct me if I am wrong, as the boat goes faster, it will ride higher in the water and things like chine walking ect would become more evident. How do people with boats my size and smaller safely put close to 1000hp into their boat, increase speeds close to 100mph and not have issues?

There is no way to put a 1000 hp in a 25 foot v-hull boat and say theres anything guaranteed when it comes to safety, gimbal breaks or you hit a wave wrong at 100 mph its not going to be pretty. I will say however, my 272 Baja runs 100mph, I have added longer trim tabs and full hyd steering, driven right by someone experienced it is super predictable to low 90's, it feels more solid at 80 than my buddys NON hyd steering Checkmate does at 70. Above 92-95 depending on the load, it is aired right out and on the edge of something very bad happening. Your boat would probably benefit from twin ram FULL hyd steering, it is night and day different, Smitty

Artic Thanks for the reply.

I am not really worried about my boat. I was just wondering how it is possible.

I did have someone explain it to me this way:

The boat gets "floaty" as it nears its top speed because you have the boat in its lowest drag settings in the water, this includes trim tabs and drive. In a boat with more power the boat will reach a higher speed with the trim tabs and drive still in the water. Then just like at the lower speed with less power, as you raise the trim tabs and trim the drive to maximise efficiency and lowering drag the boat will start to feal "floaty". So in theory the more power/speed is not the main factor in the "floatyness" it is how much boat/drive/trim tabs you have in the water.

Does this sound correct or is it way off???

This is my take on the subject...all hull designs exhibit different characteristics at higher speeds.The less wetted surface you have the less resistance there is to move forward thru the water or over the surface of the water. Applying more power to overcome this resistance reveals limitations in the design relative to adhesion to the surface of the water.

External mechanics such as trim tabs, external hydraulic steering, different prop designs,etc.tend to correct the shortcomings in any particular design relative to safety and handling at high speed.

That being said and to answer your question, many boaters (such as myself) boost the available power not necessarily to achieve a higher top speed but to improve the overall enjoyment of the boat. With big power available acceleration and load carrying ability as well as cruise speed are enhanced. I know with my old 255 Formula going from 500 to 800 horsepower in the water makes it a hell of a lot more fun to drive under all conditions as well as pushing the top end quite a bit.

Virtually every high performance boat gets a little bit "loose" at the very limit. The reason is actually pretty simple. Although water provides buoyancy, it also induces drag. So to get every last mile per hour out of any hull, you're balancing leaving as little hull in the water (to reduce drag) with leaving enough in the water to provide forward thrust and not pointing the bow at the sky at the wrong time. There are many ways to reduce the amount of drag such as trimming up to force the bow up, adding steps to the hull to aerate (lubricate) it and raising the prop shaft height relative to the bottom. And that's just a few of them. But all performance boats maximize thrust and minimize drag to get every last MPH out of a given hull / power plant combination.

Why don't family boats feel as loose at the limit? That's a pretty simple product safety thing. One doesn't want Ma and Pa Kettle buying one of your family boats and complaining that it feels loose at 45 MPH - or worse yet flipping it over with the kids onboard. Then again, it's pretty hard to loosen any hull up at 45 MPH. But, I think you get my point.

I do remember one of the editors of the former Powerboat Magazine taking a ride in a Fountain factory race boat once. He was amazed how much faster it was than a similar "stock" boat. He was also amazed how much looser it felt than the stock boat. The reasons? Everything I mentioned above, plus a whole lot more power. I can tell you from personal experience that driving a true race boat - even one set up properly - is not something you just hop in and do. It takes years of practice. And even when you do get good at it, you're still balancing the boat on the edge of oblivion in many cases. But that's how you win races.

Speaking of power, adding bags of power is guaranteed to bring out some of the worst traits in any hull. Hulls that feel perfectly safe with 500 HP at 70 MPH can become almost totally unmanageable with 800 HP at 80 or 90 MPH. That's where knowledge of setup (adjusting many variables to make a boat handle differently) comes in very, very handy. In fact it's entirely possible that adding a few hundred HP to a given hull may make it virtually un-drivable without major changes to the setup of other components.

You mentioned one of the more common nasty traits of many performance v-bottoms at the limit - chine walking. Chine walk can be managed through a combination of reducing the amount of trim (which diminishes speed), adding some trim tab (which also scrubs off speed) or working the steering wheel to counteract it (actually the best thing to do.) If you add more power though, this is only going to become more pronounced.

So if you want to add more power to your hull, think long and hard about the possible side effects first. I have many friends who have screwed up perfectly good / great handling boats by adding humongous power to them. Most of them are actually still alive to tell you all about it. But what virtually all of them ended up doing was severely limiting the resale market and value of their boats. Oh, and the reliability went down the tubes too. Hope that helps.

Tom

That sounds right on. The "floatiness" is not chine walk and dropping the drive a bit should stabilize it if in rough water or if it just feels too loose. Different hulls react differently to more power. Some keep going faster while others develop bad handling traits or just hit a wall and won't go any faster. My hull has been proven to be predictable over 100 mph (mine runs very stable 80s). As mentioned, full hydraulic steering is worth every penny. It sounds to me like your boat is running pretty good!

Not necessarily..speed is a relative dynamic that changes everything...ten more mph may make it dangerous regardless of trim or tabs. There is a design limit for most hulls regardless of mechanical influences.

Think about this...I have been running boats in the ocean and on inland Lakes and rivers for 45+ years. Your boat pushing 80 MPH is faster than most of the World Champion Offshore Power Boats 30 years ago. i remember if you had something that ran 60 you were blisteringly fast!! now we have standard power factory production step hull deep vees that run 70+ easily with a full fuel load and 4 adults on board. I think that in it's self is amazing.

I think that needs a bit of qualification. I drove a bone stock Donzi 22 a few weeks ago that we delivered new in the early 2000's. It had a 502 Magnum with a Bravo drive and whatever 3 blade prop it was delivered with. Although I wouldn't call what it did near the limit (mid 60's) evil, it did get very queasy and didn't inspire a whole lot of confidence in me trying to wring any more MPH out of it. This is where "setup" comes in. Hydraulic steering would have been really nice, but the stock steering didn't have any play in it. I think a different prop and a shorter drive would have calmed it down a ton. Adding any more power to that particular hull with its current setup would lead to a real handful.

A lot is in the set-up. These hulls like a higher X (Imco shorty). Props have an effect too but a lot of us are running Bravo 1s. I know of an Ilmor 22 Classic that runs over 103. I know of two others that run low 90s. I know of another that runs at least mid 90s. Those are the ones I'm familiar with; There are lots more! When everything is dialed in and clicking these boats are a blast to drive. Oh....and when you drive your first Donzi Classic you can throw most of your boating experience out the window! Mine scared the hell out of me the first time out and that is when it only went 73. Now driving my boat is my second most favorite thing to do....

Moose, the bow dance you describe is normal and I'd bet that your hull could handle more power easily but you need to talk to other owners of that hull first.