Re: The Physics of A Boating Accident.
 

You're right in wanting to know how your boat performs in differing conditions. You've hit on a common issue- someone moving from a highly maneuverable boat and into an "offshore" style boat. Offshore boats are made for hammering waves straight on- that means compromises in turning. Adding to this issue is the stepped hull of your boat. First, your Donzi wasn't designed to "carve water" and the physical stresses of doing so and exponential vs. a ski boat. That being said, 30 or 35 mph isn't fast- unless you want to do full-lock, full power turns at that speed. Second, stepped hulls need to be turned in the proper procedure. If your wife might go off with a boat acting "weird", think of what she'll do after getting the experience of a high-side ejection from the boat. I can't give you specifics on your boat but most steps like to be settlled then powered through turns. I'd suggest hitting one of the Donzi forums and getting with some folks who own your specific boat. I don't mean to scare you but more than a few experienced racers have been tossed in turns from not cornering properly. Also, my step-V experience isn't near what many on here have so they may be a better source of specifics. My only experiences have been a few turns at the wheel and one trip as an eject-ee.

On Tres' school- it's probably a tremendous idea but I also think alot of it might be lost on a newer perf boater. It's sort of an MBA in high speed. No one says you can't go back for a second trip, though.

To your question on tab position- you'll want to use the drives to control nose up/down. Tabs are more for yaw- if you're getting cross wind and it's sterring you off-course, drop the opposite tab and straighten the boat up. Some boats need a touch of tab at neutral drive position especially running into a head wind. You'd probably want to keep your tabs neutral when turning. Tabs will give you a little more "effective bottom" basically adding a small amount of bottom running surface to your boat. There are times that you can get better top speed by trimming out until you lose lift (bow porpoising) and tab it down just a little bit. Sometimes youll do better like this rather than neutral tabs and less drive trim- but that's really dependent on your specific boat and load- that's the fun of experimentation.

Re: The Physics of A Boating Accident.
 

Great info so far. Im really at a dissadvantage. I dont have any indicators for my tabs so I have to work them from the seat of my pants. Fortunately I do prettymuch all my boating on the rivers here so navigation and crosswinds is not an issue. I will use the tabs to help get on plane and then to counteract any porpoising. If I got the tabs too high, the bow will do this then I drop them till it smooths out. I also use them to level the boat off so its not listing to one side or the other depending on occupants etc.. So they are not always even.

The one big question I have is how much is too much trim for the drive?? I usually keep mine low enough, on smooth water for top end runs, that its not throwing a roostertail. I have a Bravo 1 drive. Nothing fancy. I have played with it some with a portable gps and have overtrimmed to throw a tail, but never noticed any gain in speed. Did notice a different feel for how stable it felt in the water. Now I know some drives are designed to throw a roostertail. But I dont believe a Bravo 1 is. So what is the highest I should trim it in desirable conditions?? Highest possible spot without loosing speed or control?? BTW. I have an old Baja 240 sport. Straight heavy hull.

Re: The Physics of A Boating Accident.
 

You can trim to where you porpoise or where you lose speed. You can trim it to where you lose stability or at least start to feel like it's going away. If you're going from neutral to rooster tail and not seeing a climb in speed or rpm, there's a problem. I don't recall the Baja having an over-conservative x-dimension so you may be in need of a better prop.

No drive is really designed to intentionally throw a roostertail. Surface drives just do but that's irrelevant here. Unless you're dealing with big power, throwing water into the air is likely more counter-productive than anything. Lots of performance boats have Bravos on them. They're actually faster than the TRS they eventually replaced but a bit less durable as you near max power. They are usually mounted at a decent x-dimension and typically uitlize a cleaver prop. That means that they can be trimmed up until just the bottom of the prop engages the water and the top actually comes out as it rotates. That's where you'll find the least amount of drag and the highest efficiency.

Someone smarter that I will have to explain how different prop designs and dimensions affect bow and stern lift and how to properly size a prop to a specific boat. It's a little science and alot of art.

Re: The Physics of A Boating Accident.
 

I appreciate the info. The factory speedo doesnt always work. So I only get to test when I borrow a handheld GPS unit. Most of my observations are seat of the pants. And you can feel when the boat gets really loose and when you get more bite from lowering the drive a little. As for the X dimension. I have no idea. Im running the stock setup on the boat which I bought used and have been happy with. IE, no money to mess with it. :)

I would have to think that once you trim too high, despite it looking cool, you are gaining too much slip and loosing performance potential. And I do know there's a difference between my cleaver and Mirage props. Thanks for the info.

And by the way.. When hitting big wake or rough water.. Make sure to trim down the drive and tabs so the nose doesnt point to the sky. Learned that one the hard way. Closest I came to loosing it. I backed off the throttle but didnt get the drive and tabs down in time. Bow went near vertical from a wake that was bigger than it looked. Kept popping up till I could get everything trimmed down and throttled down. Scariest ride I went on. Did manage to keep the boat straight though.

Re: The Physics of A Boating Accident.
 

my old boat doesnt have tabs, amd the drive trim guages work when the want too..fixing things as I learn how..right now Im driving it by feel, trim em down to get on plane, then I trim up untill the boat starts to feel lighter and seems to be working easier and adjust so its level side to side...how about a basics trimming 101 post from somebody..running flat water, bumpy water, big ugly water..running uphill, downhill etc.....

Re: The Physics of A Boating Accident.
 

Eddie Hill said that is why he stopped racing drag boats and got into car drag racing.

Re: The Physics of A Boating Accident.
 

So far there is some really great info,, Chris,, thankss!!,, I hope every one feels free on this thread to just spout on about what they know or have experienced with out any sharp shooting,, just a friendly exchange,,, I know alot more people have questions,,, and so far I have learned alot about how little I really do know,, and that helps in being cautious and responsible when out on the water. I Really Liked seeing the figures,, and drawings, that showed up in the other boat accident thread towards the end,, thats what really got me motivated to start this discussion,, hopefully we can get some of those here as well. If your a member here who has a safety class or has the experience on some of the basics, please chime in. Please remember,, alott of people even non members read through these threads,, so if this helps a guy who goes out and buys a $400k 130mph,, or even a guy whos on his first $45k 70mph type of boat,, see that there is alittle more to it than just hammering the throttles.
Thanks so far and lets keep the ino going. :D

Re: The Physics of A Boating Accident.
 

I bought a copy of "Fast Boat Seamanship" by Dag Pike, as recommended on OSO. I've found it to be very useful, especially with respect to wave conditions and the like.

Re: The Physics of A Boating Accident.
 

ROLLWITHIT I have a 88 baja 240 sport ,the x is very deep on these I put a new drive together this fall went to a 2'' shortie boat handles nice flies flatter when you see a rooster tail you are way over trimed not good, i have owned this boat since 1990 and have made lots of changes now it got 670hp 83.2gps more this spring:D SO If you want to talk I will leave my cell on this post

Re: The Physics of A Boating Accident.
 

Where did you purchase it from? Sounds like something I would like to read.