The Physics of A Boating Accident.
01-10-2007 | 08:09 PM
#21
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From: Saucier/Gulfport, MS
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.
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.
01-10-2007 | 09:35 PM
#23
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From: Saucier/Gulfport, MS
01-10-2007 | 10:15 PM
#24
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Joined: Jan 2001
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From: Edgerock Baby!!
Re: The Physics of A Boating Accident.
One thing that needs to be said. Virtually all learning on a fast boat needs to be done in little bits. 99% of the time when someone has an issue it is because of extremes. Too much speed for conditions, too much or too little drive trim, too much tab, too hard a turn, too little common sense, or too big a set of balls. Each of us has a different learning curve and each boat does too. A simple rule of thumb is do things in small increments, run faster 5 mph at a time, play with tabs and trim one notch at a time, etc. Getting the feel of a boat is one of the most satisfying experiences out there and what we all pay such extravagant sums of money for
01-11-2007 | 08:53 AM
#25
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From: Ocala, FL/Union Mills NC
Re: The Physics of A Boating Accident.
Finding out what setting work best is a danger if you dont understand the parameters. Self taught boaters instructing other boaters how to operate boats is also a danger when they dont understand how other hulls may work. That is why we put 2 other classes together to help all performance boaters in all size , speed, and configuration learn the proper way to use your craft. Using a process of discovery has to have boundaries and technique to maintain proper control. If not damage or injury may happen.
01-12-2007 | 02:50 PM
#26
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From: Delray and NJ
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.
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.
01-12-2007 | 02:53 PM
#27
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From: Delray and NJ
Re: The Physics of A Boating Accident.
there used to be a book called everything you need to know about propellers. I think Quicksilver published it. Not a bad place to start to learn about the basics of boat propolsion.
01-12-2007 | 03:54 PM
#28
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Re: The Physics of A Boating Accident.
"typically utilize a cleaver prop" That would be the last prop to use on a bravo especially on that guys baja. Cleavers are best used on outboards that are mounted very high on lighter hulls (generally), not on heavier sterndrives. I would listen to Tres when it comes to learning about high performance boating safety.
01-12-2007 | 04:26 PM
#29
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From: Pittsburgh
Re: The Physics of A Boating Accident.
Im sure that if the tabs and drive are tucked too low it will give too much stern lift coming off the wave or wake and will set you up for a bow down entry, setting you up for a stuff. The key is having the tabs and drive set right. I do know that if they are too high, the bow tends to point up too high. Thats what happened with my incident. I under-anticipated the size of the wake and did not get the tabs and drive down in time to keep my exit and entry level enough.
01-12-2007 | 04:29 PM
#30
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From: Pittsburgh
Re: The Physics of A Boating Accident.
Airtime. Ive followed the project on your 240 quite a bit. Nice to see one of those old tubs can hit 80 plus with the right power and setup. Not sure if I wanna put the money into mine or just save it for a bigger boat. I appreciate the help. I'll pm you.
