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biggie
02-12-2013, 09:35 PM
I have a 1987 Donzi Minx, does anyone know the terminal hull velocity of this model?

VetteLT193
02-13-2013, 07:22 AM
I have a 1987 Donzi Minx, does anyone know the terminal hull velocity of this model?

Seems like it would be very hard to calculate properly. The issue with planing hulls is as they go faster they go up and out of the water more. Also, the speeds are high enough that wind resistance is also a factor. So it comes down to the friction of the boat going over the water and through the air. In a nutshell if you add enough power you would run out of driver before you hit any terminal velocity.

On a displacement hull there is a calculation. It's called the Froude's Number.

Just Say N20
02-13-2013, 07:52 AM
With proper hull reinforcement, steering upgrades, engine upgrades, drive upgrades, there have been classic 16s that have run in the mid to upper 80s (with Ed D. running over 100), Classic 18s that are currently running in the upper 80s, GT-21 running in the upper 80s, a couple of Classic 22s topping 100 with several running around 90±.

I suppose, the answer to your question is probably around 130. GEOO created an 18 with a supercharged engine that was over 1,000 hp hooked to an Arneson surface drive. I have heard credible people say it ran around 125 GPS mph.

However, the Classic DONZIs are really not the best platform to start with if you are interested in making the fastest “sport” boat. The hull design is virtually unchanged, dating back from the early 1960s.

I was very fortunate to be able to have Keith Eickert build a custom SBC (starting with a 400) for my Ski-Sporter. I LOVE DONZIs, which is why I will be happy with what ever performance I get. There are many similar sized boats out there that would be 10 - 15 mph faster with this same engine in it.

If you want to even begin to achieve these 90+ mph speeds, of one thing I am sure, it will take a very large pile of money. :)

gcarter
02-13-2013, 10:53 AM
A Minx isn't as aerodynamic as other Donzi Classics. There have been a number of Minx's set up w/BBC's and supercharged SBC's.
I don't know of any that have exceeded much over 70.
GEOO's X-18 (BTW, the X-18 was the most aerodynamic Donzi Classic ever built) was capable of going 125 on a good day, but it took almost 1,000HP and an Arneson drive to do it.
A Minx is a nice comfortable, dry cruiser. I reccomend enjoying it for what it is.

katanna
02-13-2013, 06:58 PM
What type of water are you looking to use it in? My python jet with a 460 ford runs in the 90s. Throw in a little chop and my 68mph minx will run circles around it.
I will let you know how the Minx feels in the upper 70s when the lakes thaw :)

Steve

Pat McPherson
02-13-2013, 07:53 PM
GEOO created an 18 with a supercharged engine that was over 1,000 hp hooked to an Arneson surface drive. I have heard credible people say it ran around 125 GPS mph.
I ran with George a few times at gatherings here in CT. Truly the craziest captain I've ever met.
After a pass at a CT river run 6-7 years back, he showed me 114mph on his GPS. This was with the an estimate 900HP and yes he had a smaller blower pulley that would push his engine over 1000HP.
I'd say that George pushed it about as far as an 18, 20, or 22 Donzi could possibly be pushed.
No way I'd ever get in one of these that would run over 80. These hulls are simply not design for that kind of speed.

gcarter
02-13-2013, 08:15 PM
I tried to post on this this afternoon, but I got the "Moderated' message!!!!!!!!

Essentially what I said was that the X-18 is the most aerodynamic Classic ever built, and George's boat benifitted from it.
A Minx has a much larger cross section than a 22C or 18C (or any Hornet, GT, etc, etc.).
When you exceed 40 MPH, aerodynamics have to be considered and drag goes up on the cube of the speed.
Since the Minx is so tall, it'll never be able to compete on a level playing field w/a 22C or 18C.
The Minx is a wonderful, great riding, dry cruiser type of Donzi performance boat.
Enjoy it for what it is.

biggie
02-17-2013, 02:01 PM
My 350 mag will push me 50 in the oceans of Hawaii so Im thinking once I change to a 383 and move to Destin, Fl and run those bays Ill be able to cruise at 60. Ill be happy with that while I save for something faster. Thanks again for the advice.

johnnywhale
02-17-2013, 04:50 PM
FWIW I see about 65 (5000 - 5100) with a fairly strong 383 in a GT21 in saltwater.

biggie
02-17-2013, 06:58 PM
Awesome, I think I can deal with that... What do u think I could expect out of a blown 383?

katanna
02-18-2013, 09:54 AM
Running 68 in my Minx with a new 377-325hp crate motor. I have added full hyd steering this winter along with larger tabs and a hydromotive 23p four blade in place of my 3 blade spinelli. If it handles the chop of Lake St. clair pretty well after these mods, I will add better exhaust and a whipple.

I would think a 383 with 350+ hp should see 70.

Steve

biggie
02-18-2013, 11:56 AM
Thanks for the info Steve, I think Im still struggling with part combos. On one hand Im looking at a basically built 383 w/ 430 hp for $5600 and on the other Im wondering if I cant play w/ part combos to get more...in another post I was told that I need "reliable power" not sure exactly what that means but I'd hate to build a 383 and spend the same (maybe more) and not get as good results...

VetteLT193
02-18-2013, 12:44 PM
Thanks for the info Steve, I think Im still struggling with part combos. On one hand Im looking at a basically built 383 w/ 430 hp for $5600 and on the other Im wondering if I cant play w/ part combos to get more...in another post I was told that I need "reliable power" not sure exactly what that means but I'd hate to build a 383 and spend the same (maybe more) and not get as good results...

Reliable power means you need to keep in mind it's a boat, not a car. Imagine a car going up a steep hill in 1st gear constantly and you can start to imagine what a boat engine does.

There is a reason why new cars are running at 1hp per cubic inch or better consistently while boats are the opposite. A new merc 6.2 = 320HP, Corvette with a 6.2=430HP. It's not that they can't put the 430 HP version in the boat. If they did it would blow in short order.

Mercury racing is another good example. The cheapest engine, the 525 EFI, runs about 30 grand. It is a 525 HP 502 so it's just over 1hp per inch. They are considered reliable with an approximate 250 hour top end rebuild interval. I'm not saying you can't do it another way cheaper but you won't do it pennies on the dollar. You are at a power per inch ratio that Merc gets to with their 565. That is a $35k engine.

One more way to look at this is... find a decent manufacturer making a marine engine, with a warranty, that does what you are trying to do (383 with 430 or more HP).

biggie
02-18-2013, 04:41 PM
Thats a great idea and tough to switch gears to get in that mindset. I mainly wanted to build the motor based on previous builders advice so I could have the experience as well as the satisfaction of doing it all myself. I saw a few mercruiser 377 Scorpions on the internet running around 9k maybe thats something I should consider. Im not looking "polish a turd" if you will lol more so open my eyes to the world of power boats and I figured this project would be a good start.

gcarter
02-18-2013, 07:51 PM
I've been waiting for someone to build a marine GM LSX 454.
All steel bottom end w/6 bolt mains. Six bolt aluminum heads.
The only problem I see is they're currently kind of pricey.
I think it should build a very reliable 450 HP boat engine.

VetteLT193
02-19-2013, 08:20 AM
Thats a great idea and tough to switch gears to get in that mindset. I mainly wanted to build the motor based on previous builders advice so I could have the experience as well as the satisfaction of doing it all myself. I saw a few mercruiser 377 Scorpions on the internet running around 9k maybe thats something I should consider. Im not looking "polish a turd" if you will lol more so open my eyes to the world of power boats and I figured this project would be a good start.

Merc was making a 383 / 400 hp for 12k-ish dressed with CMI exhaust. you might still find one of those out there (ebay I think I saw one or two recently) It's an EFI engine too. That would be reliable and get you into the 70's without a problem. If you are easy on it, the original Alpha 1 should last too.

As far as engine builders advice... There are lots of engine builders that have burned people in the marine world. You can get away with a lot in an automotive application that you can't get away with in a boat. My brother repowered his 22 many years ago. He went with a reputable S. Fla engine builder. 1st engine was toast in a few months, 2nd lasted a couple years. He moved to north florida and found a different reputable marine engine builder and... 3rd lasted a couple of moths, 4th lasted a couple of months,... he moved back to S. Fla and went back to the original builder and the 5th lasted a couple of months, 6th was a mercury racing unit.

The original 330 HP 2 bolt main 454 Mercruiser lasted over 1000 hours with the original Alpha 1 behind it. After that I think he spent 1000 hours in labor fixing it plus a whole lot of weekends looking at his boat on the trailer Vs. using it. He is now quite good at removing and replacing the engine though :eek:

There are a lot of engine builders who give a one year unlimited hour warranty. They bet on the fact that most people don't use their boats much. They do cheap rebuilds, hope you use the boat a couple of times, and the warranty expires. Even the ones that do break the engines they simply do another cheap rebuild.

duckhunter
02-19-2013, 09:22 AM
I've been waiting for someone to build a marine GM LSX 454.
All steel bottom end w/6 bolt mains. Six bolt aluminum heads.
The only problem I see is they're currently kind of pricey.
I think it should build a very reliable 450 HP boat engine.

I agree - to me this seems like the logical progression for marine small blocks. The LSX is an evolutionary leap forward from even the most advanced Gen 1 & 2 SBCs. Better breathing, better efficiency, better oiling, much stronger bottom end. I saw (on here I think) that Volvo is replacing BBCs with LS power and it makes a lot of sense. When some hungry aftermarket outfit can come up with an affordable, reliable package that includes the bell housing, exhaust, cooling, etc to retrofit older SBCs they will probably sell a bunch of them. If someone on here has a machine shop I will take one for the team volunteer to be the test mule!

mattyboy
02-19-2013, 09:47 AM
I tried to post on this this afternoon, but I got the "Moderated' message!!!!!!!!

Essentially what I said was that the X-18 is the most aerodynamic Classic ever built, and George's boat benifitted from it.
A Minx has a much larger cross section than a 22C or 18C (or any Hornet, GT, etc, etc.).
When you exceed 40 MPH, aerodynamics have to be considered and drag goes up on the cube of the speed.
Since the Minx is so tall, it'll never be able to compete on a level playing field w/a 22C or 18C.
The Minx is a wonderful, great riding, dry cruiser type of Donzi performance boat.
Enjoy it for what it is.


George can you clarify the way I read this are you saying the minx has a larger cross section than a hornet or gt??? or are you saying the 16 18 22 classic style hull has a smaller cross section that a minx gt or hornet??

gcarter
02-19-2013, 12:33 PM
Matty, I "think", but I'm not sure, that the Minx, with its raised coaming, windshield, and engine hatch area displays more frontal area
than any other Classic era model.
I know that GT's are a larger boat and may be bigger yet, but I've not been close to one to see the difference.

Carl C
02-19-2013, 01:06 PM
George can you clarify the way I read this are you saying the minx has a larger cross section than a hornet or gt??? or are you saying the 16 18 22 classic style hull has a smaller cross section that a minx gt or hornet??


Marry, I "think", but I'm not sure, that the Minx, with its raised coaming, windshield, and engine hatch area displays more frontal area
than any other Classic era model.
I know that GT's are a larger boat and may be bigger yet, but I've not been close to one to see the difference.

I have a feeling that Matt wouldn't be too crazy about the nickname "Marry"... :nilly:

mattyboy
02-19-2013, 01:31 PM
George
Remember to take into account that the hornet is almost a foot wider, and carries that beam almost to the nose. It has a round nose and a lot of bow flare plus higher gunwales.

The gt is also about 8 inches wider but does have a pointy nose. Both models have higher windshields too in stock form

Once I waxed the deck on the hornet like waxing a football field
When you get a minx next to a hornet the hornet makes the minx look smaller
But I do agree the sleeker more aerodynamic 22 and x seem to carry faster numbers.

gcarter
02-19-2013, 04:19 PM
I did fix the spelling.
Sorry Matty...............

mattyboy
02-19-2013, 04:31 PM
not to worry George I was on the i phone all day didn't even notice been called worse one thing I hate being called is late for dinner ;)

was looking at the gt again wonder how much the windshield hurts, without the windshield it does have lines very much like the 22 .

the hornet deck is just huge both front and rear I am also toying with getting rid of the windshield not for aerodynamics but more it bothers my line of sight

VetteLT193
02-20-2013, 08:00 AM
I wonder if the flare of the Hornet helps or hurts. Part of me wants to go all Reggie Fountain on this and say it helps carry the bow. :biggrin.:

One of the distinct differences with the Minx is the windshield is not only bigger but it's already higher because the boat was truly designed for it. On top of the deck flip up under the windshield is the raised deck too.

Another thought... how much does it hurt to have the driver in the wind flow? I once saw something about motorcycle aerodynamics and how terrible they are. People aren't aerodynamic and even though bikes are small they don't go through the air well. The only way they got the flow better is with a ridiculous looking egg shaped thing that went around the whole bike. IIRC The most astounding fact was a crotch rocket motorcycle had about the same coefficient of drag as a full size pickup.

So I wonder if the Minx ends up being better because even though there is more boat, the boat is smooth and wind flows well over it and over the driver/passengers so it ends up being better?

gcarter
02-20-2013, 09:45 AM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.

This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.

The other problem these boats have is the large open cockpit (even though we think they're small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes..

gcarter
02-20-2013, 09:46 AM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.

This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.

The other problem these boats have is the large open cockpit (even though we think they're small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes..

gcarter
02-20-2013, 10:02 AM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.

This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.

The other problem these boats have is the large open cockpit (even though we think they're small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes..

gcarter
02-20-2013, 10:03 AM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.
This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.
The other problem these boats have is the large open cockpit (even though we think they're small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes..............

gcarter
02-20-2013, 10:41 AM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.

This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.

The other problem these boats have is the large open cockpit (even though we think they're small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes..

gcarter
02-20-2013, 10:45 AM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.
This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.
The other problem these boats have is the large open cockpit (even though we think they're small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes……………

gcarter
02-20-2013, 02:08 PM
Cd is important, and we all know car MFGRs spend huge sums of money to lower them. What we often forget is the Cd needs to be multiplied by the frontal area in square feet. So, a smaller vehicle w/a poor Cd can have less overall drag than a larger car, bus, truck w/a lower Cd.
This is where the larger frontal area of certain boats becomes important. As I mentioned previously, the X-18 is particularly aerodynamic. The front and rear ramps (look at a picture) really help. I posted several years ago about meeting Jack Juratovic at the Amelia Island Concours. I bought a picture from him, mentioned I had a Donzi, and he promptly told me about being responsible for the X-18 deck styling. He's a car guy who spent his whole life @ GM, Chrysler, and other design studios before starting his own. And he understands style that encapsulates aerodynamics. So Mighty Mouse has a leg up on other boats.
The other problem these boats have is the large open cockpit (even though we think they're too small), they are terrible concerning aero. What someone needs to do is build a tonneau to cover the cockpit, then see what difference it makes……………

johnnywhale
02-22-2013, 03:45 PM
Matty, I "think", but I'm not sure, that the Minx, with its raised coaming, windshield, and engine hatch area displays more frontal area
than any other Classic era model.
I know that GT's are a larger boat and may be bigger yet, but I've not been close to one to see the difference.

My GT21 is at least a foot wider has over a foot more freeboard than my friend's 18. It is a skyscraper when rafted up.
http://i225.photobucket.com/albums/dd220/johnnywhale/Donzi/IMG_1115.jpg

mattyboy
02-22-2013, 08:33 PM
love the blue and white, both good looking classics :)