Where's The Drag?

[GEOO]

A Velocity 22 (pad bottom) with my same motor and a Bravo(high X-dim.) goes 102mph. I never thought my X-18 would go that fast but 15-18mph slower seams like alot. I've tried a couple of props; run with and with out engine cover(no difference). I've taken all hook out of the hull.
I wonder if the pilot tube from the speedo and the transom mounted water pick up could cause enough drag to slow the boat 3-5 mph?
Any suggestions??
Chris, Let's start using your books!!! Can you find a formula for drag? A formula that would give lbs of drag per square inch of material in water(saltwater)? How does speed effect the drag? Does drag increase equally with speed or does the drag increase at a quicker rate? (ie. speedo pilot tube)
A funny thing, I ran with my GPS last night. I have to put it in my shirt so it doesn't fly out of the boat. I reset the Max speed and put it to the pins. Stopped it read same as speedo 82.2. I reset the max speed the next run it read 92. The third time it read 108.3. My speedo alway read around 80-83. the GPS must have been losing signal and giving false readings. I knew this but it still put a big smile on my face!!!
My O2 sensor didn't last long, it died at the Poker Run with Frank. The sensor read lean and the ECU dumped 22% extra fuel into engine. A replacement is on order. I hope it was just a bad piece and the new one last longer. GEOO

[Scott Pearson]

Geoo,
You can wet sand with 1000 grit paper from transom to bow approx. 2 feet on bottom of hull. This will releave the surface tenson. Sounds crazy but you wont believe the results. I bet you will pick up 8-10 MPH. Or you can clear the bottom of the boat with a product we just came out with that is called "self cleaning clear" There is NO surface tensom what so ever. It has a product called Auqapon in it, 100 times more resistance then Rain X. Just some thoughts.

(NJ)Scott

[PaulO]

Geoo,Geoo,Geoo.....
Welcome to the club. I too have been asking this question for some time. I love the looks and quality of my Donzi but, it is a slug. I know, the argument is that the deep V will outperform others in rough water. Truth is, it is a good rough water boat for an 18. But, when you can get better performance in 22 and 24 footers of different pedigree, how does the rough water performance really compare? Lot's of 21 Supeboats here that seem to do at least as well in the rough stuff.
I am not giving up on my Donzi and I know top speed is not everything but, speed makes it fun!
I was really depressed reading a test that was posted on the Hydrostream website. They were comparing Merc CLE gearcases to Bob's gearcases. An 18 Hydrostream with somewhat of a deep V was going anywhere from 91 to 101 with about 240 HP!!
We struggle to get our Donzis to 70!!!

I do wish I really knew why. Weight? No pad? I think the Superboats are 24 degree Vs.
PaulO

[BERTRAM BOY]

Paul O.
Actually, the Superboat 21 has a 21 degree deadrise.
BERTRAM BOY

[MattM]

Geoo, way to go, most of us would love to be at 80. Drag in a viscous fluid like air or water increases with velocity squared, power to overcome the drag increases with velocity cubed. This is why it takes so much power to see a speed increase. The drag of the water accounts for the vast majority of the total drag on a boat. Hydrostreams and the like are so fast because of the bottom and mostly because of the weight, hulls weigh less than 1000 lb. As much as we love our Donzis they are old and extremely heavy for their size.

I've looked at the velocities and fountains for years and wondered why nobody tries a pad on the bottom of a Classic. Steve Simon told me he thought it'd be a good idea, he said Donzi doesn't do it because of research investment and that the Classic designs are sacred and not to be trifled with.

Have you considered messing with the bottom?

[CDMA]

It may take a couple years but when I get this Naval Arcitecute thing under my belt a little I will start building models of classics and running them down the tank test here. For now I am still on the basics. It will take a few semesters to answer questions like that.

Chris

[PaulO]

If I hadn't just recently re-built the transom and stringers for my Merc conversion, I might be willing to experiment with a pad. Maybe next year. Interestingly, Hydrostream actually built a hook into their pads ( the pad section only ) to help eliminate blow over.
PaulO

[Barry Phillips]

Geoo: Last weekend I cruised through
a marina with some very expensive
boats in it, three guys signed great boat.
I wounder how often this happens with
a Checkmate, Hydrostream or any other
go fast boat under 22'. DONZIES are
not the fasted rides around, Im sure that a
60s Farrari GTO pails compared to a
new one, yet it is one of the most desired
cars on the planet. When people see
a Classic series DONZI they know it's
special weather experienced boaters
or not and I think thats more to the point.
80+ MPH is just the iceing on your cake,
although I think you can find some more
speed.
BE CAREFULL
SO-SLO

[PaulO]

Ah, but a 60's Ferrari will never be engaged in a contest of speed on a public road. We continually have the opportunity to run neck and neck with another boat and it is a shame when a lesser boat is faster. Not good for the Donzi mystique.
PaulO

[GEOO]

Thanks Guys,
The boat will run 80 in a 1 to 2 foot chop, pretty confidently. It's not a real dancie, flighty ride.
I think I'll take a little sand paper,(on my 3 foot straight board) to the bottom again.
Who know's maybe the speedo tube is worth 2mph?
My quest for more performance is done in part to carry foward the Donzi Mystique. I enjoy passing those other boaters, who only know of the 50mph Donzi's. GEOO

[This message has been edited by GEOO (edited 08-25-2000).]

[BigGrizzly]

PYTHON BOATS MAKE A 18 FOOT CLASIC COPY, WITH A PAD,CALLED THE VIPER. IN HOTBOAT MAG YEARS AGO THEY CLOCKED ABOUT 83 MPH. SOUNDES GERAT RIGHT!!! HERE IS THE STORY, MERC SPEEDMASTER LOWER UNIT, A GARY GRIMES TWISTER ENGINE (WOULD MAKE NASCAR GUYS WHISH THE HAD) ABOUT 600HP, 400+INCHES, AND ABOUT $30,000. SEEMS THE BOAT WAS SUPER LIGHT. MOST VIPERS ON THE LAKE WITH SMALL BLOCKS FOLLOW THE CORSICAN. SO YOUR DOING GREAT.
ADDED FEATURE HOW WILL THE BOATS LOOK IN 15 YEARS. SEEMS THESE GUYS TRADE BOATS IN EVER COUPLE OF YEARS. DO YOURSELF A FAVOR LOOK AT A USED ONE. I HAVE--YOU CAN KEEP THEM.
THANKS FOR THE LEAD ON THE E-DEIVE, JUST TOO HIGH PRICED FOR ME SO I ADDED A 22' CRITERION TO MY STABLE.
RANDY

[Blewbyu]

I've seen TWO hydrostreams blow over!!One with a stock 150 HP Merc.Both in salt water(tough on powerheads).In a past thread-thought I read that someone had tried a pad, and the stern really "waggled in the wind" and the boat was very unstable.
I'm old fashioned about staying alive.Didn't think either of the blowover drivers could have survived.Both did.One broke his neck,the other broke collarbone and both arms,serious concussion.
Easy choice.

[Forrest]

Also, you have to remember that not only is a Hydrostream a lighter boat, it doesn't have a 24-degree bottom either trying to slice through the water. The pad on the Velocity makes that boat essentially a flat bottom boat at speed. Look at all of the fast bass boats around. What do the all have in common? They all have a pad, not much Vee, and none are worth a crap in rough water. Put a pad on a Classic Donzi, and I'm sure that it will go faster - in light chop that is - but then you will have something with a hull more like a bass boat. If you want the fastest boat on the water, don't buy a Donzi. Classic Donzis were never meant to be the fastest boat made. Everyone knows that Billy Bob's drag boat will blow away any Donzi in the river. The Donzi hull design allows it to be the fastest, best handling, in rough water of any boat of it's size, period. When was the last time that you saw a 16 or 18 foot boat running (safely) over 50 mph in rough water that was not a Donzi?

------------------
Forrest

[MarkG]

I am a X Hydrostream owner and can tell you that my 18ft boat with 175 HP Merc ran well into the 70's. Why? The hull weight was 850lbs, the wetted area under the boat @ top speed was about 1 ft sq.(riding the pad). The other issue of drag is aerodynamics! The Hydrostreams were designed so that when on plane the air flowed OVER the boat. Consider the needle nose pointed frontal area of the Stream to that of a Donzi.
These boats were designed to fly, and I have been next to guys that have blown over.
I now am older/wiser, and just purchased a 21GT. You just can beat class & style, with speed! http://www.donzi.net/ubb/cool.gif