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Sam
09-12-2001, 06:00 PM
Do any of you distinguished Donzi owners know if there has ever been an established hull speed for a sixteen.

Your Humble Sevant
Sam

marcdups
09-12-2001, 06:46 PM
Sam,the max I got out of mine was on a brisk spring day, 2/3 gas and alone, slight 6" chop and saw 57.4 on gps turning 5150 rpm,s with a stock 4.3 merc 4 barrell carb 205 hp, will hope to do some bolt on mods this winter but I believe Forrest can get in the high mid 60's with his if I am not mistaken, Frank C does know a lot more about the sixteen and so does a bunch of guys here, what are you running in yours, rpm's, prop etc, speed !!

Good luck

Towel Boy

using towel to wipe a tear now and then :mad: :confused:

Sam
09-12-2001, 07:21 PM
Towel Boy ? there must be a story there, anyway I know I have more boat than motor at this time. I have a fresh 5.7 2brl with an Alpha Gen II 1.47 ratio. I turn a 21" Stelleto, @ 43500-4440 rpm I run 56-57mph(gps) in good water, in flat sucky water 55mph.

Sam

marcdups
09-12-2001, 08:05 PM
Sam, which 5.7, older model pushing 220 hp or the newer pushing 250-260 hp, flat tappets, roller tappets etc!!?

Towel Boy !!

Rootsy
09-12-2001, 08:05 PM
pretty good sam, same boat cept a 4V on the 350... 59 flat *gps* on flat water, trimmed out right on the edge of chine walk, 21 mirage @ 4500 rpm.

Digger
09-12-2001, 08:26 PM
Sam, let me share an observation about "hull speed". I think many people use the term "hull speed" to describe various speeds of a boat, but it would probably do to define the true meaning of "hull speed" according to the greybeard designers. Strictly speaking, the hull speed of any vessel is found by multipying the square root of it's waterline length times the constant 1.34, so for example the hull speed of a Donzi with a 16' LWL is 5.36 kts. This seems a ridiculous number for those of us who enjoy hurtling through the water in style at high rates of speed. So what, then, is the significance of "hull speed"? It is really applicable only to full displacement hull boats. Say, for example, a 46' full displacement hull trawler is going from Bermuda to the Azores on his Atlantic crossing. His boat (as any boat does) requires very little power to drive it through the water up to it's hull speed. To him, hull speed is a very significant number, because if he wants to go faster than hull speed his fuel consumption is going to increase dramatically, to the point where he sacrifices endurance (range) to the extent that he may not make his destination. We're talking about very small changes here, as in a change as little as one knot up (say, from 7 to 8 knots) will decrease his range on the fuel remaining by 40% or more. These single diesel engine installations sip fuel at a rate of around 4-6 gph at "efficient" speeds. So enough babbling about "hull speed". I am quite content to let my Donzi voraciously suck down several dinosaurs worth of fossil fuel to make it to the next watering hole. This probably isn't the info you were looking for but I thought I would share it anyway.

have a "Damn Donzi" day!

oldLenny
09-12-2001, 08:36 PM
Here is an unrelated, extremely boring fact (a "fact" as far as I have been educated)but on a displacemnt hull, when you look at it, as it goes by, look half way down the hull waterline of say a 75' Tug. The distance between the "crests" of the two following waves down the hullside, divided by the square root is the "travelling" speed in knots. Next time you see a boat in this situation have a look. Tugs are the easiest. 25' crest to crest along hullside, 5 knots etc etc etc. I don't believe it works for the crest distances as they travel behind the hull transom as the "following sea aspect" comes into play.

GEOO
09-12-2001, 09:13 PM
Donzi: Hull speed what's that??? GEOO

Sam
09-12-2001, 09:13 PM
Where do you guy's come up with this stuff ! As I understand hull speed it means there is a limit to how fast you can push the boat regardless of the power.

Sam

oldLenny
09-12-2001, 09:27 PM
Sam, my post was in relation to "establishing a "hulls speed" (displacement only) as it travels by. In no relation whatsoever to the original question. I believe you are right. there is a theoretical "hull speed" for any design, a relationship between friction/wetted surface and horsepower/drive components. But, all that being said, there is obviously a way to "defeat" these laws of physics as noted by Geoo.

marcdups
09-12-2001, 10:32 PM
GEOO, not fair, you have wings under your boat and a huge set of gonads, in your case it should be spelt, GONADS !!! :eek: :eek:

Towel Boy!!

can my sixteen harbour a jet?? Ted ?? :D

Jamesbon
09-12-2001, 10:54 PM
Here's my opinion on "safe hull speed" ASSUMING your rig is set up right and your traveling on flat water...

22 Classic or 21 GT's 90 mph
18 Classic 75 mph
16 Classic 65 mph

...rules are made to be broken :D

I know "we" have faster boats, but this is my "gut" guideline...

Nate

Formula Jr
09-13-2001, 07:52 AM
Geoo, Your hull actually has to BE IN THE WATER to worry about hull speed. Not a problem with your boat...... :D

CDMA
09-13-2001, 08:07 AM
Nate,

I agree exactly wih your #'s as long as you are talking about a sterndrive version. I personally think an arneson, kamma or other interesting drive could add 10 mph to each of those numbers. The 22 special with the Whipple ran low 90's and looked real in control. Just my $.02

Chris

ALLAN BROWN
09-13-2001, 08:38 AM
Some interesting reading! There is no maximum velocity for any hull shape. It is a matter of propulsion. When I built 16's, the maximum power was about 200 shp. Eaton "C", and Volvo 200 drives were high-drag. That means that high speeds equal high trim. High trim equals chine walk.(In the case of the 16', gunwale walk). As power increases, trim can be minimized, as GEOO shows. I have designed boats for Donzi, Nova, Cigarette, AlphaZ, Pro-cat, Cougar, and consulted or contributed on dozens of others. Every day, I am astounded how you "good old boys" break all the rules, and go 10 mph faster than I thought possible. Hell, 140 mph in a vee bottom, and 180 mph in a cat are poker run speeds now. I made the Gulf hall of Fame in a 28' Donzi going 65 mph. The pressure in your speedometer, and the pressure lifting your boat are identical. Pressure at 50 mph = 36.75psi, 100 mph = 147 psi, and 180 mph = 476 psi. Divide the weight of your boat by pressure in psi, and you will have an approximation of the true wetted area. Example: 42' Fountain at 142 mph (Vee bottom record) = 9,000# divided by 288 psi equals 31.25 sq. ins. What I am leading up to, what possible difference could the bottom shape make (strake placement, for example) if the wetted are is the size of a dinner plate? Anyone who says that this hull or that has a hull speed, or max speed or whatever is full of, well, beans.
AB

smokediver
09-13-2001, 06:18 PM
I have a 1998 16 w/ a 4.3 2bbl. I run 56 mph with a 24 stiletto 1.86 ratio. there is a guy here that put a 350 mag in his and said he runs 72 mph. i would love to put a 4 bbl. on one of these days

Scott Pearson
09-13-2001, 07:14 PM
Formula Jr,
Isn't that the truth about Geoo's boat....Still laughing...Very hard!

Geoo was nice enough to let me drive that "Time Machine"....Its one hell of a boat! Thanks Geoo!!!!! Next time we hook up you will have to give my slug of a boat a drive...
:D

(NJ)Scott