Sweet 16 Top speed?

[Just Say N20]

Have no worries. There have been at least 6 16s that I know of that have run 79 or faster.

The grand man of awesome, who still holds the record for the fastest 16, is Ed Donnelly at over 100!

And if he is going to do what I think he might be going to do, he will once again be running a 16 over 70. 😳

[Ghost]

Of course, the big question is what the 260 hp motor will actually do. If the current 4.3 is 225 hp, then the jump to 260 is only 35 more horses and another what, 150# of weight maybe? I don't think that will get near the theoretical 72+ mph. I'd doubt it would add more than 5 mph from the 57.7 where you are now, if that. It will need a smaller pitched prop with 1.49 gears in the drive--it'll never get to peak operating rpm.

Doing the math in my head, and only skimmed the prior posts, so apologies in advance if I goofed it up.

[woobs]

Mercury spec sheet says a 5.0 260 horse mpi is 4600-5000
I would think the fiberglass would start to melt on re entry at 72. or the driver and guest may freak..lol

Of course, all these equations are... IF the motor can swing the spec'd prop at the spec'd rpm with the spec'd gears.

So, In that light: The magic box says... 68.6 @ 4,800 (to be safe) w/10% slip

25	x	4,800	=	120,000.00	=	76.3		0.9		68.6
1.49	x	1,056	1,573.44

[Ghost]

FWIW, I would offer that the theoretical numbers mean nothing here. As Woobs noted, it's all based on the IF and the IF is about power. The only factor at the root of the math is the horsepower. Running the numbers with a 1.49 drive and 25" prop was arbitrary. We could have run the theoretical numbers just as easily with a 1.2 drive ratio and a 100 inch prop, and probably gotten a number over 200 mph. Which, of course, has nothing to do with the expected speed. Drive ratios and prop pitches are basically just gearing choices for attempting to exploit the horsepower one has. You can stick any gears on any motor, but the hp you apply will decide how fast you can go. Pick the wrong gears and you've simply lowered the EFFECTIVE horsepower. Pick the perfect gears and trim and you'll use the most HP possible. And that realized HP will decide the speed.

Applying this logic, respectfully, I don't think picking 4800 rpm means anything here. It isn't a safe estimate. It won't turn 4800. It will turn whatever the HP will turn it to, which can easily be way below the peak hp rpm range of 4600-5000. The only way to estimate the new top speed is to assess what the new hp will do for the boat. The gearing of the drive and the prop don't matter, except to the extent that they use all the hp or squander some of that hp. They can only be good enough to use all the available horsepower.

A better way to estimate the new top speed would be to get an idea that, in the neighborhood of 60 mph, properly dialed in, the boat will gain 1 mph for every x HP added. For instance, a 24 footer with offshore dead rise and our typical hull shape might see 1 mph for every 15 or so HP added, when in the ballpark of 60 mph.

With a 16, what's that x? Maybe 5-10 hp? At 5 hp per added mph, 35 gets you 7 mph. At 10, it gets you 3.5 mph. My sense is the answer is in there somewhere, likely closer to 10 hp per added mph. Hence my estimate that the best you can do with the extra 35 hp is 5 mph, and you won't see it without dropping pitch to be able to actually use that extra 35 hp.

[mattyboy]

I'd rather get my 260 hp from a warmed up 6 than an 8

260 hp ain't going to set any speed records nor will it spin a good 25 to 4800 with 1.4

If your looking to get to 70 in a 16 your going to need north of 350 hp and some kind of slippery drive

The 18 is a better platform for added hp to gain speed

The factory made a ton of 260 hp 60 mph boats

[woobs]

FWIW, I would offer that the theoretical numbers mean nothing here. As Woobs noted, it's all based on the IF and the IF is about power. The only factor at the root of the math is the horsepower. Running the numbers with a 1.49 drive and 25" prop was arbitrary. We could have run the theoretical numbers just as easily with a 1.2 drive ratio and a 100 inch prop, and probably gotten a number over 200 mph. Which, of course, has nothing to do with the expected speed. Drive ratios and prop pitches are basically just gearing choices for attempting to exploit the horsepower one has. You can stick any gears on any motor, but the hp you apply will decide how fast you can go. Pick the wrong gears and you've simply lowered the EFFECTIVE horsepower. Pick the perfect gears and trim and you'll use the most HP possible. And that realized HP will decide the speed.

Applying this logic, respectfully, I don't think picking 4800 rpm means anything here. It isn't a safe estimate. It won't turn 4800. It will turn whatever the HP will turn it to, which can easily be way below the peak hp rpm range of 4600-5000. The only way to estimate the new top speed is to assess what the new hp will do for the boat. The gearing of the drive and the prop don't matter, except to the extent that they use all the hp or squander some of that hp. They can only be good enough to use all the available horsepower.

A better way to estimate the new top speed would be to get an idea that, in the neighborhood of 60 mph, properly dialed in, the boat will gain 1 mph for every x HP added. For instance, a 24 footer with offshore dead rise and our typical hull shape might see 1 mph for every 15 or so HP added, when in the ballpark of 60 mph.

With a 16, what's that x? Maybe 5-10 hp? At 5 hp per added mph, 35 gets you 7 mph. At 10, it gets you 3.5 mph. My sense is the answer is in there somewhere, likely closer to 10 hp per added mph. Hence my estimate that the best you can do with the extra 35 hp is 5 mph, and you won't see it without dropping pitch to be able to actually use that extra 35 hp.

You're absolutely right. The big IF is just that. Where the equation is useful is after the fact. It gives a theoretical number using real life facts. In comparison to real life testing you can see just how efficient your set up is to the "paper" solution. ( I like to call it testing on lake Abacus).

When I say "safe" at 4,800 I was referring to a chosen rpm where the engine will not explode (sustained running rpm), not one that could be attained. there's no guarantee that that set up will yield 4,800 rpm on that motor, gearing, prop, etc... As you suggest, you may need to prop down and then it's a whole new result from a new equation.

You can plug any number in for gearing, prop, slip, rpm and drive yourself crazy with the wonderful world of fantasy because those numbers may not be attainable in real life. Or, you can plug in your ACTUAL numbers (gearing, prop and rpm attained, GPS speed attained) through testing and get an idea of what's going on. The more similar boats data you can compare to, the better choices you can make for your next test. And again, you can see how close you are to a theoretical "perfect" with that particular set up.

Adding 1mph for every X HP added works well as a loose rule of thumb but, due to Diminishing Returns it is not accurate. It's a moving target. IMHO, the only way you can estimate top speed is by testing your current setup, evaluating where you are and what variable you will try next. The equation is a tuning tool. That's all.

For example my 4.3 dyno'd at 236 HP. I have a 1.47:1 drive, a 19p (High Five) prop, and I turn 4,300 rpm. The equation says I can go 47.4 mph. Since my engine will pull to 5,100 on the dyno (but not in the water). I can affect this by choosing a 19p prop with less surface area. Reducing 1 blade (to 4 blades) may yield as much as 200 rpm theoretically pulling to 49.6 mph (+2mph). I can also estimate dropping to a 17p (High Five) will yield about 400 rpm and post 46.3mph which is slower. I now have an idea of how changes may affect overall performance and which options I should consider first. Keep in mind it does not tell me how much hole shot I will lose/gain or if there are any other performance trade offs/benefits that will occur to get that 2mph with one less blade. Once the change is made we go testing and plug all the data in again to see if we can chase perfection any further with the remaining options available.

note*** In actuality I have already recorded 49.7mph with the current set up (exceeding the paper 47.4 "target") so all things are relative to actual testing. Also, I realize that I chose the wrong ratio of 1.47 and should have gone with a 1.65 which would have given me more tuning options. Live and learn.

This is the proper use of the equation. But, the "what if" scenario is a great, fun game to play and hard to stay away from...

[DONZI-DON]

Has the 4.3LX with a Quick Silver 23 pitch prop - A friend of mine owns "HOT TO GO RACING", He runs/organizes a lot of the Poker Runs on the East Cost. You Tube his boat (HOT TO GO RACING BOAT), 175=MPH.........sick!!!!

http://www.youtube.com/watch?v=6wZgd8Zpp3c


As of today I have only had it out 5 times since I bought it a few weeks ago. Rob (Hot to Go) has the boat now. We are installing Thru-Hull Exhaust this week. The last time I had it out again I had my Dad and my son with me (about 500lbs) and I played with the trim tabs. I got it to 59mph but at about 5200-5300rpm's. Not real comfortable running a stock V6 at those rpm's. I don't plan on pulling skiers or tubes with this boat so after the exhaust gets done I'm gonna try a 25 pitch prop to try and get the r's down............... Rob is already coming up with a MILD V8 build for me when this V6 is tired.

FYI - Rob, HOT TO GO RACING 716-418-6131, Grand Island New York / Mention my name if you call him.

Just got back from running the boat. Thru-Hull Exhaust installation job is complete. Rob (Hot To Go Racing) installed a pair of HARDIN exhaust tips with removable baffles. Ran the boat with out the baffles. At idle, sounds like a stock V8. Not sure what it sounds like from behind while running. Didn't sound bad from inside the boat while driving it. Rob was driving my boat and we had his phone and my phone set to GPS mode and we topped out at 60mph on both phones and the rpm's at WOT went from 5200/5300 to a solid 5400......EEEK! That 23 pitch is coming off and I'm gonna try Rob's 25. Open to suggestions. I don't pull skiers or tubbers and NOT looking for fast out of the whole. What I'm looking for is good performance and a little more top end speed if possible.

Here is a link of the boat at idle on You Tube: http://youtu.be/MCVjfA1Kw10



1995 Donzi Pre-Thru-Hull 001.jpg1995 Donzi V6 With Thru-Hull 003.jpg1995 Donzi V6 With Thru-Hull 004.jpg1995 Donzi V6 With Thru-Hull 008.jpg1995 Donzi V6 With Thru-Hull 006.jpg

[TheFees]

When I inquired with Donzi way back when I first got my boat, or should I say a couple of years afterwards (I bought it in 1989 and it was a 1987) They told me that their 18's with OMC 350's were doing 64.1. That is what they said. They told me that my boat with the Mercruiser; add 3 mph, and the stainless speed prop from Mercruiser add another 3 mph = 70.1. I ran this guy with a hot runabout with a 250 outboard on it and we both stayed in it for the longest time and it was like you could tie a string across our bow's. We were perfectly matched. He told me his friend is a state cop and checked him with a radar and he said it was spot on 70. That year a 300hp was offered instead of the Magnum 270 that I had.
After I asked him what else I could do to get more speed out of it, he emphatically said, "Don't change a thing." That boat has been engineered to a T. You already have the magnum motor. Different hulls were designed for different speeds. He said the 18 begins to chime walk at 72mph. I know my boat at top speed does feel like it is dancing on a fulcrum or something. It has the tiniest rock or cradle at full throttle. It is exciting. If it was going faster I can see how it might get hairy. You can see it in my avatar at full throttle. Some of the boat has to stay in the water for steering to function. (At least part of the time )
Anyhow yes by all means see what you can do to make it a little faster, but he also very emphatically told me something else (And this guy used to work for a big mod shop in Florida) he said that everything you do to add more horsepower creates more internal temperature. So think about it. What goes wrong with an engine that is overworked? Sucked valves, holes in pistons. Imagine a valve that gets to hot it implodes, or a piston gets so hot on the surface that the explosion forms a hole.
Okay I know I am going to get slammed for saying these things, but they are true. I am in the middle of a performance boat forum, and lots of mechanics in here. So go ahead and boost away, but I wouldn't get carried away. When I was growing up in Somers Point at the Jersey shore the fastest boat on the water was doing 40mph. The amazing thing about Donzi's are the way they carve the water. They also told me from Donzi that if you don't overwork the motor you will get over a 1,000 running hours out of it. Mine has about 600 on it right now. When I bought it only 2 years old it had 105.

[DONZI-DON]

Here is a sound clip after the Thru-Hull installation on the 4.3LX, Baffles are in pipes.

http://youtu.be/8i0j73l5s2U

[DONZI-DON]

Just got back from running the boat. Thru-Hull Exhaust installation job is complete. Rob (Hot To Go Racing) installed a pair of HARDIN exhaust tips with removable baffles. Ran the boat with out the baffles. At idle, sounds like a stock V8. Not sure what it sounds like from behind while running. Didn't sound bad from inside the boat while driving it. Rob was driving my boat and we had his phone and my phone set to GPS mode and we topped out at 60mph on both phones and the rpm's at WOT went from 5200/5300 to a solid 5400......EEEK! That 23 pitch is coming off and I'm gonna try Rob's 25. Open to suggestions. I don't pull skiers or tubbers and NOT looking for fast out of the whole. What I'm looking for is good performance and a little more top end speed if possible.

Here is a link of the boat at idle on You Tube: http://youtu.be/MCVjfA1Kw10



1995 Donzi Pre-Thru-Hull 001.jpg1995 Donzi V6 With Thru-Hull 003.jpg1995 Donzi V6 With Thru-Hull 004.jpg1995 Donzi V6 With Thru-Hull 008.jpg1995 Donzi V6 With Thru-Hull 006.jpg

Picked up the New prop (MIRAGE Plus 25P) Saturday and took it out for a run today. What a difference only going up 2 on the pitch. Jack (Pier Propeller, Tonawanda NY) the guy that did the prop said I would get about 2-3 mph more and drop the rpm's about 600. The guy knows his stuff. I got 2mph (61) and the rpm's went from 5500 down to 4800 WOT and all trimmed out. What a difference it also made in going through 1.5 -2' rollers. The boat now continues to DRIVE through the waves as its cutting them rather than bog down a little bit like it did with the 23p prop.

[Just Say N20]

Nice work, very impressive numbers with the V6.

The 16 is so much better balanced with the 6.

Congratulations.

[DONZI-DON]

Nice work, very impressive numbers with the V6.

The 16 is so much better balanced with the 6.

Congratulations.

Thanks.

I've waited a long time to own my first DONZI. I will never own any other brand now that I have a owned a DONZI! Now that I own one, and have driven one I understand why they are not cheap boats to purchase new. You know what they say, "You get what you pay for". And when you buy a DONZI "YOU GET A LOT"!

My plan is to keep this one (SWEET 16) for a couple years and get lots of "Seat Time" and then jump up to a Classic 22. I won't sell mine until I have found a 22', it took me over a year to find this one. Im "OCD" and I like my stuff looking new no matter how old it is so I'm sure when the time comes to found the 22' it will be as equally challenging to find that one as it was to find my Sweet 16.

[Conquistador_del_mar]

Are you satisfied with the location of your trim tabs? Can you easily lean the boat when using them?

[Morgan's Cloud]

Thanks.

I will never own any other brand now that I have a owned a DONZI! .

Now , don't get too carried away there . You might accidentally try out a Magnum one day .

[DONZI-DON]

Are you satisfied with the location of your trim tabs? Can you easily lean the boat when using them?

This is the first boat I have owned with trim tabs, so I don't have any experience to judge it against. And yes I have noticed how easy it is to get her to lean to Port or Starboard side with just 1 click.....