Don Aronow had this in a notebook...
 

...a friend who I mentioned yesterday was into Don Aronow "tid bits" as he had an Apache' and a former Formula owner...now "looking"

He said an employee who worked with Don said this was written on a poster at Donzi Marine....for the sake of arguement let's say that's true..who knows....but it's interesting to study...after awhile it makes a lot of sense....

What's a formula for top speed?
The answer, verbatim is:

Crouch's formula:
It takes into account the weight and horsepower at the
propeller, and assumes a 50\% to 60\% efficient prop.
Most props fall into this range. Note that it doesn't take
into account the boat length, as that doesn't matter with
planing boats.

Crouch's Formula

V = C/((DISP/HP)**.5)

Where V = boat speed in knots (1 knot=1.15 mph)
C = Constant (depends on boat type)
DISP = Displacement (pounds)
Note that boat manufacturers usually give
innacurate numbers for displacement,
typically on the low side
HP = Horsepower available at the propeller

For comparison sake, here are some average values of C:
150 Typical lightweight, planing cruiser
180 High Speed Runabout
200-230 Race boats, hydroplanes etc.

Basically this means "C" is the most important factor unless you want to run a boat with 10 engines to meet your speed requirements.


...it's interesting that the size of the boat dosen't matter nearly as much as design efficiency per se'...I called a friend who works for the Big Three in the number crunching dept.(chief engineer) and faxed it to him...he looked it up and said that speed was most significantly dependent by this equation on the overall efficiency of the hull/prop combo.

What he calculated mattered most were:

-Deadrise
-Step Placement(s)
-Weight distribution along the hull/angle of running surface when underway.
-Ratio of "undisturbed water" getting to the prop(s)
-Angle of attack of the prop blades
-Blueprinting the hull to be as straight as possible



SO ...put aside brut Horsepower....when designing a boat he said it's in this order...Hull Design ultimately determines Hull/Prop efficiency most notably.
balance keeps the nose there to "cut waves" but not ride the surface needlessly...a "perfect hull would need no trim tabs or engine trim" so a perfect hull dosen't exist.

He called a cad/cam guy to do a mock up and found that as the hull efficiency increases there is a direct relationship with an improvement in propeller efficiency.
Most efficiency is lost at the prop...almost 1/2 of the boats power is lost at the prop...and changing the prop will only yield minor improvements assuming you have a decent prop like a Mirage...the way the water is "fed" into the prop and out like a jet engine determines overall efficiency more than any single factor. The hull "feeds" water to the prop from a qualitative and quantitative standpoint. (Have I lost you yet?)

So the cad/cam showed that there is no substitute for a lesser hull design without having to add more power to compensate...and much of the additional power is wasted in prop inefficiency and harder wearing of the drives. More efficient hulls are "easier" on the engine and drives...we knew that right? They jump on plane with minimal need to trim etc...

We looked at several boats and performance figures...they found using the above equations they fed into their laptop spread sheets....that Cigarettes are way up on the very high level of efficiency with their stepped hulls....what ever they did.. they did really very well....Fountains are well tweaked as well and in showing them the video of the last "speed run" they commented that the hull was very well balanced...as if on rails we said....but interestingly the Formula Hull on the 38'er was deemed a good design by the formula and performance data they felt because of a "blunter" point of entry and diffferent step geometry (one of the guys at the company has one) it's setup is to ride a bit more lower on the bow and give a greater "knifing" action to the oncoming seas sooner if you will and that adds up to less "air time" so a little slower; but great for comfort/speed ratios if that's what you need. So POSSIBLY less of a cantilever like ride..how different? I don't know...you would need to ride and test each...we did this as a meta-analysis based on available test data in magazines and on the web. Donzi's were deemed efficient based on the data we could scrounge....Powerquest showed well....Pantera's.. especially the 24' with moderate power and the 28' too were both great...probably due to a well balanced hull and an overall great design...

....Now some of the older BIG Formulas without steps/older BIG Cig's without steps (except for the 28'er which is very efficient) the older Donzi's/ older Scarabs were not as efficient at the "top end" but said to be very efficient at "knifing" their way through high seas....and good at rear hull re-entry.

....quite frankly it was hard to find a really bad hull using this equation....but we found a few...and I don't want to mention the few we found that were really bad accoring by this equation...no bad mouthing...but the bad one's were not boats we "talk about" much on OSO...they were the lighter "imitation offshore looking boats" that probably have a deck that bounces up and down constantly as it hits and bashes waves rather than "cutting them".

...we didn't have much data on OL with stock engines to figure a constant out...like a 40'er with 525's....etc so we couldn't do much there...

...so the good news is just about every boat that is a ture offshore... is "variably" efficient....but there are those outstanding one's...like the Pantera without steps does really well...we all commented them to be great values too!

But Cig's blew us away as did Fountain's...in terms of efficiency they hit their mark well...speed wise and otherwise as really well....what we are talking about is "safe high speed".....

...so on a usually boring Friday..we found something fun to do...hope it's helpful...make my job of finding a new boat easier...

The correct answer is....................Pantera!:D

QUOTE "a "perfect hull would need no trim tabs or engine trim" so a perfect hull dosen't exist"


When was the last time You seen a perfect wave :eureka:

if we tested boats to prove or disprove this equation the seas would have to be ideal....it's all on paper...but the cool thing is we showed is that there's a lot of outstanding boats out there and the task is more to match one to one's own needs rather than to look to see which is "best". So for me the comments I have read and interactions I have had here have been very useful...it's like having a bunch of people who have tested the products by their own experiences that tell you what to expect...an informed customer is the best customer...the bottom line of our calculations were to avoid jumping into something that is not tried and true...and if you buy a 40+ footer without steps that is heavey...cool....just do the math and add in some extra horsepower...

...also...efficiency in design equals less expense in purchasing and less expense in repair bills...

....and don't get too worried about the trim tab thing....I was in a boat that needed constant trim adjustment and had no business being so overpowered....if the boat needs some trim fine...but if you are all over the buttons constantly..then you have to ask why....

I see you've been doing some homework. Very well done.

LPA2106- Great post, that is some great info

that's to much reading for me at 5:50 in the morning:D :D great post:D

awesome post. 2 questions: any info on the long island boats like superboat, kryptonite, activator, progression? also, what possible solutions are there to increasing prop efficiency? (surfce drives for cleaner water, etc)

we speculated that extension boxes improve the props ability to get more "sticky" water....cupping...and additional blades have a place...prop flex was a problem with aluminum materials that were run with high HP engines...Stainless and Nibral fixed that...

...the neat thing is that we have some great products to choose from due to lots of R and D. Racing is a great test grounds. When a manufacturer wins on Sunday" we win on "Monday".

...building a FAST and SAFE boat is a challenge...it amazes me that looking at the equation that we now have big boats that run in the 80's with powerplants that are "moderate" and reliable. That means less expense and more fun!

....in addition to prop inefficiency we also have engine to outdrive power losses...the introduction of the Bravo drive for higher HP engines and what IMCO offers too was/is a big step in the right direction....in loose terms the drives are part of the prop inefficiency equation. So when trying to improve prop efficiency try to look at ways of improving drive efficiency....the bigger older drives offered a lot of "drag co-efficient" to the eqaution...#6's are very low in terms of drag as are Arneson's. A surface prop has it's pros and cons but less drag..I would imagine maybe a bit harder to dock?

...so we crunched the numbers...and if you are not happy with how your boats is running...look at the whole picture...and a lot of times it's something like sheer displacement while "planed" that is the cause. Too much boat in the water and not enough air under the hull...if you play with stepping the boat balance is critical...staggering engines a consideration as are other manufacturing consderations to balance everything out from stem to stern and from port to starboard.

....I rode in a Pantera 24' years ago with a 330HP engine and it was with a new modfied pre-Bravo drive in it. The boat was well balanced, narrow for slicing waves like a "razor blade" and it was put together perfectly. You could run at 70 all day in some rough stuff and be very safe. It's an incredible 24' boat...safer than some 26-29'ers I have driven at those speeds....so hull length dosen't matter as much as you think if the boat is designed perfectly....

.....this forum gives you the edge because the folks here look out for each other and keep things in perspective...that's a real plus!

Thanks, that was some good reading!! :cool:

we looked for data on the east coast boats and could find litttle...same for some of the west coast boats...one thing we laughed about is that if the company has "been around" chances are their is a market demand for the characteristics of the boat...these are probably well planned hulls from the littlle I could see...

...want to have an example of a poorly balanced boat? Take a 18'er designed for water skiing; maybe a bowrider and stuff a 525HP in it ....you will need lots of trim action to keep the thing under control at full speed if you could hit say 90-100mph... the first "roller" that hits and you are out of the boat...

by the way....Cats are really safe at speed...you just have to know "your limitations" in terms of speed vs. conditions...

Oh course, in reality, length matters a great deal, in boat hulls too.

Actually when we raced the 36 Skater neutral trim and no tabs was the best way to run. The only time any trim was used was in the turns to keep the rpms up.

...we had a Friday conference call with boaters from all around that we new ...we networked...and used the services of a friend at an engineering team ....we did some research Troutly..and some cutting and pasting...but it was to feed numbers into a spreadsheet that we had calculations on and force ranked hull efficiencies as best we could.

We looked at mostly Aronow designed boats along with Pantera. Why? They are the one's we are looking at as some of us are trading up...it's just the kind of boats we liked is all..so we didn't look at everything...

by the way..the 31'-35' Formula Fast-techs are deemed quite efficient by our numbers..

...we won't mention all our sources but we had techs and an ngine bulider and a v-bottom racer and a rep from a maufacturer who shall remain ananymous on the call...

...the fun thing we found is that STEPS/BOTTOM DESIGN and an efficient DRIVE rank as #1 in overall performance.

the x-dimension is determined by hull performance....and that is not easy to modify....

...so the bottom line is "our standard" for a great hull design in the 35'-40' range is one that can run in the 80+'s all day long and do it safely...with a pair of 525's or a similiar powerplant. Why 525's? High tech...reliable; dependable and reasonably priced HP engines. More fun/less headaches.

....pick up Powerboat etc and that's all you need to know...if it's 35'-40' and can run around these speeds and meets your needs you should be in good shape in having a very efficient package that you won't feel the need to tweak when you get it...

Troutly...here is a link that offeres what Crouch and Pascal mathemathetics usd to derive it came from....he was from waht research we have done..and unfortunately not much is there...an individual affiliated with NASA in some capacity. They studt hydrodynamics and extrapolate the principles to aeronautics...that's why astronauts rehearse in a water tank...trim tabs on a boat work in a similiar manner to take of wing extension tabs/flaps on a plane...a plane can shift fuel from one side to the other to trim the plane...a boat can use tabs...a polane could too...anyway here is the link...if you wish to do some cutting and pasting of your own. :)


http://homepages.borland.com/nmp/nmpIndex.htm

sure length matters...but remember in an efficient planing hull a lot of the hull is out of the water..and with steps aeriation actually floats the hulls on bubbled water....and air....so it matters more if the hull is slow to pull out and acts more on the side of a displacement hull as opposed to a very efficient planing hull...an example is an older wood Cris craft displacement hull of around 25' that has 500hp and has a top speed of 40mph. vs say a 24' Pantera with 500 Hp that can hit 80mph. The Pantera is more efficient and at full speed with this power safer than a displacement hull being "forced" to go fast by pushing huge amounts of water...the Pantera glides on the surface...

...so length matter a heck of a lot more on a displacement hull and remember if the planing hull is less efficient it has to displace more water than it's counterpart...so planing hulls displace some water obviously...but the really efficient stepped one's and cat's displae much less. It's an equation you can find at the website I sent Troutly. What a good stepped design does is combine aerodynamics with hydrodynamics...a displacement hull is all hydrodynamics...if a 42' Cig/Fountain/OL had wings it would take off in a second!
A displacement hull wouldnt ....those new Luxury cruisers that you can get with a diesel power that do 60+mph are hybrid planing/displacement hulls.

Hope all this helps...we had a fun day yesterday putsing around with all this...do we have all the answers? no ....bet we were able to "get into the head" od Aronow and his counterparts and come up with some interesting speculative observations using a simple equation and a spreadsheet....you guys can do the same thing....make a spreadsheet...put the formula in...look up data from the Magazine tests and determine co-efficients of drag based on the equation and force rank your numbers....

you will find out why fast boats go fast...how to possibly go even faster...and how to enjoy an older slower boat that is a calssic and fun to operate....hey some guys like big blower motors...my buddy at work could care less about all this...he wants a BIG 45' non-stepped boat with Sterlings and dosen't care if he hits 75.

...so we all are not the authorities on anything but a fun day with some math and principles...we got to be boat designers for a day...and quite frankly short of cutting the weight down with exotic carbon graphite composits we couldn't figure out a way to make a good 40'er do more than what's available...but we figured that with "stealth" technology and Carbon/grahphite and Sterlings you could probably hit 300mph on the cad/cam.

....so if we ever can get the tech and get it at a reasonable price 20 years from now we will be looking back and wondering haw the average boat in 20 years can do say 200 mph with a couple 525's...

it can be done...it's a "going to Mars thing"....as Chef Emeril might say!

.....BAM!

C= the following

250 Non step V-bottom
275 Step V- bottom
300-350 Cats

I have used all of these in formula as a constant except in the one that uses the gear and propellor pitch where the constant is 1056.

Use your current realistic factors for the equation and see how close you are don't forget to factor in prop slip. You can figure your prop slip by taking your current top speed and divide it by the perfect top speed with no slip factor.

So to make very long story very short...let me sum one thing up....


....all planing hulls displace a percentage of non-aeriated water....

...the less water that is displaced (and dicplaced is like taking the palm of your hand and quickly moving it in a sideways position underwater...you can feel the resistance/drag on a small scale) the easier the boat will travel from point a to point b. Period.


Some palning hulls displace more water than others beacuse:

-Balance...they bounce up and down hitting the water in the front with the bow and causing drag.

-They don't get up on plane as much as other boats or they ride at less efficient geometries.

-They don't have air bubbles under the hull which increases a sliding effect or lubricates the bottom. An air/water bubbled mix is easier to get through....it's like moving your hand through bubbled air from a jacuzzi...less resistance you can try at home....now I feel like Mr. Wizard...


....so all we did is take some complicated equations...crunch numbers and shed some light on what goes on under your boats.

.who makes the best boat and who has the best boat out there? YOU DO IF YOU ARE HAPPY WITH IT!

...so our conclusion is that steps are not a "fad" they are here to stay for those who want cutting edge efficiency... and that there are very efficient boats without steps too...but when you get bigger you displace a lot more water....anybody know Troutly of a non-stepped 42'er that does 85mph on 525's...not to pick on Troutly but this time I did the work...and we all benefit...nobody has all this anywhere to cut and paste....and it all makes sense...

....and cat's plane instantly and need less tab control becasue they are really hydroplanes in disguise....Aronow dabbled with them..I have been in a Skater and it's a blast! Why are insurance rates higher? Because there is the POTENTIAL that a weekend warrior can do some wild things and it's all about experience..someone asked if boats are going to fast...my response after doing all this carp is yea definately for the underexperienced or someone drinking and boating you bet. Weekends with the kinds on board os not the time to "do a Poker Run".....so as troutly says...boat responsibly...

-

sean stinson

Good Post and yup...Cats are exactly where you placed them..to get to 600 you have to have wings..!

Very nicely said

a little trick Don Aronow did and this is an '87 Tg ...is look at where the K-Plane comes down...he has carved a path or channel to give lots of high pressure water to the planes to work with....a little touch of the tabs and a lot of response..not all manufacturers did this....it is unique to him....go ahead..prove me wrong:)

the more we study all this and considering Aronow didn't have cad/cam he had a mind..ambition and a darn good pencil...the more he amazes me...study HIS Cigs/Apache's Donzis and Formulas not to mnetion Mangums and Aronow's and there has got to be something to be learned that we may have missed like the little thing with the channel for the K-planes...my buddies think that the velocity of directly channeled water to hit the planes versus if the hull was totally a straight "v' is most likely a factor of 2-3x....so the water moveing to the planes is accelerated because of the rounded barrier to get to the otherside of the hull it is concentrated...that was probably a huge factor in control that boat and may be the reason he beat other boats in a race...trust us we feel it didn't happen by mistake...he knew he would be putting a Plne in place and wanted high velocity water to hit them...why? faster planing and faster turns and better control in sloppy waters...


amazing or what?
:)

...Genius is in the details!

ever see what a cigarette would look like if cut in two and a tunnel put in the middle....can't say it's my favorite boat...kinda looks prototypish...but I heard they moved pretty good and where very wide and stable...but even he didn't like it a whole lot....even through designing it i heard...but he did it anyway...who ever has it..and yup this is a cut and paste...i would take it if you are tired of it! It's called a 39-1

this is a '73 I was looking at in the want ads...a Magnum...it's 31 YEAS OLD....does it look dated? My thoughts are it could pass for a 2004...his magnums were ahead of their times...most unlike this one were big and heavy and used surface tech to propel them...they were his most advanced designs...but too high priced for most....this boat is going for 40k if interested...

...i LOVE these kind of boats with a passion....just by looking you can see how great the folks were that made them...

this is a '63 Magnum..they were dominant in the 1960's and 70's.....I think this is Don's own Maltese Magnum...I think he immigrated from Malta....any info on this?

...that last boat was a 1963....it had huge chines that acted as lateral steps i heard...anyone want to argue that?

showed this to en engineer friedn of mine...the water on the pic of the '63 magnum was flat...look at how the boat rides much like a stepped boat does....on the back pad...amazing eh?

...ok done for the day...that's all we got time for....hope all this was interesting and helps generate excitement as we move into the boating season for us folks in the North anyways! Take care....any questions? Just post a reply...we will keep this ongoing if any further interest develops...otherwise...I learned a lot as did my buddies...I am not a blower guy...I want efficiency to the max...so i did it for selfish reasons....but the go fast guys in this business have my respect from the design to the prop nut!

...and to be fair remember....Mercury helped make a lot of this happen working with manufacturers....

...we were wondering if a high performance duo-prop #6 type design might be possible...it would increase prop slipage....it would ahve to be very hydrodynamic and surface skim....so not what other compnaies had for their cruisers in a dual prop...we think on paper it might be cool to run dual counter-rotating cleaver type props in a twin set up with 1050 Sterlings in an efficient hull design...it's the only suggestion we have to decrease prop slippage..it could give 30% more speed....what do you think guys at Merc?

woops...meant this would decrease slippage and be more grippy!

..one last thing...how much do you guys want to bet that Don Aronow had the attention of the outdrive builders back then and he influenced what they did too?

we need one of these to decrease prop slip in a #6...anybody want to build one?

Do you think I can just turn the key and go?;)

....just came accross this ...not bad...

Oh, and there was good info there...no matter who came up with it or where it came from!

thanks for the complement! I like your style...cautious but wise Troutly! This is for you!

...hey Troutly...tell me more about this there thing eh? Looks like a winner!

My buddies and I consider all the Aronow boats to be keepers...I wish a had a boat as nice as yours Troutly! I would buy one in a heartbeat just for the attention to detail and now I understand what makes boats tick...the formula is a very very safe fast boat....here is some interesting info you might be interested in...

The boat, designated the Formula 276, became the prototype for Aronow's first boat company, Formula Marine, a name he chose because it utilized the talents of such soon-to-be legends as Stirrat, Jim Wynne, Walt Walters, Buddy Smith, and Jake Trotter. For Aronow, this was the right formula. The shop would be the first of many that would make NE 188th Street known as Gasoline Alley and Thunderboat row and Don Aronow as its reigning monarch.

Formula Marine's race-tested production boats were an immediate success, and in 1964 Aronow sold the molds to Thunderbird while he and his team were busy moving on to the next phase of making racing history.

Aronow kept a 17-foot hull mold after the Formula sale and trimmed it to 16 feet. Launched early in 1964, the Sweet Sixteen prototype became the first boat from Donzi Marine, which got its name when record producer Morris Levy ribbed Aronow about the new boat being another Donsy," a critique of the Formula 23's less-than-macho plush interior. By the end of the year, Donzis were a force in powerboat racing.

WOW !!!!!!!!!!!! You gotta love this stuff.

Very interesting. How does this formula compare to the speed calculator on Bam marine site?