tomcat's power vs. speed calculator
01-17-2002, 09:25 PM
#1
tomcat's power vs. speed calculator
I wrote a program that I use a lot for determining power vs. speed and prop selection. What I would like to know is whether you would like to see it put on the OSO website. There are other calculators out there already but this one is different and hopefully you will think it is better.
Bam's calculator is based on Mercury equations that work well for a given type of hull when you know the weight. I use a formula that asks you to enter 1/2 power speed, to calculate a hull efficiency factor for a particular hull, and you don't have to know the weight. Either way works as well as can be expected, since there are so many things that can affect the answer, not the least of which is X dimension.
The neat thing about the program I wrote is you don't just plug in a max HP figure and get a speed. You enter the entire engine dyno curve, which is HP vs. RPM. You can then enter a prop pitch and the program converts this into a engine HP vs. speed curve. Then it plots that curve on top of the hull HP requirement vs. speed curve. Maximum speed occurs where the two curves cross. You can change engines, hulls and props to your heart's content and see the effect of more power, better hull and the best prop, without having to go back and forth several times between a speed calculator and a prop calculator.
This is a powerful little technique and it really gives you a feeling for how to prop the boat. For example, the excess of engine HP over hull HP at any given point is your potential for acceleration. You can see what happens to this excess power as you prop up for top speed. You can also see the difference between supercharged and normally aspirated power and why they should be propped differently.
The program can handle two sets of data at once so you can see the curves of both the existing engine and the proposed engine on the same hull curve. That's how I use it most of the time. Sometimes you have a great custom engine that you will keep when you sell your boat and you want to know how it will perform in a new hull. So you would plot one engine on two hull curves.
I've been thinking about substituting Mercury's formula into my program and making the program available on this website for members to use. Since not everybody has Desktop dyno or dyno curves for their engines, I would have to include a menu of engines, Mercury and common high performance combinations, to enter into the program. Members with dyno data or a dyno program could enter their own data.
I have posted the idea as a separate topic to see what the members think. If you guys like the idea, I will talk to Jeffery.
Here are some posts from another thread where this subject got started:
Katdrvr
Member
Member # 950
posted 01-17-2002 04:17 PM
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Tomcat,
Sounds like a cool program. I'll bet everyone would love to be able to run some demo's.
mike
[ 01-17-2002: Message edited by: Katdrvr ]
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Posts: 853 | From: Gretna, Ne | Registered: Feb 2001 | IP: Logged
traviss
Member
Member # 284
posted 01-17-2002 07:34 PM
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Tomcat, what is the name of this program? Would be able to get it somewhere? It probably is very expensive being boat related
thanks
Travis
--------------------
"Loose is fast and on edge your outta control"
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Posts: 4286 | From: in nothing anymore!! | Registered: Oct 2000 | IP: Logged
tomcat
Member
Member # 995
posted 01-17-2002 08:11 PM
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traviss - I didn't buy the program, I wrote it. It's a bunch of formulas in a spreadsheet, that produces a beautified chart for the output.
I proposed putting this program on the website to Jeffery a while ago, but I don't know anything about website design and I would need some help converting the spreadsheet into an application that can run on the website. I would also need to input more data on different engines and hulls to make the program user-friendly. Since I would have to pay a computer person some money to make this work, I didn't pursue the idea any further.
I think if Jeffery was convinced of the interest of the members, this program could be provided on the OSO site free of charge. Any computer whizzes out there who can help?
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Posts: 414 | From: Lake Simcoe, Ontario, Canada | Registered: Feb 2001 | IP: Logged
traviss
Member
Member # 284
posted 01-17-2002 08:23 PM
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Thanks for the info Tomcat..
--------------------
"Loose is fast and on edge your outta control"
--------------------------------------------------------------------------------
[ 01-17-2002: Message edited by: tomcat ]
Bam's calculator is based on Mercury equations that work well for a given type of hull when you know the weight. I use a formula that asks you to enter 1/2 power speed, to calculate a hull efficiency factor for a particular hull, and you don't have to know the weight. Either way works as well as can be expected, since there are so many things that can affect the answer, not the least of which is X dimension.
The neat thing about the program I wrote is you don't just plug in a max HP figure and get a speed. You enter the entire engine dyno curve, which is HP vs. RPM. You can then enter a prop pitch and the program converts this into a engine HP vs. speed curve. Then it plots that curve on top of the hull HP requirement vs. speed curve. Maximum speed occurs where the two curves cross. You can change engines, hulls and props to your heart's content and see the effect of more power, better hull and the best prop, without having to go back and forth several times between a speed calculator and a prop calculator.
This is a powerful little technique and it really gives you a feeling for how to prop the boat. For example, the excess of engine HP over hull HP at any given point is your potential for acceleration. You can see what happens to this excess power as you prop up for top speed. You can also see the difference between supercharged and normally aspirated power and why they should be propped differently.
The program can handle two sets of data at once so you can see the curves of both the existing engine and the proposed engine on the same hull curve. That's how I use it most of the time. Sometimes you have a great custom engine that you will keep when you sell your boat and you want to know how it will perform in a new hull. So you would plot one engine on two hull curves.
I've been thinking about substituting Mercury's formula into my program and making the program available on this website for members to use. Since not everybody has Desktop dyno or dyno curves for their engines, I would have to include a menu of engines, Mercury and common high performance combinations, to enter into the program. Members with dyno data or a dyno program could enter their own data.
I have posted the idea as a separate topic to see what the members think. If you guys like the idea, I will talk to Jeffery.
Here are some posts from another thread where this subject got started:
Katdrvr
Member
Member # 950
posted 01-17-2002 04:17 PM
--------------------------------------------------------------------------------
Tomcat,
Sounds like a cool program. I'll bet everyone would love to be able to run some demo's.
mike
[ 01-17-2002: Message edited by: Katdrvr ]
--------------------------------------------------------------------------------
Posts: 853 | From: Gretna, Ne | Registered: Feb 2001 | IP: Logged
traviss
Member
Member # 284
posted 01-17-2002 07:34 PM
--------------------------------------------------------------------------------
Tomcat, what is the name of this program? Would be able to get it somewhere? It probably is very expensive being boat related
thanks
Travis
--------------------
"Loose is fast and on edge your outta control"
--------------------------------------------------------------------------------
Posts: 4286 | From: in nothing anymore!! | Registered: Oct 2000 | IP: Logged
tomcat
Member
Member # 995
posted 01-17-2002 08:11 PM
--------------------------------------------------------------------------------
traviss - I didn't buy the program, I wrote it. It's a bunch of formulas in a spreadsheet, that produces a beautified chart for the output.
I proposed putting this program on the website to Jeffery a while ago, but I don't know anything about website design and I would need some help converting the spreadsheet into an application that can run on the website. I would also need to input more data on different engines and hulls to make the program user-friendly. Since I would have to pay a computer person some money to make this work, I didn't pursue the idea any further.
I think if Jeffery was convinced of the interest of the members, this program could be provided on the OSO site free of charge. Any computer whizzes out there who can help?
--------------------------------------------------------------------------------
Posts: 414 | From: Lake Simcoe, Ontario, Canada | Registered: Feb 2001 | IP: Logged
traviss
Member
Member # 284
posted 01-17-2002 08:23 PM
--------------------------------------------------------------------------------
Thanks for the info Tomcat..
--------------------
"Loose is fast and on edge your outta control"
--------------------------------------------------------------------------------
[ 01-17-2002: Message edited by: tomcat ]
01-17-2002, 10:39 PM
#3
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Tomcat, I think it's a great idea. However, I'd like to see it available in it's current state. There are a lot of us gearheads on this site that would love to plug all the torque curve numbers in....
Bob
Bob
01-17-2002, 11:07 PM
#4
It would probably make sense to have two versions, a quick and easy one with menus to choose from, and and expert version that allows you to enter all your own data. What I have running on my computer now requires all data to be entered, and I can change the formulas if I want. The expert version could also allow you to choose from the Mercury equations or the other equations which can be "calibrated" by test data from your own boat.
Something I do manually now is adjust total prop HP until the calculated speed matches the GPS results from a test. For example, a member gave me GPS results of 60 mph with a pair of 260s. I used the typical hull efficiency factor for deep vees and adjusted the total prop HP until the program gave me 60 mph. The final prop HP was 475, not far off for a pair of 800 hour small blocks rated at 260 crank HP. Once the baseline is established this way with actual data, you can throw the bigger engine into the program and see what happens.
I don't claim that any program can be perfectly accurate, but playing with the program is an education in how performance boats work.
Something I do manually now is adjust total prop HP until the calculated speed matches the GPS results from a test. For example, a member gave me GPS results of 60 mph with a pair of 260s. I used the typical hull efficiency factor for deep vees and adjusted the total prop HP until the program gave me 60 mph. The final prop HP was 475, not far off for a pair of 800 hour small blocks rated at 260 crank HP. Once the baseline is established this way with actual data, you can throw the bigger engine into the program and see what happens.
I don't claim that any program can be perfectly accurate, but playing with the program is an education in how performance boats work.
01-17-2002, 11:24 PM
#5
Charter Member #40
Charter Member
Tomcat/
I think it would be super if you could get your program on OSO. Sounds like you have developed an interesting approach to analyzing performance and I would think the members would not only learn alot but find the program benefical in their own applications once they got their boat's performance and the program showing comparable numbers! Good luck!
I think it would be super if you could get your program on OSO. Sounds like you have developed an interesting approach to analyzing performance and I would think the members would not only learn alot but find the program benefical in their own applications once they got their boat's performance and the program showing comparable numbers! Good luck!
01-18-2002, 08:49 AM
#7
Tomcat, Great work. You and I share the same enthusiasm for boats, power, speed and numbers. I am calculating all the time to figure things out. Your programs sound great. I had thought about plots of hull efficency and hp but couldn't figure how to put it together. Can you download your programs to CD? Maybe that would be initally easier. It would be the best to have it on OSO. Maybe OSO needs a 'Reference' area which would have topics of great interest like yours. Yopu're exactally right about the when the hp curve crosses the hull curve is the max speed-I love this stuff. Keep it up. Marty.
01-18-2002, 11:18 AM
#8
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It sounds like a great and valuable tool. Yes I would like to see the program on the site, or what was mentioned before on disc. You are very generous to offer this 
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