Milord

Tomcat, I was not sure about hp but I would like to hit 70 with a light load when I'm done. As far as the hull, I'm not really sure how effecient is or isn't. It's a heavy boat. I figure running on fumes with just me and a little gear in the boat I am at 5200 pounds give or take. Now I know going to aluminum exhaust manifolds and risers will pull some weight off as well as the intake manifolds so hopefully it will pick the ass end of the boat up. I don't know anyone else with this hull with big hp so it's all a guessing game at this point. What do you use for boat speed calculations. I usually just to www.go-fast.com and use their speed calculator. Is there something better?

tomcat

Bam's calculator is based on Mercury equations that work well for a given type of hull when you have an accurate weight. I use a variation of a formula that allows 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. 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 use a speed calculator and then several iterations of 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 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 stock 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 there own data.

If you guys like the idea, I will talk to Jeffery. I might post the idea as a separate topic to see what people think.

I'm sending you the curves for your boat and engines in an email.

Katdrvr

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 ]

traviss

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

tomcat

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?

traviss

Thanks for the info Tomcat..

birdog

Hey Milford don't forget when using these calculators that hull has a 8'6 beam unusual for that size boat they might not take that into acount.

Milord

Birdog, can you give me your email address. I'd like to talk to you about your old Liberator. Thanks James.

powerqrudy

I saw a guy at my marina take a 26 wellcraft novaII from 52 to 75 mph with the same package, new roller cam's canfield heads, msd..4" exhaust edelbrock intake..that boat has to be similar??? he did not do the lower end...good luck keep us posted..

jr

Powerqrudy, thats good info to know. I just did mine last winter. I've got 409's over 350's so 80 would be nice. I've got the same boat. I've got alot of testing to do yet but maybe I'll get there.

[ 01-22-2002: Message edited by: jr ]