posted 06-09-2002 04:08 PM ET (US)         

Look familiar!

Jim we need a site search 'engine' more than a copied so called prop. calculator!!!!!!!!!

posted 06-10-2002 12:10 AM ET (US)            

Mine just happens to resemble the RBBI model in is fundamental approach, but that's because it's a pretty fundamental approach and it was interesting that it could calculate any of the five values.

Mine works better, in my opinion, since it does not constantly trap you into an annoying error message if you have five inputs. On the other hand, the RBBI works without server involvement.

My son and I worked it out between periods of the Red Wings game yesterday to relieve the tension of the triple overtime.

posted 06-10-2002 06:52 PM ET (US)            

The 'prop propulsion' calculation is totally based on the prop 'bite' as it 'screws' it's way through the water. One unknown input parameter in the calculation is the slippage which the calculation is totally based on and which will vary widely. As such, the calculation might get you in the ball-park - but again, many factors (condition of the prop, cup/no-cup, number of blades, pitch, fresh/salt water, elevation, wind, speed, et.al) will affect the slippage.

posted 06-10-2002 07:41 PM ET (US)            

For example, I have a 17-inch prop on my boat and I can turn it to 5400 RPM. If I raise the pitch to 21-inches the calculator will compute a much higher speed, but I know that there is no way my engine could ever turn a 21-inch prop to 5400 RPM.

The higher the pitch of the prop, the more horsepower it takes to turn it, and thus props are usually sized according to the engine horsepower. Just to suggest a few common props, you might see this:

50-HP = 15 in. pitch
70-HP = 17 in. pitch
100-HP = 19 in. pitch

Those might apply to a lightweight boat. If the boat is heavier, the pitch will have to be lowered.

posted 06-11-2002 01:51 PM ET (US)            

For instance:

1) Insert all parameters except Speed.

2) Hit calculate, it calculates Speed.

3) Change pitch.

4) Hit Calculate, it does nothing. It would be nice if it calculated speed again.

posted 06-12-2002 11:44 AM ET (US)            

Here is a real-world example. On my boat I have twin engines with 17-inch pitch props. When the engines turn 4000 RPM, the boat goes 25 MPH.

If I had a single engine with the same gear ratio, turning a 17-inch prop at 4000 RPM would produce the same speed.

It is likely that the prop diameter would be bigger on the single, and the horsepower would have to be double the twin's horspower, but the boat would go the same speed (or close to it).

posted 06-13-2002 12:05 AM ET (US)            

By the way, there is no way for the calculator to differentiate between cupped or not-cupped props (at the moment) so there is no way for you to communicate to the calculator that you are using a cupped prop.

posted 06-17-2002 11:25 PM ET (US)            

If you give it five parameters, the calculator now tries to guess which parameter you meant to have recalculated. To let you see which parameter was actually calculated the cells containing that value are shaded in a darker color (if you have style sheets enabled in your browser).

Also implemented was a choice to change the units of the BOAT SPEED parameter, now available in either MPH, KN (nautical miles per hour), or KPH (kilometers per hour).

The cool part of the calculator is the modular nature of the code.

The HTML is contained in a template.

The appearance of the HTML in your browser is controlled mainly by style sheets, like most of everything else on this website except the forum areas.

The calculations are contained in a separate program module (or "class").

The connection between the user and the sever is accomplished with a CGI Application module ("class").

Don't think I understand all of this quite yet either, as my son the computer programmer knitted most of it together. I hacked out some of the HTML and Style Sheets.

Let me know how you like the new variant of the Prop Calculator.