weight vs. horsepower

[smith411]

is there a race calculater for boats, like there is for cars? How much weight is too much? !982 Baja, '95 200 Xri, shaved heads and tuner, 9" setback, 6" CMC hydraulic jack. I just scaled it at about 2100 lbs. I don't know where to shave weight. How much horsepower would it take to gain 10 mph? Right now it runs right at 70-71MPH with 22P chopper at about 6600Rpm.

[kingsbiship]

Those numbers don't add up!

[Ted Stryker]

There not drastically off, sounds about like an average speedometer.. If your pitch and rpm are correct, your probably running 63-65 mph... Bring those rpm's down to about 6,000 with more pitch, and get that motor on top of where the power is... Your robbing yourself of horsepower by spinning the engine that high... Maybe try around a 26 pitch prop at least, and try as many props as you can with different engine heights... You can gain a lot of those 10 mph that your looking for with your current engine by sharpening your set-up... Keeping punching away at it, that's the fun part... Good luck

[dynobo]

If that 2100 lbs is trailered weight then those numbers could be fairly close. I show 4-5% slip would be 70-71 mph, especially if that is a cupped 22p. Ted is absolutely correct that you will generally gain a few mph just by running your motor in the "sweet spot" and get your boat dialed in. Ofcourse if you are only getting 4-5% slip then you are alraedy pretty darn well dialed in.

[baja200merk]

10mph? 300x, 10inchs of setback and a 12inch wide pad on the bottom <img src="http://www.clicksmilies.com/s0105/lachen/laughing-smiley-008.gif"width=2%>
kevin

[transomstand]

The Hydrostream Registry used to have a downloadable prop calculator that had a "what if" section. You could enter different horsepower figures to see what you need for more speed. It proved suprisingly accurate for my boat.

Pete

[smith411]

I scaled the boat at a truck stop. Boat and trailer weighed 2740 lbs., the tag on the trailer shows the trailer at 580 lbs. Plus I had some misc. stuff from coming back from the lake. So I'm guessing at about 2100lbs. that doesn't include me, so add another 200lbs. I have 15" of setback. Which now will bring the bow up, before the front end wouldn't carry very well. The speed is GPS. The prop is heavily cupped, maybe 1/2" of cup? I need to dyno the motor, I think I'm in the 220HP range but I'm guessing again. I run the jack down about 2" from the top that puts the propshaft about even with the hull. I run the trim all the way up then bump it down till it hits top speed, which is about four taps of the trim button. (High Tech huh?) I guess without a lot more HP I'm at the end for now.

Thanks again,
Kevin

[Mark75H]

There is no simple weight/speed calculator for boats, because weight is just one of many factors affecting speed. If all boats had the same bottom shape and length/width aspect it would be possible, but these dimensions vary within the same model from year to year sometimes.