Use Marc's method for measuring pipe lengths,if you do it any other way you are asking for trouble.Measuring in straight lines is silly because there are different offsets on headers some use 1" some as much as 3" so if you measure in a straight line you could be as much as 2" out .Allways measure the total length by going round the centreline of the header and pipe and you will never go wrong.By the way the stock rcmk prefers small props ,they rev high but dont have the grunt of a good modded zenoah.Email dasboata he will sort you out with a great prop im sure.My mate runs one on the t boat i built him with the rcmk and best speed he gets with the racers edge 6717/3 is arround 50 mph,def go smaller in my opinion.
Mart

galoi wrote:
Did you use the GPS to find out the best setting like strut height and pipe length and etc? the incorrect strut height would cost you a few mph, the cat is fun and runs fast if you treat it right..lol, check my yellow 41" cat vid and hope you like it.

www.motionbox.com/videos/a79ed5be1111e02e

@ken0276: Your boat is nice and run verry good. I'm a new bile and this is the first CAT i buil. I know the method to measure the speed by GPS device. In vietnam, it difficult to buy. How about the price of a GPS device?

My Garmin foretrex 101 cost me $45, check this site out, you might get one cheaper than mines, here's my another 41" cat with the GPS, I placed it in a small container made by the swimming noodle, for your first built, it looks good to me.


catalog.ebay.com/Garmin-FORETR...d=p3286.c0.m271

This is my cat prop.

I have cut the pipe down to 32cm, and test with 6717/3 prop. My boat run verry good. Thanks all for help me edit my boat.

galoi wrote:
Found an almost 3 years old video of my Stryker cat that ran with a 6717 prop and 260 engine, can't remember the engine was mod or not...the cat ran ok not the fastest one but had so much fun that time.

www.motionbox.com/videos/a79fdab11112e22e