I'm hoping there's some propeller experts out there that can help me. My boat was overpropped - black smoke and about 100 revs off top when fully loaded. So, I invested in a pair of shiny new wheels from a major prop manufacturer. The props are now on, and guess what - I'm now150 revs off top and you can see my smoke cloud miles off! Now the details - original props were four bladed 24x24 bronze uncupped. The new ones are four bladed 24.5x22.5 nibral cupped. Although the pitch is less than the original ones, it appears the increase in diameter and addition of cupping more than compensates for this. The engines are Cat 3208TA at 375HP, with Twin Disc 1.98.1 transmissions. It's a 45' planing hull with top speed of 20kts at 2800rpm. The manufacturer claims that his original sizing program indicated 24.5x22.5 with "custom variable pitch" and "custom cup" was required for my vessel, but that what the local dealer ordered, and therefore what I got, was 24.5x22.5 "standard". The manufacturer is now offering me two options to rectify the problem. One is to redo the propellers with "custom variable pitch distribution and custom cup, as was originally intended for this vessel"; the other is to simply reduce the pitch by another 1.5" to 21. I must admit to being a bit dubious about their claims of custom this and that. Sounds like an excuse to me, especially as their website suggests variable pitch distribution is standard on all their performance propellers. Can anyone please enlighten me as to what variable pitch distribution is, and whether it has to be custom to each vessel, and whether it could really make a difference equivalent to removing 1.5" of pitch? And what about the cupping - I've heard it's unnecessary on anything below 30kts, but has the equivalent effect of adding 1" of pitch. I'm tempted to ignore all the talk of custom do-dahs and just ask them to remove the cupping and reduce pitch by an inch. What do the list's propeller experts think? Any advice appreciated, as it's gonna cost me a bundle to get the props re-done and I want to make sure I get it right this time! Thanks. Andy Cutt Horizon 45 Hong Kong

>I must admit to being a bit dubious about their claims of custom this and >that. Sounds like an excuse to me, especially as their website suggests >variable pitch distribution is standard on all their performance propellers. >Can anyone please enlighten me as to what variable pitch distribution is, >and whether it has to be custom to each vessel, and whether it could really >make a difference equivalent to removing 1.5" of pitch? And what about the >cupping - I've heard it's unnecessary on anything below 30kts, but has the >equivalent effect of adding 1" of pitch. I'm tempted to ignore all the talk >of custom do-dahs and just ask them to remove the cupping and reduce pitch >by an inch. What do the list's propeller experts think? Any advice >appreciated, as it's gonna cost me a bundle to get the props re-done and I >want to make sure I get it right this time! Thanks. > >Andy Cutt >Horizon 45 >Hong Kong ========================================================== Andy-------------You are right in your thinking, EXCEPT, having a wheel repitched ruins the efficiency of the wheel. You no longer have a true pitch, and you will lose speed compared to a new wheel with out an altered pitch. In repitching they can only twist the outer third of the wheel and not the part near the hub, so you will no longer have a wheel with true pitch and will suffer a loss in efficiency. This can only be proven by installing new wheels of the proper size and doing test runs, which I went through the expense of trying, and because I was right the prop company ate the altered wheels and I ended up with new wheels at their expense because I was willing to gamble. I would have no qualms having repitched wheels for spares. I would first have the cups banged out for they are of no help to you and just load up the engine. Keep me posted. . Captain Al Pilvinis "M/V Driftwood"--Prairie 47 2630 N.E. 41st Street Lighthouse Point, Fl 33064-8064 Voice 954-941-2556 Fax 954 788-2666 Email yourcaptain@earthlink.net Website http://home.earthlink.net/~yourcaptain