Another prop option, Crestliner VT-18

[MattVT18]

I finally got around to messing with the setup on my Crestliner VT-18. I haven't moved my engine height any at all, still in the 2nd hole down. Had a 19P Spitfire aluminum prop from the factory. I could get 40mph or so top speed before blowing out the prop and that was straight line only. Boat speed stopped increasing after about 5300 RPMs. I took the boat to have the motor raised and had an interesting talk with the owner of the shop. He noticed the paint was chipping off my prop, said that was the first sign of cavitation and the paint was actually being burned off and that he wouldn't recommend moving the engine any higher with that prop. He recommended a stainless steel prop in the same pitch. I ordered a Turning Point Express Mach4 19P 4 blade prop to try. The difference was amazing as soon as I took off. The hole shot was much better (not that it was bad before) and the top speed increased to 45-46 depending on chop and wind. Before the prop change I could get 40-41 mph in a straight line, but you could forget turning as the prop would blow out almost immediately. Now I can trim the engine to run 6K RPMs and actually drive the boat without worry. I'm not sure I'll raise the engine as it performs pretty good where it is. I might consult the shop owner again to get his thoughts on raising the engine. So far, this guy has been spot on in his advice on everything I took him. I know alot of RT188 and VT-18 guys are running Laser IIs and Spitfire X7s, but this Turning Point Express is pretty good for less coin. I've got $350 for the prop and hub kit in it and couldn't find a Laser or X7 for less than $425 new shipped.

[Grahamb]

Interesting. Can you describe what you mean by “blowing out the prop”? I have what I’m calling porpoising but maybe it’s the same thing?

[GeauxTide]

Blowing out the prop is when the prop loses bite and the RPMs spike. Porpoising is the boat bouncing up and down. Both conditions can be caused by over trimming the motor. Semi-Vee hulls are prone to porpoise without some kind of wedge on the bottom.

MattVT18, you should be able to raise the motor to hole #3 with a 4 Blade. What is your motor and WOT RPM?

[cire06]

I have a 17 vt18 with the x7 19p. My motor is mounted on the 1st hole (very top) and it's pushing it around 50 with WOT 6k

[MattVT18]

I could probably raise it up a hole, maybe two. Right now I'm getting 45 MPH (GPS) and 5800 or so RPMs via Vessel View. I have a lot more trim available now than with the original prop. My 115 ProXS can spin 6300 WOT, so there is still some RPMs to gain. If I go much farther on the trim than where I get the reported numbers it starts losing grip again and blowing out when turning. Cire06, are you saying your motor is as far up as it can go? Are you getting the speed and RPMs via the gauges on the boat? If your gauges are like mine they are not very accurate...my speedo is about 4 MPH higher than actual speed and the tach is about 300 RPMs fast as well. Right now it's very comfortable to drive...I'd like to get it to 50 or so MPH but mot sure I'd do it if ride and handling were sacrificed. Grahamb, I currently have zero porposing. My boat has never experienced that at all even though a lot of VT18 guys have. Not sure why mine doesn't do it and others do.