Ok. I've wanted to start this thread for a long time, but never have. I occassionally see discussion about what speed to expect from a Hydrodyne 18 with various engine set-ups, props, etc. Jim reminds us - and he is correct - that these boats are not made for speed, and may be unsafe at high speeds. However, the question still hangs out there.... what is the fastest speed that a Hydrodyne 18 has hit and with what engines? (The twin car engine Hydrodyne Crosby race boat comes to mind....). I once read somewhere that the classic Hydrodyne 18 ski boat "hits a wall" at about 55 to 60 MPH due to the hull design. My own experience tells me that this is probably true. The hull is flat-bottomed, with no V-pad at the back, and with soft chines. The V'd bow washes out pretty quickly, with the majority of the boat bottom being flat. All of this means two things. First, a very small wake. Second, a heck of a lot of drag. My boat is set up in a way that, in theory, should be a good platform for playing with the top end speed capability of this hull. I haven't done much to explore. I have a 2006 Optimax 225 on my boat. With a 19 Mirage Plus, my boat will easily hit 55MPH, even with the seats filled. If I am alone in the boat, I can trim it up and sometimes hit 60 MPH. This is the prop I usually use. I also have a Mirage Plus 21, which is a backup. This prop will get the boat up into the 65MPH range with me alone in the boat. However, the loss of speed holding at lower speeds is noticeable. Thus, I don't use this prop. I also have a Miarage 25. If I use this prop, I actually get LESS top end than I do with the 21. Quite simply, there just is not enough power to overcome the drag with such a tall prop. The same engine and prop on, for example, a 20 foot bass boat, would likely see speeds upwards of 75 MPH. However, the drag on the Dyne 18 just seems to be too much, even for this motor, when you get into taller props. On a side note, I do not know at what speeds this boat might become unstable. However, I can tell you that, at 65MPH, the boat is rock-solid steady. I just don't think that a typical engine/prop setup are likely to see this boat hit much higher. I think you would need a heck of a lot more power to get over the drag. I'd love to hear what other people have experienced with big block power and different props on these boats. Am I right that this boat's great skiing characteristics also make it a limited "speed" boat? How about the newer, 20' Hydrodynes? I think I have read that these boats may see higher top end than an older 18 with the same size engines. Is this true? Is this due to a difference in hull design? Also - Is the best top end always achieved with a single engine? Does a twin rig result in more drag due to having two engine shafts in the water? I'm counting on the experts to join in here.... MarkBano
I could get into the upper 60's with my first Dyne, it was a 72 Dyne, 91 225 Johnson and 21 pitch prop on it. Had to have all thirty gallons in the tank up front though. My I/O will run in the upper 50's with a 21 and about 61 or 62 with a 23.
With a couple of 19s on my boat I can hit about 56 trimmed out, I start to porpus though due to the wieght in the back and side saddle tanks. It runs better with an observer to balance out the torque of the engines and adds a bit of forward wieght to help keep the porpus down. Daniel
With low fuel and trimmed up so the motor is about level, mine will bury the 55 mph speedometers with a Torque Shift prop which adjusts the pitch to maintain max recommended rpm. 150 hp Fast Strike. http://pete.esquared.net/prop.htm http://www.torqueshift.aeromarine.com/ jim
We had a 20 foot 89 dyne with twin 150's trimmed down and hammered it was 45 miles an hour and the best barefoot wake you could imagine. I could do a toothhold in the bubbles in huge waves.
