hydro vs runabout setup

[john david]

I realize that setup (prop shaft height, kickout, type of prop, hull ,weight, cg etc. etc.) can only be found after many trials and experimentation. Can anybody generalize the prop shaft height of csr versus csh? I'm not a racer yet. I am trying to gather info. I understand that hydros run higher with surface piercing cleavers. What about runabouts? If the prop is buried does it decrease stern lift and cause porpoising? What transome angle is built into hulls? What transom height allows for a little experimentation. Happy new year john david

[Ron Hill]

I always considered myself a RUNABOUT PERSON, but when I started racing hydros, I frequently won. I always set my hydros up just like my runabout.

I'm dating myself, but at the 1977 Nationals, I won D Runabout and was second in DSH ....

I always ran very high and kicked under....with today's rules, at least in APBA, where they have transom heights, I really don't know the rules....

My son ran only four heats of ASH in his life and won them ALL...Winter Nationals a few years ago...borrowed a new Zorkan Hydro and we set it up just like his J Runabout, we used an old C Runabout TWO BLADE from a MERC, I've heard this is still a pretty good prop for ASH.

ON an OMC "A", we ran a quarter inch kick under in the length of the cavitation plate....

I don't know others set ups, but I like them under and up....

[B1PRORACER]

I have run runabouts and hydros- both Stock & PRO,
I set them up the same! If you already have a setup on your CSH, try putting a "question mark" on the prop shaft and measure from the same points -front & back. Measure between the actual boat bottom and the edge of the checker. If your boat has a tunnel, bridge the tunnel and measure from the edge of the bridge. Put your engine on the runabout and adjust the height and kick-out to prodice the same measurements. Run the same prop and then carefully try it! I did this from my ASR to a Furnell ASH in the 80's at the Regionals and out ran Ken Rosado and Tommy Good to win! I did it again in my first 250ccR race at the USTS Constantine, Mich. race and won the first heat. I did it with my kiloboat many years ago and broke the 250ccR kilo record by almost 7 MPH..... Try it, it works!

[john david]

Thanx for your response. I guess I should have posted this question in the rookie lounge. I am understanding that surfacing props is just as important in runabout as in hydros. I understand that certain classes have height restrictions for the prop shaft. Seems ya want as high as you can get away with. If the prop is buried rpms hp and speed suffer. Are runabouts dependent on a high prop setting to allow enough stern lift to prevent porpoising. Thanks again

[B1PRORACER]

I don’t think your question needs to be in the “rookie lounge”…! If you have a good runabout hull, there is often NOT MUCH MORE running friction or resistance than a hydro. If you have a decent “all purpose” propeller, it will run good on both the hydro and your runabout. Now this is the basic theory…and it applies to your questions- it is all relative: If you place your engine on a boat, start off by running the prop shaft parallel with the boat bottom (usually a neutral setting). MEASURE your starting point for a reference. This starting point should be a lower engine height than you expect to eventually run the engine. The propeller, because of its fixed pitch and diameter is basically a fixed load on the engine. As you proceed, you will begin sliding shim sticks under the clamp brackets after each trial. Remember to RECORD each trial!!! As you raise the propeller higher, you will reduce the amount of water that is introduced to the propeller. This reduces the load on the engine and allows the engines speed to increase (more RPMs). The GOAL is to allow the engine to run at the RPM that corresponds to its maximum horsepower. This will produce the maximum power going to the propeller. In turn this creates the maximum thrust and therefore the best performance. When you are all done testing, you will find that the distance from the propeller shaft to the bottom of the boat will almost be the same between a runabout and a hydro. The goal is not to run the engine as high as you can…! The goal is to run your prop at the OPTIMUM height! This is the height that your ENGINE likes to turn the prop. Each prop might have a different OPTIMUM height. It is important that at your “optimum height” is not higher than the maximum allowable height for your class. If you understand what I have told you, it will answer your questions. About the “porpoising”… the runabout generally doesn’t have the large amount of compereesed air under it that a hydro does. The rules for a runabout guarentee that the compressed air will vent out of each side of the boat. If the boat is “properly shaped”, the runabout can still run remarkably clean and free. It is important that the bottom of the boat be flat and straight right up to the break point (normally). The balance is extremely important too. Depending on the boat design, it is important that you (generally) move as much weight to the back as possible. You might have to change the propeller shaft angle in order to “trim” the boat a little. If you do it right- you should have a fast, stable ride with NO “porpoising” and you just might out-run some hydros in your engine size!

[john david]

thanks B1Pro. You answered my question very well!