60 MPH Club, finally made it!

Well, this turned out to be a good weekend for me. Saturday afternoon after some rains came thru and most peole were off the lake I took out the 77 Ski Nautique which has a stroker 351W, now 392 cubic inches spinning lefty.Previously I was running a Acme 431 and spinning 5700-5800 rpm's and getting 57-58mph. Since this engines peak horsepower is at 5500 I decided to get a Acme 1459 and try it out. Made a pass back and forth on the third basin of Lake James and looked at the GPS and it was 60.1 mph.Definately made my day as I was grinning ear to ear. The prop brought the rpm's down to 5000-5100 at WOT. Now if I want I can throw some more mod's at the motor to gain some more hp. Still smiling on Monday on my way to work.

Wow....


The 84 Ski Tique made it up to 64 MPH this morning....on the trailer

Can I get a ride??

I dont know if he is that far off on the 431 numbers.. back when I was running that prop I also found it to fall off a cliff at the upper limits, the last 200 rpm werent worth a half mile an hour.. I attributed it to flex/slippage

Joe, In the past with the 431 prop at 55+ the boat had tended to porpoise at times, not always, but a lot of times. This back to back run actually did not porpoise at all and I did not realize I was going that fast due to the engine rpm's being only around 5000. I was really happily surprised by this. At slow speeds it does list to the starboard side but no problems with its handling.

Tim, like I noted above 55+ would at time porpoise but I don't know if was attributed to Lake conditions or not. I will not take the boat out on speed runs unless the water is relatively calm. As for the build specs it is just an older 392 Ford Racing crate engine rated at 430 hp at 5500 rpm's. 9.7:1 compression, roller cam .563 lift intake and .584 lift exhaust,GT-40 heads with 1.94 intake and 1.54 exhaust.It has an Edelbrock dual plane with a Barry Grant marine demon 750 and some Hiteks.

Tim, I wondered about tach accuracy and also it being such a small sweep on my boat so I changed the tach to a Autometer pro-comp marine 0-7000 RPM with a hourmeter along with the rest of the gauges and senders this spring. I didn't want to be guessing about the RPM'S and then making changes. The new tach is much easier to get an accurate reading.

Holy cow, that is really fast. What is the wake like at that speed? I can read the 80's WaterSki Magazine review now (back when their boat reviews were really awesome):

"The table was a little rough and hard, but the wakes are very minimal and easy to cross. You'll have to contend with some spray at short line lengths, which really stings at 60 MPH."

GottaSki wrote: I suspect the porpiosing with the other prop was due to being on the wrong side of the torque curve, it was falling off above 5500, setting up an oscillation. Now that its pulling harder, it runs flat.

I don't doubt there is some of that going on, but I have also noticed that on several of the heavily powered boats you go past a speed where you will see any porpiosing. My boat will run relatively bow high until about 57 then it is nose planted until you run out of motor or cavitate the rudder, and I am running well past the hump of my torque curve in the 5900+ range. The boat also behaves pretty similarly but slightly slower with the big prop that only runs 5000 or so rpm. Similar behavior occurs with reids orange and white mustang even though there is less than factory hook left in the hull. Tims barefoot (when it is running) also seems pretty well planted at higher speeds.

Just be careful to keep the rudder in the water, and particularily careful coming down the backside of waves traveling in the same direction.. they help the nose down and the rudder up.. slowing down mid wave is also not encouraged as you can drop the nose quick. A lanyard kill switch is not a bad idea either..

JoeinNY wrote: Tims barefoot (when it is running) also seems pretty well planted at higher speeds.

Ouch!

Very true though. I havent driven the boat enough to know exactly when it plants the nose, but its well north of 50mph, thats for sure. I suspect that at some point, the steep shaft angle simply overcomes the hull's propensity to porpoise.



No one stated it above, but I dont consider porpoising to be a bad or scary tendency. If youre bouncing, it means youve got plenty of bow lift- and getting the hull out of the water will generally speed the boat up a bit. If you look at pictures of some of the boats doing speed runs, you'll notice that there will generally be some weight in the back seat (1-3 passengers) and only the driver up front. Things like chine locking, rudder stalling, etc- that cause unpredictable and uncontrolled maneuvers at speed are the types of things you want to prevent.

Joe, a little off topic here- but I was looking at the boat on the lift the other day and couldnt help but notice how much further the prop extends into the water past the rudder. Its a safety requirement on v-drive flat/drag boats that the rudder extend a certain distance past the prop. Something to think about.

got you by a yr ?

What is rudder stall?

Way to go Papa. It's great to see what you and Bryan have done with my old boat.

pictures/video or it didnt happen!

connorssons wrote: I have experanced rudder stall in my mustang at high speeds the ride is extremly wild after that. a kill switch is advisable.

Great idea from you and Joe both. I will definately put one in.