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Mitch Pixley
07-11-2005, 03:49 PM
Looking for prop recommendations for my 1980 18 2+3 Classic which I had repowered with a 320HP Indmar engine. The stern drive is the Merc. 260 (Alpha One) unit. Current propeller is a clever design 21" pitch but my engine easily over revs Indmar's recommended 4,800 RPM max.

Ranman
07-11-2005, 04:43 PM
The only way to really find the right prop is to try as many as you can get your hands on. I'm assuming you have a 1.5:1 drive ratio or thereabout. If your ratio is lower 1.65:1 you will need to swing an even bigger pitch than I'm suggesting. If you r ration is higher 1.35:1, you'll take a little less pitch.

My recommendations assuming you have 1:5:1:

For top speed go for either a Mercury Mirage Plus arounf 23P or a Precision Propellers Turbo One also at 23P. If you over rev these, try a 25P. The short way to describe the Mirage + and Turbo is loose and fast.

If you want better midrange cruising and a very solid stable feel to the boat, try a Hydromotive Quad IV at arounf 22" of pitch. If that over revs, try a 24". On an 18 Classic, you will typically swing 1" less pitch when running a 4 blade vs. a 3 blade.

P.S. In my opinion, cleavers are old technology and are very rarely the best available choice given todays advanced propellers.

Also, remember this is not hard and fast. I'm just trying to give you a sound starting point and solid recommendations.

Oh, one more thing, 320 HP on an Alpha One is approaching the limit. If you take it easy on her you should be fine. If you're hard on the boat with that much HP, you may soon be in the market for a new gearset.

Good luck.

DonCig
07-11-2005, 10:01 PM
Mitch, Randy Oak (Ranman) and have both gone thru the prop testing quagmire. I still have a few props for sale that I would let you try, but it would help to know your out drive ratio to start. In my experience I have come to the conclusion that one mans garbage is another mans filet mignon, with a few obvious exceptions. Try to test as many props as you can on the same day in the same weather conditions. Use a stopwatch, but most of all use your perceptions. Your mind seems to send good info. when you are about to kill yourself! Remember that you must define your goals before you set out on the quest.

Please prioritize the following items before starting down the testing path.





Top Speed

Lowest available planing speed (Skiers and knee boarders)

Mid range Cruise (Fuel Efficiency) Don't Laugh, your S/B boat will consume about 23 gallons per hour at full throttle and 8-9 gallons per hour at 3000 rpm. For you big block boys you are going to eat gas at 31-33 Gallons Per Hour at Full WOT.

Mid range acceleration. Seat of the pants or a stopwatch from 30 to 50 mph is a good indicator.

Turning Capability thru the speed range, seat of the pants.

Cost- from $100 to $1,200 for a prop.

Variable Conditions such as passenger load and fuel and accessory weight.



I have tested a number of combinations (Over 20 combined!) with my

1997 Classic 18 and there is no perfect combination for all of the above points, but the most balanced combo that I achieved was able to meet most of the above criteria. In my opinion if you ignore top speed in your ranking and then use it to sort out the finalists you will be ahead in this game. You can also make it real easy and stop the testing when you find the first prop that works well and call it well enough. Boats are Money Pits, just like Race Cars.



DonCig



Please email me if you want to discuss further

txtaz
07-11-2005, 10:30 PM
Don, What did you run on your Bravo (I assume you have a 1.5:1 ratio)? I'm running a 25 Mirage Plus now and planning on tweaking the ECM in the morning to get up to 5200 RPM. Should see 74-75. We will see.
Wes

Mr X
07-11-2005, 10:34 PM
Don, What did you run on your Bravo (I assume you have a 1.5:1 ratio)? I'm running a 25 Mirage Plus now and planning on tweaking the ECM in the morning to get up to 5200 RPM. Should see 74-75. We will see.
Wes


:) wes, good to see her up to speed again!

DonCig
07-11-2005, 10:51 PM
Wes, I started this process with a stock Bravo 1 1:65 ratio, 350 Mag MPI, 25 pitch Mirage Plus and a little/lot chine walking thrown in for entertainment. I then switched to a few Hydromotive props for comparison. The I added a IMCO -2" Shorty and host of 3 and 4 blade props. Merc. Bravo, Hydro Quad 1 and Quad 1V, Turbo 1, and Hydromotive 3 Blades. Then I bolted on a Merc. Blackhawk outdrive and am in the process of playing with the props and gear ratios in the BH.

What I have learned is that you should do your own testing. I am currently learning to like the Blackhawk, it is not perfect, but it has been a fun experiment. I will have the BH on my boat at PK for anybody that is interested in driving the combo, look me up. Up to 50 mph, it is just like most other outdrives other than having a slower planeing time. On a positive, it corners like it is on rails. It is tab and drive trim sensitive, as are most outdrives. And I can shoot a BIG Rooster Tail when I feel like soaking the little pain in the arse jetskiers!

DonCig