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prop size

P

paul colley

New member
i have a 1996 checmate diplomat 17' with a 90 hp evinrude V-4. THE PROP ON IT NOW IS A 13 1/4 BY 17.
With this prop on, my boat went just under 40 mph. i also have a 12 3/4 a 23 prop. how much more speed, if any would this second prop give me?
 
i have a 1996 checmate diplomat 17' with a 90 hp evinrude V-4. THE PROP ON IT NOW IS A 13 1/4 BY 17.
With this prop on, my boat went just under 40 mph. i also have a 12 3/4 a 23 prop. how much more speed, if any would this second prop give me?
 
Hard to tell, it really depends on the engine( if it will turn it and stay in the rpm range) and the prop. Has the right properties for the boat. Bow lift ect.
I say bolt it on and run it.
 
Hi Paul:

Real quick prop 101 here (i'm takin' a study break here). Ok, you could spin a 12 x 44 if you wanted to (if you could find one) but if you're not in the engines recommend WOT you'll be blowing your brains out. A prop that is 12 x 19 means the following: the first number (12) in the prop size is the diameter in inches, the second (19) is the travel in inches for one revolution (in theory only). I won't even mention slip. Anyway, if your engine is making max rpm with the prop on it your pretty much done. By going up in pitch, the engine speed will slow down (called lugging). Your engine will drop approx 200-400 rpm for every 2" step up in pitch. If you went from a 19 to a 23 you could lose anywhere from 400-800 rpm off of WOT. This is fine if you are over revving to start. If your already in the range then by adding more pitch you will end up doing serious damage to your engine because it will be working too hard. Someone may try to steer you towards a stainless prop but if you're not hitting 50 mph you won't see enough benefit to justify the price. The big benefit of stainless is that it doesn't flex. The big drawback to stainless is that it doesn't flex (especially when it meets a rock). Keep in mind that checkmates are heavy hulls for their size (a good thing) and they need lots of power to perform. Your 90 may be working just fine but we need to know what RPM you're running before that can be determined. Proping is all about trial and error. Unfortunatly, you don't have a lot of options with that size engine. Get up in the 200hp range and the possiblities are endless. Anyway hope this helps and i know others will be itching to get their 2 cents in so I'll let someone else take it from here as i need to get back to the books!
 
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