Help with picking a new prop

[jonnydz]

i have a 1993 Sea Ray laguna 21' CC and just put a 2006 175 Zuke on it (engine is new to me only 300 hrs). It came with a 16" 18.5" pitch SS prop. I can only get 40mph at 6100 rpm trimmed up. I do have bottom paint and a T-top. Do you think I should try a 14.5" 21" or 22" pitch to get more speed and better economy? The 2 test boats (21 proline and 21 dusky) have those props and seem to be getting 46mph.

Thanks Jon

[keakar]

a prop should be sized to give you about 2 to 3 hundred rpms less then the recommended red line for the engine when the boat is perfectly trimmed on smooth water with an empty boat an only one person in the boat. this is so that during any other conditions the motor will stay lower in rpms then that and not allow over reving of the engine.

if you are going to maximize the hole shot or looking for the max top speed then you better have a very accurate tach when doing this and its manditory your rpms never reach red line.

if you need more speed then the proper prop for the boat allows then you need a bigger motor not a different prop.

[Harper]

However, since you're right at redline with that prop, you might try a 20 or 21 pitch. I would not go any smaller on the diameter with your current rpms. I have a 20' CC, modified V hull, with T-top pushed by a DF150 with the same prop as yours, and top out at 5900 & 37 mph (gps).

[Wes Blow]

a prop should be sized to give you about 2 to 3 hundred rpms less then the recommended red line for the engine when the boat is perfectly trimmed on smooth water with an empty boat an only one person in the boat. this is so that during any other conditions the motor will stay lower in rpms then that and not allow over reving of the engine.

if you are going to maximize the hole shot or looking for the max top speed then you better have a very accurate tach when doing this and its manditory your rpms never reach red line.

if you need more speed then the proper prop for the boat allows then you need a bigger motor not a different prop.

What is the prop supposed to give you at these conditions keeping it 200-300 from red line?

[keakar]

What is the prop supposed to give you at these conditions keeping it 200-300 from red line?

every boat is different so there is nothing to say this prop with this boat gives you this speed but all you can do is assume someone with the same rig should get the same results as yours. following that logic thats the person to give you their size you can try.

short of that you just need to try a prop and see, the shop should have a book to give a pretty accurate size recommendation of 2 or 3 prop sizes as a starting point and if its not right try another one.

when i needed a prop the shop gave me 3 of them to try and said find the one that works best and return the other two. at first they were only charging me for one prop and trusting me to bring the other two back in the next day or two but when i said i couldnt bring the others back for maybe a week or two they just charged all 3 to my credit card and then gave me a refund credit when i returned them, in my case i returned all 3 and bought a stainless prop once i had the right size and pitch for my boat.

cant say every shop will do this for you but the good ones who give good customer service will