20sf Prop?`

[WaveWalker]

I have a merc 2006 opti 175 and i dont know what the size or pitch is. iI top out at about 37 mph at 4300 rpm's. The prop looks small compared to alot of props i've seen. it has no hole shot and the max rpm's im getting is 4500 maybe.

[eggsuckindog]

doesn't matter it ain't close to correct - I have to guess a 17" pitch, on my 20 I kinda stumbled in a Stilletto prop and couldn't be happier. It produces incredibily low slip numbers and trim responce is outstanding. It will want to be mounted high on the transom, my cavatation plate is 2 1/2" above the hull bottom but worked much better after I raised it another hole. Yamaha bought the company a few years ago and it is the same as a Trophy, they are reseaonably priced around 300 new.

[muddywater]

Eggsuckingdog is right. Your prop probably has way too much pitch and to forget about diameter. When choosing a prop, instead just concentrate on pitch and prop model. If you post the serial number off the prop we could probably figure out what you have. If the last three characters happen to be something like 21P that would tell you that you have a 21 pitch prop for example.

Not only do you probably have way too much pitch, your engine could be mounted too low. On my other boat, I just remounted the engine and tested this weekend. My anti-ventilation plate was 1-inch below the the bottom of the hull. After remounting the engine 1 bolt hole up (3/4 of an inch), I gained 250 rpm and 2-4 mph and it is actually still mounted too low. That is a pretty big performance gain with no change in prop. Btw, those Mercury lifting rings they sell on ebay for like $15 work great for remounting an engine if you end up having to do that. With a cheap Harbor Freight hoist, it made remounting the engine a 1-man job.

Do a search on CSC as there are a zillion prop threads.

[eggsuckindog]

Engine height makes an enormous difference in the way the rides and handles, much more than most think. I would try 1 more since its easy for you, if it doesn't blow out your good. If you think about it, it changes the thrust angle

[McGillicuddy]

That combo should get close to 50mph top end and great economy at cruise even with that overweight motah. It sounds like your have way too much pitch and cup and no stern lift. 15 x 17 Mirage plus or 15 x17 Powertech MQS3 will get you happy but first check your engine height. anti-cavitation plate needs to be 1-1/2" or more above keel when parallel. Also might want to check for a dead cylinder. Your numbers are intolerable... good luck and get her dun

[Teasem]

I had a 2010 Suzuki 225 on my 21... I ran a 23 pitch

[eggsuckindog]

Zukes don't help, they run a lower gear ratio than OMC or Merc

[McGillicuddy]

exactly right ESD...

[WaveWalker]

Thanks for all the replys. I'm going to start off by raising the motor, it's mounted on the top hole which is way to low.

[Tiny]

ESD, you talking a 3 blade or 4?