prop change - overpropped

sushieater

sushieater

Member
I have a 16' zodiac rib that I bought this spring. Boat and motor only weigh about 1000lbs. Side console. 2007 Yamaha f50 came with the boat. Currently running 11.25"x14 prop. I only do 20-22 knots top speed. Sometimes less. I have a hard time getting on plane with 4 adults.

I recently added a tach and most of the time WOT is only 4k rpm. In perfect conditions I've hit 4600. I verified my faria tach is correct by checking against my multimeter on frequency mode. Motor should be 5-6k WOT. Idle looks set correct

Would 10⅜×13 be a good prop to try next?
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10-3/8X13RH Quicksilver Black Diamond Propeller (QA2078X)

10-3/8X13RH Quicksilver Black Diamond propeller for your Mercury, Mariner, Force, Yamaha or Honda. Flo Torq hub kit included. Part #s QA2078X, 48-73136A40, 58130-ZV5-012AH, and 6H5-45943-00-EL.
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Stay with same diameter if you can, easier to track changes.
 
Thanks, but I'm not sure if I can stay with the same diameter. I think I'm looking for another 1k of rpm or more. 5" of pitch change would give me 750-1000 more rpm, but that would drop me to 11.25x9 and there's not a lot of prop options around that pitch for my motor that I've seen.
 
Rob my buddy recently bought a boat with a blown Yamaha 75. I’ll see if he has a prop still.

Edit: motor is gone. I work with Marc by the way.
 
Thanks anyways corey! I guess my secret identity has been blown!
I'm guessing 10⅜×13 will bring me towards the top end of my range, but it's really only a guess. Cheap to test, but was curious if anyone had any strong opinions on the subject. I couldn't find any hard numbers of rpm change based on diameter size changes.
 
depending on where you are? poco marine is a solas dealer, has many props in the shop.. small deposit and go testing with a few.
 
I have 50hp on 16/17 whaler. Prop selection makes a big difference when motor is small and boat is loaded. 10.25 x 14 was no good for me but might be for you. 10.5 x 12 and 10.75 x 12 both work well on mine. A fin really helps with lift to get on plane.
 
sushieater said:
Thanks anyways corey! I guess my secret identity has been blown!
I'm guessing 10⅜×13 will bring me towards the top end of my range, but it's really only a guess. Cheap to test, but was curious if anyone had any strong opinions on the subject. I couldn't find any hard numbers of rpm change based on diameter size changes.
Click to expand...
Secret identity doesn’t go far once you post about your boat haha
 
Thanks for help everyone!

I neglected to mention that I already have an Attwood hydro stabalizer on it.
old.attwoodmarine.com

Attwood Marine

Attwood Marine offers a broad range of boating and marine accessories. Visit us to find info for Hydro-Stabilizer and to find out where to buy.
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different shape than the ones i have have used.
 
I checked my throttle cable and all looks good.
I raised my motor all the way up. 2 holes up and cavitation plate is perfectly level with hull now. I went out for a test run and gained 1-2 knots and now wot was at 5k. Hit 5200 at one point. It looked like about 400rpm gain. This is with my original 11.25x14 prop

I then bought a used 10x15 prop in good shape for $20 and took that for a run last night. I expected rpms to be ~450 more than my original 11.25x14 prop, but they were actually very similar. WOT was 5k. I did gain ~2 knots speed and hit 25knots for the first time in this boat. Conditions were not ideal or identical for either test run, so it's hard to compare exactly. Both tests with 2 adults and 3/4 tank gas.

It seems like 10⅜×13 would only give me another ~150/200rpm over the 10x15. Something like 10x11 or 10x12 would get me to 6k.

@tubber Do you know who makes the 10.5x12 prop that you said worked for you?
 
sushieater said:
I checked my throttle cable and all looks good.
I raised my motor all the way up. 2 holes up and cavitation plate is perfectly level with hull now. I went out for a test run and gained 1-2 knots and now wot was at 5k. Hit 5200 at one point. It looked like about 400rpm gain. This is with my original 11.25x14 prop

I then bought a used 10x15 prop in good shape for $20 and took that for a run last night. I expected rpms to be ~450 more than my original 11.25x14 prop, but they were actually very similar. WOT was 5k. I did gain ~2 knots speed and hit 25knots for the first time in this boat. Conditions were not ideal or identical for either test run, so it's hard to compare exactly. Both tests with 2 adults and 3/4 tank gas.

It seems like 10⅜×13 would only give me another ~150/200rpm over the 10x15. Something like 10x11 or 10x12 would get me to 6k.

@tubber Do you know who makes the 10.5x12 prop that you said worked for you?
Click to expand...
check solas catalog
 
sushieater said:
@tubber Do you know who makes the 10.5x12 prop that you said worked for you?
Click to expand...
Mercury Black Max aluminum. 10.625 (10 5/8) X 12 seems easier to find.
I think my 2003 Merc 50 was made by Yamaha.
Pretty sure there is something called a Flo-Torq (2,3,4?) hub to make it fit a Yamaha.
I was just googling- prices are outrageous. I got mine and a spare used for $50 total from a guy getting out of boating.
 
10.625 x 12 should do well since raising your engine. Switching brands isn't always a direct comparison due to differences in design.
 
Question what’s that Zodiak rated for? Could be way under powered as well. Was just thinking a family member had a 12ft Zodiak with a 40 was a hard bottom with steering wheel and it went pretty good but not as fast as I thought it would have been. Haven’t seen your boat but it’s probably rated for 90-115hp max. If it is you will probably always be let down by performance no matter what you do especially with a full load may not find the perfect prop for changing loads day to day. From what I have read over the years seems lowest hp you want is minimum 80% of your max rating. Max rating hp always shines imo don’t need throttles down for a nice cruise and when you have a heavy load still lots of jamb out of the hole. I could be off on your boat but another angle to look at.
 
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