FN Prop size

Duane,
I don't see any mention of getting a shop tach hooked up to check the WOT RPM. The 4000 is low. I don't feel you should do anything especially increase the pitch until that figure is checked.

You mentioned a fresh 350. Do you suspect your engine now has some high hours on it? Has a compression check been done on it?

I got the prop back in brand new condition and put it on. It is now a 13 x 11. I ran the boat and it ran right at 4000 RPM, and clocked 33.5 on the handheld GPS. Not the numbers I was looking for. I am wondering if I should go back to the 13 x 12 since it seemed to accelerate better and really ran the same speed. I will run it a couple more times and see if I can get some consistent data. I know this boat can run the 40 mph with a brand new rebuilt Chevy 350, or can it? I am also going to try a 14 x 11 or maybe a 13x14 four blade Acme #504 (like Michigan Dave said he runs), and see what that will do whenever I find one cheap enough.

Alright, Nice weather, bit of a stiff breeze (7-10 mph), almost no chop, and here's the data. To plane, (Not really sure if there's an exact way to measure, but I went off of feel) it planes around 14 to 17 mph. With the wind, the boat maxed out at 32.5 mph and 3900 RPMs. Into the wind, the boat maxed out at 30.6 mph at 3900 RPMs. The prop was a bit tattered on the edges, but not severe. The current prop size is a 13 x 12 cup. I also had a 13 x 13 cup that was a spare but is currently MIA. I called Woody at Southeast and he said the FN was rated for a 14 x 11 cup. I already dropped it off at Admiral B and C Prop in S. Tampa and he recommended taking an inch out of the pitch, taking it down to a 13 x 11 in order to give the engine a few more RPMs. I believe I should be getting around 4200 RPMs and as close to that MPHs (around 37-40). The prop will be reconditioned and 13 x 11 by Monday. Any suggestions on what size the prop should be with this data? (If I had to, I could always use this for a spare and buy another size). Anyone have the 14 x 11 cup for sale or know where I can get one for a reasonable price? Today's prop repair and repitch cost $140. Also, if the 13 x 11 gives the engine 4200 RPMs, does this make the engine run hotter, use more fuel, or is everything going to be exactly the same, except with more RPMs.

Gary S,
Thanks for the info. One other question about the trim tabs: I looked at them on the Shopping option on Google (18x9 is what they suggest for 23'inboard) and they greatly range in price ($383.58 to $737.66 new), depending on what kind of control you get I guess. What is the basic, or is there one so that is so-badaz that I have to get it for the extra dough. The swith and difference in price confuses me.

Alright, I was supposed to be inputing data today, but the wind was gusty and the temp was pretty cold still/ I am making some modifications this week to the boat. First thing is mounting some side bunk on the trailer. Next is mounting roll control for some scuba tanks, so I can carry them for the seatrial on the advice of setting the boat as you would before a normal fishing trip/ Sooo I am getting the tanks up front, filling up the gas tank, and getting a buddy to go along to make it three people. Other than that, I should have the data put in next week sometime. Standby/

fly944, mentioned looking at trim tabs first. I have wanted these ever since the beginning of the rebuild, but man are they expensive. I saw a pair of manual trim tabs that were held down by sturdy springs on an older boat my buddy was going to buy, There were no hydraulics or adjusting, they just used the water pressure to even the boat out on turns, get up on plane, and almost acted like flaps on an airplane when you let off the throttle. Anybody have an opinion on these? Junk? Should I just save my money for some Bennetts in like three years? What would you suggest as far as size and price for this beast?

Thanks jimsport93,
I will update after I run it this weekend. S/F

I would call Woody (formerly of SE CC) and see what the original prop was for that boat and motor.
Beyond that, my recommendation is to load the boat like you would normally use it. Several people, full gas, coolers, batteries, water in live wells and gear. Then run it up to wide open throttle. See what your max rpms are. If rpms are too low then go down in prop pitch to raise rpms. You want to achieve max rpms at wide open throttle with full load.

GottaSki wrote: After WOT RPM, inches vacuum at your comfortable cruise speed could be a secondary indicator when comparing props.

GottaSki,
Can you explain this a little, The inches vacuum confuses me. I asked a Navy Lt Cmdr who sits in front of me and he started explaining something about Russian Subs propeller cavitation at certain speeds. Is that what you mean? Probably not... ha ha . Anyways, its a Small Block, Does anyone know what the original prop size was that came with this boat?

wipe open throttle

Duane,
The WOT RPM is the key.