FN Prop size
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=16393
Printed Date: November-18-2024 at 5:36am
Topic: FN Prop size
Posted By: SemperFIsh
Subject: FN Prop size
Date Posted: January-28-2010 at 7:57am
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First off, the only thread I can find on this subj is
http://www.correctcraftfan.com/forum/forum_posts.asp?TID=5663&PID=57981&title=fish-nautique-prop-question - Fish Nautique Prop Thread I am about to embark on the same journey trying to get the full benifit of a freshly rebuilt Chevy 350 accounting for the extra weight of a bigger TTop and the fresh engine. I believe the old prop might be close to what I need (13x13 cup) but am starting this thread to input data into and get suggestions. What exactly do I need to record this weekend when I take it for a sea trial? I am thinking WOT speed marked by GPS and RPM's at WOT. I will also record minimum speed and RPMs needed to get on plane, Anything else?  ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Replies:
Posted By: 8122pbrainard
Date Posted: January-28-2010 at 9:19am
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Duane,
The WOT RPM is the key. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Keeganino
Date Posted: January-28-2010 at 12:42pm
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Please help educate this newbie. I looked all over for what WOT stands for. There are about 1000 mentions when you search the site for WOT, but nobody explains the terminology. I am grasping the concept of rpm's at different speeds, with different props. Glad I am not getting into all that on my restoration, but its good knowledge to have all the same. ------------- "working on these old boats may not be cost effective but as it shows its what it brings into your life that matters" -Roger http://www.correctcraftfan.com/diaries/details.asp?ID=4897" rel="nofollow - 1973 Skier |
Posted By: 79nautique
Date Posted: January-28-2010 at 12:47pm
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wipe open throttle ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: GottaSki
Date Posted: January-28-2010 at 1:22pm
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WOT = WFO
To my uneducated mind, 13x13 sounds much too big unless you had a BB. After WOT RPM, inches vacuum at your comfortable cruise speed could be a secondary indicator when comparing props. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: SemperFIsh
Date Posted: January-28-2010 at 10:26pm
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? ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
GottaSki wrote:Posted By: Gary S
Date Posted: January-28-2010 at 11:02pm
My Dads Shamrock, a 20 footer with a 302 runs a 13x13. A Fish Nautique,3 feet longer,an inch wider, and 1000 lbs heaver,but with more power,might just run the same one ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: jimsport93
Date Posted: January-29-2010 at 1:32am
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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. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2798 - 93 Sport Nautique |
Posted By: jimsport93
Date Posted: January-29-2010 at 1:44am
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Almost forgot...
Semper Fi! ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2798 - 93 Sport Nautique |
Posted By: SemperFIsh
Date Posted: January-29-2010 at 1:52am
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Thanks jimsport93,
I will update after I run it this weekend. S/F ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: GottaSki
Date Posted: January-29-2010 at 11:53am
Yeah, firstly, like has been said, you wish to be able to spin rated WOT rpms when loaded like you are going to use the boat, even if that means you may be may have to use some judice with the throttle when running empty, this can narrow down the basic sizing very quickly. Using a vacuum gauge to map manifold pressure at various speeds, could be useful when comparing props. Different diameters, brands, 3 or 4 balade may produce similar WOT rpms, but could be very different efficiencies at cruise. You boat likely has a sweet spot speed it likes to run at where the ride is comfortable in the swells and spray. A prop that produces the highest manifold vacuum at that speed is a good measure of efficiency at cruise. So, its an option if you wanted to throw more science at the problem. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: SemperFIsh
Date Posted: January-29-2010 at 1:32pm
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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? ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: fly944
Date Posted: January-29-2010 at 1:52pm
| I will measure mine and get back to you. I have watched all your vids and love your boat. Tabs should definitely help with your bow-up issues and improve your ride significantly. I would suggest either bennet or lenco. |
Posted By: SemperFIsh
Date Posted: January-31-2010 at 10:38pm
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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/ ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: Gary S
Date Posted: February-01-2010 at 12:32am
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Save your money till you can afford hydraulic ones you won't be sorry. With them you can adjust if one side of the boat is heavier,push the nose down to cut thru waves etc.Bennett seems to have a good product, my Dad has had them on both Shamrocks,the second boat he bought used,the pump did not work,they fixed it for free,no questions asked. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: SemperFIsh
Date Posted: February-01-2010 at 1:43am
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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. ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: Gary S
Date Posted: February-03-2010 at 10:41pm
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I honestly have no idea,my Dad had an 87 Shamrock that he bought new with them on. He also has an 77 that had them put on by the previous owner. They both had a joy stick control, which I don't see on their site,so they must have changed them. The 77 is here by me,when I get a chance I'll measure them ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: SemperFIsh
Date Posted: February-04-2010 at 6:46pm
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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. ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: SemperFIsh
Date Posted: February-07-2010 at 2:46am
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Bumping for some answers. Today I am adding some guide on poles to the trailer, that cross wind sucks! ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: SemperFIsh
Date Posted: February-11-2010 at 2:21am
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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. ------------- Capt Duane Tampa, FL Semper FIsh N Dive |
Posted By: hotboat
Date Posted: February-11-2010 at 4:36pm
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4000 rpm = 240000 rph, 11 pitch prop = .91666667ft per rev, 240000 rph at 11 pitch = 220000 ft p hr divide by 5280 ft/mile = 41.66 mph at no slip, 33.5 on gps/41.66 mph theoretically= 19.6% slip. I'm not familiar with the fish but the prop manufacturer and number of blades can change your percentage of slip. I have seen worse ------------- Brian |
Posted By: 8122pbrainard
Date Posted: February-11-2010 at 4:53pm
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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? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: TRBenj
Date Posted: February-11-2010 at 5:01pm
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The slip percentage is in the ballpark for a boat that size. Its still underperforming though- I would agree that a fresh 350 should be capable of pushing that boat close to 40. It shouldnt have a problem turning a 13x11 prop either. 4000rpm is way low (it should be closer to 4500) so something is up. Either the boat is way heavy or the engine is down on power.
FYI, saying youre using a "cup" prop isnt helpful... just about every modern inboard prop is cupped. Exactly how much cup is important- so if you know that number, please share it. Adding cup to a prop will allow it to act like it has more pitch (decreased RPM's at speed). When talking prop sizes, the first number is the diameter and the second is the pitch. Decreasing pitch will also improve the holeshot- you seem to have this backwards. Give us some more info on the engine build and we may be able to help. Chevies tend to breathe better than the Fords (stock) so it may want to turn 4600-4800 for best performance. ------------- |