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Old 08-12-2020, 02:50 PM   #1
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Post Prop size 34 LRC

Doing some real world testing on my 34 LRC Californian with the 210hp cats,



1. first props 3 blade - 23 x 21(with cupping) - WOT = 18.5 Knts with full load of fuel(250 gal) and water, 12.5 knt cruise around 2200 rpm.


2. new 3 blade prop 21 x 23 WOT = 17 Knts at 2750 RPM with full fuel and water, cruise is now 12 knts at 2400 rpm


3. Now looking to buy a set of 4 blade props to try again
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Old 08-12-2020, 04:48 PM   #2
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Why replace the first set of props?

What was the WOT on that loaded at 18.5 Kts?
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Old 08-12-2020, 05:55 PM   #3
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Cat 3208's are rated at 2800 rpm. Your first goal is get a prop that will hit that number. Your first set of props appear to hit that. (if you were at 2750)

Not sure I see any difference between 3 and 4 blade. You will have to reduce pitch to reach the 2800 so you won't get any more speed out of it.
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Old 08-12-2020, 06:50 PM   #4
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WOT was 2650 with the first set of props. Corrosion caused a failure of one of the blades so i had to replace one of the props, however i decided to replace both and wanted to try to optimize the performance of the boat hence the smaller props but i am learning that bigger is better additionally the boat maneuverability went way down with the smaller props.
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Old 08-12-2020, 06:59 PM   #5
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Makes sense. Are you employing the aid of a pro or are you swinging in the wind for the right combo of dia/pitch/blade count?

If not, there are online calculators that might help you.
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Old 08-12-2020, 07:35 PM   #6
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A 23x20 would probably be in the ballpark. It'll get you back the blade area you lost by going smaller and hopefully hit rated rpm. What's your transmission ratio?
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Old 08-12-2020, 08:15 PM   #7
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Originally Posted by rslifkin View Post
A 23x20 would probably be in the ballpark. It'll get you back the blade area you lost by going smaller and hopefully hit rated rpm. What's your transmission ratio?
Agree unless you go to 4 blades in which case you would have to drop an inch or two of pitch.
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Old 08-19-2020, 12:53 AM   #8
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Anyone know what size prop was original with the 210hp boats, I think I had 24" not sure on pitch, I did a major repower a few days after buying the boat, (2001) prop shop freshened up the old props,, cut the props down to 22" and 26 pitch,, due to wear... New Engs, Gears, Shafts, and 6kw Genset,, I ran out of new Prop money back then..
To this day many yrs later, I still run the same 3 blade: 22x26 props / power: JD 225hp w ZF 220A gear boxes (2/1) / my gov kicks in wide open (21-24kts based on clean bottom & seas cond) , so I need to add dia and reduce pitch is what I'm thinking?? For the past 19 yrs,, lol...
Shopping for new blades now, yep they held up just fine,, but time & a few dings... Time to upgrade.

How do you upload pictures?
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Old 08-19-2020, 07:34 AM   #9
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Folks, either contact the user's group or a good prop shop. They will definitely know.
Of course, you will have to make a decision between speed and economy.
Also, you can get the prop tuned. Last I heard, there are 4 options..... 4 being the best for a fast boat. I had my prop tuned to the 3 option.
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Old 08-20-2020, 05:16 PM   #10
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After talking with the prop shop they are recommending a 4 blade prop to help the hole shot and 23 x 21 for the size just a little gun shy to spend another $2500 to upgrade
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Old 08-20-2020, 08:22 PM   #11
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Quote:
Originally Posted by d1alaska View Post
After talking with the prop shop they are recommending a 4 blade prop to help the hole shot and 23 x 21 for the size just a little gun shy to spend another $2500 to upgrade
Did you find the user's group?
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Old 08-20-2020, 10:07 PM   #12
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Hi all, here are my numbers for a LRC 34 with twin cat 3208's (210 hp):
When I bought Outer Marker she came with 3 blade 21x25 props which gave 16 knots at WOT (2800 rpm). I generally keep the rpm on the lower side to conserve fuel. At 1800 rpm these props gave 8.5 knots while using about 3.5 gph (per engine). I think the original owner used these smaller diameter props to get a slower idle speed for fishing.

The original sales receipt (which came with the boat) showed that the original props were 23x20's. I purchased a pair of these ( 3 blade) and get 9 knots at 1800 rpm while consuming 2.5 gph. At 2200 rpm boat speed is 13 knots. I have not tried WOT yet. Idle speed (at about 600 rpm) is considerably faster than the 21" props. Note that a lot of changes have been made that would also affect efficiency: new bottom paint, engine/shaft alignment, new engine mounts, etc.
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Old 08-24-2020, 12:39 PM   #13
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What prop shop did you call?
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Old 08-24-2020, 03:42 PM   #14
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34 Cali

The prop shop in mulikelita WA they where helpful
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Old 08-24-2020, 04:30 PM   #15
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Call Kroger & Sons in Seattle just south of Ballard.

They did the props for Marin Faure who was once a very active member here.
They raised his rpm and lowered his fuel burn while maintaining speed.
He had a 36 GB twin w old FL’s.
He was very happy w them.

This re-propping was documented here on TF but I’d guess about 6years ago.
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Old 08-24-2020, 05:45 PM   #16
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Originally Posted by d1alaska View Post
After talking with the prop shop they are recommending a 4 blade prop to help the hole shot and 23 x 21 for the size just a little gun shy to spend another $2500 to upgrade
faster hole shot? Your're trying to get the water skiers you are pulling up faster???

Sounds like prop shop is making a little extra on this transaction.
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Old 08-24-2020, 06:20 PM   #17
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faster hole shot? Your're trying to get the water skiers you are pulling up faster???

Sounds like prop shop is making a little extra on this transaction.

The same things that give a better hole shot on a ski boat also give more bite at idle on a trawler, which can be a benefit for close quarters maneuvering. It also means you'll gain less slip / lose less speed at a given RPM when load is added, such as if you sometimes tow a large tender or have a wide range between lightly loaded and fully loaded.

So while the hole shot may not matter, blade area for low speed performance may. And on a hull that can plane, a bit more blade area can help the boat get onto plane more easily.
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Old 08-24-2020, 06:22 PM   #18
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Hole shot whatever .... you’ll have less power w less rpm.
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Old 09-18-2020, 12:58 PM   #19
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real world testing

final results, went back to 23 x 21 with stage 2 cupping. final results are 19knts at 2780 rpm. and 14 knt cruise around 2300 rpm. I feel that the best prop for speed would be 23 x 23 but i am not going to swap props again and i need the slow troll for salmon fishing.
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Old 09-18-2020, 07:12 PM   #20
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Waiting on new nibrel 4 blade props to arv, 22x26 no cup,
Present are 3 blade 22x26 no cup, produce 22-24kts wide open, 2,750rpm (2,600 rpm eng) over rev 150rpm,
225hp JD 6068,s
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