prop size

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Majic man
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prop size

Post by Majic man »

What size props for a 33ft with cat 3208
Capn Tony
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Post by Capn Tony »

I did new props last year. My engines are 3116 Cats 350HP ea. I ended up with 21X20 with a 4 cup. Both engines now 50 to 75 rpms above rated. I’ll be interested to see what this year holds after having the bottom soda blasted this past fall.
Thanks Capn' T Roamin' Beauty 33'Bert SF 3116 Cats Hyannis MA.
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Post by Chum Bucket »

I run 4 blade, Dynaquads, 22-5/8" x 21 with a medium cup. The trailing tip edge of the blade was rounded just a skosh to bring up rpms by about 100. When the prop guru suggested this, I was more than horribly skeptical. After splashing again and going into the wind, up the river, I was a believer. After 2000 rpms, I cruise 20 knot to 28 knots at 2800 with a moderate load. WOT with a light load on a flat ocean, min wind and current, I can turn 2900rpm at just over 29 knots. I typically cruise 2200-2400 when the ocean allows. Its taken 3 prop tweaks without changing pitch to achieve these results. I don't think I can get any better performance out of these props with 320hp. I would love to try a pair of Acme 3 blades, but other than maybe a little more speed, not sure the cost benefit is there. Most folks are amazed my 39 year boat cruises 20 plus effortlessly.
Kevin D "Chum Bucket" 1979 Sportfish 3208T 320hp Cats
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Post by Capn Tony »

Sounds like you are right on. It also took me 3 tweeks to get to where i am. Two tries on the old props and one on the new ones. I forgot to mention that I too am running 4 bladed and run at 2200 to 2300 rpms with speeds of 21 to 23 knots.
Thanks Capn' T Roamin' Beauty 33'Bert SF 3116 Cats Hyannis MA.
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Post by PleasureBay »

I have 21 X 22 3 blade on my 33SF and cruise at 17-20 knots at 2350 with a top speed of 26 -27 knots at 2800 I think they are Equipoise. I don't know how to add a photo but my boat has a hardtop and tower with 270 hp 3208 CATS
Jack Van Deman
"Why Knot?" '82 33SF 3208CATS
Little River, SC
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Post by Chum Bucket »

If you haven't cupped your blades, you may want to consider doing so next haulout. I ran straight blades for 3 seasons before I added cupping. Made a noticeable difference coming up on plane, turning at cruise, and upped the speed a bit. Your 3208s will turn 2350 all day long. I've read not push 3208s more than 80% of WOT for extended times which is 2240, but most folks agree these hulls just like running at 22+ knots. 20 is good, 21 is better, and 22 and higher is just so much better. Sometimes I just run 2400 on a nice day....just bcuz I get bored running 30-40nm and like seeing the SOG rise!
Kevin D "Chum Bucket" 1979 Sportfish 3208T 320hp Cats
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Post by PleasureBay »

Thanks for the advice, I've thought about 4 blade props and sure wish I had about 310-320 hp. I noticed that when I hit 25 knots she rolled over the top and flattened out it was like she went into overdrive. I'm sure when she was new before the hard top and tower she ran faster at lower RPM.
Jack Van Deman
"Why Knot?" '82 33SF 3208CATS
Little River, SC
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Gccornelius
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Post by Gccornelius »

I’m running 19-3/4â€� x 21-1/2â€� 3 bladed woth no cup. At 2350-2400 I am running 18.5-20 knts depending on current, wind, and bottom growth. Max wot 2800 rpms I’m running about 26-28 knts. It seems I’m a little under sized based on everyone else’s response. I’m ok with the numbers i can hit. More importantly I can hit 2800 rpms wot. Mostly cruise 2300-2400 rpms.
George Cornelius 82' Bertram 35 "Osprey" 3208T Cats Annapolis MD
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Post by Chum Bucket »

Do you have trim tabs? The originals I have are undersized and do very little. I don't know if mine even work at the moment. Something to consider given the hp you have. Still cheaper than a repower or convert to 320hp. Set of 36" x 9" might be just what you need to get over the B33 hump, bow down, maybe pick up speed and efficiency? Just a thought. The way the factory installed tabs under the transom work great for fisherman like me. If you fish and don't mind shearing off on the tabs, I'd prob do a traditional install right off the transom. Bennett has a new auto tab control that takes all the guesswork, backing down or docking.
Kevin D "Chum Bucket" 1979 Sportfish 3208T 320hp Cats
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Post by Gccornelius »

I assume I have the original tabs. If I do play with them I can get more speed out of her. I’m very content with the numbers I have until I hit the lottery to start trying new props and tabs. I’m averaging 21-22 gph at 2350-2400 and 18.5-20 knts. Not the fastest boatnon the Chesapeake but for what I do is fine by me. I think that equates to a 0.86 mpg. (Maybe-first time actually calculating that)
George Cornelius 82' Bertram 35 "Osprey" 3208T Cats Annapolis MD
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Post by eyecatcher »

Hey chumbucket thats a pretty big diameter, do you know what gear and how heavy your boat is?. Do you have any cockpit noise harmonics from the tip clearance?
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Post by Chum Bucket »

I'm 14 tons according to the "net 14" painted in the bilge. Gears are ZF220 1.5:1 with 1.75" shafts. No harmonic issues unless the rpms are not synced. I always thought my tip to hull clearance was too low, but the prop guru says unless I'm peeling bottom paint then I have nothing to worry about.
Kevin D "Chum Bucket" 1979 Sportfish 3208T 320hp Cats
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Post by eyecatcher »

MIne was 26000 on the scale pretty much fully loaded. same gears but i got 350hp 3126 and 22X23 3 blade props no cup on 1.5 shaft and my has a slight hum, i do about the same speed on the top end 28 knots@ 2800. The alignment and wheels are true. I considered demoing Acme 3 blades variable pitch, but I think i'm going to 4 blades. I have a feeling you got the numbers reversed. 21 diameter by 22 5/8 pitch makes more sense.
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Post by IRGuy »

With Cummins 6B, 315 HP engines, and 3 bladed props (21" dia by 23" pitch) on 1 1/2" shafts and trans ratio of 1.5:1 "Phoenix" gets almost exactly 1nm per gallon with both engines running. Speeds are 1nm per 100 RPM so I get 7 kn at 700 RPM, 12 knots at 1,200 RPM, 18 knots at 1,800 RPM, etc, etc. As Jack VanDeman said above, at 2,400-2,500 RPM she seems to actually rise up in the water and seems "happy". I have no cup, and prop mfg is unknown. I can get the engines, rated at 2,800 RPM, up to 150 RPM above rating speed with the throttles pegged.
Frank B - IRGuy@aol.com "Phoenix" 1983 FBC Cummins 6Bs - 315HP Wilmington, NC
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Post by eyecatcher »

That sounds great. I know mine is heavy setup for canyon runs.., my generator is in the back location and I have 100 Gallons in two tanks fwd of the engines. The 3 blades can't handle it unless i run light, then she peforms pretty fast 24-25 sometimes at 2400. But with full load and fwd tanks im doing 1600 RPM 11 knots, 1800 RPM 14.5 knots, 2000 RPM 18 knots, 2400 RPM 23 knots, 2600 RPM 26 knots, 2800 RPM 28 knots.
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