PROP SIZE

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PLAYMATE
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PROP SIZE

Post by PLAYMATE » Tue Dec 12, 2017 11:54 am

HI ALL, IM TRYING TO FIND THE RIGHT PROP SIZE FOR MY BOAT. I HAVE AN F-36, THE ENGINES HAVE BEEN SWAPPED OUT. IT CAME WITH 440'S I BELIEVE. RE POWERED TO 360'S, 1TO1 RATIO, 20X21 PROPS NOW. CANNOT GET OVER 16.4 KNTS AT 3200 RPM'S. THINKIN THESE ARE THE PROPS FOR THE BIG BLOCKS. ?
COULD YOU HELP WITH THE CORRECT PROP SIZE NEEDED?
I'M THINKING WITH THE RIGHT PROPS I SHOULD GET 20-22 AT 3200 ?
HELP PLEASE!
THX.

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prowlersfish
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Re: PROP SIZE

Post by prowlersfish » Tue Dec 12, 2017 12:07 pm

20x21 would be for the big block 440 with a 2 to1 gears . 20-22 knots at 3200 would be pushing it even with the 440s ( some one running them will respond I hope . There is no way you could turn 3200 with 1 to 1 gears and the 20x21 props . So I don't believe you have 1 to 1 gears

How about some engine and gear photos , I could tell if they are 1 to 1 .

what year and is this a sedan/conv. or a tricabin ?
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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prowlersfish
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Re: PROP SIZE

Post by prowlersfish » Tue Dec 12, 2017 4:52 pm

I forgot to ask what rpm are you getting at Wide open ?
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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WayWeGo
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Re: PROP SIZE

Post by WayWeGo » Tue Dec 12, 2017 4:56 pm

I am thinking you have the 1.91:1 transmissions if you are getting 16+ knots at 3200 RPMs. It is hard to tell without more data like top speed and RPM, but I am guessing you are over propped.

We get about 25 knots at our 4,000 RPM redline and 16 knots at 3,200 RPM, but do not have the standard 20x21 props for a 440. Our props are 18.5x19 and not cupped. One of these days, I would like to play around with some bigger wheels, but not sure we are going to be able to pull a 21" pitch without some major engine work.
Last edited by WayWeGo on Tue Jan 02, 2018 1:51 am, edited 1 time in total.
1975 F-36 Convertible
Twin Chrysler 440's

PLAYMATE
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Re: PROP SIZE

Post by PLAYMATE » Wed Dec 13, 2017 7:26 am

THANKS FOR RESPONDING. THE F-36 IS A 1974. THE ENGINES ARE 1977.
IT IS A SEDAN/CONVERTIBLE W/FLY BRIDGE, I LOOKED YESTERDAY THE TRANS IS 1:91:1. I COULD NOT GET THE MODEL NUMBER, WORN OFF. WOT-PORT 3200, WOT-STARBOARD 3600. WITH THAT WOT RPM I'M LOOKING AT 16.4KNTS WITH CLEAN BOTTOM. AND THAT'S PUSHING IT. THE PROPS WHERE REDONE 2 YEARS AGO, I'M THINKING THE PORT WHEEL IS NOT RIGHT.
WHEN THE WHEELS WHERE REDONE THEY HAD NO PITCH, THE GUY SAID HE WAS GOING TO ADD
SOME PITCH, NOT SURE WHAT HE DID. STILL AFTER READING SOME POSTS HERE IT SEEMS LIKE
THE WHEELS ARE TO BIG ANYWAY.
HULL WEIGHT LIST AS 18,000 LB, I THINK IT IS LESS THAN THAT.
IF IT MATTERS , I'M IN THE CHESAPEAKE BAY NORTH.
ANY INFO IS APPRECIATED.
THANKS'

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WayWeGo
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Re: PROP SIZE

Post by WayWeGo » Wed Dec 13, 2017 10:26 am

Marine 360s from that era made 250 HP as far as I know. The 440s made 330 HP, so your boat is at about 75% of the HP it came with.

I believe your engines should redline at 4,000 RPM, so different props would probably help out. You should probably verify that your tachs are correct. A couple hundred RPM difference could be a gauge/wiring problem.
1975 F-36 Convertible
Twin Chrysler 440's

PLAYMATE
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Re: PROP SIZE

Post by PLAYMATE » Wed Dec 13, 2017 12:47 pm

Tachs seem fine. when at idle they are right on 650.
Upper and lower stations are the same. Engines run great. Just not the speed.
Seems there should be some way to size the correct prop based on engine,trans, shaft.
Shaft is 1 3/8".
?

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Re: PROP SIZE

Post by mikeandanne » Wed Dec 13, 2017 1:28 pm

Seems you have a unique combo there.A good prop shop should be able to put you in the ballpark with all the info you have ,hull type,weight,engine Hp and gear ratio......for what its worth the F32 version is about 5,000 lbs lighter, 4 feet shorter, but with the same engines as you have, comes with a 16x16 prop/1.5 or so gears.That probably makes it even more cloudy, huh.
78 F 32

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prowlersfish
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Re: PROP SIZE

Post by prowlersfish » Sat Dec 16, 2017 9:11 am

Playmate ,

I ran some numbers on a Calulator 20x18 what I came up with (staying w/20" wheels ) . If you have 20x21 I would have them take down to 20x19 as 2" is the limit of adjustment on most wheels , and see how it goes . Have your prop shop look for sure . This will not increases your speed at 3200 ( unless your props are screwed up now) while this likely will lower your speed at cruse you won't be over loading the engines . Good chance it will increases top end as you will be able to get your full HP out of the engine if you get to 4000

This is based on your engines being 250 HP @4000
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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prowlersfish
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Re: PROP SIZE

Post by prowlersfish » Sat Dec 16, 2017 9:16 am

Playmate , you and WayWeGo should swap props , by the numbers that's what both boats need . :D
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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bjanakos
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Re: PROP SIZE

Post by bjanakos » Fri Dec 22, 2017 8:33 am

PLAYMATE wrote:HI ALL, IM TRYING TO FIND THE RIGHT PROP SIZE FOR MY BOAT.
I'm in the same "boat" as you... However, I do have the correct stated props on mine. Upon doing some research it seems most F-Model trojans fall well below manufacturer performance numbers and standard expectations. The coveted 20 knots cruise seems to be absolute top-end and only under absolute perfect condition.

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prowlersfish
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Re: PROP SIZE

Post by prowlersfish » Mon Dec 25, 2017 4:46 pm

bjanakos wrote:
PLAYMATE wrote:HI ALL, IM TRYING TO FIND THE RIGHT PROP SIZE FOR MY BOAT.
I'm in the same "boat" as you... However, I do have the correct stated props on mine. Upon doing some research it seems most F-Model trojans fall well below manufacturer performance numbers and standard expectations. The coveted 20 knots cruise seems to be absolute top-end and only under absolute perfect condition.

Playmate , is very much under powered and will need smaller props to get up the rpm . 80 HP per side short so you should expect it to be slower and not be able to turn up full rpm with stock props . Most F36 and 32s will do will well over 20 knots top end if not something is wrong . Cruse is normally in the mid- high teens . There are some boats with issues but most are pretty close to what they should be .taking into account they are not brand new and in the real world conditions . Props that are way off ( despite markings ) Lack of engine power for a number of reasons and or course dirty bottoms and running gear . Rudder toe being off too . You will notice Some boats toping out around 20 are not getting full rpm . Likely power issues or out of whack props ( assuming all is clean ) . I have no issues with speed and cruse . Yes I have diesels , but less total HP then most F36s . One word on props is you need a good shop , not a have hammer will tune prop shop . Nothing like having 3 blades with all different pitch , more common then you think . As we add some weight sometime knocking off a little pitch will help get the engine in its power band . With a 40 year old boat there can be more the one issue some times many.. 3 Things I never take for granted when looking at speed or rpm issues are Props , Tachs , the numbers on both lie more the most fishermen :mrgreen: the 3rd thing is that the bottom is clean .
TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

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prowlersfish
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Re: PROP SIZE

Post by prowlersfish » Thu Dec 28, 2017 7:16 pm

TROJAN F36 Conv.
6BTA Cummins diesels
Life is to short for a ugly boat :D
2009 TROJAN RENDEZVOUS
Port Kinsale 2010 & 2011. Solomons get together 2011.

PLAYMATE
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Joined: Fri May 05, 2017 9:43 am
Location: NORTH POINT CREEK, MD.

Re: PROP SIZE

Post by PLAYMATE » Wed Jan 10, 2018 7:37 am

Thanks' for the info guy's. looks like the props have been changed.
I pulled them and they are 18x19 slight cup. going to send them to
the shop and converse with the prop guy to tune properly.
I appreciate all the help. We will see.

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