Propeller Size

Kennet E. Tand · Post by **Kennet E. Tand** » Sat Aug 25, 2012 12:58 pm

Can someone guide me to the proper propeller size for a 1968 42 foot Sea Voyager [Old Woody] with twin 440 Crysler engines that are in excellent condition? My current crusing speed is about 8 mph at 1,500 rpm to keep from blowing the two old boy's heads up thru the deck.

prowlersfish · Post by **prowlersfish** » Sat Aug 25, 2012 1:06 pm

Do you know what your max RPM is now at wide open ? ( with clean running gear ? )

Kennet E. Tand · Post by **Kennet E. Tand** » Wed Aug 29, 2012 4:33 pm

2000 rpm is the maximun that I have ran the boat at.

It is rated 330hp at 3,500rpm.

I use it as a trawler at about 1500 rpm.

I do not want to over torque the motors with a lage prop!!

prowlersfish · Post by **prowlersfish** » Wed Aug 29, 2012 8:18 pm

I don't think you would hurt them to run them at 1500 and 8 mph . to really know for sure if its propped right then you need to know what the engines will turn at wide open under load ( in gear) The 440 is rated at I believe 4000 or a Little more , not 3500 rpm . so you be able to turn up 4000 rpm or so at wide open with a clean bottom and running gear.

I can use a calculator to see what is called for , but I need the gear ratio and weight of you boat. but thats only a guide the prof is in a wide open run .

The way you are running now should not hurt it ( 8 mph @ 1500 rpm ) assuming your not giving it a lot of throttle to get to 1500 rpm. 8 mph is around hull speed and it should be very easy to push it at that speed.

remember a dirty hull and or running gear put a extra load on .

pwollsch · Post by **pwollsch** » Wed Aug 29, 2012 9:00 pm

Hey guys, have same question. I am running 22x22 on twin Chrysler M400's on an F36...she was heavy new empty at 16,000 lbs.....

Anyway, I top out at 3000 at 25 mph...which is plenty. I am more concerned about cruising on and off plane at 17 and 10 mph respectively. My newborns say 22x22 may be too big for my rig?

She runs good and sounds great...but the motors are 2000 hrs and tired. Just wanna take care of her.

prowlersfish · Post by **prowlersfish** » Wed Aug 29, 2012 9:40 pm

pwollsch , you are way over propped , 22x22 is way too much Thats what I am running with diesels . I believe F36 boats that came with 20x20 with 440s and 454s some ran 20x21 . I am assuming you are running the stock gear ratio . you also should be turning 4000+ rpm at wide open ( clean bottom and gear )

Edit I belive after looking around many of the F36s with 400 cid used 20x17 props

Allen Sr · Post by **Allen Sr** » Thu Aug 30, 2012 6:04 am

My F36 with 454's have 20x20's. Soon as I read your post I thought of Prowlersfish boat!

Kennet E. Tand · Post by **Kennet E. Tand** » Thu Aug 30, 2012 7:52 am

The gear ratio is 2.57:1

The boat weight is 25,000 lbs. and the draft is 3 feet.

The hull is clean.

Again, I want to use it as a trawler and get maxium fuel economy.

It came with 24/20s that were damaged by electrolysis, and I put on a set of used 22/22s.

I recently purchased a set of 24/27s off ebay, and they will need to be cut down and repitched.

prowlersfish · Post by **prowlersfish** » Thu Aug 30, 2012 12:14 pm

I will run the numbers , as far as cutting down props , no good prop shop would recommend it , good way to trash a set of props .

prowlersfish · Post by **prowlersfish** » Thu Aug 30, 2012 9:18 pm

For got to ask 3 or 4 blade ( both sets )

Kennet E. Tand · Post by **Kennet E. Tand** » Fri Aug 31, 2012 8:29 am

All props are 3 blade.

Kennet E. Tand · Post by **Kennet E. Tand** » Fri Aug 31, 2012 8:29 am

All props are 3 blade.

Kennet E. Tand · Post by **Kennet E. Tand** » Fri Aug 31, 2012 8:30 am

All props are 3 blade.

pwollsch · Post by **pwollsch** » Fri Aug 31, 2012 9:18 pm

22x22...,. So is what I an told!! Wow! I will check what I have when I pull out this winter....

I am going by my survey.... I was not there at hull inspection, just bought her this year. Man... Do not wanna buy new props!!

Thanks guys

prowlersfish · Post by **prowlersfish** » Sat Sep 01, 2012 9:31 am

Kennet E. Tand wrote:The gear ratio is 2.57:1

The boat weight is 25,000 lbs. and the draft is 3 feet.

The hull is clean.

Again, I want to use it as a trawler and get maxium fuel economy.

It came with 24/20s that were damaged by electrolysis, and I put on a set of used 22/22s.

I recently purchased a set of 24/27s off ebay, and they will need to be cut down and repitched.

Both the 24x20 and the 22/22 s come up as the right size on the calculator . of course there are real life variables , so the only to be 100%sure its propped right is the wide open run checking for max rpm . even thought both sizes come up on the calculator , the 24x20 prop may have some advantage when running the way you do .

Why do you think you maybe straining the engines ? am I missing something ?

Now running at 1500 rpm and 8 mph there is no way you are over loading or straining your engines even if you would happen to be over propped .

as far as the 24x27 props sell them or trade them . there is nothing that can be done to make them work . when you change the pitch more then 2" you start making too change to the curve of blades , As far cutting down a prop your changing the shape of the blades completely and really can make the prop totally inefficient and posable vibatition issues