40’supersport prop question

Get the engine serial numbers and call Johnson & Towers and ask for a copy of the start-up report. They most likely did the start-up trials for your boat and would have recorded the information on their data sheet. Hopefully they still have them in an archive file somewhere.

https://www.johnsontowers.com/marine/

Darn! Always learn from you PacBlue ! I drive by there Mt Laurel NJ office at least once a week. Never knew about this. I would like to know for my props as well. Mine are just plain old and hard to read, but the are smooth as can be and perform well. I would like to get a spare set sometime, so I hope Jeff at J&T parts counter can help.

We bought a used 38’ Blackfin FB awhile back and it had J&T 6V-92TA’s. I contacted them and they where able to get the factory start-up Test Reports with all the original Sea Trial data, nice to have that baseline information.

Good Detroit Diesel network still works, although it is getting a bit harder as the guys are retiring now as time rolls on.

Hey PacBlue! I finally stopped in J & T yesterday at the parts counter , nice kid took the time to go to the filling cabinet and came back with a nice file on my boat/engines . It had everything, parts list, start up notes, transmission info, and yup test reports. I was able to get copies of the test reports, trans info and injector info. They would not let me have a copy of the parts list.
As you said the test reports have Rpms, prop sizes , oil pressures, water temps all No load and load info.
The guys told me at the parts counter the big cast iron heat exchanger tanks are no longer available and the rectangle sen-dure Heat exchanger are very hard to get if at all, 6 month lead time.

Thank you so much for the tip.

Glad it worked out for you, like to hear success stories

Well it's told me what my motors did, it's not what they due now...I replaced port side governor a while back, now top RPMs are low , a reliabilt unit , and it's not working top end like the old one...maybe shimmed wrong ? 400/500 rpms off top end.

Finally got my prop size after four years of ownership. Could never find good markings on them . Lol, good Captian I am , no bangs or bumps on the since ownership that includes many trips on the Debris infested Delaware River and upper Chesapeake bay...props are still true and smooth underway.
Lol, lots of good luck too. So I've never had to. Work on them or replace, but I need spares which I do not have.

Any reason for not giving up the parts list?

Whatever the prop size is, deduct 2" of pitch. Every Ocean I've ever dealt with needed the props cut after being 5 years old or older.

PamMotors, not Sails Lol , now that you have that Sunliner btw.

I assume they won't give up the parts list, so you are kind of forced into buying parts from them or so you can not give the parts list to your own mechanic and not use a J&T mechanic.

Why is that? Which one is the pitch number again the first or second number.
I don't have the size with me at the moment , they are home .
May be 28 x 26 or 24 ? I can't remember .

The PMY review and performance test on my 2007 Ocean Yachts 46 were done using 28x38 props. Now a 2” pitch reduction to 28x36 seems to be nearly perfect. My WOT seatrial was with nearly full fuel, lots of gear and the addition of an 800# Seakeeper. The Series 60 engines turned up to 2350 at 99% load.

Is the 2” reduction typical only for Oceans or common across other brands, just sportfish or other types of boats too?

The first number is propeller diameter the second number is pitch.

If you think you have a throttle linkage issue , get that fixed first.

A rule of thumb is that 1” pitch reduction is a 200 rpm gain. I personally don’t like taking more than 2” of pitch out of a propeller. After removing 2” of pitch and having them scanned to Class S, sea trial the boat and if that is not enough I would keep them as spares and buy new for the final numbers.

Prefer Nibral propellers, and remember, have them scanned to a Class S for the best tolerance available, ask for a copy of the scan reports.

On a diesel 1" of pitch generally gets you 50 rpms. Gas inboards 1" gets you 200 rpms.

A lot of boats need to be re-pitched as they get older. Some more than others. But Oceans in particular, every single one I've ever ran, eventually needed 2" of pitch taken out of the props. I think they were origionally propped a little overzealously when new to meet performance goals, combined with engines aging, hell becoming a little less efficient and heavier. I think water and air temps in NJ had something to do with the engines making a little more power also.

No.

Quoted from the Caterpillar Marine Application Guide:


They are giving a rule of thumb of 450 rpm/2" pitch = 225 rpms per 1" of pitch. I toned it done to an approximation of 200 rpm gain per 1" pitch reduction. He has at least 400 rpm to make up, by your method he would need to add 400/50 = 8" of pitch which is unheard of, then you go back to recommending a 2" Pitch reduction for every Ocean which lines up with EXACTLY what I said.

Do the math.

Generally on a 2300 rpm diesel inboard, I've always seen 1" of pitch gets you 50-75 rpms. It also depends greatly on the reduction ratio as to how many rpm's, 1" of pitch will change the rpm's. On a 2:1 reduction (or less) 1" of pitch will change rpm's a lot more (twice as much, all other things being equal: boat type/HP/speed) than on a 4:1 reduction. Is the CAT marine application guide that you're quoting is from a higher rpm diesel such as a 3208 TA?

According to a calculator......it's showing the same results that a 1" pitch change is around a 50-75 rpm difference on a 2300-2350 rpm engine. Plugging in a 2:1 reduction, 40 mph speed, 36" pitch gives 2347 rpms, 37" pitch gives 2283 rpms, 35" pitch gives 2414 rpms (this is with prop slip set at 0, and calculating RPMS.

www.heringpropellers.com/prop-slip

The rule of thumb from the CAT Application Guide book is not engine specific, works great on Detroit's, Cummins, MAN, MTU's, etc. Great for ratios from 1.5 - 2.5/1, like practically most boats out there.

The Prop Calculator site you are referencing is not relevant for this discussion as it is mainly for propellers that are operating at high speeds in or near super-cavitating regions, surface piercers and sterndrives that are going airborne, applications that account for a lot of aeration. Has nothing to do with diesel inboards and conventional shafting/props remaining in a submersed environment.

Getting back to the cleanslate's situation - he needs to make up 400/500 rpm. Are you advocating that he remove at least 400/50 = 8" or 400/75" = 5.333" of Pitch?

I recommend that he goes to a propeller shop with his numbers (rpm/speed/weight/diameter/pitch/gear reduction) and have them plug it into their computer and advise him. And his situation, try to see if they have any used ones that he can try to get some base line numbers.

My posting was based on the ORIGIONAL posters JOHN36MC's question. I've run lots of ocean SF over the years. I managed/maintained a 63' for almost 20 years, and it needed 3" of pitch taken out as the years progressed even after a major overhaul. The others all needed the props cut as time went on.

The OP just wanted to know the prop size for a 1980 4o’ Ocean as they were stolen and not on the boat.