new Campbell Sailer prop, loss of rpms

jokemo · Post by **jokemo** » Jun 15th, '06, 00:49

I just installed a new 14x9 3 blade CS prop on our CD 33. I replaced a 14x10 2 blade. We have a 5424 Universal with the Hurth 2:1 transmission. I tested the boat for a couple of hours on two different occasions and discovered that the boat's engine will only get to 1800 rpms with the throttle wide open. The boat does get to 5 1/2 knots which is slightly faster than the old prop pushed it at 2200 rpm. Reading some past discussions I see that this is somewhat of a common dilemna and that overheating is usually a long range problem associated with high rpms. I just haven't been out enough to know. So far, my temp guage says 160. Do I re-pitch or can I adjust the throttle cables to get more production? New and confused. Thanks all. john

Boyd · Post by **Boyd** » Jun 15th, '06, 09:51

Hi John:

Please search for my previous posts on this subject. I documneted my several month long process of sorting out the correct pitch in painful detail. What you describe sounds identical to my experience. The guy who sells these has no clue how to size them and you appear to be another case of a severly mismatched prop. Continuing to run your engine in what amounts to an overloaded condition is not good for it.

After you have verified that your engine is in good health and putting out close to its rated hp your next option is to repitch the prop. I suggest you make them send you a new prop in exchange, hence minimizing your expense.

If after reading my posts you want more detail on the process I used to sort it out, send me a private message.

Boyd
s/v Tern
CD30 MkII
Fort Lauderdale, Fla.

s.v. LaVida · Post by **s.v. LaVida** » Jun 16th, '06, 09:15

I've the same problem and have gone through two CSP's and still don't have the right one.

rit

M. R. Bober · Post by **M. R. Bober** » Jun 16th, '06, 09:37

The general rule of thumb in the prop business is when going from 2 blades to 3 keep the diamater and reduce the pitch by 2". The acid test is to run the engine in neutral to max rpm (not above redline) note the rpm. Then reduce throttle to idle, put transmission in forward gear and run engine to max rpm. The rpm in gear should be within 100 rpm of the rpm in neutral. If you cannot come to with 100 rpm of the speed in neutral, you have too much prop. (Note: high output alternators can "confuse" tachometers)

I tried a 3 blade 14X9 with the same engine/transmission combination that you have and had to have the prop repitched to 14x8. It wasn't expensive.

Good luck,
Mitchell Bober
Sunny Annapolis (where the winds are always fair and the Chamber of Commerce shouldn't be your source for weather info.),MD

Zeida · Post by **Zeida** » Jun 17th, '06, 09:55

Hi, all...

FWIW,... on Bandolera, my 1982 CD-33 Hull #73, I also have the Universal 5424 Model 30 with the Hurth 100 2:1 tranny. The boat came with a 3-blade Michigan prop 14 x 13. I must admit I do not know the pitch, but she makes 5-6 knots under power at 2200 rpm's without overheating. The temperature gage goes up to the 180 - 190 degrees, which is normal for that engine. I can, and have, pushed the engine to the full open throttle at 2500 rpms, but then, the engine overheats and I come down to the 2200 cruising speed, which is fine as far as I am concerned...

I am convinced that part of the overheating problem is the small 2" Sendure heat exchanger that came with the engine. Even the Manual recommends upgrading it to the 3", but I have not done it yet. If we come out OK from this hurricane season, I will do so after it ends.

Kurt · Post by **Kurt** » Jun 17th, '06, 10:53

I'm not familiar with the 5424 Model 30 but I suspect it's a Kubota based engine. Check your owners manual and note the rated RPM for the horsepower it's rated for. I would guess it's around 3000-3200. The rated RPM is what you want to reach when motoring in calm water with the throttle wide open.

Kurt · Post by **Kurt** » Jun 17th, '06, 11:01

I just looked it up on the internet. The 5424 is rated at 24hp@2800 RPM. Therefore, 2800 RPM is what you want to achieve at wide open throttle while motoring in calm water.

Zeida · Post by **Zeida** » Jun 17th, '06, 20:46

Kurt...

that is what the manual says, but I can tell you that my CD-33 with that same Universal engine and the same Hurth tranny will NOT get up to the rated 2800 rpms. I wished it did. The most she makes with full open throttle is at 2500 rpm's.

Kurt · Post by **Kurt** » Jun 18th, '06, 08:11

Zeida, assuming all else is okay with your engine (compression, injection, alignment, etc), I suggest you have a prop shop remove 1" of pitch...that'll get you up to 2800 rpm.
Kurt

Al Levesque · Post by **Al Levesque** » Jun 18th, '06, 10:07

When we bought our CD33 the PO had depitched the prop from 14x11 to 14x9. We could not get much over 2200 rpm. I later found the engine was misaligned and realigned it. The max went up to 2500. We could get between 5 and 6 knots at 2000 and the temp ran 180 to 190 for long periods without incident.

With our new engine and new prop we seem to have a good match. We reach the max of the max engine speed range. At 80% of that we do 7 knots. At about 75% we get the 6.6 knots hull speed.

I am convinced that we were overloading the old Universal and should probably either had a 2 bladed prop or depitched to 14x8 or 14x7 on the 3 blade.

jokemo · Post by **jokemo** » Jun 18th, '06, 21:39

Boyd, Zeida, Kurt, Mitchell, Al and rit...thank you for taking the time to share your experience and stategies regarding my prop problem. Its definitely reassuring to have a support group. I plan to reduce the pitch and go from there. best regards, john

The Cape Dory Board

new Campbell Sailer prop, loss of rpms

new Campbell Sailer prop, loss of rpms

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