Rocket Prop Talk!
Thanks to fellow WoodyBoater Mark Bigda AKA “Rocket man” for sending in this story on his Rocket prop experience. Isn’t that name of a country song? Good Ole Rocket Prop? Maybe not. Anyway, his experience with size and ordering a new prop. Man we have been there! Take it away Mark.
Ever since I have been running Rocket Man I have gotten up to 2600 RPMs and then a whole lot of non response after that. I questioned the timing or maybe fuel delivery as possible causes. I decided consult with the engine experts that had gotten me in the water in the first place. After describing the symptoms – well I might not have even finished the sentence – and the response was “you have the wrong propeller”.
Okay so now what. I have been running the propeller that came with the boat not knowing any better. A 12 inch diameter 14 pitch. The boat went forward and backward so what’s the big deal ? It fits on the shaft and clears the hull. Works for me. Needs to be better though. On the original build sheet it is called out a wheel #684 which according to posts on the Boat Buzz is a 12.5 inch diameter 13 pitch.
What conspires next is my personal experience and in no way is a negative spin on any manufacturer or business but rather something that is information to be shared. ( We at WoodyBoater only have heard great things regarding ACME BTW, and ACME took the prop back no problems.)
After hearing several stories of lore of the modern propeller designs I decided to go the ACME propeller route. I did not deal with them directly but instead went through someone that I trusted that has far more experience with these motors and boats that I do. All of my information was relayed to ACME and I was advised that they would select the closest production propeller so that I would not have to wait forever and it could be returned if there was an issue. Both made sense to me.
The ACME propeller arrived in short time and looked great. The design and machining was indeed impressive.
It was a 12.5 inch diameter 10.5 pitch. I carefully removed it from the box and went out to the boat for a test fit. I was concerned how close the blades would get to the hull with the extra ½ inch diameter. Well unfortunately I never got that far as the trailing edge instead hit the rudder. Ouch! Never saw that one coming.
After relaying the information beck to my broker it was agreed that the propeller would be returned for a full refund. Just for the record in addition to the problem with the rudder interference the propeller was actually ¼ inch deeper and rode higher on the shaft and would have contacted the strut as well.
Now what. A call to Jim Staib from Fine Wood Boat’s and a confirmation that he had an original wheel # 684 in stock. I ordered it and received it a couple days later. It fit perfectly and was ready for a test run.
What a run it was. I quickly and easily got up on plane and achieved 30 mph at 3,000 RPMs. Right where I should be according to Jim. I would have pushed it more but the water was choppy and had neglected to put on a depends. Will try again on a calm day.
So this again is not an attempt to dissuade anyone from ACME propellers but instead share an experience. Maybe I should have listened to Seth Katz at Katz’s Marina who told me that if I had an original Mickey Mouse ear propeller then stick with it.
Jimmy s the man!
I start every parts search with Jim. If he doesn’t have it he knows the most likely place you can find it.
Troy I always figure if Jim doesn’t have it I probably don’t need it!!! (to quote a good friend of mine)
What are the specs on the good working prop?
A good read if you’ve got the time:
The good working prop is a 12.5 inch diameter 13 pitch. If you go to some of the propeller web sites they have a rough calculator form and then they give you a ballpark recommendation. One was very close to the above spec.s
Henry H. Smith Propeller Co., Algonac, MI been in business for 100 years, They know their stuff when it comes to Props and Chris Crafts.
I’ve had nothing but great things to say about Acme Propeller. I have them on both of my boats. Both were over propped when I purchased them and both run perfectly now. JMHO: I don’t think that one can hold a propeller manufacturer responsible for the prop placement on a boat.
Don,t usually comment anymore buttt, I hear ya, no dig on ACME/ sent the GPS speed, Electronic Tach readout, and measurements of clearance, they told me what prop I needed for the Shepherd, boy I was skeptical because of all of the EXPERT info I had received , but boy did those guys nail it on the first time, and a much better prop than a cast unit.
NO DIG ON JIM EITHER:):) supplies what ya need.
Agree Phil, they are great guys, this was a spec issue, and they did take the return. Mark was sure to just fit it, no scratches or anything. I imagine ACME would have been glad to try another prop. I personaly stick with factory specs since the engeneers matched them up and they perform as they are supposed to. I will also add that many of our boats have the props that the local marina “Make” fit. That was the case on WECATCHEM. The factory prop performed perfect!
All those FACTORY SPECS go out the window when you deal with new technology MACHINED props, as they are so far advanced it would be like the difference between a BAG PHONE and the latest I Phone, and the difference in performance even on our boats is much better than that old cast prop.
Out the hole
Up on plane
drops the bow down so you can see where you are going ( a must on CC & C:):):)
I don’t think anyone is debating the merits of the ACME design and performance here.
Knowing the size envelope that we live in with our boats it would be great if they could make a revised version that still fit and had a significant performance improvement over the original.
I would buy one for sure.
Both Acme and OJ props are CNC machined to exacting tolerances meaning they really are the pitch that they say they are and they’re available with numerous rakes, pitches, and cups, plus almost any diameter, bore, and number of blades that you could ever hope for, all in Nibral.
If you ever require a replacement, that prop will push the boat at the same mph and be within 10 rpm which is rare when it comes to props that were formed on die blocks in years past.
Every change in pitch and/or cup can drastically change the rooster also which isn’t usually a concern with woodyboaters but is more important with ski boats.
Ain’t technology wonderful!
All I knew was my 14hp Nanni diesel needed to hit 3600 rpm at full throttle or the guarantee was void. The first prop wouldn’t go past 2600 rpm. I had space for a 10′ diameter on a tapering 25cm shaft. I saw a lone prop in an antique shop for about $20 with those dimensions, but no pitch details. I had bought it in case I needed an alternative. We machined the shaft, tried it in the water and she hit 3600rpm at full throttle. Couldn’t believe my luck. I still don’t know what pitch it is!
I have three different props for my boat, each has a different pitch, guess which one works the best……………. The one as spec per the CC hull card.
This story hits home with me….My one off Argentine runabout won’t hit the speed that I know it should….it too just has the “prop that is came with”…..which might clearly not be the best….I am now motivated to investigate and innovate.
John in Va.
Acme props are superior in every way to the OE props. The one downfall is that you may have to trim 1/4″ from the leading edge of the rudder (which makes zero difference in rudder performance) because of the additional rake in their design. They say their 4-blade (typically used in V8 applications) will bolt right on because they have less rake. Their basic rule of thumb is to subtract 1.5″ of pitch from the stock Chris-Craft numbers. All of Acme’s props have some amount of cup, which varies depending on the prop you choose.
So don’t be discouraged, just do your homework and the performance will far exceed the 50-90 year old stock designs. Fluid dynamics have come a long way.
The bigger issue with Mark’s prop is the prop to strut clearance. That is unusual. I have not had that experience with Acme props.
Here is the new hot set up for my ’52 Racing Runabout:
I say all this as a high-ranking financial supporter of Fine Wood Boats.
Which is supposed to be the leading edge of the prop – the straight edge, or the curved? It should push water the same direction either way, but it might affect the clearances around struts, rudders and hulls. And probably affect performance as well.
The rotation is clockwise so the straight edge is the trailing edge and that is what hits the rudder. I originally thought that if that edge was more rounded then it might clear but Brian is correct that the rake (if that is the curve) is what brings the blade into the rudder which I am sure is key to the whole performance design. In my case the interference was more on the order of 1/2 inch
I recently spoke to ACME about a new prop for Flash, and they told me before I even started to measure the clearance to the rudder. He said I might have to trim it just a bit and was super helpful. Unfortunately, after examining my prop, I have very little clearance with the factory prop and don’t think I can take the required meat out of my rudder.
The guys at ACME are first rate and I agree with Brian that the new technology is far superior to the 30-70 year old factory stuff. I just wish I could make it work on my boat. I’m going to take my prop to Delta and have it worked and balanced instead of replacing it.
Are these the same guys that do all the work for the Coyote???
As far as clearance goes, you’d have to wonder if some of the restored boats struts and rudders were put back in the absolute right place? Are the original clearance specs for distance between struts and rudders available?
CAD-CAM cannot produce a more efficient prop for planes, than the Wright Bros. Air- water is still a fluid. My ski boat has 13×13 left rotation. Great hole shot, big top end, but after hammering; still 700 rpm short. With over 600 lbs of torque, flattens nibrows. Guess need stainless, but want something to give upon strike.
Steve, your statement couldn’t be further from the truth. Modern airplane props are much better than what was available even 50 years ago.
Good to hear from Phil and any mention of Shepherds. Like the tech posts every once in awhile and maybe good to cover rudders again. I remember a few comments years ago either here or in boatbuzz about a women at some rudder shop who was An expert about rudders and “speed rudders.”
I just replaced a traditional 13 by 13 on a 24 hacker triple 1928 with Acme 13 by 12 … seems to fit fine , old prop topped out well over wide open throttle of 4000, and gave no more speed after 3000… I will try this out tomorrow and let you know . Acme gave advice for choosing the new prop
I have been doing some playing with props for our Shepard we have 7 different props until we found the ideal one, a 19 pitch nibral, did not really know why they performed so differently other than pitch and diameter and material. Shepherd top speed at WOT 5000rpm is 33knots. For our Chris craft 32ft Express cruiser we also tried 6 different props, quite a lot harder as each prop change requires a haul out. I am quite satisfied with the props we have now but WOT we reach 4500rpm and 27knots, however we have no difference between 4000rpm and 4500rpm I did believe this was due to cavitation at the prop and could not be done anything about it unless you would have a reduction gear that I have no room for. Do these modern props have less cavitation
Only if you have a 354 Hemi should you turn that high of an RPM, and even then you should prop for 4300 RPM Tops, and on a 22′ Shepherd you should be at 38 mph all my info is documented with GPS and electric tach.
M45SP3 275 HP conservative.
22′ Model 110 1948
Gross weight with full fuel 4560 lb
4 /230 lb men in the boat / 920 lb
4300 RPM top don’t want 4400 RED line
38 mph on GPS
1954 Model 110 will be a heavier boat but will have a wider beam and falter planning surface in the stern.
running a four blade Acme prop with a small cup. Ill get exact prop specks if you like as there are things sometimes I have a hard time remembering.
That extra 500 RPM is the result of overpowering / revving engine
Is there anything more beautiful than this?
Yes, a propeller, but AKA “Men’s Jewelry”
mifne, so true on plane props….and hey, your boy Glenn Curtis from the finger lakes had some radical and fast ones back in the earliest days.
John in Va.
Had the same fitting problem as Rocket man, it was a 12.5×10.5 as well. I made the clearance for it to fit and ran it, but it was worse all the way around than the 12×13 Michigan I usually run. I feel like they are way off on the guesses they make on the replacement sizes at Acme. Might just be these old boats, but the space age design and manufacture of the props doesn’t make them good enough to take 2.5″ out of the pitch and see a gain, I had to add 600 rpm to get the same cruise speed. A replacement of the same pitch might work, or might fit even worse, I don’t know. I sent mine back and went back to the Michigan, no more ski boat props for me.
My acme 13 by 12 pushed the Hacker with 270 hp engine to 44 mph .. fast out of the hole and top rpm of 4700… going to try 13 by 13 acme prop to see if I can get any more .. acme suggested the additional pitch would add 2 miles per hour and decrease top rpm by 300
I put an ACME prop on my 57′ Sea Skiff and I love it. Better acceleration, top speed at lower RPM’s, and lower fuel consumption.