Can anyone tell me the clearance needed in the prop aperture when deciding on prop size?
I’d like to upgrade to a two or three-blade Max Prop from my current fixed three-blade 15/11 and am considering the 17" models. Looking at the aperture in pictures from the last haul out, an inch on either side seems okay, but there are likely forces at work I’m not aware of. Any suggestions from two or three-blade Max Prop owners greatly appreciated.
i was told by max prop that for optimal performance with the prop centered within the aperature you should have 11%-15% of diameter in clearance.
so for me (i have a falmouth 26) the aperature is 19 3/4"- with a 16" prop that left me about 11% of diameter of clearance. a 15" prop would have given me just over 15% clearance.
I’m pretty sure most everyone has the 16", I know I do. Should be some older posts about it if you try a quick search.
I’m pretty sure most everyone has the 16", I know
I do. Should be some older posts about it if you
try a quick search.–
Ben Eriksen
BCC #91 ElizabethWeb Design | BCC Elizabeth
Itchen’s is 15". There is much discussion of this and rpm and maxprop pitch settings and tachometer error concerns in the archives (2005?).
Scott
A quick search reveals over 150 postings on this topic (That’s what the search link if for!)
Here are some of the results:
http://www.samlmorse.com/forum/read.php?5,9699,9699#msg-9699
http://www.samlmorse.com/forum/read.php?5,7996,7996#msg-7996
http://www.samlmorse.com/forum/read.php?5,4422,4463#msg-4463
http://www.samlmorse.com/forum/read.php?5,4422,4423#msg-4423
I did a search for Max Prop and Maxprop and came up with just two messages. Of course I just now remember I need to set the date parameters. D’oh!
Thanks!
Look at Kiwiprops.co.nz It has worked well for us and is much cheaper and simpler.
I have enclosed an accurate drawing which may be of use toanyone sizing a porp to fot the aperture, it was of great assisitance to me.
Hello,
First of all, I’d like to introduce myself to the members of the forum. I’m Patrick, and I am the proud new owner of Roger’s Nereus. Not only do I consider myself blessed to have acquired such a beautiful, well built and designed sailing vessel, but,in the process, have also acquired a good friend in Roger. Life doesn’t get much better than this.
Secondly, I am in the process of installing a 3 blade 16" Maxprop Classic. Through detailed informantion acquired on the forum, particularly from Two Loose, I was able to anticipate a problem with the Max Prop sitting too far back in the aperture and am making the appropriate adjustments with the prop shaft. Things rarely go smoothly the first time, especially when a boat is involved, and it is nice to know about a problem before it occurs. Thank you for that.
As you all are aware, in 2005-2006 there was an extensive thread on the Max Prop. At that time, the concensus was a 16-18 degrees setting on the blade angle with the 16" prop, with one vote of 20 degrees with a 15 inch prop. Does anyone have any updates with their experiences since then? Has anyone been at both 16 and 18 degrees and prefer one over the other? Anyone with a 16"prop set at 20 degrees?
Thanks again
Patrick
Welcome onboard Patrick , we appreciate any and all your questions , as , often we have to re-think things from new perspectives, here !
I reasearched prop tip clearence to dead wood area , and most recommendations I found , say a 20% prop tip clearence is desireable to prevent erroding cavitation of the prop.
This issue is an ongoing field of study and can cause much discussion .
BCC Nereus is a most special boat , built with the utmost care for his own use , by a former Sam L Morse, company owner . I can attest personally to how much care and love went into the construction of that BCC .
Congratulations on your purchase , and we hope that you get as much fun from your new boat as we do all of ours .
Douglas
Hi I fitted a Maxprop classic 16" 3 blade on Stravaigin last summer, the engine was lightly used, my sense was that it was over revving on a setting of 16 degrees. She would easily go to 3500 and speed would be 6 to 6.5 knots. My horse sense was that 18 degrees may be better, maybe next year I will set to that and see what happens… the newer yanmars of which I have one give an extra couple horses and that may have made the difference. I also looked at the threads and thought that the concensus was 16 degrees. Nice to have you on the team Patrick, you must be excited.
The Propeller Handbook (Dave Geer 2001) gives the following guidance:
The distance between the tip of the blade and the top/bottom of the aperture should be between 15% and 20% of the blade’s diameter. My 15” MaxProp provides 3” here which is 20% of its diameter. If I had a 16” MaxProp in this same location, it would be 15%. Thus either size MaxProp fits this formula.
With respect to front/back positioning, you want the blades closer to the rudder and away from the deadwood. The book suggests 30% of the diameter as a minimum distance from the deadwood. You measure between the deadwood and the middle of a single blade. For my boat that is 9.5“ which is 63%.
Putting the propeller close to the rudder gives better control under power. However, you can’t get too close to the rudder. The book suggests 15% of diameter as a minimum distance. Here you measure between the rudder and the leading edge of a blade. On my boat that measurement is 2.75 inch at the point where the prop and rudder are closest. That is 18% for my boat which is fine.
My rudder does not hit the blade when turned at an extreme angle. However, for other reasons, my rudder has lines which limit its range of motion to 35 degree turns.
The 15” blade came with the boat. I thus have no opinion on the merits of 15” versus 16” blades. I get 3600 RPM on the tachometer with the throttle fully open and I get 6 knots at 2600 RPM which is the rate at which I usually cruise. Thus I‘m not sure that switching to a 16” blade would gain me much. I have not recorded the prop settings.
I just went to the file cabinet and pulled my MaxProp folder. I was looking for my pitch setting. However, I found lots more.
The file (inherited from the previous owner) includes photocopies of emails between PYI and Sam L. Morse and a few BCC owners. It is from the early 2000’s and debates putting a 15 inch or a 16 inch MaxProp on a BCC.
The conclusion was that the 15" was the better choice because it gets pitched at 20 degrees, exactly in the middle of the prop’s adjustment range. The 16" also works but is pitched at a lower angle which is less optimal.
Anyway, as I noted above, the previous owner acquired a 15" MaxProp. It is set for right rotation, 20 degree pitch X=K, Y=E. This is 10.3 inches of pitch. I get 3600 RPM on the tachometer with the throttle fully open and I get 6 knots at 2600 RPM which is the rate at which I usually cruise.
I currently do not have a flex coupling but plan to add one this winter (which implies shortening my shaft).
You might want to check some of the posts on Flex couplings as I believe one of them did not require shaft shortening. Which would make the operation more simple!
Craig,
I “just” installed a Federal flex coupling on Shanti. I did not need to shorten the shaft. I did have to have a keyway machined in, but otherwise it went right in with no problems.
Hi Gary , what no photos ? Did you also drill “detents” into the shaft for seating the two set screws and btw did you safety wire those set screws ?
What about that safety feature of installing a round shaft zinc just ahead of the stuffing box, did you do that too ?
The Federal Flex coupling on Calliste has worked a treat and has been trouble free, for 11 years, and 2,500 engine hours.
Douglas
Hey Douglas,
yes, detents were drilled. But did not see any faclitlity for a safety wire. Used a zink forward of the “new” stuffing box.
I will have some photos…patience young man.
This will be a month long haulout when all is said and done. It is my annual 2 year haulout every 3 years 
Will be installing a Kiwi feathering prop next haulout.
Cheers,
Gary
Found the holes in the set screws. Wired now.
Hi Gary , that’s great , sounds like you can scratch that item off the list . Good To Go !
BTW , I had a concern about the rubberized steel pins or are they called trunions, that are entraped in the cage. I didn’t know how long the rubber would last.
I purchased an extra set of 4 trunions to keep as spares, but so far the rubber that Federal used has shown no wear or deterioration.
Of course Murphy’s law would be at work here too !
Good Luck on the rest of your haul out list, don’t let the moon get in Fresno .
Douglas