New Props ACME vs MICH WHEEL

OK, good, you have an engine rated rpm of 2500 , our ultimate target would be 2550 rpm at WOT, and you have confirmed a robust no load rpm of 2700, which means the engines are in a great state of tune, fuel racks properly set, full travel available on throttles, and cable linkage is good.

I am concerned that the water depth is too shallow for correct propeller selection. 14' of depth minus an estimated 4' of draft only gives you 10' below the props, would like to see twice that much. As I mentioned before, while a real get up and go planing boat can see a reduction in drag in certain shallow depths, the propeller efficiency may decrease at the same time. If the reduction in drag is greater than the decrease in efficiency, you may see a speed improvement, but it can go the other way too.

Past example > I had two identical 61' Pilothouse MY's with QSM11 715 hp engines, about a 24 knot set-up. One in San Diego Bay, no issues, ran like a champ. The other was delivered up to the Sacramento Delta. Not a single issue from Newport Beach to the Delta, once in the Delta, running in narrow and shallow channels, ran like crap, vibrated, couldn't make speed, etc. Ran back to SF Bay, no issues, there was just too much skinny water for her displacement, also was brackish so she sat a little lower on her lines.

Need to test/collect performance data in a more open, deeper channel, with data taken two ways (need the average in opposite directions).

As far as cup, the ACME style of prop seems to prefer some, in your case .045" is a very mild cup, at .015" per unit on a scale of 1 - 12, it is only a #3 and is not as big a factor as we may suspect. What is your top speed before the prop change and after? Let's get into some deeper water before making any suggestions for changes.

Overpropping is hard on your engines during the spin up. You're slower to achieve plane because your engines are bogged down when they need to be free to spin and allow your engines to build torque. You don't want to keep running like that for the season. 3 inches is a ton of pitch to remove, although your props should handle the change fine. However 3 inches will result in a blade shape that is not the same as the original prop, nor the same as the right sized prop purchased new. You'll be defeating the efficiency design of the prop as it was intended, at least to some small degree. Best outcome is the right sized prop to begin with, although I'm guessing the dimensions were your call, hence no recourse?

Its hard to judge between two different brands of propellers as they most likely have two different blade shapes. The MW may be a Dyna-Quad or other model, ACME is not publishing a lot of specs like BAR or DAR, so it is hard to make a judgement on dropping 3" of pitch from one brand to the next brand without all the geometry specifications. It is the yard's responsibility to make the proper assessment if the blades are of different designs, areas, shapes, etc.

Physically removing 2" of pitch is about my own personal limit on a Nibral Propeller, but I still have to wonder why the miss on the shipyard's part? Are they in consultation with the ACME propeller engineers? Are they a hit and miss and readjust on the fly yard, with not much knowledge of propeller sizing? I would have expected better because they should have knowledge how the two different brands of propellers and how they compare to each other. As far as cup goes, they are both mild so that appears to be a wash at the moment.

The data will be a good starting point, make sure it is two-ways.

Then ACME needs to make it better. I would push against adjusting your new wheels also.

Absolutely! If Acme made the call, Acme needs to make the replacement. If the yard did it, they need to own the problem. Don't make the problem yours unless that's where the issue lands.

The props can be adjusted, but you cannot adjust the base of the blade, the thicker edge that approaches the hub. This adjusted prop will not have the same shape as the new prop, therefore it will not have the same efficiency dynamic with which it was designed.

I hope that makes sense when you read it.....

To account for current/wind direction, take two sets of data in opposite directions.

If your first run is north, take your second run south (-180 degrees) and then average the two speeds to get a single true speed. You don't want to take the data in just one direction only.

This is an issue that your yard needs to make right, from obtaining the proper wheels to the replacement of them on your boat. If I'm in this position I'm making it the yard's issue, because I'm paying them, and they're standing in front of me wanting my return business and word of mouth recommendations. Let the yard haggle with Acme as to who pays for what behind the scenes. You know that you didn't make the call, and your yard knows that you didn't. Did you happen to pay by Amex?

I am open minded that I am interpreting you incorrectly but you seem to be implying that the OP should push the blame onto the yard even though he can’t remember one way or the other. If that is the case then your post illustrates how in my lifetime business has changed for the worse. If it is my fault I own it. Now it is somewhat rare to encounter some one or an entity that operates that way. This mentality is prevalent these days when a problem occurs the first things most parties do is not defend themselves but to find a way to blame someone else. Fortunately I don’t have to pursue business that I don’t want (that could change with a recession) but if I was the yard and suspected the OP was doing that I would attempt to make sure we did everything right or close and I would probably compromise and do the minimum i had to to get him satisfied and I would never do business with him again. Once again it is certainly possible that I am misinterpreted your post but if not to me the actions you recommend are at a minimum borderline dishonest.

Think your missing the big point. The way I read this; The owner (OP) did not spec the prop. Either the yard or ACME did.
Seems they may have it wrong.
So, you drive a GM car and need a new gizmo. The shop calls around and a mfg says this Ford part will work better with some mods. The shop talks you into it but the gizmo does not work better..
Now the shop says more mods are needed that you will pay fore now and later.
Your gizmo is not new anymore.
Warranties are probably gone.
High-tech & new engineering (what you paid for first of all) is now gone.
Who are you going to point a finger at? Or B O A T ?? *


* Bend Over & Take It

Now in the old days;
My old prop shop an the MFGs did all the magic numbers for me and still arranged for some test wheels to try before the final purchase; used ones off the shops shelf, customers spares or MFG loaners.
Just to make sure.

Perhaps you can be open minded about this quote?

Make them order you new props NOW, in the proper size and now. 2" of pitch reduction still might not be enough and can't reduce pitch anymore. Get them to order you new wheels. Call ACME directly and ask them about the issue and speak to them directly. They may offer to swap them out without any hassle.

But the yard is also possibly on the hook, so I'd think yard manager/owner in a meeting with Acme on speaker, all parties talk through it, and resolve the whole "who's gonna do the swap" issue. My guess is that Acme swaps the wheels, and yard eats the short haul and effort. Might be a long haul if Acme wants the wheels out of harms way before sending new ones.