Propping for WOT and 80% cruise

Are you worried about a 15 rpm and 5% load difference? Seriously?

How long have you owned the boat?
Does it make or exceed RPM when the boat is light?
Do trim tabs help?

Helping the boat may make more sense.
Unloading unused stuff and diver services may help after a good bottom wipe and fine prop cleaning.

Why would you buy new different props rather than 1 matching prop for the one you damaged? Obviously the boat likes the Hytorq props better.

That being said, the motors are rated to run at 80% load all day REGARDLESS of rpms, rpms will change depending on how much actual load is on the motors (cleanliness of bottom and running gear, weight (fuel/water/people/personal belongings/air and water temp) will all change what rpms your engines make 80% load at. So just run them at 80% load, 75% load won't hurt anything running all day either or 65%, you'll just be cruising at less knots. That being said, with full fuel/water and make sure engines are operating perfectly with clean fuel and air filters and bottom, I'd shoot for 2350rpms WOT and then 80% load would bump up another 70 rpms also and you'll pick up speed.

What condition is your bottom in? Any growth makes a big difference. Capt J summed it well, the 80% load is not tied to a set RPM and will vary. I have CAT C-18’s. When I sea trialed with 3 CAT techs aboard after installing my C-18s we made around 2375 rpm’s at WOT. I’m going by memory and it was 5 years ago so I may be off a few RPMs but I know it was well above 2300 rated and above 2350. All 3 CAT techs told me not do a dang thing with the props.

As others have suggested, I would shoot for the 2350 range at WOT. It’s odd that you went down in pitch from 38 to 37 but lost RPM on top end if all things are equal. Do your new props have more cup? Did you actually have the old props measured? Just because they may be stamped 28x38 doesn’t mean they weren’t altered at some point in the past. It’s not uncommon for shops to take add/subtract pitch or cup and not change the stamp on the props.

I ran twin 3406E 800's. I propped them for 2350 at a light to moderate load. I recall the rating to be 2325 at WOT? When you're setting up the propping, your vessel is at its premium condition for hull cleanliness and performance. A bit of slime or three barnacles will temper those RPM.

Also, you've got some terrific lower end torque, so be sure you run with some cup. I found a terrific sweet spot for cruising at 1750-1800. Of course every boat will differ.

Yes, best economy at speed. I don’t recall but would assume load was down in the low 70’s. I logged rpm, speed and consumption at 20 rpm increments above what felt like a planing speed. I was careful to blend in some high RPM on pretty much every trip out. But I ran her where I felt I was taking good care of longevity.

To each his or her own, but I rarely cared about finding a fast cruising speed unless there was a deadline or weather at play. I dialed in for economy and a smooth ride, lowering consumption, stress, and vibration.

Treat your gear the way you want to be treated.

Put the boat on a diet and get any weight that's un-necessary out of it. That will be your cheapest way of picking up speed. But taking pitch out and raising your rpm's at 80% load to where the engines make more HP will also pick up more cruising speed. Soda Blasting the bottom on your 20+ year old boat and getting rid of all that weight of a million layers of bottom paint will also pick up speed.

I'm running big 5 blade Veems now, albeit at displacement cruising. Lost 70% of the noise and vibration with the style and extra blade. Sharrow has my attention in that regard. But the added surface area also allowed me to drop around 75 RPM to hold the same speed at sea. That equated to around 1/10th of a fuel savings in addition to the "softer" ride.

I've always been much more focused on the sweet spot of cruising on any vessel at any speed. Perhaps I'm an outlier for a conversation chasing an extra knot.

You're close enough to not worry about it, but technically YES. If you would be 50 rpms or 100 rpms short at WOT you would be overloaded at 80% load, and have high exhaust gas temperature and so forth. The engine technically is an air pump, the faster you turn the engine, the more air it pumps through it and the more power it makes (within mechanical limits), so performance everywhere would suffer. The faster you spin the motor at 80% load, the more HP it is making and faster cruise speed, provided you're not severely underpropped.

Think of riding a bicycle up a hill and being in 1 gear too high, you have to put a lot more effort than you should be for the circumstances.

Every single yacht, mostly new yachts, where rpm's were short at WOT, we picked up speed at cruise and WOT by taking pitch out of the props, usually 2 knots but in one case one a new 66' Sunseeker we picked up 5 knots, but boat only turned 2200 rpms new and light WOT. I have run A LOT of different new yachts where the manufacturers played with props.

WHY are you stuck on cruising at 1900 rpms. Nowhere in your CAT owners manual does it state that rated cruise is 1900 rpms or ANY rpms, it states cruise is based on a percentage of load.

Rtrafford- Veems are definately a step above Michigan/Federal etc propellers. Usually a lot smoother and faster and more efficient and a lot less vibration. Very noticeable which Cabo's had Veems and which ones didn't just by manuevering the boat at the dock, much less chatter in reverse, plus they didn't suffer from prop burn.

Yes, I was skeptical about the props themselves, but I had wrinkled the set I was running on and saw a fresh used set available close to what was needed. Since I was going to the prop shop regardless, I cut a deal and took a chance...well, not much of a chance.

Prop man was very knowledgeable about Veems. For my displacement needs he recommended and performed the infill of the cup grooves. He re-pitched to the right pitch projection (estimate going from 4 to 5 blades), and he took the point off each blade. He had a theory about the point and gaining added hull clearance and lowering any deflective vibrations at those tips. I trusted and rolled with his experience. Outcome has been terrific. It was immediately noticeable even at low speeds in the master stateroom. At cruise that difference was incredible. At the tachometer I think we dropped 50 RPM to achieve and maintain hull speed in a sea, but it could be closer to 100.

Good recommendation, that soda blasting. Yes, it's a handsome investment. I did mine last in 2023. Paid $8k for 68 feet, including plastic and cleanup. When we finished our hull work and it was time to reseal, we first applied the barrier epoxy coat, but then we layered two coats of ablative in a light blue tint followed by three coats of the black that I typically use. The ablative paint color change over time cues me as to when the paint is running "thin", especially at the water line. I haul on 18 month intervals as a rough guideline, an aluminum hull needs to be monitored a bit more carefully than FRP. When we hauled this past spring I only added one fresh coat to the hull, but put three more back at the waterline, down perhaps three feet. I did have some blue showing around the transom area and rear quarters, much of which was likely the diver working hard. The concept allows me to better understand how to monitor the amount of paint I am carrying, and if I am safe to stretch the next haul given the boating plans for that moment.

I don't think I invented this technique, but however it came to me I am very happy that I chose to follow it. My work over the past five years has been in Ft Pierce. I can share the soda man's information if needed.