RPM question: Engine Survey - Sea trial

[krush]

That is correct, I don't believe we were even close to plane.

GJH, rwappleton: You are correct, way over-propped. Apparently done deliberately by PO that wanted better "economy cruise" and didn't care about the upper end of the power curve. I've seen from researching other threads that the consensus is to stick with OEM specs on the wheels.

There's nothing wrong with higher pitch for economy cruise, as long as you don't run it WOT. A guy here did that several years ago for hull speed cruising (went up in pitch) and got 20-30% fuel reduction.

[Liquid Asset]

There's nothing wrong with higher pitch for economy cruise, as long as you don't run it WOT. A guy here did that several years ago for hull speed cruising (went up in pitch) and got 20-30% fuel reduction.

If your not reaching wide open throttle rated RPM's, then you are overloaded at all ranges of RPM. Over pitched, is over pitched and will shorten the life of your engines. My opinion is you need to get the bottom paint straightened out and drop some pitch out of those props to get your RPM's back.

[davidwigler]

I have same engines on the same boat and mine came with 28 x 31 four-blade bronze props. Both engines reached 2300 RPM WOT at the sea trial, with the vessel reaching 15 knots on a dirty fresh water bottom.

[krush]

If your not reaching wide open throttle rated RPM's, then you are overloaded at all ranges of RPM.

This is not true at all. Look at propeller curves vs engine HP curves. Cummins even puts a generic prop curve on it's dyno plots.

[Milacron]

Speaking of props if the boat has a spare set it is helpful to compare their specs to what it should have come with to see if they are "emergency get home" ones or "swap and keep on there" ones. If there is no spare set, keep in mind they are amazingly expensive, even used. ($8K to $12K a pair...or even more...for used !)

I always want a spare set of props, so the lack thereof or vastly inappropriate sized or beat up spares actually entered into my accept or reject decisions on a number of boats. But if the boat price is right you can always get a used set from Sams. Just be aware they are amazingly expensive for something so simple.

My Viking has a shiney never used set of appropriate spec props secured under the master bed ! Woe be unto whoever might someday have to actually lift those suckers out from under the bed, up the spiral stairway, across the salon, down to the cockpit, however !! Hope it's not me !!

Did you fire up the Sea Keeper gyros for the sea trial ??

[jim rosenthal]

This is not true at all. Look at propeller curves vs engine HP curves. Cummins even puts a generic prop curve on it's dyno plots.

It isn't true that you would be overloaded at all rpms if the boat was overpropped. Part of the problem is that you can't figure out where the overload starts- maybe if you had boost and pyrometer gauges you could?

In any case, the solution is pretty clear- make sure the bottom is squeaky clean, the boat doesn't weigh more than she has to, and take some pitch out of the wheels.

[Milacron]

...the boat doesn't weigh more than she has to,

Wonder how much weight the two Sea Keeper gyro's add ? And then there is the Home Depot aft deck plastic timbers... some wind resistance from two sat domes

[nautibake]

It isn't true that you would be overloaded at all rpms if the boat was overpropped. Part of the problem is that you can't figure out where the overload starts- maybe if you had boost and pyrometer gauges you could?

In any case, the solution is pretty clear- make sure the bottom is squeaky clean, the boat doesn't weigh more than she has to, and take some pitch out of the wheels.

In researching some of the other threads on this topic it is interesting to see the range of opinions. I don't want to do something in the name of fuel economy (i.e. keep the current pitch) that is outweighed by future mechanical expense. I don't mind managing a demand curve within tolerances (did that on similar vintage airplanes for years) for a desired outcome. I'll look into the additional gauges, sounds like not a bad idea anyway.

Speaking of props if the boat has a spare set it is helpful to compare their specs to what it should have come with to see if they are "emergency get home" ones or "swap and keep on there" ones.

Unfortunately no spare wheels included.

Did you fire up the Sea Keeper gyros for the sea trial ??

Yes, we spooled up the gyro stabilizers and tested them independently as well as in tandem. One is sufficient to stabilize a 58MY but the PO wanted redundancy. Although it was a flat day on the gulf, we wheeled in some hard 180 turns to port and then to starboard at 12-14 knots and she remained absolutely level, as if she was on rails. No heel whatsoever. It was impressive from the FB.

Wonder how much weight the two Sea Keeper gyro's add ?

The Seakeeper M8000's weigh in at 1210 lbs each (so x2).

[krush]

You can reset the governors to do a max rpm so you don't overload the engines.

[Milacron]

Yes, we spooled up the gyro stabilizers and tested them independently as well as in tandem. One is sufficient to stabilize a 58MY but the PO wanted redundancy. Although it was a flat day on the gulf, we wheeled in some hard 180 turns to port and then to starboard at 12-14 knots and she remained absolutely level, as if she was on rails. No heel whatsoever. It was impressive from the FB.

The Seakeeper M8000's weigh in at 1210 lbs each (so x2).

Cool. Any interesting info gained from the fuel consumption monitor system ?