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Old 07-03-2019, 09:18 AM   #39
Nomad Willy
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City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
Probably most that are overpropped are because the boat came that way.

Then when they haul out and perhaps think about prop load they notice many here on TF are overpropped and most seem experienced or even old salts. Then they recall hearing one will burn less fuel and of course the’ve had the experience of going to the fuel float (of barge) and getting shocked at the cost. And that’s it. They just keep on keep’in on thereafter.

Then a few come along every now and then w a bunch of numbers and theories that are very overwhelming and it’s rejected because even the experts on TF continue to argue about whether it’s good or bad. Then they think of fuel again. So the motive to change is very small so they chime in w the others claiming it’s the smart thing to do. So if it’s the smart thing to do it would be dumb to do any different and they get to talk about how smart it is to do w the big boys on TF too. And it goes on and on.

But another thing goes on and on. That’s the fact that no engine manufacturer recommends overpropping.
Then there’s hull speed. All the old salts talk about hull speed. So many attempt to or do run their boat at hull speed. May be the perfect speed for SD boats not close to FD but for those close to hull speed it’s not the speed to go. And for FD it’s the speed to never ever go unless the boat is overpowered (most are) and you’re doing a spring check on systems engine wise.

But if you’re at all concerned about fuel consumption most SD and all FD boats should be run 1/2 to one knot below hull speed. But the average TF guy is confused again and hears many run at a “sweet spot” and then we have license to find a speed he feels is nice. Almost always the speed that is run at the rpm where there is the least vibration and hence noise as well and almost absolutely everybody like that. Hard not to like smooth and relatively quiet. And the old salts on TF are frequently talk’in about it so it must be the thing to do.

But re overpropping is not recommended by any engine manufacturer.
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Eric

North Western Washington State USA
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