Join Date: Feb 2010
Location: Narragansett Bay
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Re: Maxprop, J-Prop, Variprop
Be careful with the adjustable prop pitch. If you lower the pitch, you'll get better responsiveness at the low end around the dock, however, you may get a higher wide open rpm than your engine is rated for. I've also heard of some cruisers that will increase the pitch so they get mid-range cruising speed at lower rpms to save fuel and extend range. Both of these are not great for the engine over time. If you have the pitch set correctly, your motor will run at its rated max rpm, when you are underway in calm water with a wide open throttle. It's a test that should be made for a few seconds occasionally. Then, whatever you get for near slip or underway performance just is what it is for that prop. It shouldn't be messed with by changing pitch.
There are other factors, such as blade diameter or blade shape/design that also affect various performance scenarios. For example, if you look at a fixed prop, the blades typically present a different shape going forward or backward through the water, particularly at the leading edge, with forward being more efficient. Your transmission probably has a different gear reduction ratio for reverse too. Feathering props try to accommodate some of this by moving the blades themselves to a new orientation.
As for moving props between engines/transmissions, I'm hopeful that would only require a pitch adjustment to accommodate the new max rpm and hp specs. However, that's not always the case, or they would not need to make different diameters and blade designs. I would want to know this was true, by asking the prop company about the likely motor upgrade, if I thought there was any chance I'd be swapping it out in the future.
In extreme cases, a significant hp increase can require a new shaft diameter too, but sailboats don't pimp their motors that much, unless their original shaft was poorly undersized. Nevertheless, many smaller shafts, like found on sailboats, become slightly out of plumb over time and one could learn this during their drive train upgrade. Or, your new engine/gear combo needs a longer shaft or the new gear doesn't have a shaft coupler for your diameter.
Not trying to be dramatic, I would just look into all of this, if I was hoping to carry it over.
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In the harsh marine environment, something is always in need of repair. Margaritas fix everything.