Raised my motor, but questions...

[Bushwacker]

Originally Posted by erebus

Unfortunately my prop has absolutely no identifying characteristics whatsover. No stamps, no numbers, no nothin'. So I have no idea what I'm running which is frustrating.

I bet if you take that prop to a good prop shop, they can figure out pitch and diameter, and maybe even assess how much cup it has in it, so that will give you a rough baselne to start from.

Did you happen to get any pics of the AV plate while you were up on plane? Now that you know it handles ok at the current height, I'd be inclined to raise it another hole to see if you can run even higher . . . might pick up another 50-100 rpm at WOT.

How heavily were you loaded today? When testing props, I always test with a full load of fuel, fill the galley seat water jug and live well, and fill my 65 and 70 qt coolers with sea water to simulate the max cruising load I expect to carry. Unless you don't ever run heavily loaded, you run the risk of picking a prop with too much pitch if you don't test with the max load you intend to carry! I'd also check min planing speed on every prop you try. I suspect that's real important for where you're running, because the 18-20' SeaCrafts are pretty light and will start going airborne at about 20 kts when seas get up around 3', so in those conditions, it's nice to be able to slow down and hang on plane at 12-15 mph, which you easily be able to do with that fairly light motor! Any 4B prop will have more stern lift than a 3B and improve low speed planning, and may be more efficient at cruising speed, although it may be a bit slower at WOT.

Merc has some good props, so once you know what you're running, you might contact Ken at Prop Gods, who seems to recommend mostly Merc props. Michigan also makes some very nice reasonably priced props, and their 2-piece hub system is more robust than the Merc Flo-Torque hubs, which have a reputation for shearing the plastic insert. Some PowerTech props also use the Michigan hub system. The 14 1/8 X 20P 4B Michigan Apollo was the first SS prop I tried and it was the most efficient prop I've ever tested, giving me a solid 5.0 mpg at cruise, and with a light load it also gave me 49.8 mph @ WOT, the highest speed I've ever seen! However I could only spin it up to about 5200 with a light load and only 4600 with a very heavy load (this is why I recommend testing @ max load!), and my optimum WOT rpm is 5300-5500, so I needed a lot less pitch!