Correct prop for 206G Overnighter?? Advice welcome

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RonnyBass

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I'm hoping that the experience on this forum can help me out. Last summer I inherited a 1986 Grady 206G Overnighter with a 200hp 2.5L Mercury 2 stroke on the back. Just repowered the Mercury about a month ago but not getting nearly enough out of it. I fully realize this boat is not meant for speed, but I think I should be getting a lot more out of it than 33-34 mph at WOT. I don't want to damage the new powerhead by over propping, but clearly I think a prop change is needed.

Current prop: 15 dia x 17 pitch, 3 blade aluminum
WOT: 5500 rpm
Top speed: 34 mph

I'm thinking I need to go to a 15 x 15 stainless steel 3 bladed prop. From everything I've read I should be closer to 40 mph at the same rpm by going to a 15 pitch versus my current 17 pitch, but again, I don't want to over prop and damage my brand new powerhead - that wasn't cheap.

Thoughts and advice welcome please!

Thank you!
 
You've got things backwards, there, Ron. If you go DOWN in pitch, you will LOSE speed, given the same RPM. However, you will gain RPM which "could" offset the speed loss and end up at about the same speed, albeit at a higher RPM. What is the RPM operating range for your engine?

Other thoughts... Dirty bottom? Are you trimming up properly? How much extra weight do you have in the boat, aside from yourself and about a half-tank's worth of fuel? Compression test on engine? Fuel quality?
 
Thanks for the reply, Dennis. That's what I thought, but I talked to the PropGods guy and he said go down in pitch. So confused. To answer your questions...

The last time out (yesterday) I was running WOT with just 2 souls and 1/2 tank of gas (approx 30 gals). Engine was properly trimmed, actually trimmed slightly up to even get to that speed. Bottom is painted, not great a few spots missing but nothing significant enough to make that much of a difference in my opinion.

While I have you, what's the verdict on 3 versus 4 bladed props on Gradys? I boat only in the Upper Chesapeake Bay, choppy but no swells.
 
Was going to suggest ken at prop gods! he is Highly recommended by many on a well know fishing (boating) website
 
heycharlie said:
Was going to suggest ken at prop gods! he is Highly recommended by many on a well know fishing (boating) website
Click to expand...

Yep, saw his name over and over again on that other well known site. So I called him. More confused now.
 
What's your engine's max RPM range?

Before you do anything else... it sounds like you may not be trimming it up enough for max speed? With calm conditions, trim it up until either:

-- You reach your max RPM (for testing purposes, it's OK to go over by a hundred or two for short bursts)
-- Your speed no longer increases
-- The prop starts to ventilate.

There is no way that a same style 15" will give you more speed than a 17" at the same RPM. You would have to increase RPM to do that. Physics works! :)

I've never used PropGods, but I have heard good things about them.
 
hi i basically have the same boat adventure 208... i run a yamaha 200 2stroke i had the same problem when i bought her.. my trim tabs were too low, i brang them all of the way up and jut use the motor trim.. i now get 5100 rpms and about 43 mph not great but much better than my old speed of 4800rpms and 30 mph. also look at the speed on ur GPS and see what it is reading
 
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