QUICK PROP QUESTION

cm5408

Seaman
Joined
Feb 12, 2006
Messages
68
current props used
14.25 dia 21 pitch 3 blade alum uncupped
14.25 dia 19 pitch 3 blade alum

i first started off with the 21 pitch and the boat ran wot around 49 mph. the boat did not come out of the hole like i wanted.

switched to the 19 pitch uncupped and the boat struggled to even get on plane (seemed like the prop was slipping too much out of the hole). when on plane the boat wot would run 40 mph.

took the 19 pitch and cupped the trailing edge. boat comes out of the hole better (slightly better than with the 21 pitch) but not like i want it too (boat is a v8 and should pull out of the hole better). once on plane the boat will run 45 mph and wot is higher than with the 21 by about 100 - 200 rpms.

i have an option of a new prop

15 dia 17 pitch 4 blade SS cupped

what will happen here?

the dia is larger by 3/4 in ( i have the room for the larger dia), 4 blades appossed to 3, SS vs Alum, Factory cupped vs what i cupped on the alum 19 (factory cup is more aggressive)
 

Ron G

Commander
Joined
Apr 28, 2005
Messages
2,905
Re: QUICK PROP QUESTION

sorry im a little slow but theres alot of holes in your thread..first of all what kind of boat,what v8 motor ,what year and what was the rpms on all these runs?
 

Crownie2

Petty Officer 1st Class
Joined
Jul 26, 2006
Messages
378
Re: QUICK PROP QUESTION

Yes - we need a little more information.

One thing I would say is get rid of that 19" prop - it's not doing you any favors.

If I had to guess, I'd say you don't need that large a diameter 4 blade.

Bob
 

cm5408

Seaman
Joined
Feb 12, 2006
Messages
68
Re: QUICK PROP QUESTION

boat - 1989 - 21 ft baretta cuddy
aprox boat wieght - 3600

motor 5.0l - 305gm volvo penta rated at 229 hp at crank 209 at prop

21 pitch at 49 mph around 4600 - 4700 rpms (wot is either 4600 or 4800)

19 pitch before cupping would go well over 5000 if i allowed it to

19 pitch after cupping 4700 - 4800

One thing I would say is get rid of that 19" prop - it's not doing you any favors

why is this? what do you suggest?
 

Crownie2

Petty Officer 1st Class
Joined
Jul 26, 2006
Messages
378
Re: QUICK PROP QUESTION

Well before your modifications it didn't do anything well and now it's better and it's still 4mph slower.

I think you would be OK with a 19" or possibly 20" SS three blade if you can find one for that drive, IMO.

Bob
 
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