different prop

xasis4343

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1991 2459 bayliner trophy offshore 5.0 alpha 1, gear ratio 1.47- 1, dry weight 4300 lbs . loaded weight plus fuel 5900. 14.5 x 17 aluminum 3 blade on it now. want to go to a 4 blade. boat is primarily erie fishing boat. My research suggests a 14.5 x 15. Any suggestios would be appreciated.
 

Scott Danforth

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1991 2459 bayliner trophy offshore 5.0 alpha 1, gear ratio 1.47- 1, dry weight 4300 lbs . loaded weight plus fuel 5900. 14.5 x 17 aluminum 3 blade on it now. want to go to a 4 blade. boat is primarily erie fishing boat. My research suggests a 14.5 x 15. Any suggestios would be appreciated.
welcome aboard

what WOT RPM are you getting with your 14.5 x 17? are the blades cupped?

you sure about the 5.0/1.47:1 ratio? usually the 1.47:1 is behind a 5.7 and a 1.62:1 is behind a 5.0
 

xasis4343

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yes drive was replaced with aftermarket 1.47 x 1. max rpm 4300 doesnt get out of the hole and on plane very quick even with trim tabs
 

QBhoy

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Hi. I’d double check that ratio at Scott says. I have a 1.47 on my 5.0…but it’s an mpi and on a performance hull. Be quite a rare pairing otherwise I’d think…especially on a boat that size and a carb. That’s unless it used to have a 5.7 in her previously perhaps ?
Anyway. I’d guess that if she is a 1.47 ratio right enough, even with a 17”…you must surely be lugging that engine and struggling to see the rpm range I’d guess. If you are managing into the 4400-4800 range, to me that would almost certainly confirm that you have a lower ratio on her. Otherwise you’d be seeing some seriously high speeds for a boat like that, if you were in the range.
 

QBhoy

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Ah. Just posted that above between you responding there. Even getting 4300 is doing fairly well. Fair play.
In that case, I’d be careful around a 4 blade, just with some of them returning lower rpms than the same pitch 3 blade. Not all…but some certainly will. You’re also on the edge of running out of off the shelf props at anything mich lower than the pitch you have. 15” would be about the lowest generally available easily. Some guys in your situation and similar have had success with the big bladed 16x16 black max prop. Give you a little extra out the hole and decent cruising efficiency. Might get you into the rpms too. 50/50. I’d be between that and a good 15” stainless perhaps.
 

Scott Danforth

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yes drive was replaced with aftermarket 1.47 x 1. max rpm 4300 doesnt get out of the hole and on plane very quick even with trim tabs
you have the wrong gear ratio. best you can do is drop down to a 13p in a 4 blade.

you are killing your motor by lugging it
 

xasis4343

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se106 1.47 new replacement for the alpha one. don't really care about top speed mainly getting up on plane quick and saving fuel. Thanks for input
 

Scott Danforth

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se106 1.47 new replacement for the alpha one. don't really care about top speed mainly getting up on plane quick and saving fuel. Thanks for input
you need to understand gear ratios engine RPM's and hull weight

has nothing to do with top speed.

you installed the wrong ratio drive. your only choice is to go as low of pitch that you can buy to get the RPM's back up, or replace the 5.0 with a 5.7
 

xasis4343

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you need to understand gear ratios engine RPM's and hull weight

has nothing to do with top speed.

you installed the wrong ratio drive. your only choice is to go as low of pitch that you can buy to get the RPM's back up, or replace the 5.0 with a 5.7
looking at a 3 blade s.s. 15 dia./14 pitch. thoughts?
 

QBhoy

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se106 1.47 new replacement for the alpha one. don't really care about top speed mainly getting up on plane quick and saving fuel. Thanks for input
Scott is right to be fair. Really don’t want to be below the rpm range. Puts a load of strain on the engine, in terms of premature bearing and component wear.
That aside, if you can…go into a reputable shop or dealer and see if you can try out a 15” or anything close, to see where you are. As I perhaps said earlier…you’re on the verge of running out of easily obtainable props for her, at anything much below that size. Perhaps consider a pvs vented prop as an option too. Have a google at mercury pvs prop technology, if you aren’t already aware of the concept.
Best of luck.
 

QBhoy

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solas rubex hr3 ss 3 blade 15 dia. 14 pitch
Worth a try, if it’s cheap enough to take a gamble on, or if you can try it first. If you have a trim anode fin, have it in mind that you may need to replace it with the recessed or more likely, the flat one…just for clearance
 
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