Just thought I'd add my .02
I have a 98 20 footer with 102 inch wide beam, which doesn't make for a very fast boat. It has a 5.7L carb alpha1 250hp, rpm range 4400-4800. I believe in 97 they were 210hp rpm range 4200-4600.
That said, with the stock 19p alum. prop I was running 53-54 mph and bumped the rev limiter at 4950 rpm .Went to 19p stainless and run 57-58 mph at 4700 rpm.
My humble advice would be to find a prop shop that sells and customizes props. Start with a 19p stainless steel and work with the shop to get it tweeked to run right at your max of 4600 rpm. I talked to Bronson Hill of Hill Props at the LA boat show and I know his shop is one of many that offer this service.
I have a 94 21 foot Kal Kustom with a 5.7 magnum alpha one. I run a 23p stainless and get 57MPH recorded by a police radar gun. I posted asking about more HP on tha alpha drive. with the higher HP I hope to get to 70 MPH with a 24p four blade. With a diff prop you should push 57 to 60 MPH. Anyone know if 400 HP is too much for the Alpha??
Larry S.
[This message has been edited by larry smith (edited September 11, 2001).]
I have seen the experts of the motor guys turn small block chevys to 4,900 rpm -light load -at boat builder dealer meetings to get the best top speed.
I have seen boat hulls that go no faster at 4,900 versas 4,250 rpm using different props.
I have seen very few boats that do not gain 2-4 mph going from a alum. to a stainless prop.
For the sake of comparison:
My previous boat was a Wellcraft Eclipse 21'
bowrider (1994) with a 260HP Merc 350 Mag,
Alpha 1 and 21 pitch SS prop. It also had
Corsa switchable thru-hull exhaust. This was
a carbureted (Carter AFB), flat-tappet engine
and it would go 59 MPH on the GPS at
4,900 RPM.
For the sake of comparison:
My previous boat was a Wellcraft Eclipse 21'
bowrider (1994) with a 260HP Merc 350 Mag,
Alpha 1 and 21 pitch SS prop. It also had
Corsa switchable thru-hull exhaust. This was
a carbureted (Carter AFB), flat-tappet engine
and it would go 59 MPH on the GPS at
4,900 RPM.
I have a 98 5.7gs 2bbl carbed; I switched my alum 14 1/4 x 21 3 blade to a 14 3/4 21 SS 3 blade and gained a solid 3MPH. The best $350 I spent while waiting for my log dinged alum prop to be refinished. The grab was like night and day and the top end is very sticky compared. The alum has never been back on the boat.
Originally posted by larry smith:
I have a 94 21 foot Kal Kustom with a 5.7 magnum alpha one. I run a 23p stainless and get 57MPH recorded by a police radar gun. I posted asking about more HP on tha alpha drive. with the higher HP I hope to get to 70 MPH with a 24p four blade. With a diff prop you should push 57 to 60 MPH. Anyone know if 400 HP is too much for the Alpha??
Larry S.
[This message has been edited by larry smith (edited September 11, 2001).]
Larry - Good rule of thumb. Anything over 300hp will kill an alpha1.
I HAVE A 20FOOT CENTURY CUDDYCABIN 260HP 5.7 ALPHA1. IHAVE A 19 PITCH HIGHFIVE AND AM LOOKING FOR MORE TOP END.WILL A 21 PITCH HELP OR NOT NET WIEGHT IS 2500# THE HIGHFIVE IS TURNING 46-4700 WOT WITH OUTDRIVE ALL THE WAY DOWN.I ALSO HAVE THRU HULL IF THAT HELPS.
Originally posted by monte:
IHAVE A 19 PITCH HIGHFIVE AND AM LOOKING FOR MORE TOP END.WILL A 21 PITCH HELP OR NOT
IMO- get rid of the High Five- that's a bottom end prop. Perhaps a 21" SS 3-blade- you're probably going to have to experiment with the diameters and blades.
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