newb need help with searay boat prop

Joined
May 5, 2008
Messages
2
hey guys im new to the board.
I can honestly say i know very little about props and need some help. last summer my father and i purchased a 290 searay sundancer with a 7.4L mercruiser with a bravo 2 leg. unfortunately the prop that came with it was in very poor shape and an incounter with a dead head finished it off. it was a 19x19 aluminum three blade we believe (paper leftover from previous owner indicates this). Now seeing as we where on a trip and where not ready to go home we purchased the only available prop in the area that would work with our boat which was a 16.5 pitch 21" diameter four blade prop. last christmas we installed a fuel flow meter on our boat and we recently had it out and it indicated that we where burning 24gal/hr at 3200rpm, which was far from what we where expecting also we can not reach the manufactures rated rpm of 4600 we have a max of 4000. with the original aluminum prop we could only reach 4000 rpm as well.

the Searay site says that i should be running a 17.5x23Al

if anyone could tell me what type of prop would be better suited for me i would love to know. im hoping the fuel burn rate and lack of rpm we are getting is an indicator of an incorecct prop but i have no idea.

thanks in advance

Richard
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: newb need help with searay boat prop

I can't help too much with prop selection but I'll get you started.
First of all your probably 300 hp, wot(wide open throttle) GPH is about 10% of the hp.So your GPH.at WOT will be about 30.
Assuming your engine is healthy you appear to be over propped.Generally a 4 blade will produce slightly lower rpm than a 3 blade of similar demension.
Your various numbers don't add up. Prop demensions are given diameter first X pitch so your original prop was a 19 X 19 Dia.X pitch.( diameter is the product of prop design)generally not directly involved in selection.I have to wonder if the diameter isn't closer to 17"
Your replacement you said to be 21 X 16.5 dia X pitch.I can't help think you have the numbers reversed..Sea Ray says 17.5 X 23.
Very different from your original (17)19 X 19.It seems to me that 23" pitch is too much for a single screw setup. it would seem the 17 X 19 is closer.
The experts should be along with more specific info.
 

jaxnjil

Lieutenant
Joined
Aug 3, 2007
Messages
1,368
Re: newb need help with searay boat prop

i just got done sorting out my wifes 230 and found a 15x21 with a 1.65 to 1 final drive ratio got me 4200 rpm at 3600 ft elevation,
her 454 has 41 to 42 hundred rpm max wide open throttle printed on the valve cover
i also instaled a fuel flow gauge and was 22 gal per hr and 43 (gps) mph at wot.
best econmeny came at 3000 rpm 10 to 11 gal per hr and 29 to 30 mph
this boat is real close to 6200 lb full of fuel and gear
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: newb need help with searay boat prop

Looks like you have her dialed in real nice.
 

jaxnjil

Lieutenant
Joined
Aug 3, 2007
Messages
1,368
Re: newb need help with searay boat prop

richard; one of the things i found when looking for props was that there are aluminium that are not rated for any higher than 250 hp. allso you might want to look a stainless with your 7.4 to eleminate any prop flex associated with aluminium
i lucked out and found two mucruiser stainless on close out for 200 each.
the 21 pitch above and a 19 pitch. they are real nice for the money. they are mercury marine mirage plus's
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,082
Re: newb need help with searay boat prop

it was a 19x19 aluminum three blade we believe (paper leftover from previous owner indicates this).

Ayuh,....

If it ran Good with That prop,..... Get Another 1......

Jaxnjil,..... He's got a Bravo II,.... It takes Much different Props.....
 

quint4

Cadet
Joined
Jun 24, 2006
Messages
12
Re: newb need help with searay boat prop

I just put a Stainless Steel 18.5 X 17 powertech prop on my Sea Ray 290 7.4 BII Friday.I ran all day Yesterday with it. It is a cupped prop and I am at 4400 WOT at 32 mph lightly loaded. My boat is bottom painted and I have a generator so it's a bit heavy. I am happy with the performance so far although I have no fuel burn numbers to relate....by the way it was $600 !
 
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